This guide covers system administration tasks like maintaining, monitoring and customizing an initially installed system.
- Preface
- I Common tasks
- 1 Bash and Bash scripts
- 2
sudo
basics - 3 Using YaST
- 4 YaST in text mode
- 5 YaST online update
- 6 Managing software with command line tools
- 7 System recovery and snapshot management with Snapper
- 7.1 Default setup
- 7.2 Using Snapper to undo changes
- 7.3 System rollback by booting from snapshots
- 7.4 Enabling Snapper in user home directories
- 7.5 Creating and modifying Snapper configurations
- 7.6 Manually creating and managing snapshots
- 7.7 Automatic snapshot clean-up
- 7.8 Showing exclusive disk space used by snapshots
- 7.9 Frequently asked questions
- 8 Live kernel patching with KLP
- 9 Transactional updates
- 10 Remote graphical sessions with VNC
- 11 File copying with RSync
- II Booting a Linux system
- III System
- 16 32-bit and 64-bit applications in a 64-bit system environment
- 17
journalctl
: Query thesystemd
journal - 18
update-alternatives
: Managing multiple versions of commands and files - 19 Basic networking
- 19.1 IP addresses and routing
- 19.2 IPv6—the next generation Internet
- 19.3 Name resolution
- 19.4 Configuring a network connection with YaST
- 19.5 Configuring a network connection manually
- 19.6 Basic router setup
- 19.7 Setting up bonding devices
- 19.8 Setting up team devices for Network Teaming
- 19.9 Software-defined networking with Open vSwitch
- 20 Printer operation
- 21 Graphical user interface
- 22 Accessing file systems with FUSE
- 23 Managing kernel modules
- 24 Dynamic kernel device management with
udev
- 24.1 The
/dev
directory - 24.2 Kernel
uevents
andudev
- 24.3 Drivers, kernel modules and devices
- 24.4 Booting and initial device setup
- 24.5 Monitoring the running
udev
daemon - 24.6 Influencing kernel device event handling with
udev
rules - 24.7 Persistent device naming
- 24.8 Files used by
udev
- 24.9 More information
- 24.1 The
- 25 Special system features
- 26 Using NetworkManager
- 27 Power management
- 28 Persistent memory
- IV Services
- 29 Service management with YaST
- 30 Time synchronization with NTP
- 31 The domain name system
- 32 DHCP
- 33 SLP
- 34 The Apache HTTP server
- 34.1 Quick start
- 34.2 Configuring Apache
- 34.3 Starting and stopping Apache
- 34.4 Installing, activating, and configuring modules
- 34.5 Enabling CGI scripts
- 34.6 Setting up a secure Web server with SSL
- 34.7 Running multiple Apache instances on the same server
- 34.8 Avoiding security problems
- 34.9 Troubleshooting
- 34.10 More information
- 35 Setting up an FTP server with YaST
- 36 Squid caching proxy server
- 36.1 Some facts about proxy servers
- 36.2 System requirements
- 36.3 Basic usage of Squid
- 36.4 The YaST Squid module
- 36.5 The Squid configuration file
- 36.6 Configuring a transparent proxy
- 36.7 Using the Squid cache manager CGI interface (
cachemgr.cgi
) - 36.8 Cache report generation with Calamaris
- 36.9 More information
- 37 Web Based Enterprise Management using SFCB
- V Troubleshooting
- A An example network
- B GNU licenses
- 4.1 Main window of YaST in text mode
- 4.2 The software installation module
- 5.1 YaST online update
- 5.2 Viewing retracted patches and history
- 5.3 YaST online update configuration
- 7.1 Boot loader: snapshots
- 10.1 vncviewer
- 10.2 Remmina's main window
- 10.3 Remote desktop preference
- 10.4 Quick-starting
- 10.5 Remmina viewing remote session
- 10.6 Reading path to the profile file
- 10.7 Remote administration
- 10.8 VNC session settings
- 10.9 Joining a persistent VNC session
- 13.1 Secure boot support
- 13.2 UEFI: secure boot process
- 14.1 GRUB 2 boot editor
- 14.2 Boot code options
- 14.3 Code options
- 14.4 Boot loader options
- 14.5 Kernel parameters
- 15.1 Services Manager
- 17.1 YaST systemd journal
- 19.1 Simplified layer model for TCP/IP
- 19.2 TCP/IP ethernet packet
- 19.3 Configuring network settings
- 19.4
wicked
architecture - 26.1 GNOME Network Connections dialog
- 26.2
firewalld
zones in NetworkManager - 29.1 YaST service manager
- 30.1 NTP configuration window
- 30.2 Adding a time server
- 31.1 DNS server installation: forwarder settings
- 31.2 DNS server installation: DNS zones
- 31.3 DNS server installation: finish wizard
- 31.4 DNS server: logging
- 31.5 DNS server: Zone Editor (Basics)
- 31.6 DNS server: Zone Editor (NS Records)
- 31.7 DNS server: Zone Editor (MX Records)
- 31.8 DNS server: Zone Editor (SOA)
- 31.9 Adding a record for a master zone
- 31.10 Adding a reverse zone
- 31.11 Adding a reverse record
- 32.1 DHCP server: card selection
- 32.2 DHCP server: global settings
- 32.3 DHCP server: dynamic DHCP
- 32.4 DHCP server: start-up
- 32.5 DHCP server: host management
- 32.6 DHCP server: chroot jail and declarations
- 32.7 DHCP server: selecting a declaration type
- 32.8 DHCP server: configuring subnets
- 32.9 DHCP server: TSIG configuration
- 32.10 DHCP server: interface configuration for dynamic DNS
- 32.11 DHCP server: network interface and firewall
- 34.1 HTTP server wizard: default host
- 34.2 HTTP server wizard: summary
- 34.3 HTTP server configuration: listen ports and addresses
- 34.4 HTTP server configuration: server modules
- 35.1 FTP server configuration — start-up
- 39.1 HTML report generated by SCA tool
- 39.2 HTML report generated by SCA appliance
- 1.1 Bash configuration files for login shells
- 1.2 Bash configuration files for non-login shells
- 1.3 Special files for Bash
- 1.4 Overview of a standard directory tree
- 1.5 Useful environment variables
- 6.1 Essential RPM query options
- 6.2 RPM verify options
- 15.1 Service management commands
- 15.2 Commands for enabling and disabling services
- 15.3 System V runlevels and
systemd
target units - 19.1 Private IP address domains
- 19.2 Parameters for /etc/host.conf
- 19.3 Databases available via /etc/nsswitch.conf
- 19.4 Configuration options for NSS “databases”
- 19.5 Feature comparison between bonding and team
- 21.1 Generating PFL from fontconfig rules
- 21.2 Results from generating PFL from fontconfig rules with changed order
- 21.3 Results from generating PFL from fontconfig rules
- 25.1
ulimit
: Setting resources for the user - 37.1 Commands for managing sfcbd
- 38.1 Man pages—categories and descriptions
- 39.1 Comparison of features and file names in the TAR archive
- 40.1 Log files
- 40.2 System information with the
/proc
file system - 40.3 System information with the
/sys
file system
- 1.1 A shell script printing a text
- 6.1 Zypper—list of known repositories
- 6.2
rpm -q -i wget
- 6.3 Script to search for packages
- 7.1 Example timeline configuration
- 14.1 Usage of grub2-mkconfig
- 14.2 Usage of grub2-mkrescue
- 14.3 Usage of grub2-script-check
- 14.4 Usage of grub2-once
- 15.1 List active services
- 15.2 List failed services
- 15.3 List all processes belonging to a service
- 18.1 Alternatives System of the
java
command - 19.1 Writing IP addresses
- 19.2 Linking IP addresses to the netmask
- 19.3 Sample IPv6 address
- 19.4 IPv6 address specifying the prefix length
- 19.5 Common network interfaces and some static routes
- 19.6
/var/run/netconfig/resolv.conf
- 19.7
/etc/hosts
- 19.8
/etc/networks
- 19.9
/etc/host.conf
- 19.10
/etc/nsswitch.conf
- 19.11 Output of the command ping
- 19.12 Configuration for load balancing with Network Teaming
- 19.13 Configuration for DHCP Network Teaming device
- 20.1 Error message from
lpd
- 20.2 Broadcast from the CUPS network server
- 21.1 Specifying rendering algorithms
- 21.2 Aliases and family name substitutions
- 21.3 Aliases and family name substitutions
- 21.4 Aliases and family names substitutions
- 24.1 Example
udev
rules - 25.1 Entry in /etc/crontab
- 25.2 /etc/crontab: remove time stamp files
- 25.3
ulimit
: Settings in~/.bashrc
- 31.1 Forwarding options in named.conf
- 31.2 A basic /etc/named.conf
- 31.3 Entry to disable logging
- 31.4 Zone entry for example.com
- 31.5 Zone entry for example.net
- 31.6 The /var/lib/named/example.com.zone file
- 31.7 Reverse lookup
- 32.1 The configuration file /etc/dhcpd.conf
- 32.2 Additions to the configuration file
- 34.1 Basic examples of name-based
VirtualHost
entries - 34.2 Name-based
VirtualHost
directives - 34.3 IP-based
VirtualHost
directives - 34.4 Basic
VirtualHost
configuration - 34.5 VirtualHost CGI configuration
- 36.1 A request with
squidclient
- 36.2 Defining ACL rules
- 39.1 Output of
hostinfo
when logging in asroot
Copyright © 2006–2024 SUSE LLC and contributors. All rights reserved.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled “GNU Free Documentation License”.
For SUSE trademarks, see https://www.suse.com/company/legal/. All third-party trademarks are the property of their respective owners. Trademark symbols (®, ™ etc.) denote trademarks of SUSE and its affiliates. Asterisks (*) denote third-party trademarks.
All information found in this book has been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. Neither SUSE LLC, its affiliates, the authors nor the translators shall be held liable for possible errors or the consequences thereof.
Preface #
1 Available documentation #
- Online documentation
Our documentation is available online at https://documentation.suse.com. Browse or download the documentation in various formats.
Note: Latest updatesThe latest updates are usually available in the English-language version of this documentation.
- SUSE Knowledgebase
If you have run into an issue, also check out the Technical Information Documents (TIDs) that are available online at https://www.suse.com/support/kb/. Search the SUSE Knowledgebase for known solutions driven by customer need.
- Release notes
For release notes, see https://www.suse.com/releasenotes/.
- In your system
For offline use, the release notes are also available under
/usr/share/doc/release-notes
on your system. The documentation for individual packages is available at/usr/share/doc/packages
.Many commands are also described in their manual pages. To view them, run
man
, followed by a specific command name. If theman
command is not installed on your system, install it withsudo zypper install man
.
2 Improving the documentation #
Your feedback and contributions to this documentation are welcome. The following channels for giving feedback are available:
- Service requests and support
For services and support options available for your product, see https://www.suse.com/support/.
To open a service request, you need a SUSE subscription registered at SUSE Customer Center. Go to https://scc.suse.com/support/requests, log in, and click .
- Bug reports
Report issues with the documentation at https://bugzilla.suse.com/.
To simplify this process, click the
icon next to a headline in the HTML version of this document. This preselects the right product and category in Bugzilla and adds a link to the current section. You can start typing your bug report right away.A Bugzilla account is required.
- Contributions
To contribute to this documentation, click the
icon next to a headline in the HTML version of this document. This will take you to the source code on GitHub, where you can open a pull request.A GitHub account is required.
Note:only available for EnglishThe
icons are only available for the English version of each document. For all other languages, use the icons instead.For more information about the documentation environment used for this documentation, see the repository's README.
You can also report errors and send feedback concerning the documentation to <doc-team@suse.com>. Include the document title, the product version, and the publication date of the document. Additionally, include the relevant section number and title (or provide the URL) and provide a concise description of the problem.
3 Documentation conventions #
The following notices and typographic conventions are used in this document:
/etc/passwd
: Directory names and file namesPLACEHOLDER: Replace PLACEHOLDER with the actual value
PATH
: An environment variablels
,--help
: Commands, options, and parametersuser
: The name of a user or grouppackage_name: The name of a software package
Alt, Alt–F1: A key to press or a key combination. Keys are shown in uppercase as on a keyboard.
AMD/Intel This paragraph is only relevant for the AMD64/Intel 64 architectures. The arrows mark the beginning and the end of the text block.
IBM Z, POWER This paragraph is only relevant for the architectures
IBM Z
andPOWER
. The arrows mark the beginning and the end of the text block.Chapter 1, “Example chapter”: A cross-reference to another chapter in this guide.
Commands that must be run with
root
privileges. You can also prefix these commands with thesudo
command to run them as a non-privileged user:#
command
>
sudo
command
Commands that can be run by non-privileged users:
>
command
Commands can be split into two or multiple lines by a backslash character (
\
) at the end of a line. The backslash informs the shell that the command invocation will continue after the line's end:>
echo
a b \ c dA code block that shows both the command (preceded by a prompt) and the respective output returned by the shell:
>
command
outputNotices
Warning: Warning noticeVital information you must be aware of before proceeding. Warns you about security issues, potential loss of data, damage to hardware, or physical hazards.
Important: Important noticeImportant information you should be aware of before proceeding.
Note: Note noticeAdditional information, for example about differences in software versions.
Tip: Tip noticeHelpful information, like a guideline or a piece of practical advice.
Compact Notices
Additional information, for example about differences in software versions.
Helpful information, like a guideline or a piece of practical advice.
4 Support #
Find the support statement for SUSE Linux Enterprise Server and general information about technology previews below. For details about the product lifecycle, see https://www.suse.com/lifecycle.
If you are entitled to support, find details on how to collect information for a support ticket at https://documentation.suse.com/sles-15/html/SLES-all/cha-adm-support.html.
4.1 Support statement for SUSE Linux Enterprise Server #
To receive support, you need an appropriate subscription with SUSE. To view the specific support offers available to you, go to https://www.suse.com/support/ and select your product.
The support levels are defined as follows:
- L1
Problem determination, which means technical support designed to provide compatibility information, usage support, ongoing maintenance, information gathering and basic troubleshooting using available documentation.
- L2
Problem isolation, which means technical support designed to analyze data, reproduce customer problems, isolate a problem area and provide a resolution for problems not resolved by Level 1 or prepare for Level 3.
- L3
Problem resolution, which means technical support designed to resolve problems by engaging engineering to resolve product defects which have been identified by Level 2 Support.
For contracted customers and partners, SUSE Linux Enterprise Server is delivered with L3 support for all packages, except for the following:
Technology previews.
Sound, graphics, fonts, and artwork.
Packages that require an additional customer contract.
Some packages shipped as part of the module Workstation Extension are L2-supported only.
Packages with names ending in -devel (containing header files and similar developer resources) will only be supported together with their main packages.
SUSE will only support the usage of original packages. That is, packages that are unchanged and not recompiled.
4.2 Technology previews #
Technology previews are packages, stacks, or features delivered by SUSE to provide glimpses into upcoming innovations. Technology previews are included for your convenience to give you a chance to test new technologies within your environment. We would appreciate your feedback. If you test a technology preview, please contact your SUSE representative and let them know about your experience and use cases. Your input is helpful for future development.
Technology previews have the following limitations:
Technology previews are still in development. Therefore, they may be functionally incomplete, unstable, or otherwise not suitable for production use.
Technology previews are not supported.
Technology previews may only be available for specific hardware architectures.
Details and functionality of technology previews are subject to change. As a result, upgrading to subsequent releases of a technology preview may be impossible and require a fresh installation.
SUSE may discover that a preview does not meet customer or market needs, or does not comply with enterprise standards. Technology previews can be removed from a product at any time. SUSE does not commit to providing a supported version of such technologies in the future.
For an overview of technology previews shipped with your product, see the release notes at https://www.suse.com/releasenotes.
Part I Common tasks #
- 1 Bash and Bash scripts
Today, many people use computers with a graphical user interface (GUI) like GNOME. Although GUIs offer many features, they're limited when performing automated task execution. Shells complement GUIs well, and this chapter gives an overview of some aspects of shells, in this case the Bash shell.
- 2
sudo
basics Running certain commands requires root privileges. However, for security reasons and to avoid mistakes, it is not recommended to log in as
root
. A safer approach is to log in as a regular user, and then usesudo
to run commands with elevated privileges.- 3 Using YaST
YaST is a SUSE Linux Enterprise Server tool that provides a graphical interface for all essential installation and system configuration tasks. Whether you need to update packages, configure a printer, modify firewall settings, set up an FTP server, or partition a hard disk—you can do it using YaST. …
- 4 YaST in text mode
The ncurses-based pseudo-graphical YaST interface is designed primarily to help system administrators to manage systems without an X server. The interface offers several advantages compared to the conventional GUI. You can navigate the ncurses interface using the keyboard, and there are keyboard sho…
- 5 YaST online update
SUSE offers a continuous stream of software security updates for your product. By default, the update applet is used to keep your system up-to-date. Refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.5 “The GNOME package updater” for further information on the…
- 6 Managing software with command line tools
This chapter describes Zypper and RPM, two command line tools for managing software. For a definition of the terminology used in this context (for example,
repository
,patch
, orupdate
) refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.1 “Definition of terms”.- 7 System recovery and snapshot management with Snapper
Snapper allows creating and managing file system snapshots. File system snapshots allow keeping a copy of the state of a file system at a certain point of time. The standard setup of Snapper is designed to allow rolling back system changes. However, you can also use it to create on-disk backups of user data. As the basis for this functionality, Snapper uses the Btrfs file system or thinly-provisioned LVM volumes with an XFS or Ext4 file system.
- 8 Live kernel patching with KLP
This document describes the basic principles of the Kernel Live Patching (KLP) technology, and provides usage guidelines for the SLE Live Patching service.
- 9 Transactional updates
Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root file system is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not affect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the admin must decide if a reboot is more expensive than disturbing running services. If reboots are too expensive then do not use transactional updates.
Transactional updates are run daily by the
transactional-update
script. The script checks for available updates. If there are any updates, it creates a new snapshot of the root file system in the background, and then fetches updates from the release channels. After the new snapshot is completely updated, it is marked as active and will be the new default root file system after the next reboot of the system. Whentransactional-update
is set to run automatically (which is the default behavior) it also reboots the system. Both the time that the update runs and the reboot maintenance window are configurable.Only packages that are part of the snapshot of the root file system can be updated. If packages contain files that are not part of the snapshot, the update could fail or break the system.
RPMs that require a license to be accepted cannot be updated.
- 10 Remote graphical sessions with VNC
Virtual Network Computing (VNC) enables you to access a remote computer via a graphical desktop, and run remote graphical applications. VNC is platform-independent and accesses the remote machine from any operating system. This chapter describes how to connect to a VNC server with the desktop clients vncviewer and Remmina, and how to operate a VNC server.
SUSE Linux Enterprise Server supports two different kinds of VNC sessions: One-time sessions that “live” as long as the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated.
A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.
- 11 File copying with RSync
Today, a typical user has several computers: home and workplace machines, a laptop, a smartphone or a tablet. This makes the task of keeping files and documents in synchronization across multiple devices all the more important.
1 Bash and Bash scripts #
Today, many people use computers with a graphical user interface (GUI) like GNOME. Although GUIs offer many features, they're limited when performing automated task execution. Shells complement GUIs well, and this chapter gives an overview of some aspects of shells, in this case the Bash shell.
1.1 What is “the shell”? #
Traditionally, the Linux shell is Bash (Bourne again Shell). When this chapter speaks about “the shell” it means Bash. There are more shells available (ash, csh, ksh, zsh, …), each employing different features and characteristics.
1.1.1 Bash configuration files #
A shell can be invoked as an:
Interactive login shell. This is used when logging in to a machine, invoking Bash with the
--login
option or when logging in to a remote machine with SSH.Interactive non-login shell. This is normally the case when starting xterm, konsole, gnome-terminal, or similar command-line interface (CLI) tools.
Non-interactive non-login shell. This is invoked when invoking a shell script at the command line.
Depending on the type of shell you use, different configuration files will be read. The following tables show the login and non-login shell configuration files.
Bash looks for its configuration files in a specific order depending on
the type of shell where it is run. Find more details on the Bash man
page (man 1 bash
). Search for the headline
INVOCATION
.
File |
Description |
---|---|
|
Do not modify this file, otherwise your modifications may be destroyed during your next update! |
|
Use this file if you extend |
|
Contains system-wide configuration files for specific programs |
|
Insert user specific configuration for login shells here |
Note that the login shell also sources the configuration files listed under Table 1.2, “Bash configuration files for non-login shells”.
|
Do not modify this file, otherwise your modifications may be destroyed during your next update! |
|
Use this file to insert your system-wide modifications for Bash only |
|
Insert user specific configuration here |
Additionally, Bash uses some more files:
File |
Description |
---|---|
|
Contains a list of all commands you have typed |
|
Executed when logging out |
|
User defined aliases of frequently used commands. See
|
No-Login Shells#
There are special shells that block users from logging into
the system: /bin/false
and
/sbin/nologin
. Both fail silently
when the user attempts to log into the system. This was intended
as a security measure for system users, though modern
Linux operating systems have more effective tools for controlling system
access, such as PAM and AppArmor.
The default on SUSE Linux Enterprise Server is to assign /bin/bash
to human users, and /bin/false
or
/sbin/nologin
to system users.
The nobody
user has /bin/bash
for historical reasons, as
it is a minimally-privileged user that used to be the default for system users.
However, whatever little bit of security gained by using
nobody
is lost when
multiple system users use it. It should be possible to change it to
/sbin/nologin
; the fastest way to test it is change
it and see if it breaks any services or applications.
Use the following command to list which shells are assigned to all users,
system and human users, in /etc/passwd
. The output
varies according to the services and users on your system:
>
sort -t: -k 7 /etc/passwd | awk -F: '{print $1"\t" $7}' | column -t
tux /bin/bash
nobody /bin/bash
root /bin/bash
avahi /bin/false
chrony /bin/false
dhcpd /bin/false
dnsmasq /bin/false
ftpsecure /bin/false
lightdm /bin/false
mysql /bin/false
postfix /bin/false
rtkit /bin/false
sshd /bin/false
tftp /bin/false
unbound /bin/false
bin /sbin/nologin
daemon /sbin/nologin
ftp /sbin/nologin
lp /sbin/nologin
mail /sbin/nologin
man /sbin/nologin
nscd /sbin/nologin
polkitd /sbin/nologin
pulse /sbin/nologin
qemu /sbin/nologin
radvd /sbin/nologin
rpc /sbin/nologin
statd /sbin/nologin
svn /sbin/nologin
systemd-coredump /sbin/nologin
systemd-network /sbin/nologin
systemd-timesync /sbin/nologin
usbmux /sbin/nologin
vnc /sbin/nologin
wwwrun /sbin/nologin
messagebus /usr/bin/false
scard /usr/sbin/nologin
1.1.2 The directory structure #
The following table provides a short overview of the most important higher-level directories that you find on a Linux system. Find more detailed information about the directories and important subdirectories in the following list.
Directory |
Contents |
---|---|
|
Root directory—the starting point of the directory tree. |
|
Essential binary files, such as commands that are needed by both the system administrator and normal users. Usually also contains the shells, such as Bash. |
|
Static files of the boot loader. |
|
Files needed to access host-specific devices. |
|
Host-specific system configuration files. |
|
Holds the home directories of all users who have accounts on the system.
However, |
|
Essential shared libraries and kernel modules. |
|
Mount points for removable media. |
|
Mount point for temporarily mounting a file system. |
|
Add-on application software packages. |
|
Home directory for the superuser |
|
Essential system binaries. |
|
Data for services provided by the system. |
|
Temporary files. |
|
Secondary hierarchy with read-only data. |
|
Variable data such as log files. |
|
Only available if you have both Microsoft Windows* and Linux installed on your system. Contains the Windows data. |
The following list provides more detailed information and gives some examples of which files and subdirectories can be found in the directories:
/bin
Contains the basic shell commands that may be used both by
root
and by other users. These commands includels
,mkdir
,cp
,mv
,rm
andrmdir
./bin
also contains Bash, the default shell in SUSE Linux Enterprise Server./boot
Contains data required for booting, such as the boot loader, the kernel, and other data that is used before the kernel begins executing user-mode programs.
/dev
Holds device files that represent hardware components.
/etc
Contains local configuration files that control the operation of programs like the X Window System. The
/etc/init.d
subdirectory contains LSB init scripts that can be executed during the boot process./home/USERNAME
Holds the private data of every user who has an account on the system. The files located here can only be modified by their owner or by the system administrator. By default, your e-mail directory and personal desktop configuration are located here in the form of hidden files and directories, such as
.gconf/
and.config
.Note: Home directory in a network environmentIf you are working in a network environment, your home directory may be mapped to a directory in the file system other than
/home
./lib
Contains the essential shared libraries needed to boot the system and to run the commands in the root file system. The Windows equivalent for shared libraries are DLL files.
/media
Contains mount points for removable media, such as CD-ROMs, flash disks, and digital cameras (if they use USB).
/media
generally holds any type of drive except the hard disk of your system. When your removable medium has been inserted or connected to the system and has been mounted, you can access it from here./mnt
This directory provides a mount point for a temporarily mounted file system.
root
may mount file systems here./opt
Reserved for the installation of third-party software. Optional software and larger add-on program packages can be found here.
/root
Home directory for the
root
user. The personal data ofroot
is located here./run
A tmpfs directory used by
systemd
and various components./var/run
is a symbolic link to/run
./sbin
As the
s
indicates, this directory holds utilities for the superuser./sbin
contains the binaries essential for booting, restoring and recovering the system in addition to the binaries in/bin
./srv
Holds data for services provided by the system, such as FTP and HTTP.
/tmp
This directory is used by programs that require temporary storage of files.
Important: Cleaning up/tmp
at boot timeData stored in
/tmp
is not guaranteed to survive a system reboot. It depends, for example, on settings made in/etc/tmpfiles.d/tmp.conf
./usr
/usr
has nothing to do with users, but is the acronym for Unix system resources. The data in/usr
is static, read-only data that can be shared among various hosts compliant with theFilesystem Hierarchy Standard
(FHS). This directory contains all application programs including the graphical desktops such as GNOME and establishes a secondary hierarchy in the file system./usr
holds several subdirectories, such as/usr/bin
,/usr/sbin
,/usr/local
, and/usr/share/doc
./usr/bin
Contains generally accessible programs.
/usr/sbin
Contains programs reserved for the system administrator, such as repair functions.
/usr/local
In this directory the system administrator can install local, distribution-independent extensions.
/usr/share/doc
Holds various documentation files and the release notes for your system. In the
manual
subdirectory find an online version of this manual. If more than one language is installed, this directory may contain versions of the manuals for different languages.Under
packages
find the documentation included in the software packages installed on your system. For every package, a subdirectory/usr/share/doc/packages/PACKAGENAME
is created that often holds README files for the package and sometimes examples, configuration files or additional scripts.If HOWTOs are installed on your system
/usr/share/doc
also holds thehowto
subdirectory in which to find additional documentation on many tasks related to the setup and operation of Linux software./var
Whereas
/usr
holds static, read-only data,/var
is for data which is written during system operation and thus is variable data, such as log files or spooling data. For an overview of the most important log files you can find under/var/log/
, refer to Table 40.1, “Log files”./windows
Only available if you have both Microsoft Windows and Linux installed on your system. Contains the Windows data available on the Windows partition of your system. Whether you can edit the data in this directory depends on the file system your Windows partition uses. If it is FAT32, you can open and edit the files in this directory. For NTFS, SUSE Linux Enterprise Server also includes write access support. However, the driver for the NTFS-3g file system has limited functionality.
1.2 Writing shell scripts #
Shell scripts provide a convenient way to perform a wide range of tasks: collecting data, searching for a word or phrase in a text and other useful things. The following example shows a small shell script that prints a text:
#!/bin/sh 1 # Output the following line: 2 echo "Hello World" 3
The first line begins with the Shebang
characters ( | |
The second line is a comment beginning with the hash sign. We recommend that you comment difficult lines. With proper commenting, you can remember the purpose and function of the line. Also, other readers will hopefully understand your script. Commenting is considered good practice in the development community. | |
The third line uses the built-in command |
Before you can run this script, there are a few prerequisites:
Every script should contain a Shebang line (as in the example above). If the line is missing, you need to call the interpreter manually.
You can save the script wherever you want. However, it is a good idea to save it in a directory where the shell can find it. The search path in a shell is determined by the environment variable
PATH
. Usually a normal user does not have write access to/usr/bin
. Therefore it is recommended to save your scripts in the users' directory~/bin/
. The above example gets the namehello.sh
.The script needs executable permissions. Set the permissions with the following command:
>
chmod +x ~/bin/hello.sh
If you have fulfilled all of the above prerequisites, you can execute the script in the following ways:
As absolute path. The script can be executed with an absolute path. In our case, it is
~/bin/hello.sh
.Everywhere. If the
PATH
environment variable contains the directory where the script is located, you can execute the script withhello.sh
.
1.3 Redirecting command events #
Each command can use three channels, either for input or output:
Standard output. This is the default output channel. Whenever a command prints something, it uses the standard output channel.
Standard input. If a command needs input from users or other commands, it uses this channel.
Standard error. Commands use this channel for error reporting.
To redirect these channels, there are the following possibilities:
Command > File
Saves the output of the command into a file, an existing file will be deleted. For example, the
ls
command writes its output into the filelisting.txt
:>
ls > listing.txtCommand >> File
Appends the output of the command to a file. For example, the
ls
command appends its output to the filelisting.txt
:>
ls >> listing.txtCommand < File
Reads the file as input for the given command. For example, the
read
command reads in the content of the file into the variable:>
read a < fooCommand1 | Command2
Redirects the output of the left command as input for the right command. For example, the
cat
command outputs the content of the/proc/cpuinfo
file. This output is used bygrep
to filter only those lines which containcpu
:>
cat /proc/cpuinfo | grep cpu
Every channel has a file descriptor: 0 (zero) for
standard input, 1 for standard output and 2 for standard error. It is
allowed to insert this file descriptor before a <
or
>
character. For example, the following line searches
for a file starting with foo
, but suppresses its errors
by redirecting it to /dev/null
:
>
find / -name "foo*" 2>/dev/null
1.4 Using aliases #
An alias is a shortcut definition of one or more commands. The syntax for an alias is:
alias NAME=DEFINITION
For example, the following line defines an alias lt
that
outputs a long listing (option -l
), sorts it by
modification time (-t
), and prints it in reverse sorted order (-r
):
>
alias lt='ls -ltr'
To view all alias definitions, use alias
. Remove your
alias with unalias
and the corresponding alias name.
1.5 Using variables in Bash #
A shell variable can be global or local. Global variables, or environment variables, can be accessed in all shells. In contrast, local variables are visible in the current shell only.
To view all environment variables, use the printenv
command. If you need to know the value of a variable, insert the name of
your variable as an argument:
>
printenv PATH
A variable, be it global or local, can also be viewed with
echo
:
>
echo $PATH
To set a local variable, use a variable name followed by the equal sign, followed by the value:
>
PROJECT="SLED"
Do not insert spaces around the equal sign, otherwise you get an error. To
set an environment variable, use export
:
>
export NAME="tux"
To remove a variable, use unset
:
>
unset NAME
The following table contains some common environment variables which can be used in you shell scripts:
|
the home directory of the current user |
|
the current host name |
|
when a tool is localized, it uses the language from this environment
variable. English can also be set to |
|
the search path of the shell, a list of directories separated by colon |
|
specifies the normal prompt printed before each command |
|
specifies the secondary prompt printed when you execute a multi-line command |
|
current working directory |
|
the current user |
1.5.1 Using argument variables #
For example, if you have the script foo.sh
you can
execute it like this:
>
foo.sh "Tux Penguin" 2000
To access all the arguments which are passed to your script, you need
positional parameters. These are $1
for the first argument,
$2
for the second, and so on. You can have up to nine
parameters. To get the script name, use $0
.
The following script foo.sh
prints all arguments from 1
to 4:
#!/bin/sh echo \"$1\" \"$2\" \"$3\" \"$4\"
If you execute this script with the above arguments, you get:
"Tux Penguin" "2000" "" ""
1.5.2 Using variable substitution #
Variable substitutions apply a pattern to the content of a variable either from the left or right side. The following list contains the possible syntax forms:
${VAR#pattern}
removes the shortest possible match from the left:
>
file=/home/tux/book/book.tar.bz2>
echo ${file#*/} home/tux/book/book.tar.bz2${VAR##pattern}
removes the longest possible match from the left:
>
file=/home/tux/book/book.tar.bz2>
echo ${file##*/} book.tar.bz2${VAR%pattern}
removes the shortest possible match from the right:
>
file=/home/tux/book/book.tar.bz2>
echo ${file%.*} /home/tux/book/book.tar${VAR%%pattern}
removes the longest possible match from the right:
>
file=/home/tux/book/book.tar.bz2>
echo ${file%%.*} /home/tux/book/book${VAR/pattern_1/pattern_2}
substitutes the content of VAR from the PATTERN_1 with PATTERN_2:
>
file=/home/tux/book/book.tar.bz2>
echo ${file/tux/wilber} /home/wilber/book/book.tar.bz2
1.6 Grouping and combining commands #
Shells allow you to concatenate and group commands for conditional execution. Each command returns an exit code which determines the success or failure of its operation. If it is 0 (zero) the command was successful, everything else marks an error which is specific to the command.
The following list shows, how commands can be grouped:
Command1 ; Command2
executes the commands in sequential order. The exit code is not checked. The following line displays the content of the file with
cat
and then prints its file properties withls
regardless of their exit codes:>
cat filelist.txt ; ls -l filelist.txtCommand1 && Command2
runs the right command, if the left command was successful (logical AND). The following line displays the content of the file and prints its file properties only, when the previous command was successful (compare it with the previous entry in this list):
>
cat filelist.txt && ls -l filelist.txtCommand1 || Command2
runs the right command, when the left command has failed (logical OR). The following line creates only a directory in
/home/wilber/bar
when the creation of the directory in/home/tux/foo
has failed:>
mkdir /home/tux/foo || mkdir /home/wilber/barfuncname(){ ... }
creates a shell function. You can use the positional parameters to access its arguments. The following line defines the function
hello
to print a short message:>
hello() { echo "Hello $1"; }You can call this function like this:
>
hello Tuxwhich prints:
Hello Tux
1.7 Working with common flow constructs #
To control the flow of your script, a shell has while
,
if
, for
and case
constructs.
1.7.1 The if control command #
The if
command is used to check expressions. For
example, the following code tests whether the current user is Tux:
if test $USER = "tux"; then echo "Hello Tux." else echo "You are not Tux." fi
The test expression can be as complex or simple as possible. The following
expression checks if the file foo.txt
exists:
if test -e /tmp/foo.txt ; then echo "Found foo.txt" fi
The test expression can also be abbreviated in square brackets:
if [ -e /tmp/foo.txt ] ; then echo "Found foo.txt" fi
Find more useful expressions at https://bash.cyberciti.biz/guide/If..else..fi.
1.7.2 Creating loops with the for
command #
The for
loop allows you to execute commands to a list of
entries. For example, the following code prints some information about PNG
files in the current directory:
for i in *.png; do ls -l $i done
1.8 More information #
Important information about Bash is provided in the man pages man
bash
. More about this topic can be found in the following list:
https://tldp.org/LDP/Bash-Beginners-Guide/html/index.html—Bash Guide for Beginners
https://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html—BASH Programming - Introduction HOW-TO
https://tldp.org/LDP/abs/html/index.html—Advanced Bash-Scripting Guide
http://www.grymoire.com/Unix/Sh.html—Sh - the Bourne Shell
2 sudo
basics #
Running certain commands requires root privileges. However, for security
reasons and to avoid mistakes, it is not recommended to log in as
root
. A safer approach is to log in as a regular user, and
then use sudo
to run commands with elevated privileges.
On SUSE Linux Enterprise Server, sudo
is configured to work similarly to su
. However,
sudo
provides a flexible mechanism that allows users to run commands with
privileges of any other user. This can be used to assign roles with specific
privileges to certain users and groups. For example, it is possible to allow
members of the group users
to run a command with the privileges of
user wilber
. Access to the command can be further restricted by
disallowing any command options. While su always requires the root
password for authentication with PAM, sudo
can be configured to
authenticate with your own credentials. This means that the users do not have
to share the root
password, which improves security.
2.1 Basic sudo
usage #
The following chapter provides an introduction to basic usage of sudo
.
2.1.1 Running a single command #
As a regular user, you can run any command as root
by
adding sudo
before it. This prompts you to provide the root password. If
authenticated successfully, this runs the command as root
:
>
id -un
1 tux>
sudo
id -un
root's password:2 root>
id -un
tux3>
sudo
id -un
4 root
The | |
The password is not shown during input, neither as clear text nor as masking characters. | |
Only commands that start with | |
The elevated privileges persist for a certain period of time, so you
do not need to provide the |
When using sudo
, I/O redirection does not work:
>
sudo
echo s > /proc/sysrq-trigger bash: /proc/sysrq-trigger: Permission denied>
sudo
cat < /proc/1/maps bash: /proc/1/maps: Permission denied
In the example above, only the echo
and
cat
commands run with elevated privileges. The
redirection is done by the user's shell with user privileges. To perform
redirection with elevated privileges, either start a shell as in Section 2.1.2, “Starting a shell” or use the dd
utility:
echo s | sudo dd of=/proc/sysrq-trigger sudo dd if=/proc/1/maps | cat
2.1.2 Starting a shell #
Using sudo
every time to run a command with elevated privileges is not
always practical. While you can use the sudo bash
command, it is recommended to use one of the built-in mechanisms to start a
shell:
sudo -s (<command>)
Starts a shell specified by the
SHELL
environment variable or the target user's default shell. If a command is specified, it is passed to the shell (with the-c
option). Otherwise the shell runs in interactive mode.tux:~ >
sudo -s root's password:root:/home/tux #
exittux:~ >
sudo -i (<command>)
Similar to
-s
, but starts the shell as a login shell. This means that the shell's start-up files (.profile
etc.) are processed, and the current working directory is set to the target user's home directory.tux:~ >
sudo -i root's password:root:~ #
exittux:~ >
By default, sudo
does not propagate environment variables. This behavior
can be changed using the env_reset
option (see Useful flags and options).
2.2 Configuring sudo
#
sudo
provides a wide range on configurable options.
If you accidentally locked yourself out of sudo
, use su
-
and the root
password to start a root shell.
To fix the error, run visudo
.
2.2.1 Editing the configuration files #
The main policy configuration file for sudo
is
/etc/sudoers
. As it is possible to lock yourself out
of the system if the file is malformed, it is strongly recommended to use
visudo
for editing. It prevents editing conflicts and
checks for syntax errors before saving the modifications.
You can use another editor instead of vi by setting the
EDITOR
environment variable, for example:
sudo EDITOR=/usr/bin/nano visudo
Keep in mind that the /etc/sudoers
file is supplied by
the system packages, and modifications done directly in the file may break
updates. Therefore, it is recommended to put custom configuration into
files in the /etc/sudoers.d/
directory. Use the
following command to create or edit a file:
sudo visudo -f /etc/sudoers.d/NAME
The command bellow opens the file using a different editor (in this case,
nano
):
sudo EDITOR=/usr/bin/nano visudo -f /etc/sudoers.d/NAME
/etc/sudoers.d
The #includedir
directive in
/etc/sudoers
ignores files that end with the
~
(tilde) character or contain the .
(dot) character.
For more information on the visudo
command, run
man 8 visudo
.
2.2.2 Basic sudoers configuration syntax #
The sudoers configuration files contain two types of options: strings and flags. While strings can contain any value, flags can be turned either ON or OFF. The most important syntax constructs for sudoers configuration files are as follows:
# Everything on a line after # is ignored 1 Defaults !insults # Disable the insults flag 2 Defaults env_keep += "DISPLAY HOME" # Add DISPLAY and HOME to env_keep tux ALL = NOPASSWD: /usr/bin/frobnicate, PASSWD: /usr/bin/journalctl 3
There are two exceptions: | |
Remove the | |
-
targetpw
This flag controls whether the invoking user is required to enter the password of the target user (ON) (for example
root
) or the invoking user (OFF).Defaults targetpw # Turn targetpw flag ON
-
rootpw
If set,
sudo
prompts for theroot
password. The default is OFF.Defaults !rootpw # Turn rootpw flag OFF
-
env_reset
If set,
sudo
constructs a minimal environment withTERM
,PATH
,HOME
,MAIL
,SHELL
,LOGNAME
,USER
,USERNAME
, andSUDO_*
. Additionally, variables listed inenv_keep
are imported from the calling environment. The default is ON.Defaults env_reset # Turn env_reset flag ON
-
env_keep
List of environment variables to keep when the
env_reset
flag is ON.# Set env_keep to contain EDITOR and PROMPT Defaults env_keep = "EDITOR PROMPT" Defaults env_keep += "JRE_HOME" # Add JRE_HOME Defaults env_keep -= "JRE_HOME" # Remove JRE_HOME
-
env_delete
List of environment variables to remove when the
env_reset
flag is OFF.# Set env_delete to contain EDITOR and PROMPT Defaults env_delete = "EDITOR PROMPT" Defaults env_delete += "JRE_HOME" # Add JRE_HOME Defaults env_delete -= "JRE_HOME" # Remove JRE_HOME
The Defaults
token can also be used to create aliases
for a collection of users, hosts, and commands. Furthermore, it is possible
to apply an option only to a specific set of users.
For detailed information about the /etc/sudoers
configuration file, consult man 5 sudoers
.
2.2.3 Basic sudoers rules #
Each rule follows the following scheme
([]
marks optional parts):
#Who Where As whom Tag What User_List Host_List = [(User_List)] [NOPASSWD:|PASSWD:] Cmnd_List
User_List
One or several (separated by comma) identifiers: either a user name, a group in the format
%GROUPNAME
, or a user ID in the format#UID
. Negation can be specified with the!
prefix.Host_List
One or several (separated by comma) identifiers: either a (fully qualified) host name or an IP address. Negation can be specified with the
!
prefix.ALL
is a common choice forHost_List
.NOPASSWD:|PASSWD:
The user is not prompted for a password when running commands matching
Cmd_List
afterNOPASSWD:
.PASSWD
is the default. It only needs to be specified when bothPASSWD
andNOPASSWD
are on the same line:tux ALL = PASSWD: /usr/bin/foo, NOPASSWD: /usr/bin/bar
Cmnd_List
One or several (separated by comma) specifiers: A path to an executable, followed by an optional allowed argument.
/usr/bin/foo # Anything allowed /usr/bin/foo bar # Only "/usr/bin/foo bar" allowed /usr/bin/foo "" # No arguments allowed
ALL
can be used as User_List
,
Host_List
, and Cmnd_List
.
A rule that allows tux
to run all commands as root without
entering a password:
tux ALL = NOPASSWD: ALL
A rule that allows tux
to run systemctl restart
apache2
:
tux ALL = /usr/bin/systemctl restart apache2
A rule that allows tux
to run wall
as
admin
with no arguments:
tux ALL = (admin) /usr/bin/wall ""
Do not use rules like ALL ALL =
ALL
without Defaults targetpw
. Otherwise
anyone can run commands as root
.
2.3 sudo
use cases #
While the default configuration works for standard usage scenarios, you can customize the default configuration to meet your specific needs.
2.3.1 Using sudo
without root
password #
By design, members of the group
wheel
can run all commands
with sudo
as root. The following procedure explains how to add a user
account to the wheel
group.
Verify that the
wheel
group exists:>
getent group wheel
If the previous command returned no result, install the system-group-wheel package that creates the
wheel
group:>
sudo
zypper install system-group-wheel
Add your user account to the group
wheel
.If your user account is not already a member of the
wheel
group, add it using thesudo usermod -a -G wheel USERNAME
command. Log out and log in again to enable the change. Verify that the change was successful by running thegroups USERNAME
command.Authenticate with the user account's normal password.
Create the file
/etc/sudoers.d/userpw
using thevisudo
command (see Section 2.2.1, “Editing the configuration files”) and add the following:Defaults !targetpw
Select a new default rule.
Depending on whether you want users to re-enter their passwords, uncomment the appropriate line in
/etc/sudoers
and comment out the default rule.## Uncomment to allow members of group wheel to execute any command # %wheel ALL=(ALL) ALL ## Same thing without a password # %wheel ALL=(ALL) NOPASSWD: ALL
Make the default rule more restrictive.
Comment out or remove the allow-everything rule in
/etc/sudoers
:ALL ALL=(ALL) ALL # WARNING! Only use this together with 'Defaults targetpw'!
Warning: Dangerous rule in sudoersDo not skip this step. Otherwise any user can execute any command as
root
!Test the configuration.
Run
sudo
as member and non-member ofwheel
.tux:~ >
groups users wheeltux:~ >
sudo id -un tux's password: rootwilber:~ >
groups userswilber:~ >
sudo id -un wilber is not in the sudoers file. This incident will be reported.
2.3.2 Using sudo
with X.Org applications #
Starting graphical applications with sudo
usually results in the following
error:
>
sudo
xterm xterm: Xt error: Can't open display: %s xterm: DISPLAY is not set
A simple workaround is to use xhost to temporarily allow the root user to access the local user's X session. This is done using the following command:
xhost si:localuser:root
The command below removes the granted access:
xhost -si:localuser:root
Running graphical applications with root privileges has security implications. It is recommended to enable root access for a graphical application only as an exception. It is also recommended to revoke the granted root access as soon as the graphical application is closed.
2.4 More information #
The sudo --help
command offers a brief overview of the
available command line options, while the man sudoers
command provides detailed information about sudoers
and its configuration.
3 Using YaST #
YaST is a SUSE Linux Enterprise Server tool that provides a graphical interface for all essential installation and system configuration tasks. Whether you need to update packages, configure a printer, modify firewall settings, set up an FTP server, or partition a hard disk—you can do it using YaST. Written in Ruby, YaST features an extensible architecture that makes it possible to add new functionality via modules.
Additional information about YaST is available on the project's official Web site at https://yast.opensuse.org/.
3.1 YaST interface overview #
YaST has two graphical interfaces: one for use with graphical desktop environments like KDE and GNOME, and an ncurses-based pseudo-graphical interface for use on systems without an X server (see Chapter 4, YaST in text mode).
In the graphical version of YaST, all modules in YaST are grouped by category, and the navigation sidebar allows you to quickly access modules in the desired category. The search field at the top makes it possible to find modules by their names. To find a specific module, enter its name into the search field, and you should see the modules that match the entered string as you type.
The list of installed modules for the ncurses-based and GUI version of YaST may differ. Before starting any YaST module, verify that it is installed for the version of YaST that you are using.
3.2 Useful key combinations #
The graphical version of YaST supports keyboard shortcuts
- Print Screen
Take and save a screenshot. It may not work on certain desktop environments.
- Shift–F4
Enable and disable the color palette optimized for visually-impaired users.
- Shift–F7
Enable/disable logging of debug messages.
- Shift–F8
Open a file dialog to save log files to a user-defined location.
- Ctrl–Shift–Alt–D
Send a DebugEvent. YaST modules can react to this by executing special debugging actions. The result depends on the specific YaST module.
- Ctrl–Shift–Alt–M
Start and stop macro recorder.
- Ctrl–Shift–Alt–P
Replay macro.
- Ctrl–Shift–Alt–S
Show style sheet editor.
- Ctrl–Shift–Alt–T
Dump widget tree to the log file.
- Ctrl–Shift–Alt–X
Open a terminal window (xterm). Useful for installation process via VNC.
- Ctrl–Shift–Alt–Y
Show widget tree browser.
4 YaST in text mode #
The ncurses-based pseudo-graphical YaST interface is designed primarily to help system administrators to manage systems without an X server. The interface offers several advantages compared to the conventional GUI. You can navigate the ncurses interface using the keyboard, and there are keyboard shortcuts for practically all interface elements. The ncurses interface is light on resources, and runs fast even on modest hardware. You can run the ncurses-based version of YaST via an SSH connection, so you can administer remote systems. Keep in mind that the minimum supported size of the terminal emulator in which to run YaST is 80x25 characters.
To launch the ncurses-based version of YaST, open the terminal and run the
sudo yast2
command. Use the Tab or
arrow keys to navigate between interface elements like menu
items, fields, and buttons. All menu items and buttons in YaST can be
accessed using the appropriate function keys or keyboard shortcuts. For
example, you can cancel the current operation by pressing
F9, while the F10 key can be used to accept
the changes. Each menu item and button in YaST's ncurses-based interface
has a highlighted letter in its label. This letter is part of the keyboard
shortcut assigned to the interface element. For example, the letter
Q
is highlighted in the
button. This means that you can activate the button by pressing
Alt–Alt+Q.
If a YaST dialog gets corrupted or distorted (for example, while resizing the window), press Ctrl–L to refresh and restore its contents.
4.2 Advanced key combinations #
The ncurses-based version of YaST offers several advanced key combinations.
- Shift–F1
List advanced hotkeys.
- Shift–F4
Change color schema.
- Ctrl–Q
Quit the application.
- Ctrl–L
Refresh screen.
- Ctrl–DF1
List advanced hotkeys.
- Ctrl–DShift–D
Dump dialog to the log file as a screenshot.
- Ctrl–DShift–Y
Open YDialogSpy to see the widget hierarchy.
4.3 Restriction of key combinations #
If your window manager uses global Alt combinations, the Alt combinations in YaST might not work. Keys like Alt or Shift can also be occupied by the settings of the terminal.
- Using Alt instead of Esc
Alt shortcuts can be executed with Esc instead of Alt. For example, Esc–H replaces Alt–H. (Press Esc, then press H.)
- Backward and forward navigation with Ctrl–F and Ctrl–B
If the Alt and Shift combinations are taken over by the window manager or the terminal, use the combinations Ctrl–F (forward) and Ctrl–B (backward) instead.
- Restriction of function keys
The function keys (F1 ... F12) are also used for functions. Certain function keys might be taken over by the terminal and may not be available for YaST. However, the Alt key combinations and function keys should always be fully available on a text-only console.
4.4 YaST command line options #
Besides the text mode interface, YaST provides a command line interface. To get a list of YaST command line options, use the following command:
>
sudo
yast -h
4.4.1 Installing packages from the command line #
If you know the package name, and the package is provided by an active
installation repository, you can use the command line option
-i
to install the package:
>
sudo
yast -i package_name
or
>
sudo
yast --install -i package_name
package_name can be a single short package name (for example gvim) installed with dependency checking, or the full path to an RPM package, which is installed without dependency checking.
While YaST offers basic functionality for managing software from the command line, consider using Zypper for more advanced package management tasks. Find more information on using Zypper in Section 6.1, “Using Zypper”.
4.4.2 Working with individual modules #
To save time, you can start individual YaST modules using the following command:
>
sudo
yast module_name
View a list of all modules available on your system with yast
-l
or yast --list
.
4.4.3 Command line parameters of YaST modules #
To use YaST functionality in scripts, YaST provides command line support for individual modules. However, not all modules have command line support. To display the available options of a module, use the following command:
>
sudo
yast module_name help
If a module does not provide command line support, it is started in a text mode with the following message:
This YaST module does not support the command line interface.
The following sections describe all YaST modules with command line support, along with a brief explanation of all their commands and available options.
4.4.3.1 Common YaST module commands #
All YaST modules support the following commands:
- help
Lists all the module's supported commands with their description:
>
sudo
yast lan help- longhelp
Same as
help
, but adds a detailed list of all command's options and their descriptions:>
sudo
yast lan longhelp- xmlhelp
Same as
longhelp
, but the output is structured as an XML document and redirected to a file:>
sudo
yast lan xmlhelp xmlfile=/tmp/yast_lan.xml- interactive
Enters the interactive mode. This lets you run the module's commands without prefixing them with
sudo yast
. Useexit
to leave the interactive mode.
4.4.3.2 yast add-on #
Adds a new add-on product from the specified path:
>
sudo
yast add-on http://server.name/directory/Lang-AddOn-CD1/
You can use the following protocols to specify the source path: http:// ftp:// nfs:// disk:// cd:// or dvd://.
4.4.3.3 yast audit-laf #
Displays and configures the Linux Audit Framework. Refer to the Book “Security and Hardening Guide” for more details. yast audit-laf
accepts the following commands:
- set
Sets an option:
>
sudo
yast audit-laf set log_file=/tmp/audit.logFor a complete list of options, run
yast audit-laf set help
.- show
Displays settings of an option:
>
sudo
yast audit-laf show diskspace space_left: 75 space_left_action: SYSLOG admin_space_left: 50 admin_space_left_action: SUSPEND action_mail_acct: root disk_full_action: SUSPEND disk_error_action: SUSPENDFor a complete list of options, run
yast audit-laf show help
.
4.4.3.4 yast dhcp-server #
Manages the DHCP server and configures its settings. yast
dhcp-server
accepts the following commands:
- disable
Disables the DHCP server service.
- enable
Enables the DHCP server service.
- host
Configures settings for individual hosts.
- interface
Specifies to which network interface to listen to:
>
sudo
yast dhcp-server interface current Selected Interfaces: eth0 Other Interfaces: bond0, pbu, eth1For a complete list of options, run
yast dhcp-server interface help
.- options
Manages global DHCP options. For a complete list of options, run
yast dhcp-server options help
.- status
Prints the status of the DHCP service.
- subnet
Manages the DHCP subnet options. For a complete list of options, run
yast dhcp-server subnet help
.
4.4.3.5 yast dns-server #
Manages the DNS server configuration. yast dns-server
accepts the following commands:
- acls
Displays access control list settings:
>
sudo
yast dns-server acls show ACLs: ----- Name Type Value ---------------------------- any Predefined localips Predefined localnets Predefined none Predefined- dnsrecord
Configures zone resource records:
>
sudo
yast dnsrecord add zone=example.org query=office.example.org type=NS value=ns3For a complete list of options, run
yast dns-server dnsrecord help
.- forwarders
Configures DNS forwarders:
>
sudo
yast dns-server forwarders add ip=10.0.0.100>
sudo
yast dns-server forwarders show [...] Forwarder IP ------------ 10.0.0.100For a complete list of options, run
yast dns-server forwarders help
.- host
Handles 'A' and its related 'PTR' record at once:
>
sudo
yast dns-server host show zone=example.orgFor a complete list of options, run
yast dns-server host help
.- logging
Configures logging settings:
>
sudo
yast dns-server logging set updates=no transfers=yesFor a complete list of options, run
yast dns-server logging help
.- mailserver
Configures zone mail servers:
>
sudo
yast dns-server mailserver add zone=example.org mx=mx1 priority=100For a complete list of options, run
yast dns-server mailserver help
.- nameserver
Configures zone name servers:
>
sudo
yast dns-server nameserver add zone=example.com ns=ns1For a complete list of options, run
yast dns-server nameserver help
.- soa
Configures the start of authority (SOA) record:
>
sudo
yast dns-server soa set zone=example.org serial=2006081623 ttl=2D3H20SFor a complete list of options, run
yast dns-server soa help
.- startup
Manages the DNS server service:
>
sudo
yast dns-server startup atbootFor a complete list of options, run
yast dns-server startup help
.- transport
Configures zone transport rules. For a complete list of options, run
yast dns-server transport help
.- zones
Manages DNS zones:
>
sudo
yast dns-server zones add name=example.org zonetype=masterFor a complete list of options, run
yast dns-server zones help
.
4.4.3.6 yast disk #
Prints information about all disks or partitions. The only supported
command is list
followed by either of the following
options:
- disks
Lists all configured disks in the system:
>
sudo
yast disk list disks Device | Size | FS Type | Mount Point | Label | Model ---------+------------+---------+-------------+-------+------------- /dev/sda | 119.24 GiB | | | | SSD 840 /dev/sdb | 60.84 GiB | | | | WD1003FBYX-0- partitions
Lists all partitions in the system:
>
sudo
yast disk list partitions Device | Size | FS Type | Mount Point | Label | Model ---------------+------------+---------+-------------+-------+------ /dev/sda1 | 1.00 GiB | Ext2 | /boot | | /dev/sdb1 | 1.00 GiB | Swap | swap | | /dev/sdc1 | 698.64 GiB | XFS | /mnt/extra | | /dev/vg00/home | 580.50 GiB | Ext3 | /home | | /dev/vg00/root | 100.00 GiB | Ext3 | / | | [...]
4.4.3.7 yast ftp-server #
Configures FTP server settings. yast ftp-server
accepts
the following options:
- SSL, TLS
Controls secure connections via SSL and TLS. SSL options are valid for the
vsftpd
only.>
sudo
yast ftp-server SSL enable>
sudo
yast ftp-server TLS disable- access
Configures access permissions:
>
sudo
yast ftp-server access authen_onlyFor a complete list of options, run
yast ftp-server access help
.- anon_access
Configures access permissions for anonymous users:
>
sudo
yast ftp-server anon_access can_uploadFor a complete list of options, run
yast ftp-server anon_access help
.- anon_dir
Specifies the directory for anonymous users. The directory must already exist on the server:
>
sudo
yast ftp-server anon_dir set_anon_dir=/srv/ftpFor a complete list of options, run
yast ftp-server anon_dir help
.- chroot
Controls change root environment (chroot):
>
sudo
yast ftp-server chroot enable>
sudo
yast ftp-server chroot disable- idle-time
Sets the maximum idle time in minutes before FTP server terminates the current connection:
>
sudo
yast ftp-server idle-time set_idle_time=15- logging
Determines whether to save the log messages into a log file:
>
sudo
yast ftp-server logging enable>
sudo
yast ftp-server logging disable- max_clients
Specifies the maximum number of concurrently connected clients:
>
sudo
yast ftp-server max_clients set_max_clients=1500- max_clients_ip
Specifies the maximum number of concurrently connected clients via IP:
>
sudo
yast ftp-server max_clients_ip set_max_clients=20- max_rate_anon
Specifies the maximum data transfer rate permitted for anonymous clients (KB/s):
>
sudo
yast ftp-server max_rate_anon set_max_rate=10000- max_rate_authen
Specifies the maximum data transfer rate permitted for locally authenticated users (KB/s):
>
sudo
yast ftp-server max_rate_authen set_max_rate=10000- port_range
Specifies the port range for passive connection replies:
>
sudo
yast ftp-server port_range set_min_port=20000 set_max_port=30000For a complete list of options, run
yast ftp-server port_range help
.- show
Displays FTP server settings.
- startup
Controls the FTP start-up method:
>
sudo
yast ftp-server startup atbootFor a complete list of options, run
yast ftp-server startup help
.- umask
Specifies the file umask for
authenticated:anonymous
users:>
sudo
yast ftp-server umask set_umask=177:077- welcome_message
Specifies the text to display when someone connects to the FTP server:
>
sudo
yast ftp-server welcome_message set_message="hello everybody"
4.4.3.8 yast http-server #
Configures the HTTP server (Apache2). yast http-server
accepts the following commands:
- configure
Configures the HTTP server host settings:
>
sudo
yast http-server configure host=main servername=www.example.com \ serveradmin=admin@example.comFor a complete list of options, run
yast http-server configure help
.
- hosts
Configures virtual hosts:
>
sudo
yast http-server hosts create servername=www.example.com \ serveradmin=admin@example.com documentroot=/var/wwwFor a complete list of options, run
yast http-server hosts help
.
- listen
Specifies the ports and network addresses where the HTTP server should listen:
>
sudo
yast http-server listen add=81>
sudo
yast http-server listen list Listen Statements: ================== :80 :81>
sudo
yast http-server delete=80For a complete list of options, run
yast http-server listen help
.
- mode
Enables or disables the wizard mode:
>
sudo
yast http-server mode wizard=on
- modules
Controls the Apache2 server modules:
>
sudo
yast http-server modules enable=php5,rewrite>
sudo
yast http-server modules disable=ssl>
sudo
http-server modules list [...] Enabled rewrite Disabled ssl Enabled php5 [...]
4.4.3.9 yast kdump #
Configures kdump
settings. For more information
on kdump
, refer to the
Book “System Analysis and Tuning Guide”, Chapter 20 “Kexec and Kdump”, Section 20.7 “Basic Kdump configuration”. yast kdump
accepts the following commands:
- copykernel
Copies the kernel into the dump directory.
- customkernel
Specifies the kernel_string part of the name of the custom kernel. The naming scheme is
/boot/vmlinu[zx]-kernel_string[.gz]
.>
sudo
yast kdump customkernel kernel=kdumpFor a complete list of options, run
yast kdump customkernel help
.- dumpformat
Specifies the (compression) format of the dump kernel image. Available formats are 'none', 'ELF', 'compressed', or 'lzo':
>
sudo
yast kdump dumpformat dump_format=ELF- dumplevel
Specifies the dump level number in the range from 0 to 31:
>
sudo
yast kdump dumplevel dump_level=24- dumptarget
Specifies the destination for saving dump images:
>
sudo
kdump dumptarget taget=ssh server=name_server port=22 \ dir=/var/log/dump user=user_nameFor a complete list of options, run
yast kdump dumptarget help
.- immediatereboot
Controls whether the system should reboot immediately after saving the core in the kdump kernel:
>
sudo
yast kdump immediatereboot enable>
sudo
yast kdump immediatereboot disable- keepolddumps
Specifies how many old dump images are kept. Specify zero to keep them all:
>
sudo
yast kdump keepolddumps no=5- kernelcommandline
Specifies the command line that needs to be passed off to the kdump kernel:
>
sudo
yast kdump kernelcommandline command="ro root=LABEL=/"- kernelcommandlineappend
Specifies the command line that you need to append to the default command line string:
>
sudo
yast kdump kernelcommandlineappend command="ro root=LABEL=/"- notificationcc
Specifies an e-mail address for sending copies of notification messages:
>
sudo
yast kdump notificationcc email="user1@example.com user2@example.com"- notificationto
Specifies an e-mail address for sending notification messages:
>
sudo
yast kdump notificationto email="user1@example.com user2@example.com"- show
Displays
kdump
settings:>
sudo
yast kdump show Kdump is disabled Dump Level: 31 Dump Format: compressed Dump Target Settings target: file file directory: /var/crash Kdump immediate reboots: Enabled Numbers of old dumps: 5- smtppass
Specifies the file with the plain text SMTP password used for sending notification messages:
>
sudo
yast kdump smtppass pass=/path/to/file- smtpserver
Specifies the SMTP server host name used for sending notification messages:
>
sudo
yast kdump smtpserver server=smtp.server.com- smtpuser
Specifies the SMTP user name used for sending notification messages:
>
sudo
yast kdump smtpuser user=smtp_user- startup
Enables or disables start-up options:
>
sudo
yast kdump startup enable alloc_mem=128,256>
sudo
yast kdump startup disable
4.4.3.10 yast keyboard #
Configures the system keyboard for virtual consoles. It does not affect
the keyboard settings in graphical desktop environments, such as GNOME
or KDE. yast keyboard
accepts the following commands:
- list
Lists all available keyboard layouts.
- set
Activates new keyboard layout setting:
>
sudo
yast keyboard set layout=czech- summary
Displays the current keyboard configuration.
4.4.3.11 yast lan #
Configures network cards. yast lan
accepts the
following commands:
- add
Configures a new network card:
>
sudo
yast lan add name=vlan50 ethdevice=eth0 bootproto=dhcpFor a complete list of options, run
yast lan add help
.- delete
Deletes an existing network card:
>
sudo
yast lan delete id=0- edit
Changes the configuration of an existing network card:
>
sudo
yast lan edit id=0 bootproto=dhcp- list
Displays a summary of network card configuration:
>
sudo
yast lan list id name, bootproto 0 Ethernet Card 0, NONE 1 Network Bridge, DHCP
4.4.3.12 yast language #
Configures system languages. yast language
accepts the
following commands:
- list
Lists all available languages.
- set
Specifies the main system languages and secondary languages:
>
sudo
yast language set lang=cs_CZ languages=en_US,es_ES no_packages
4.4.3.13 yast mail #
Displays the configuration of the mail system:
>
sudo
yast mail summary
4.4.3.14 yast nfs #
Controls the NFS client. yast nfs
accepts the following
commands:
- add
Adds a new NFS mount:
>
sudo
yast nfs add spec=remote_host:/path/to/nfs/share file=/local/mount/pointFor a complete list of options, run
yast nfs add help
.- delete
Deletes an existing NFS mount:
>
sudo
yast nfs delete spec=remote_host:/path/to/nfs/share file=/local/mount/pointFor a complete list of options, run
yast nfs delete help
.- edit
Changes an existing NFS mount:
>
sudo
yast nfs edit spec=remote_host:/path/to/nfs/share \ file=/local/mount/point type=nfs4For a complete list of options, run
yast nfs edit help
.- list
Lists existing NFS mounts:
>
sudo
yast nfs list Server Remote File System Mount Point Options ---------------------------------------------------------------- nfs.example.com /mnt /nfs/mnt nfs nfs.example.com /home/tux/nfs_share /nfs/tux nfs
4.4.3.15 yast nfs-server #
Configures the NFS server. yast nfs-server
accepts the
following commands:
- add
Adds a directory to export:
>
sudo
yast nfs-server add mountpoint=/nfs/export hosts=*.allowed_hosts.comFor a complete list of options, run
yast nfs-server add help
.- delete
Deletes a directory from the NFS export:
>
sudo
yast nfs-server delete mountpoint=/nfs/export- set
Specifies additional parameters for the NFS server:
>
sudo
yast nfs-server set enablev4=yes security=yesFor a complete list of options, run
yast nfs-server set help
.- start
Starts the NFS server service:
>
sudo
yast nfs-server start- stop
Stops the NFS server service:
>
sudo
yast nfs-server stop- summary
Displays a summary of the NFS server configuration:
>
sudo
yast nfs-server summary NFS server is enabled NFS Exports * /mnt * /home NFSv4 support is enabled. The NFSv4 domain for idmapping is localdomain. NFS Security using GSS is enabled.
4.4.3.16 yast nis #
Configures the NIS client. yast nis
accepts the
following commands:
- configure
Changes global settings of a NIS client:
>
sudo
yast nis configure server=nis.example.com broadcast=yesFor a complete list of options, run
yast nis configure help
.- disable
Disables the NIS client:
>
sudo
yast nis disable- enable
Enables your machine as NIS client:
>
sudo
yast nis enable server=nis.example.com broadcast=yes automounter=yesFor a complete list of options, run
yast nis enable help
.- find
Shows available NIS servers for a given domain:
>
sudo
yast nis find domain=nisdomain.com- summary
Displays a configuration summary of a NIS client.
4.4.3.17 yast nis-server #
Configures a NIS server. yast nis-server
accepts the
following commands:
- master
Configures a NIS master server:
>
sudo
yast nis-server master domain=nisdomain.com yppasswd=yesFor a complete list of options, run
yast nis-server master help
.- slave
Configures a NIS slave server:
>
sudo
yast nis-server slave domain=nisdomain.com master_ip=10.100.51.65For a complete list of options, run
yast nis-server slave help
.- stop
Stops a NIS server:
>
sudo
yast nis-server stop- summary
Displays a configuration summary of a NIS server:
>
sudo
yast nis-server summary
4.4.3.18 yast proxy #
Configures proxy settings. yast proxy
accepts the
following commands:
- authentication
Specifies the authentication options for proxy:
>
sudo
yast proxy authentication username=tux password=secretFor a complete list of options, run
yast proxy authentication help
.- enable, disable
Enables or disables proxy settings.
- set
Changes the current proxy settings:
>
sudo
yast proxy set https=proxy.example.comFor a complete list of options, run
yast proxy set help
.- summary
Displays proxy settings.
4.4.3.19 yast rdp #
Controls remote desktop settings. yast rdp
accepts the
following commands:
- allow
Allows remote access to the server's desktop:
>
sudo
yast rdp allow set=yes- list
Displays the remote desktop configuration summary.
4.4.3.20 yast samba-client #
Configures the Samba client settings. yast samba-client
accepts the following commands:
- configure
Changes global settings of Samba:
>
sudo
yast samba-client configure workgroup=FAMILY- isdomainmember
Checks whether the machine is a member of a domain:
>
sudo
yast samba-client isdomainmember domain=SMB_DOMAIN- joindomain
Makes the machine a member of a domain:
>
sudo
yast samba-client joindomain domain=SMB_DOMAIN user=username password=pwd- winbind
Enables or disables Winbind services (the
winbindd
daemon):>
sudo
yast samba-client winbind enable>
sudo
yast samba-client winbind disable
4.4.3.21 yast samba-server #
Configures Samba server settings. yast samba-server
accepts the following commands:
- backend
Specifies the back-end for storing user information:
>
sudo
yast samba-server backend smbpasswdFor a complete list of options, run
yast samba-server backend help
.- configure
Configures global settings of the Samba server:
>
sudo
yast samba-server configure workgroup=FAMILY description='Home server'For a complete list of options, run
yast samba-server configure help
.- list
Displays a list of available shares:
>
sudo
yast samba-server list Status Type Name ============================== Disabled Disk profiles Enabled Disk print$ Enabled Disk homes Disabled Disk groups Enabled Disk movies Enabled Printer printers- role
Specifies the role of the Samba server:
>
sudo
yast samba-server role standaloneFor a complete list of options, run
yast samba-server role help
.- service
Enables or disables the Samba services (
smb
andnmb
):>
sudo
yast samba-server service enable>
sudo
yast samba-server service disable- share
Manipulates a single Samba share:
>
sudo
yast samba-server share name=movies browseable=yes guest_ok=yesFor a complete list of options, run
yast samba-server share help
.
4.4.3.22 yast security #
Controls the security level of the host. yast security
accepts the following commands:
- level
Specifies the security level of the host:
>
sudo
yast security level serverFor a complete list of options, run
yast security level help
.- set
Sets the value of a specific option:
>
sudo
yast security set passwd=sha512 crack=yesFor a complete list of options, run
yast security set help
.- summary
Displays a summary of the current security configuration:
sudo
yast security summary
4.4.3.23 yast sound #
Configures sound card settings. yast sound
accepts the
following commands:
- add
Configures a new sound card. Without any parameters, the command adds the first detected card.
>
sudo
yast sound add card=0 volume=75For a complete list of options, run
yast sound add help
.- channels
Lists available volume channels of a sound card:
>
sudo
yast sound channels card=0 Master 75 PCM 100- modules
Lists all available sound kernel modules:
>
sudo
yast sound modules snd-atiixp ATI IXP AC97 controller (snd-atiixp) snd-atiixp-modem ATI IXP MC97 controller (snd-atiixp-modem) snd-virtuoso Asus Virtuoso driver (snd-virtuoso) [...]- playtest
Plays a test sound on a sound card:
>
sudo
yast sound playtest card=0- remove
Removes a configured sound card:
>
sudo
yast sound remove card=0>
sudo
yast sound remove all- set
Specifies new values for a sound card:
>
sudo
yast sound set card=0 volume=80- show
Displays detailed information about a sound card:
>
sudo
yast sound show card=0 Parameters of card 'ThinkPad X240' (using module snd-hda-intel): align_buffer_size Force buffer and period sizes to be multiple of 128 bytes. bdl_pos_adj BDL position adjustment offset. beep_mode Select HDA Beep registration mode (0=off, 1=on) (default=1). Default Value: 0 enable_msi Enable Message Signaled Interrupt (MSI) [...]- summary
Prints a configuration summary for all sound cards on the system:
>
sudo
yast sound summary- volume
Specifies the volume level of a sound card:
sudo
yast sound volume card=0 play
4.4.3.24 yast sysconfig #
Controls the variables in files under /etc/sysconfig
.
yast sysconfig
accepts the following commands:
- clear
Sets empty value to a variable:
>
sudo
yast sysconfig clear=POSTFIX_LISTENTip: Variable in multiple filesIf the variable is available in several files, use the VARIABLE_NAME$FILE_NAME syntax:
>
sudo
yast sysconfig clear=CONFIG_TYPE$/etc/sysconfig/mail- details
Displays detailed information about a variable:
>
sudo
yast sysconfig details variable=POSTFIX_LISTEN Description: Value: File: /etc/sysconfig/postfix Possible Values: Any value Default Value: Configuration Script: postfix Description: Comma separated list of IP's NOTE: If not set, LISTEN on all interfaces- list
Displays summary of modified variables. Use
all
to list all variables and their values:>
sudo
yast sysconfig list all AOU_AUTO_AGREE_WITH_LICENSES="false" AOU_ENABLE_CRONJOB="true" AOU_INCLUDE_RECOMMENDS="false" [...]- set
Sets a value for a variable:
>
sudo
yast sysconfig set DISPLAYMANAGER=gdmTip: Variable in multiple filesIf the variable is available in several files, use the VARIABLE_NAME$FILE_NAME syntax:
>
sudo
yast sysconfig set CONFIG_TYPE$/etc/sysconfig/mail=advanced
4.4.3.25 yast tftp-server #
Configures a TFTP server. yast tftp-server
accepts the
following commands:
- directory
Specifies the directory of the TFTP server:
>
sudo
yast tftp-server directory path=/srv/tftp>
sudo
yast tftp-server directory list Directory Path: /srv/tftp- status
Controls the status of the TFTP server service:
>
sudo
yast tftp-server status disable>
sudo
yast tftp-server status show Service Status: false>
sudo
yast tftp-server status enable
4.4.3.26 yast timezone #
Configures the time zone. yast timezone
accepts the
following commands:
- list
Lists all available time zones grouped by region:
>
sudo
yast timezone list Region: Africa Africa/Abidjan (Abidjan) Africa/Accra (Accra) Africa/Addis_Ababa (Addis Ababa) [...]- set
Specifies new values for the time zone configuration:
>
sudo
yast timezone set timezone=Europe/Prague hwclock=local- summary
Displays the time zone configuration summary:
>
sudo
yast timezone summary Current Time Zone: Europe/Prague Hardware Clock Set To: Local time Current Time and Date: Mon 12. March 2018, 11:36:21 CET
4.4.3.27 yast users #
Manages user accounts. yast users
accepts the following
commands:
- add
Adds a new user:
>
sudo
yast users add username=user1 password=secret home=/home/user1For a complete list of options, run
yast users add help
.- delete
Deletes an existing user account:
>
sudo
yast users delete username=user1 delete_homeFor a complete list of options, run
yast users delete help
.- edit
Changes an existing user account:
>
sudo
yast users edit username=user1 password=new_secretFor a complete list of options, run
yast users edit help
.- list
Lists existing users filtered by user type:
>
sudo
yast users list systemFor a complete list of options, run
yast users list help
.- show
Displays details about a user:
>
sudo
yast users show username=wwwrun Full Name: WWW daemon apache List of Groups: www Default Group: wwwrun Home Directory: /var/lib/wwwrun Login Shell: /sbin/nologin Login Name: wwwrun UID: 456For a complete list of options, run
yast users show help
.
5 YaST online update #
SUSE offers a continuous stream of software security updates for your product. By default, the update applet is used to keep your system up-to-date. Refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.5 “The GNOME package updater” for further information on the update applet. This chapter covers the alternative tool for updating software packages: YaST Online Update.
The current patches for SUSE® Linux Enterprise Server are available from an update software repository. If you have registered your product during the installation, an update repository is already configured. If you have not registered SUSE Linux Enterprise Server, you can do so by starting the in YaST. Alternatively, you can manually add an update repository from a source you trust. To add or remove repositories, start the Repository Manager with › in YaST. Learn more about the Repository Manager in Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.4 “Managing software repositories and services”.
If you are not able to access the update catalog, this might be because of an expired subscription. Normally, SUSE Linux Enterprise Server comes with a one-year or three-year subscription, during which you have access to the update catalog. This access will be denied after the subscription ends.
If an access to the update catalog is denied, you will see a warning message prompting you to visit the SUSE Customer Center and check your subscription. The SUSE Customer Center is available at https://scc.suse.com//.
By default, the firewall on SUSE Linux Enterprise Server only blocks incoming connections. If your system is behind another firewall that blocks outgoing traffic, make sure to allow connections to https://scc.suse.com/ and https://updates.suse.com on ports 80 and 443 in order to receive updates.
SUSE provides updates with different relevance levels:
- Security updates
Fix severe security hazards and should always be installed.
- Recommended updates
Fix issues that could compromise your computer.
- Optional updates
Fix non-security relevant issues or provide enhancements.
5.1 The online update dialog #
To open the YaST yast2 online_update
.
The
window consists of four sections.
The SUSE Linux Enterprise Server. The patches are sorted by security relevance:
security
, recommended
, and
optional
. You can change the view of the
section by selecting one of the following options
from :
- (default view)
Non-installed patches that apply to packages installed on your system.
Patches that either apply to packages not installed on your system, or patches that have requirements which have already have been fulfilled (because the relevant packages have already been updated from another source).
All patches available for SUSE Linux Enterprise Server.
Each list entry in the Shift–F1. Actions required by Security
and
Recommended
patches are automatically preset. These
actions are ,
and .
If you install an up-to-date package from a repository other than the update repository, the requirements of a patch for this package may be fulfilled with this installation. In this case a check mark is displayed in front of the patch summary. The patch will be visible in the list until you mark it for installation. This will in fact not install the patch (because the package already is up-to-date), but mark the patch as having been installed.
Select an entry in the
section to view a short at the bottom left corner of the dialog. The upper right section lists the packages included in the selected patch (a patch can consist of several packages). Click an entry in the upper right section to view details about the respective package that is included in the patch.5.2 Installing patches #
The YaST Online Update dialog allows you to either install all available patches at once or manually select the desired patches. You may also revert patches that have been applied to the system.
By default, all new patches (except optional
ones) that
are currently available for your system are already marked for installation.
They will be applied automatically once you click
or .
If one or multiple patches require a system reboot, you will be notified
about this before the patch installation starts. You can then either decide
to continue with the installation of the selected patches, skip the
installation of all patches that need rebooting and install the rest, or go
back to the manual patch selection.
Start YaST and select
› .To automatically apply all new patches (except
optional
ones) that are currently available for your system, click or .First modify the selection of patches that you want to apply:
Use the respective filters and views that the interface provides. For details, refer to Section 5.1, “The online update dialog”.
Select or deselect patches according to your needs and wishes by right-clicking the patch and choosing the respective action from the context menu.
Important: Always apply security updatesDo not deselect any
security
-related patches without a very good reason. These patches fix severe security hazards and prevent your system from being exploited.Most patches include updates for several packages. To change actions for single packages, right-click a package in the package view and choose an action.
To confirm your selection and apply the selected patches, proceed with
or .
After the installation is complete, click
to leave the YaST . Your system is now up-to-date.
5.3 Viewing retracted patches #
Maintenance updates are carefully tested, to minimize the risk of introducing a bug. If a patch proves to contain a bug, it is automatically retracted. A new update (with a higher version number) is issued to revert the buggy patch, and is blocked from being installed again. You can see retracted patches, and their history, on the
tab.5.4 Automatic online update #
You may configure automatic updates with a daily, weekly, or
monthly schedule with YaST. Install the
yast2-online-update-configuration
package.
By default, updates are downloaded as delta RPMs. Since rebuilding RPM packages from delta RPMs is a memory- and processor-intensive task, certain setups or hardware configurations might require you to disable the use of delta RPMs for the sake of performance.
Some patches, such as kernel updates or packages requiring license agreements, require user interaction, which would cause the automatic update procedure to stop. You can configure skipping patches that require user interaction.
Use the
tab in the YaST module to review available and installed patches, including references to bug reports and CVE bulletins.After installation, start YaST and select yast2-online-update-configuration is not installed, you will be prompted to do that.
› . Choose › . If theFigure 5.3: YaST online update configuration #Alternatively, start the module with
yast2 online_update_configuration
from the command line.Choose the update interval:
, , or .Sometimes patches may require the attention of the administrator, for example when restarting critical services. For example, this might be an update for Docker Open Source Engine that requires all containers to be restarted. Before these patches are installed, the user is informed about the consequences and is asked to confirm the installation of the patch. Such patches are called “Interactive Patches”.
When installing patches automatically, it is assumed that you have accepted the installation of interactive patches. If you prefer to review these patches before they get installed, check
. In this case, interactive patches will be skipped during automated patching. Make sure to periodically run a manual online update, to check whether interactive patches are waiting to be installed.To automatically accept any license agreements, activate
.To automatically install all packages recommended by updated packages, activate
.To disable the use of delta RPMs (for performance reasons), un-check
.To filter the patches by category (such as security or recommended), check
and add the appropriate patch categories from the list. Only patches of the selected categories will be installed. It is a good practice to enable only automatic updates, and to manually review all others. Patching is usually reliable, but you may wish to test non-security patches, and roll them back if you encounter any problems.supply patches for package management and YaST features and modules.
patches provide crucial updates and bugfixes.
patches are optional bugfixes and enhancements.
are new packages.
is equivalent to miscellaneous.
is unused.
Confirm your configuration by clicking
.
The automatic online update does not automatically restart the system afterward. If there are package updates that require a system reboot, you need to do this manually.
6 Managing software with command line tools #
This chapter describes Zypper and RPM, two command line tools for managing
software. For a definition of the terminology used in this context (for
example, repository
, patch
, or
update
) refer to
Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.1 “Definition of terms”.
6.1 Using Zypper #
Zypper is a command line package manager for installing, updating and removing packages. It also manages repositories. It is especially useful for accomplishing remote software management tasks or managing software from shell scripts.
6.1.1 General usage #
The general syntax of Zypper is:
zypper[--global-options]
COMMAND[--command-options]
[arguments]
The components enclosed in brackets are not required. See zypper
help
for a list of general options and all commands. To get help
for a specific command, type zypper help
COMMAND.
- Zypper commands
The simplest way to execute Zypper is to type its name, followed by a command. For example, to apply all needed patches to the system, use:
>
sudo
zypper patch- Global options
Additionally, you can choose from one or more global options by typing them immediately before the command:
>
sudo
zypper --non-interactive patchIn the above example, the option
--non-interactive
means that the command is run without asking anything (automatically applying the default answers).- Command-specific options
To use options that are specific to a particular command, type them immediately after the command:
>
sudo
zypper patch --auto-agree-with-licensesIn the above example,
--auto-agree-with-licenses
is used to apply all needed patches to a system without you being asked to confirm any licenses. Instead, licenses will be accepted automatically.- Arguments
Some commands require one or more arguments. For example, when using the command
install
, you need to specify which package or which packages you want to install:>
sudo
zypper install mplayerSome options also require a single argument. The following command will list all known patterns:
>
zypper search -t pattern
You can combine all of the above. For example, the following command will
install the mc and vim packages from
the factory
repository while being verbose:
>
sudo
zypper -v install --from factory mc vim
The --from
option keeps all repositories
enabled (for solving any dependencies) while requesting the package from the
specified repository. --repo
is an alias for --from
, and you may use either one.
Most Zypper commands have a dry-run
option that does a
simulation of the given command. It can be used for test purposes.
>
sudo
zypper remove --dry-run MozillaFirefox
Zypper supports the global --userdata
STRING
option. You can specify a string
with this option, which gets written to Zypper's log files and plug-ins
(such as the Btrfs plug-in). It can be used to mark and identify
transactions in log files.
>
sudo
zypper --userdata STRING patch
6.1.2 Using Zypper subcommands #
Zypper subcommands are executables that are stored in the zypper_execdir,
/usr/lib/zypper/commands
. If a subcommand is not found
in the zypper_execdir, Zypper automatically searches the rest of your $PATH
for it. This enables writing your own local extensions and storing them in
userspace.
Executing subcommands in the Zypper shell, and using global Zypper options are not supported.
List your available subcommands:
>
zypper help subcommand
[...]
Available zypper subcommands in '/usr/lib/zypper/commands'
appstream-cache
lifecycle
migration
search-packages
Zypper subcommands available from elsewhere on your $PATH
<none>
View the help screen for a subcommand:
>
zypper help appstream-cache
6.1.3 Installing and removing software with Zypper #
To install or remove packages, use the following commands:
>
sudo
zypper install PACKAGE_NAME>
sudo
zypper remove PACKAGE_NAME
Do not remove mandatory system packages like glibc , zypper , kernel . If they are removed, the system can become unstable or stop working altogether.
6.1.3.1 Selecting which packages to install or remove #
There are various ways to address packages with the commands
zypper install
and zypper remove
.
- By exact package name
>
sudo
zypper install MozillaFirefox- By exact package name and version number
>
sudo
zypper install MozillaFirefox-52.2- By repository alias and package name
>
sudo
zypper install mozilla:MozillaFirefoxWhere
mozilla
is the alias of the repository from which to install.- By package name using wild cards
You can select all packages that have names starting or ending with a certain string. Use wild cards with care, especially when removing packages. The following command will install all packages starting with “Moz”:
>
sudo
zypper install 'Moz*'Tip: Removing all-debuginfo
packagesWhen debugging a problem, you sometimes need to temporarily install a lot of
-debuginfo
packages which give you more information about running processes. After your debugging session finishes and you need to clean the environment, run the following:>
sudo
zypper remove '*-debuginfo'- By capability
For example, to install a package without knowing its name, capabilities come in handy. The following command will install the package MozillaFirefox:
>
sudo
zypper install firefox- By capability, hardware architecture, or version
Together with a capability, you can specify a hardware architecture and a version:
The name of the desired hardware architecture is appended to the capability after a full stop. For example, to specify the AMD64/Intel 64 architectures (which in Zypper is named
x86_64
), use:>
sudo
zypper install 'firefox.x86_64'Versions must be appended to the end of the string and must be preceded by an operator:
<
(lesser than),<=
(lesser than or equal),=
(equal),>=
(greater than or equal),>
(greater than).>
sudo
zypper install 'firefox>=74.2'You can also combine a hardware architecture and version requirement:
>
sudo
zypper install 'firefox.x86_64>=74.2'
- By path to the RPM file
You can also specify a local or remote path to a package:
>
sudo
zypper install /tmp/install/MozillaFirefox.rpm>
sudo
zypper install http://download.example.com/MozillaFirefox.rpm
6.1.3.2 Combining installation and removal of packages #
To install and remove packages simultaneously, use the
+/-
modifiers. To install emacs and
simultaneously remove vim , use:
>
sudo
zypper install emacs -vim
To remove emacs and simultaneously install vim , use:
>
sudo
zypper remove emacs +vim
To prevent the package name starting with the -
being
interpreted as a command option, always use it as the second argument. If
this is not possible, precede it with --
:
>
sudo
zypper install -emacs +vim # Wrong>
sudo
zypper install vim -emacs # Correct>
sudo
zypper install -- -emacs +vim # Correct>
sudo
zypper remove emacs +vim # Correct
6.1.3.3 Cleaning up dependencies of removed packages #
If (together with a certain package), you automatically want to remove any
packages that become unneeded after removing the specified package, use the
--clean-deps
option:
>
sudo
zypper rm --clean-deps PACKAGE_NAME
6.1.3.4 Using Zypper in scripts #
By default, Zypper asks for a confirmation before installing or removing a
selected package, or when a problem occurs. You can override this behavior
using the --non-interactive
option. This option must be
given before the actual command (install
,
remove
, and patch
), as can be seen in
the following:
>
sudo
zypper--non-interactive
install PACKAGE_NAME
This option allows the use of Zypper in scripts and cron jobs.
6.1.3.5 Installing or downloading source packages #
To install the corresponding source package of a package, use:
>
zypper source-install PACKAGE_NAME
When executed as root
, the default location to install source
packages is /usr/src/packages/
and
~/rpmbuild
when run as user. These values can be
changed in your local rpm
configuration.
This command will also install the build dependencies of the specified
package. If you do not want this, add the switch -D
:
>
sudo
zypper source-install -D PACKAGE_NAME
To install only the build dependencies use -d
.
>
sudo
zypper source-install -d PACKAGE_NAME
Of course, this will only work if you have the repository with the source packages enabled in your repository list (it is added by default, but not enabled). See Section 6.1.6, “Managing repositories with Zypper” for details on repository management.
A list of all source packages available in your repositories can be obtained with:
>
zypper search -t srcpackage
You can also download source packages for all installed packages to a local directory. To download source packages, use:
>
zypper source-download
The default download directory is
/var/cache/zypper/source-download
. You can change it
using the --directory
option. To only show missing or
extraneous packages without downloading or deleting anything, use the
--status
option. To delete extraneous source packages, use
the --delete
option. To disable deleting, use the
--no-delete
option.
6.1.3.6 Installing packages from disabled repositories #
Normally you can only install or refresh packages from enabled
repositories. The --plus-content
TAG
option helps you specify
repositories to be refreshed, temporarily enabled during the current Zypper
session, and disabled after it completes.
For example, to enable repositories that may provide additional
-debuginfo
or -debugsource
packages, use --plus-content debug
. You can specify this
option multiple times.
To temporarily enable such 'debug' repositories to install a specific
-debuginfo
package, use the option as follows:
>
sudo
zypper --plus-content debug \ install "debuginfo(build-id)=eb844a5c20c70a59fc693cd1061f851fb7d046f4"
The build-id
string is reported by
gdb
for missing debuginfo packages.
Repositories from the SUSE Linux Enterprise Server installation media are still
configured but disabled after successful installation. You can use the
--plus-content
option to install packages from the
installation media instead of the online repositories. Before calling
zypper
, ensure the media is available, for example by
inserting the DVD into the computer's drive.
6.1.3.7 Utilities #
To verify whether all dependencies are still fulfilled and to repair missing dependencies, use:
>
zypper verify
In addition to dependencies that must be fulfilled, some packages “recommend” other packages. These recommended packages are only installed if actually available and installable. In case recommended packages were made available after the recommending package has been installed (by adding additional packages or hardware), use the following command:
>
sudo
zypper install-new-recommends
This command is very useful after plugging in a Web cam or Wi-Fi device. It will install drivers for the device and related software, if available. Drivers and related software are only installable if certain hardware dependencies are fulfilled.
6.1.4 Updating software with Zypper #
There are three different ways to update software using Zypper: by
installing patches, by installing a new version of a package or by updating
the entire distribution. The latter is achieved with zypper
dist-upgrade
. Upgrading SUSE Linux Enterprise Server is discussed in
Book “Upgrade Guide”, Chapter 1 “Upgrade paths and methods”.
6.1.4.1 Installing all needed patches #
Patching SUSE Linux Enterprise is the most reliable way to install new versions of installed packages. It guaranties that all required packages with correct versions are installed and ensures that package versions considered as conflicting are omitted.
To install all officially released patches that apply to your system, run:
>
sudo
zypper patch
All patches available from repositories configured on your computer are
checked for their relevance to your installation. If they are relevant (and
not classified as optional
or
feature
), they are installed immediately.
If zypper patch
succeeds, it is guaranteed that no
vulnerable version package is installed unless you confirmed the exception.
Note that the official update repository is only
available after registering your SUSE Linux Enterprise Server installation.
If a patch that is about to be installed includes changes that require a system reboot, you will be warned before.
The plain zypper patch
command does not apply patches
from third party repositories. To update also the third party repositories,
use the with-update
command option as follows:
>
sudo
zypper patch --with-update
To install also optional patches, use:
>
sudo
zypper patch --with-optional
To install all patches relating to a specific Bugzilla issue, use:
>
sudo
zypper patch --bugzilla=NUMBER
To install all patches relating to a specific CVE database entry, use:
>
sudo
zypper patch --cve=NUMBER
For example, to install a security patch with the CVE number
CVE-2010-2713
, execute:
>
sudo
zypper patch --cve=CVE-2010-2713
To install only patches which affect Zypper and the package management itself, use:
>
sudo
zypper patch --updatestack-only
Bear in mind that other command options that would also update other
repositories will be dropped if you use the
updatestack-only
command option.
6.1.4.2 Listing patches #
To find out whether patches are available, Zypper allows viewing the following information:
- Number of needed patches
To list the number of needed patches (patches that apply to your system but are not yet installed), use
patch-check
:>
zypper patch-check Loading repository data... Reading installed packages... 5 patches needed (1 security patch)This command can be combined with the
--updatestack-only
option to list only the patches which affect Zypper and the package management itself.- List of needed patches
To list all needed patches (patches that apply to your system but are not yet installed), use
zypper list-patches
.- List of all patches
To list all patches available for SUSE Linux Enterprise Server, regardless of whether they are already installed or apply to your installation, use
zypper patches
.
It is also possible to list and install patches relevant to specific
issues. To list specific patches, use the zypper
list-patches
command with the following options:
- By Bugzilla issues
To list all needed patches that relate to Bugzilla issues, use the option
--bugzilla
.To list patches for a specific bug, you can also specify a bug number:
--bugzilla=NUMBER
. To search for patches relating to multiple Bugzilla issues, add commas between the bug numbers, for example:>
zypper list-patches --bugzilla=972197,956917- By CVE number
To list all needed patches that relate to an entry in the CVE database (Common Vulnerabilities and Exposures), use the option
--cve
.To list patches for a specific CVE database entry, you can also specify a CVE number:
--cve=NUMBER
. To search for patches relating to multiple CVE database entries, add commas between the CVE numbers, for example:>
zypper list-patches --bugzilla=CVE-2016-2315,CVE-2016-2324- List retracted patches
In the SUSE Linux Enterprise 15 codestream, some patches are automatically retracted. Maintenance updates are carefully tested, because there is a risk that an update contains a new bug. If an update proves to contain a bug, a new update (with a higher version number) is issued to revert the buggy update, and the buggy update is blocked from being installed again. You can list retracted patches with
zypper
:>
zypper lp --all |grep retracted
SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-1965 | recommended | important | --- | retracted | Recommended update for multipath-tools SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-2689 | security | important | --- | retracted | Security update for cpio SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-3655 | security | important | reboot | retracted | Security update for the Linux KernelSee complete information on a retracted (or any) patch:
>
zypper patch-info SUSE-SLE-Product-SLES-15-2021-2689
Loading repository data... Reading installed packages... Information for patch SUSE-SLE-Product-SLES-15-2021-2689: --------------------------------------------------------- Repository : SLE-Product-SLES15-LTSS-Updates Name : SUSE-SLE-Product-SLES-15-2021-2689 Version : 1 Arch : noarch Vendor : maint-coord@suse.de Status : retracted Category : security Severity : important Created On : Mon 16 Aug 2021 03:44:00 AM PDT Interactive : --- Summary : Security update for cpio Description : This update for cpio fixes the following issues: It was possible to trigger Remote code execution due to a integer overflow (CVE-2021-38185, bsc#1189206) UPDATE: This update was buggy and could lead to hangs, so it has been retracted. There will be a follow up update. [...]- Patch with conflicting packages
Information for patch openSUSE-SLE-15.3-2022-333: ------------------------------------------------- Repository : Update repository with updates from SUSE Linux Enterprise 15 Name : openSUSE-SLE-15.3-2022-333 Version : 1 Arch : noarch Vendor : maint-coord@suse.de Status : needed Category : security Severity : important Created On : Fri Feb 4 09:30:32 2022 Interactive : reboot Summary : Security update for xen Description : This update for xen fixes the following issues: - CVE-2022-23033: Fixed guest_physmap_remove_page not removing the p2m mappings. (XSA-393) (bsc#1194576) - CVE-2022-23034: Fixed possible DoS by a PV guest Xen while unmapping a grant. (XSA-394) (bsc#1194581) - CVE-2022-23035: Fixed insufficient cleanup of passed-through device IRQs. (XSA-395) (bsc#1194588) Provides : patch:openSUSE-SLE-15.3-2022-333 = 1 Conflicts : [22] xen.src < 4.14.3_06-150300.3.18.2 xen.noarch < 4.14.3_06-150300.3.18.2 xen.x86_64 < 4.14.3_06-150300.3.18.2 xen-devel.x86_64 < 4.14.3_06-150300.3.18.2 xen-devel.noarch < 4.14.3_06-150300.3.18.2 [...]
The above patch conflicts with the affected or vulnerable versions of 22 packages. If any of these affected or vulnerable packages are installed, it triggers a conflict, and the patch is classified as needed.
zypper patch
tries to install all available patches. If it encounters problems, it reports them, thus informing you that not all updates are installed. The conflict can be resolved by either updating the affected or vulnerable packages or by removing them. Because SUSE update repositories also ship fixed packages, updating is a standard way to resolve conflicts. If the package cannot be updated—for example, due to dependency issues or package locks—it is deleted after the user's approval.
To list all patches regardless of whether they are needed, use the option
--all
additionally. For example, to list all patches with
a CVE number assigned, use:
>
zypper list-patches --all --cve
Issue | No. | Patch | Category | Severity | Status
------+---------------+-------------------+-------------+-----------+----------
cve | CVE-2019-0287 | SUSE-SLE-Module.. | recommended | moderate | needed
cve | CVE-2019-3566 | SUSE-SLE-SERVER.. | recommended | moderate | not needed
[...]
6.1.4.3 Installing new package versions #
If a repository contains only new packages, but does not provide patches,
zypper patch
does not show any effect. To update
all installed packages with newer available versions, use the following command:
>
sudo
zypper update
zypper update
ignores problematic packages.
For example, if a package is locked, zypper update
omits the package, even if a higher version of it is available. Conversely,
zypper patch
reports a conflict if the package is
considered vulnerable.
To update individual packages, specify the package with either the update or install command:
>
sudo
zypper update PACKAGE_NAME>
sudo
zypper install PACKAGE_NAME
A list of all new installable packages can be obtained with the command:
>
zypper list-updates
Note that this command only lists packages that match the following criteria:
has the same vendor like the already installed package,
is provided by repositories with at least the same priority than the already installed package,
is installable (all dependencies are satisfied).
A list of all new available packages (regardless whether installable or not) can be obtained with:
>
sudo
zypper list-updates --all
To find out why a new package cannot be installed, use the zypper
install
or zypper update
command as described
above.
6.1.4.4 Identifying orphaned packages #
Whenever you remove a repository from Zypper or upgrade your system, some packages can get in an “orphaned” state. These orphaned packages belong to no active repository anymore. The following command gives you a list of these:
>
sudo
zypper packages --orphaned
With this list, you can decide if a package is still needed or can be removed safely.
6.1.5 Identifying processes and services using deleted files #
When patching, updating or removing packages, there may be running processes
on the system which continue to use files having been deleted by the update
or removal. Use zypper ps
to list processes using deleted
files. In case the process belongs to a known service, the service name is
listed, making it easy to restart the service. By default zypper
ps
shows a table:
>
zypper ps
PID | PPID | UID | User | Command | Service | Files
------+------+-----+-------+--------------+--------------+-------------------
814 | 1 | 481 | avahi | avahi-daemon | avahi-daemon | /lib64/ld-2.19.s->
| | | | | | /lib64/libdl-2.1->
| | | | | | /lib64/libpthrea->
| | | | | | /lib64/libc-2.19->
[...]
PID: ID of the process |
PPID: ID of the parent process |
UID: ID of the user running the process |
Login: Login name of the user running the process |
Command: Command used to execute the process |
Service: Service name (only if command is associated with a system service) |
Files: The list of the deleted files |
The output format of zypper ps
can be controlled as
follows:
zypper ps
-s
Create a short table not showing the deleted files.
>
zypper ps -s PID | PPID | UID | User | Command | Service ------+------+------+---------+--------------+-------------- 814 | 1 | 481 | avahi | avahi-daemon | avahi-daemon 817 | 1 | 0 | root | irqbalance | irqbalance 1567 | 1 | 0 | root | sshd | sshd 1761 | 1 | 0 | root | master | postfix 1764 | 1761 | 51 | postfix | pickup | postfix 1765 | 1761 | 51 | postfix | qmgr | postfix 2031 | 2027 | 1000 | tux | bash |zypper ps
-ss
Show only processes associated with a system service.
PID | PPID | UID | User | Command | Service ------+------+------+---------+--------------+-------------- 814 | 1 | 481 | avahi | avahi-daemon | avahi-daemon 817 | 1 | 0 | root | irqbalance | irqbalance 1567 | 1 | 0 | root | sshd | sshd 1761 | 1 | 0 | root | master | postfix 1764 | 1761 | 51 | postfix | pickup | postfix 1765 | 1761 | 51 | postfix | qmgr | postfix
zypper ps
-sss
Only show system services using deleted files.
avahi-daemon irqbalance postfix sshd
zypper ps
--print "systemctl status %s"
Show the commands to retrieve status information for services which might need a restart.
systemctl status avahi-daemon systemctl status irqbalance systemctl status postfix systemctl status sshd
For more information about service handling refer to
Chapter 15, The systemd
daemon.
6.1.6 Managing repositories with Zypper #
All installation or patch commands of Zypper rely on a list of known repositories. To list all repositories known to the system, use the command:
>
zypper repos
The result will look similar to the following output:
>
zypper repos
# | Alias | Name | Enabled | Refresh
--+--------------+---------------+---------+--------
1 | SLEHA-15-GEO | SLEHA-15-GEO | Yes | No
2 | SLEHA-15 | SLEHA-15 | Yes | No
3 | SLES15 | SLES15 | Yes | No
When specifying repositories in various commands, an alias, URI or
repository number from the zypper repos
command output
can be used. A repository alias is a short version of the repository name
for use in repository handling commands. Note that the repository numbers
can change after modifying the list of repositories. The alias will never
change by itself.
By default, details such as the URI or the priority of the repository are not displayed. Use the following command to list all details:
>
zypper repos -d
6.1.6.1 Adding repositories #
To add a repository, run
>
sudo
zypper addrepo URI ALIAS
URI can either be an Internet repository, a network resource, a directory or a CD or DVD (see https://en.opensuse.org/openSUSE:Libzypp_URIs for details). The ALIAS is a shorthand and unique identifier of the repository. You can freely choose it, with the only exception that it needs to be unique. Zypper will issue a warning if you specify an alias that is already in use.
6.1.6.2 Refreshing repositories #
zypper
enables you to fetch changes in packages from
configured repositories. To fetch the changes, run:
>
sudo
zypper refresh
zypper
By default, some commands perform refresh
automatically, so you do not need to run the command explicitly.
The refresh
command enables you to view changes also in
disabled repositories, by using the --plus-content
option:
>
sudo
zypper --plus-content refresh
This option fetches changes in repositories, but keeps the disabled repositories in the same state—disabled.
6.1.6.3 Removing repositories #
To remove a repository from the list, use the command zypper
removerepo
together with the alias or number of the repository
you want to delete. For example, to remove the repository
SLEHA-12-GEO
from Example 6.1, “Zypper—list of known repositories”, use one of the following commands:
>
sudo
zypper removerepo 1>
sudo
zypper removerepo "SLEHA-12-GEO"
6.1.6.4 Modifying repositories #
Enable or disable repositories with zypper modifyrepo
.
You can also alter the repository's properties (such as refreshing
behavior, name or priority) with this command. The following command will
enable the repository named updates
, turn on
auto-refresh and set its priority to 20:
>
sudo
zypper modifyrepo -er -p 20 'updates'
Modifying repositories is not limited to a single repository—you can also operate on groups:
-a : all repositories |
-l : local repositories |
-t : remote repositories |
-m TYPE : repositories
of a certain type (where TYPE can be one of the
following: http , https , ftp ,
cd , dvd , dir , file ,
cifs , smb , nfs , hd ,
iso ) |
To rename a repository alias, use the renamerepo
command. The following example changes the alias from Mozilla
Firefox
to firefox
:
>
sudo
zypper renamerepo 'Mozilla Firefox' firefox
6.1.7 Querying repositories and packages with Zypper #
Zypper offers various methods to query repositories or packages. To get lists of all products, patterns, packages or patches available, use the following commands:
>
zypper products>
zypper patterns>
zypper packages>
zypper patches
To query all repositories for certain packages, use
search
. To get information regarding particular packages,
use the info
command.
6.1.7.1 Searching for software #
The zypper search
command works on package names, or,
optionally, on package summaries and descriptions. Strings wrapped in
/
are interpreted as regular expressions. By default,
the search is not case-sensitive.
- Simple search for a package name containing
fire
>
zypper search "fire"- Simple search for the exact package
MozillaFirefox
>
zypper search --match-exact "MozillaFirefox"- Also search in package descriptions and summaries
>
zypper search -d fire- Only display packages not already installed
>
zypper search -u fire- Display packages containing the string
fir
not followed bee
>
zypper se "/fir[^e]/"
6.1.7.2 Searching for packages across all SLE modules #
To search for packages both within and outside of currently enabled SLE
modules, use the search-packages
subcommand. This
command contacts the SUSE Customer Center and searches all modules for matching packages,
for example:
>
zypper search-packages package1 package2
zypper search-packages
provides the following options:
Search for an exact match of your search string:
-x
,--match-exact
Group the results by module (default: group by package):
-g,
--group-by-module
Display more detailed information about packages:
-d
,--details
Output search results in XML:
--xmlout
6.1.7.3 Searching for specific capability #
To search for packages which provide a special capability, use the command
what-provides
. For example, if you want to know which
package provides the Perl module SVN::Core
, use the
following command:
>
zypper what-provides 'perl(SVN::Core)'
The what-provides
PACKAGE_NAME
is similar to
rpm -q --whatprovides
PACKAGE_NAME, but RPM is only able to query the
RPM database (that is the database of all installed packages). Zypper, on
the other hand, will tell you about providers of the capability from any
repository, not only those that are installed.
6.1.7.4 Showing package information #
To query single packages, use info
with an exact package
name as an argument. This displays detailed information about a package. In
case the package name does not match any package name from repositories,
the command outputs detailed information for non-package matches. If you
request a specific type (by using the -t
option) and the
type does not exist, the command outputs other available matches but
without detailed information.
If you specify a source package, the command displays binary packages built from the source package. If you specify a binary package, the command outputs the source packages used to build the binary package.
To also show what is required/recommended by the package, use the options
--requires
and --recommends
:
>
zypper info --requires MozillaFirefox
6.1.8 Showing lifecycle information #
SUSE products are generally supported for 10 years. Often, you can extend that standard lifecycle by using the extended support offerings of SUSE which add three years of support. Depending on your product, find the exact support lifecycle at https://www.suse.com/lifecycle.
To check the lifecycle of your product and the supported package, use the
zypper lifecycle
command as shown below:
#
zypper lifecycle
Product end of support Codestream: SUSE Linux Enterprise Server 15 2028-07-31 Product: SUSE Linux Enterprise Server 15 SP3 n/a* Module end of support Basesystem Module n/a* Desktop Applications Module n/a* Server Applications Module n/a* Package end of support if different from product: autofs Now, installed 5.1.3-7.3.1, update available 5.1.3-7.6.1
6.1.9 Configuring Zypper #
Zypper now comes with a configuration file, allowing you to permanently
change Zypper's behavior (either system-wide or user-specific). For
system-wide changes, edit /etc/zypp/zypper.conf
. For
user-specific changes, edit ~/.zypper.conf
. If
~/.zypper.conf
does not yet exist, you can use
/etc/zypp/zypper.conf
as a template: copy it to
~/.zypper.conf
and adjust it to your liking. Refer to
the comments in the file for help about the available options.
6.1.10 Troubleshooting #
If you have trouble accessing packages from configured repositories (for example, Zypper cannot find a certain package even though you know it exists in one of the repositories), refreshing the repositories may help:
>
sudo
zypper refresh
If that does not help, try
>
sudo
zypper refresh -fdb
This forces a complete refresh and rebuild of the database, including a forced download of raw metadata.
6.1.11 Zypper rollback feature on Btrfs file system #
If the Btrfs file system is used on the root partition and
snapper
is installed, Zypper automatically calls
snapper
when committing changes to the file system to
create appropriate file system snapshots. These snapshots can be used to
revert any changes made by Zypper. See Chapter 7, System recovery and snapshot management with Snapper for
more information.
6.1.12 More information #
For more information on managing software from the command line, enter
zypper help
, zypper help
COMMAND or refer to the
zypper(8)
man page. For a complete and detailed command
reference, cheat sheets
with the most important commands,
and information on how to use Zypper in scripts and applications, refer to
https://en.opensuse.org/SDB:Zypper_usage. A list of
software changes for the latest SUSE Linux Enterprise Server version can be found at
https://en.opensuse.org/openSUSE:Zypper_versions.
6.2 RPM—the package manager #
RPM (RPM Package Manager) is used for managing software packages. Its main
commands are rpm
and rpmbuild
. The
powerful RPM database can be queried by the users, system administrators and
package builders for detailed information about the installed software.
rpm
has five modes: installing, uninstalling
(or updating) software packages, rebuilding the RPM database, querying RPM
bases or individual RPM archives, integrity checking of packages and signing
packages. rpmbuild
can be used to build installable
packages from pristine sources.
Installable RPM archives are packed in a special binary format. These
archives consist of the program files to install and certain meta information
used during the installation by rpm
to configure the
software package or stored in the RPM database for documentation purposes.
RPM archives normally have the extension .rpm
.
For several packages, the components needed for software development
(libraries, headers, include files, etc.) have been put into separate
packages. These development packages are only needed if you want to compile
software yourself (for example, the most recent GNOME packages). They can
be identified by the name extension -devel
, such as the
packages alsa-devel
and
gimp-devel
.
6.2.1 Verifying package authenticity #
RPM packages have a GPG signature. To verify the signature of an RPM
package, use the command rpm --checksig
PACKAGE-1.2.3.rpm to determine whether the
package originates from SUSE or from another trustworthy facility. This is
especially recommended for update packages from the Internet.
While fixing issues in the operating system, you might need to install a Problem Temporary Fix (PTF) into a production system. The packages provided by SUSE are signed against a special PTF key. However, in contrast to SUSE Linux Enterprise 11, this key is not imported by default on SUSE Linux Enterprise 12 systems. To manually import the key, use the following command:
>
sudo
rpm --import \ /usr/share/doc/packages/suse-build-key/suse_ptf_key.asc
After importing the key, you can install PTF packages on your system.
6.2.2 Managing packages: install, update, and uninstall #
Normally, the installation of an RPM archive is quite simple: rpm
-i
PACKAGE.rpm. With this command the
package is installed, but only if its dependencies are fulfilled and if
there are no conflicts with other packages. With an error message,
rpm
requests those packages that need to be installed to
meet dependency requirements. In the background, the RPM database ensures
that no conflicts arise—a specific file can only belong to one
package. By choosing different options, you can force rpm
to ignore these defaults, but this is only for experts. Otherwise, you risk
compromising the integrity of the system and possibly jeopardize the ability
to update the system.
The options -U
or --upgrade
and
-F
or --freshen
can be used to update a
package (for example, rpm -F
PACKAGE.rpm). This command removes the files of
the old version and immediately installs the new files. The difference
between the two versions is that -U
installs packages that
previously did not exist in the system, while -F
merely
updates previously installed packages. When updating, rpm
updates configuration files carefully using the following strategy:
If a configuration file was not changed by the system administrator,
rpm
installs the new version of the appropriate file. No action by the system administrator is required.If a configuration file was changed by the system administrator before the update,
rpm
saves the changed file with the extension.rpmorig
or.rpmsave
(backup file) and installs the version from the new package. This is done only if the originally installed file and the newer version are different. If this is the case, compare the backup file (.rpmorig
or.rpmsave
) with the newly installed file and make your changes again in the new file. Afterward, delete all.rpmorig
and.rpmsave
files to avoid problems with future updates..rpmnew
files appear if the configuration file already exists and if thenoreplace
label was specified in the.spec
file.
Following an update, .rpmsave
and
.rpmnew
files should be removed after comparing them,
so they do not obstruct future updates. The .rpmorig
extension is assigned if the file has not previously been recognized by the
RPM database.
Otherwise, .rpmsave
is used. In other words,
.rpmorig
results from updating from a foreign format to
RPM. .rpmsave
results from updating from an older RPM
to a newer RPM. .rpmnew
does not disclose any
information to whether the system administrator has made any changes to the
configuration file. A list of these files is available in
/var/adm/rpmconfigcheck
. Some configuration files (like
/etc/httpd/httpd.conf
) are not overwritten to allow
continued operation.
The -U
switch is not only an
equivalent to uninstalling with the -e
option and
installing with the -i
option. Use -U
whenever possible.
To remove a package, enter rpm -e
PACKAGE. This command only deletes the package if
there are no unresolved dependencies. It is theoretically impossible to
delete Tcl/Tk, for example, as long as another application requires it. Even
in this case, RPM calls for assistance from the database. If such a deletion
is, for whatever reason, impossible (even if no
additional dependencies exist), it may be helpful to rebuild the RPM
database using the option --rebuilddb
.
6.2.3 Delta RPM packages #
Delta RPM packages contain the difference between an old and a new version of an RPM package. Applying a delta RPM onto an old RPM results in a completely new RPM. It is not necessary to have a copy of the old RPM because a delta RPM can also work with an installed RPM. The delta RPM packages are even smaller in size than patch RPMs, which is an advantage when transferring update packages over the Internet. The drawback is that update operations with delta RPMs involved consume considerably more CPU cycles than plain or patch RPMs.
The makedeltarpm
and applydelta
binaries are part of the delta RPM suite (package
deltarpm
) and help you create and apply delta RPM
packages. With the following commands, you can create a delta RPM called
new.delta.rpm
. The following command assumes that
old.rpm
and new.rpm
are present:
>
sudo
makedeltarpm old.rpm new.rpm new.delta.rpm
Using applydeltarpm
, you can reconstruct the new RPM from
the file system if the old package is already installed:
>
sudo
applydeltarpm new.delta.rpm new.rpm
To derive it from the old RPM without accessing the file system, use the
-r
option:
>
sudo
applydeltarpm -r old.rpm new.delta.rpm new.rpm
See /usr/share/doc/packages/deltarpm/README
for
technical details.
6.2.4 RPM queries #
With the -q
option rpm
initiates
queries, making it possible to inspect an RPM archive (by adding the option
-p
) and to query the RPM database of installed packages.
Several switches are available to specify the type of information required.
See Table 6.1, “Essential RPM query options”.
|
Package information |
|
File list |
|
Query the package that contains the file FILE (the full path must be specified with FILE) |
|
File list with status information (implies |
|
List only documentation files (implies |
|
List only configuration files (implies |
|
File list with complete details (to be used with |
|
List features of the package that another package can request with
|
|
Capabilities the package requires |
|
Installation scripts (preinstall, postinstall, uninstall) |
For example, the command rpm -q -i wget
displays the
information shown in Example 6.2, “rpm -q -i wget
”.
rpm -q -i wget
#Name : wget Version : 1.14 Release : 17.1 Architecture: x86_64 Install Date: Mon 30 Jan 2017 14:01:29 CET Group : Productivity/Networking/Web/Utilities Size : 2046483 License : GPL-3.0+ Signature : RSA/SHA256, Thu 08 Dec 2016 07:48:44 CET, Key ID 70af9e8139db7c82 Source RPM : wget-1.14-17.1.src.rpm Build Date : Thu 08 Dec 2016 07:48:34 CET Build Host : sheep09 Relocations : (not relocatable) Packager : https://www.suse.com/ Vendor : SUSE LLC <https://www.suse.com/> URL : http://www.gnu.org/software/wget/ Summary : A Tool for Mirroring FTP and HTTP Servers Description : Wget enables you to retrieve WWW documents or FTP files from a server. This can be done in script files or via the command line. Distribution: SUSE Linux Enterprise 15
The option -f
only works if you specify the complete file
name with its full path. Provide as many file names as desired. For example:
>
rpm -q -f /bin/rpm /usr/bin/wget
rpm-4.14.1-lp151.13.10.x86_64
wget-1.19.5-lp151.4.1.x86_64
If only part of the file name is known, use a shell script as shown in Example 6.3, “Script to search for packages”. Pass the partial file name to the script shown as a parameter when running it.
#! /bin/sh for i in $(rpm -q -a -l | grep $1); do echo "\"$i\" is in package:" rpm -q -f $i echo "" done
The command rpm -q --changelog
PACKAGE displays a detailed list of change
information about a specific package, sorted by date.
With the installed RPM database, verification checks can be made. Initiate
these with -V
, or --verify
. With this
option, rpm
shows all files in a package that have been
changed since installation. rpm
uses eight character
symbols to give some hints about the following changes:
|
MD5 check sum |
|
File size |
|
Symbolic link |
|
Modification time |
|
Major and minor device numbers |
|
Owner |
|
Group |
|
Mode (permissions and file type) |
In the case of configuration files, the letter c
is
printed. For example, for changes to /etc/wgetrc
(wget
package):
>
rpm -V wget
S.5....T c /etc/wgetrc
The files of the RPM database are placed in
/var/lib/rpm
. If the partition
/usr
has a size of 1 GB, this database can occupy
nearly 30 MB, especially after a complete update. If the database is
much larger than expected, it is useful to rebuild the database with the
option --rebuilddb
. Before doing this, make a backup of the
old database. The cron
script
cron.daily
makes daily copies of the database (packed
with gzip) and stores them in /var/adm/backup/rpmdb
.
The number of copies is controlled by the variable
MAX_RPMDB_BACKUPS
(default: 5
) in
/etc/sysconfig/backup
. The size of a single backup is
approximately 1 MB for 1 GB in /usr
.
6.2.5 Installing and compiling source packages #
All source packages carry a .src.rpm
extension (source
RPM).
Source packages can be copied from the installation medium to the hard disk
and unpacked with YaST. They are not, however, marked as installed
([i]
) in the package manager. This is because the source
packages are not entered in the RPM database. Only
installed operating system software is listed in the
RPM database. When you “install” a source package, only the
source code is added to the system.
The following directories must be available for rpm
and
rpmbuild
in /usr/src/packages
(unless you specified custom settings in a file like
/etc/rpmrc
):
SOURCES
for the original sources (
.tar.bz2
or.tar.gz
files, etc.) and for distribution-specific adjustments (mostly.diff
or.patch
files)SPECS
for the
.spec
files, similar to a meta Makefile, which control the build processBUILD
all the sources are unpacked, patched and compiled in this directory
RPMS
where the completed binary packages are stored
SRPMS
here are the source RPMs
When you install a source package with YaST, all the necessary components
are installed in /usr/src/packages
: the sources and the
adjustments in SOURCES
and the relevant
.spec
file in SPECS
.
Do not experiment with system components
(glibc
,
rpm
, etc.), because this
endangers the stability of your system.
The following example uses the wget.src.rpm
package.
After installing the source package, you should have files similar to those
in the following list:
/usr/src/packages/SOURCES/wget-1.19.5.tar.bz2 /usr/src/packages/SOURCES/wgetrc.patch /usr/src/packages/SPECS/wget.spec
rpmbuild
-bX
/usr/src/packages/SPECS/wget.spec
starts the
compilation. X is a wild card for various stages
of the build process (see the output of --help
or the RPM
documentation for details). The following is merely a brief explanation:
-bp
Prepare sources in
/usr/src/packages/BUILD
: unpack and patch.-bc
Do the same as
-bp
, but with additional compilation.-bi
Do the same as
-bp
, but with additional installation of the built software. Caution: if the package does not support the BuildRoot feature, you might overwrite configuration files.-bb
Do the same as
-bi
, but with the additional creation of the binary package. If the compile was successful, the binary should be in/usr/src/packages/RPMS
.-ba
Do the same as
-bb
, but with the additional creation of the source RPM. If the compilation was successful, the binary should be in/usr/src/packages/SRPMS
.--short-circuit
Skip some steps.
The binary RPM created can now be installed with rpm
-i
or, preferably, with rpm
-U
. Installation with rpm
makes it
appear in the RPM database.
Keep in mind that the BuildRoot
directive in the spec
file is deprecated. If you still need this feature, use the
--buildroot
option as a workaround.
6.2.6 Compiling RPM packages with build #
The danger with many packages is that unwanted files are added to the
running system during the build process. To prevent this use
build
, which creates a defined environment in which
the package is built. To establish this chroot environment, the
build
script must be provided with a complete package
tree. This tree can be made available on the hard disk, via NFS, or from
DVD. Set the position with build --rpms
DIRECTORY. Unlike rpm
, the
build
command looks for the .spec
file in the source directory. To build wget
(like in
the above example) with the DVD mounted in the system under
/media/dvd
, use the following commands as
root
:
#
cd /usr/src/packages/SOURCES/#
mv ../SPECS/wget.spec .#
build --rpms /media/dvd/suse/ wget.spec
Subsequently, a minimum environment is established at
/var/tmp/build-root
. The package is built in this
environment. Upon completion, the resulting packages are located in
/var/tmp/build-root/usr/src/packages/RPMS
.
The build
script offers several additional options. For
example, cause the script to prefer your own RPMs, omit the initialization
of the build environment or limit the rpm
command to one
of the above-mentioned stages. Access additional information with
build
--help
and by reading the
build
man page.
6.2.7 Tools for RPM archives and the RPM database #
Midnight Commander (mc
) can display the contents of RPM
archives and copy parts of them. It represents archives as virtual file
systems, offering all usual menu options of Midnight Commander. Display the
HEADER
with F3. View the archive
structure with the cursor keys and Enter. Copy archive
components with F5.
A full-featured package manager is available as a YaST module. For details, see Book “Deployment Guide”, Chapter 21 “Installing or removing software”.
7 System recovery and snapshot management with Snapper #
Snapper allows creating and managing file system snapshots. File system snapshots allow keeping a copy of the state of a file system at a certain point of time. The standard setup of Snapper is designed to allow rolling back system changes. However, you can also use it to create on-disk backups of user data. As the basis for this functionality, Snapper uses the Btrfs file system or thinly-provisioned LVM volumes with an XFS or Ext4 file system.
Snapper has a command-line interface and a YaST interface. Snapper lets you create and manage file system snapshots on the following types of file systems:
Btrfs, a copy-on-write file system for Linux that natively supports file system snapshots of subvolumes. (Subvolumes are separately mountable file systems within a physical partition.)
You can also boot from
Btrfs
snapshots. For more information, see Section 7.3, “System rollback by booting from snapshots”.Thinly-provisioned LVM volumes formatted with XFS or Ext4.
Using Snapper, you can perform the following tasks:
Undo system changes made by
zypper
and YaST. See Section 7.2, “Using Snapper to undo changes” for details.Restore files from previous snapshots. See Section 7.2.2, “Using Snapper to restore files” for details.
Do a system rollback by booting from a snapshot. See Section 7.3, “System rollback by booting from snapshots” for details.
Manually create and manage snapshots, within the running system. See Section 7.6, “Manually creating and managing snapshots” for details.
7.1 Default setup #
Snapper on SUSE Linux Enterprise Server is set up as an undo and recovery
tool for system changes. By default, the root partition
(/
) of SUSE Linux Enterprise Server is formatted with
Btrfs
. Taking snapshots is automatically enabled if the
root partition (/
) is big enough (more
than approximately 16 GB). By default, snapshots are disabled on partitions
other than /
.
If you disabled Snapper during the installation, you can enable it at any time later. To do so, create a default Snapper configuration for the root file system by running:
>
sudo
snapper -c root create-config /
Afterward enable the different snapshot types as described in Section 7.1.4.1, “Disabling/enabling snapshots”.
Note that on a Btrfs root file system, snapshots require a file system with subvolumes set up as proposed by the installer and a partition size of at least 16 GB.
When a snapshot is created, both the snapshot and the original point to the
same blocks in the file system. So, initially a snapshot does not occupy
additional disk space. If data in the original file system is modified,
changed data blocks are copied while the old data blocks are kept for the
snapshot. Therefore, a snapshot occupies the same amount of space as the
data modified. So, over time, the amount of space a snapshot allocates,
constantly grows. As a consequence, deleting files from a
Btrfs
file system containing snapshots may
not free disk space!
Snapshots always reside on the same partition or subvolume on which the snapshot has been taken. It is not possible to store snapshots on a different partition or subvolume.
As a result, partitions containing snapshots need to be larger than partitions not containing snapshots. The exact amount depends strongly on the number of snapshots you keep and the amount of data modifications. As a rule of thumb, give partitions twice as much space as you normally would. To prevent disks from running out of space, old snapshots are automatically cleaned up. Refer to Section 7.1.4.4, “Controlling snapshot archiving” for details.
7.1.1 Default settings #
- Disks larger than 16 GB
Configuration file:
/etc/snapper/configs/root
USE_SNAPPER=yes
TIMELINE_CREATE=no
- Disks smaller than 16 GB
Configuration file: not created
USE_SNAPPER=no
TIMELINE_CREATE=yes
7.1.2 Types of snapshots #
Although snapshots themselves do not differ in a technical sense, we distinguish between three types of snapshots, based on the events that trigger them:
- Timeline snapshots
A single snapshot is created every hour. Using the YaST OS installation method (default), timeline snapshots are enabled, except for the root file system. You can configure timeline snapshots to be taken at different intervals: hourly, daily, weekly, monthly and yearly. Old snapshots are automatically deleted. By default, the first snapshot of the last ten days, months and years is kept.
- Installation snapshots
Whenever one or more packages are installed with Zypper or YaST, three installation snapshots are created. In case an important system component such as the kernel has been installed, the snapshot pair is marked as important. Old snapshots are automatically deleted. Installation snapshots are enabled by default.
- Administration snapshots
Whenever you make changes to the system using Zypper or YaST, a pair of snapshots is created: one prior to the system change (“pre”) and the other one after the system change (“post”). Old snapshots are automatically deleted. Administration snapshots are enabled by default.
7.1.3 Directories that are excluded from snapshots #
Some directories need to be excluded from snapshots for different reasons. The following list shows all directories that are excluded:
/boot/grub2/i386-pc
,/boot/grub2/x86_64-efi
,/boot/grub2/powerpc-ieee1275
,/boot/grub2/s390x-emu
A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The first two directories are present on AMD64/Intel 64 machines, the latter two on IBM POWER and on IBM Z, respectively.
/home
If
/home
does not reside on a separate partition, it is excluded to avoid data loss on rollbacks./opt
Third-party products usually get installed to
/opt
. It is excluded to avoid uninstalling these applications on rollbacks./srv
Contains data for Web and FTP servers. It is excluded to avoid data loss on rollbacks.
/tmp
All directories containing temporary files and caches are excluded from snapshots.
/usr/local
This directory is used when manually installing software. It is excluded to avoid uninstalling these installations on rollbacks.
/var
This directory contains many variable files, including logs, temporary caches, third party products in
/var/opt
, and is the default location for virtual machine images and databases. Therefore this subvolume is created to exclude all of this variable data from snapshots and has Copy-On-Write disabled.
7.1.4 Customizing the setup #
SUSE Linux Enterprise Server comes with a reasonable default setup, which should be sufficient for most use cases. However, all aspects of taking automatic snapshots and snapshot keeping can be configured according to your needs.
7.1.4.1 Disabling/enabling snapshots #
Each of the three snapshot types (timeline, installation, administration) can be enabled or disabled independently.
- Disabling/enabling timeline snapshots
Enabling.
snapper -c root set-config "TIMELINE_CREATE=yes"
Disabling.
snapper -c root set-config "TIMELINE_CREATE=no"
Using the YaST OS installation method (default), timeline snapshots are enabled, except for the root file system.
- Disabling/enabling installation snapshots
Enabling: Install the package
snapper-zypp-plugin
Disabling: Uninstall the package
snapper-zypp-plugin
Installation snapshots are enabled by default.
- Disabling/enabling administration snapshots
Enabling: Set
USE_SNAPPER
toyes
in/etc/sysconfig/yast2
.Disabling: Set
USE_SNAPPER
tono
in/etc/sysconfig/yast2
.Administration snapshots are enabled by default.
7.1.4.2 Controlling installation snapshots #
Taking snapshot pairs upon installing packages with YaST or Zypper is
handled by the
snapper-zypp-plugin
. An XML
configuration file, /etc/snapper/zypp-plugin.conf
defines, when to make snapshots. By default the file looks like the
following:
1 <?xml version="1.0" encoding="utf-8"?> 2 <snapper-zypp-plugin-conf> 3 <solvables> 4 <solvable match="w"1 important="true"2>kernel-*3</solvable> 5 <solvable match="w" important="true">dracut</solvable> 6 <solvable match="w" important="true">glibc</solvable> 7 <solvable match="w" important="true">systemd*</solvable> 8 <solvable match="w" important="true">udev</solvable> 9 <solvable match="w">*</solvable>4 10 </solvables> 11 </snapper-zypp-plugin-conf>
The match attribute defines whether the pattern is a Unix shell-style
wild card ( | |
If the given pattern matches and the corresponding package is marked as important (for example kernel packages), the snapshot will also be marked as important. | |
Pattern to match a package name. Based on the setting of the
| |
This line unconditionally matches all packages. |
With this configuration snapshot, pairs are made whenever a package is installed (line 9). When the kernel, dracut, glibc, systemd, or udev packages marked as important are installed, the snapshot pair will also be marked as important (lines 4 to 8). All rules are evaluated.
To disable a rule, either delete it or deactivate it using XML comments. To prevent the system from making snapshot pairs for every package installation for example, comment line 9:
1 <?xml version="1.0" encoding="utf-8"?> 2 <snapper-zypp-plugin-conf> 3 <solvables> 4 <solvable match="w" important="true">kernel-*</solvable> 5 <solvable match="w" important="true">dracut</solvable> 6 <solvable match="w" important="true">glibc</solvable> 7 <solvable match="w" important="true">systemd*</solvable> 8 <solvable match="w" important="true">udev</solvable> 9 <!-- <solvable match="w">*</solvable> --> 10 </solvables> 11 </snapper-zypp-plugin-conf>
7.1.4.3 Creating and mounting new subvolumes #
Creating a new subvolume underneath the /
hierarchy
and permanently mounting it is supported. Such a subvolume will be
excluded from snapshots. You need to make sure not to create it inside an
existing snapshot, since you would not be able to delete snapshots anymore
after a rollback.
SUSE Linux Enterprise Server is configured with the /@/
subvolume
which serves as an independent root for permanent subvolumes such as
/opt
, /srv
,
/home
and others. Any new subvolumes you create and
permanently mount need to be created in this initial root file system.
To do so, run the following commands. In this example, a new subvolume
/usr/important
is created from
/dev/sda2
.
>
sudo
mount /dev/sda2 -o subvol=@ /mnt>
sudo
btrfs subvolume create /mnt/usr/important>
sudo
umount /mnt
The corresponding entry in /etc/fstab
needs to look
like the following:
/dev/sda2 /usr/important btrfs subvol=@/usr/important 0 0
A subvolume may contain files that constantly change, such as
virtualized disk images, database files, or log files. If so, consider
disabling the copy-on-write feature for this volume, to avoid duplication
of disk blocks. Use the nodatacow
mount option in
/etc/fstab
to do so:
/dev/sda2 /usr/important btrfs nodatacow,subvol=@/usr/important 0 0
To alternatively disable copy-on-write for single files or directories,
use the command chattr +C
PATH
.
7.1.4.4 Controlling snapshot archiving #
Snapshots occupy disk space. To prevent disks from running out of space and thus causing system outages, old snapshots are automatically deleted. By default, up to ten important installation and administration snapshots and up to ten regular installation and administration snapshots are kept. If these snapshots occupy more than 50% of the root file system size, additional snapshots will be deleted. A minimum of four important and two regular snapshots are always kept.
Refer to Section 7.5.1, “Managing existing configurations” for instructions on how to change these values.
7.1.4.5 Using Snapper on thinly provisioned LVM volumes #
Apart from snapshots on Btrfs
file systems, Snapper
also supports taking snapshots on thinly-provisioned LVM volumes (snapshots
on regular LVM volumes are not supported) formatted
with XFS, Ext4 or Ext3. For more information and setup instructions on LVM
volumes, refer to Book “Deployment Guide”, Chapter 10 “.
”, Section 10.2 “LVM configuration”
To use Snapper on a thinly-provisioned LVM volume you need to create a
Snapper configuration for it. On LVM it is required to specify the file
system with
--fstype=lvm(FILESYSTEM)
.
ext3
, etx4
or xfs
are valid values for FILESYSTEM. Example:
>
sudo
snapper -c lvm create-config --fstype="lvm(xfs)" /thin_lvm
You can adjust this configuration according to your needs as described in Section 7.5.1, “Managing existing configurations”.
7.2 Using Snapper to undo changes #
Snapper on SUSE Linux Enterprise Server is preconfigured to serve as a tool that lets you
undo changes made by zypper
and YaST. For this purpose,
Snapper is configured to create a pair of snapshots before and after each
run of zypper
and YaST. Snapper also lets you restore
system files that have been accidentally deleted or modified. Timeline
snapshots for the root partition need to be enabled for this
purpose—see
Section 7.1.4.1, “Disabling/enabling snapshots” for details.
By default, automatic snapshots as described above are configured for the
root partition and its subvolumes. To make snapshots available for other
partitions such as /home
for example, you can create
custom configurations.
When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:
- Undoing changes
When undoing changes as described in the following, two snapshots are being compared and the changes between these two snapshots are made undone. Using this method also allows to explicitly select the files that should be restored.
- Rollback
When doing rollbacks as described in Section 7.3, “System rollback by booting from snapshots”, the system is reset to the state at which the snapshot was taken.
When undoing changes, it is also possible to compare a snapshot against the current system. When restoring all files from such a comparison, this will have the same result as doing a rollback. However, using the method described in Section 7.3, “System rollback by booting from snapshots” for rollbacks should be preferred, since it is faster and allows you to review the system before doing the rollback.
There is no mechanism to ensure data consistency when creating a snapshot.
Whenever a file (for example, a database) is written at the same time as
the snapshot is being created, it will result in a corrupted or partly written
file. Restoring such a file will cause problems. Furthermore, some system
files such as /etc/mtab
must never be restored.
Therefore it is strongly recommended to always closely
review the list of changed files and their diffs. Only restore files that
really belong to the action you want to revert.
7.2.1 Undoing YaST and Zypper changes #
If you set up the root partition with Btrfs
during the
installation, Snapper—preconfigured for doing rollbacks of YaST or
Zypper changes—will automatically be installed. Every time you start
a YaST module or a Zypper transaction, two snapshots are created: a
“pre-snapshot” capturing the state of the file system before
the start of the module and a “post-snapshot” after the module
has been finished.
Using the YaST Snapper module or the snapper
command
line tool, you can undo the changes made by YaST/Zypper by restoring
files from the “pre-snapshot”. Comparing two snapshots the
tools also allow you to see which files have been changed. You can also
display the differences between two versions of a file (diff).
Start the
module from the section in YaST or by enteringyast2 snapper
.Make sure
is set to . This is always the case unless you have manually added own Snapper configurations.Choose a pair of pre- and post-snapshots from the list. Both, YaST and Zypper snapshot pairs are of the type
. YaST snapshots are labeled aszypp(y2base)
in the ; Zypper snapshots are labeledzypp(zypper)
.Click
to open the list of files that differ between the two snapshots.Review the list of files. To display a “diff” between the pre- and post-version of a file, select it from the list.
To restore one or more files, select the relevant files or directories by activating the respective check box. Click
and confirm the action by clicking .To restore a single file, activate its diff view by clicking its name. Click
and confirm your choice with .
snapper
command #Get a list of YaST and Zypper snapshots by running
snapper list -t pre-post
. YaST snapshots are labeled asyast MODULE_NAME
in the ; Zypper snapshots are labeledzypp(zypper)
.>
sudo
snapper list -t pre-post Pre # | Post # | Pre Date | Post Date | Description ------+--------+-------------------------------+-------------------------------+-------------- 311 | 312 | Tue 06 May 2018 14:05:46 CEST | Tue 06 May 2018 14:05:52 CEST | zypp(y2base) 340 | 341 | Wed 07 May 2018 16:15:10 CEST | Wed 07 May 2018 16:15:16 CEST | zypp(zypper) 342 | 343 | Wed 07 May 2018 16:20:38 CEST | Wed 07 May 2018 16:20:42 CEST | zypp(y2base) 344 | 345 | Wed 07 May 2018 16:21:23 CEST | Wed 07 May 2018 16:21:24 CEST | zypp(zypper) 346 | 347 | Wed 07 May 2018 16:41:06 CEST | Wed 07 May 2018 16:41:10 CEST | zypp(y2base) 348 | 349 | Wed 07 May 2018 16:44:50 CEST | Wed 07 May 2018 16:44:53 CEST | zypp(y2base) 350 | 351 | Wed 07 May 2018 16:46:27 CEST | Wed 07 May 2018 16:46:38 CEST | zypp(y2base)Get a list of changed files for a snapshot pair with
snapper status
PRE..POST. Files with content changes are marked with , files that have been added are marked with and deleted files are marked with .>
sudo
snapper status 350..351 +..... /usr/share/doc/packages/mikachan-fonts +..... /usr/share/doc/packages/mikachan-fonts/COPYING +..... /usr/share/doc/packages/mikachan-fonts/dl.html c..... /usr/share/fonts/truetype/fonts.dir c..... /usr/share/fonts/truetype/fonts.scale +..... /usr/share/fonts/truetype/みかちゃん-p.ttf +..... /usr/share/fonts/truetype/みかちゃん-pb.ttf +..... /usr/share/fonts/truetype/みかちゃん-ps.ttf +..... /usr/share/fonts/truetype/みかちゃん.ttf c..... /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4 c..... /var/lib/rpm/Basenames c..... /var/lib/rpm/Dirnames c..... /var/lib/rpm/Group c..... /var/lib/rpm/Installtid c..... /var/lib/rpm/Name c..... /var/lib/rpm/Packages c..... /var/lib/rpm/Providename c..... /var/lib/rpm/Requirename c..... /var/lib/rpm/Sha1header c..... /var/lib/rpm/Sigmd5To display the diff for a certain file, run
snapper diff
PRE..POST FILENAME. If you do not specify FILENAME, a diff for all files will be displayed.>
sudo
snapper diff 350..351 /usr/share/fonts/truetype/fonts.scale --- /.snapshots/350/snapshot/usr/share/fonts/truetype/fonts.scale 2014-04-23 15:58:57.000000000 +0200 +++ /.snapshots/351/snapshot/usr/share/fonts/truetype/fonts.scale 2014-05-07 16:46:31.000000000 +0200 @@ -1,4 +1,4 @@ -1174 +1486 ds=y:ai=0.2:luximr.ttf -b&h-luxi mono-bold-i-normal--0-0-0-0-c-0-iso10646-1 ds=y:ai=0.2:luximr.ttf -b&h-luxi mono-bold-i-normal--0-0-0-0-c-0-iso8859-1 [...]To restore one or more files run
snapper -v undochange
PRE..POST FILENAMES. If you do not specify a FILENAMES, all changed files will be restored.>
sudo
snapper -v undochange 350..351 create:0 modify:13 delete:7 undoing change... deleting /usr/share/doc/packages/mikachan-fonts deleting /usr/share/doc/packages/mikachan-fonts/COPYING deleting /usr/share/doc/packages/mikachan-fonts/dl.html deleting /usr/share/fonts/truetype/みかちゃん-p.ttf deleting /usr/share/fonts/truetype/みかちゃん-pb.ttf deleting /usr/share/fonts/truetype/みかちゃん-ps.ttf deleting /usr/share/fonts/truetype/みかちゃん.ttf modifying /usr/share/fonts/truetype/fonts.dir modifying /usr/share/fonts/truetype/fonts.scale modifying /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4 modifying /var/lib/rpm/Basenames modifying /var/lib/rpm/Dirnames modifying /var/lib/rpm/Group modifying /var/lib/rpm/Installtid modifying /var/lib/rpm/Name modifying /var/lib/rpm/Packages modifying /var/lib/rpm/Providename modifying /var/lib/rpm/Requirename modifying /var/lib/rpm/Sha1header modifying /var/lib/rpm/Sigmd5 undoing change done
Reverting user additions via undoing changes with Snapper is not recommended. Since certain directories are excluded from snapshots, files belonging to these users will remain in the file system. If a user with the same user ID as a deleted user is created, this user will inherit the files. Therefore it is strongly recommended to use the YaST
tool to remove users.7.2.2 Using Snapper to restore files #
Apart from the installation and administration snapshots, Snapper creates timeline snapshots. You can use these backup snapshots to restore files that have accidentally been deleted or to restore a previous version of a file. By using Snapper's diff feature you can also find out which modifications have been made at a certain point of time.
Being able to restore files is especially interesting for data, which may
reside on subvolumes or partitions for which snapshots are not taken by
default. To be able to restore files from home directories, for example,
create a separate Snapper configuration for /home
doing automatic timeline snapshots. See
Section 7.5, “Creating and modifying Snapper configurations” for instructions.
Snapshots taken from the root file system (defined by Snapper's root configuration), can be used to do a system rollback. The recommended way to do such a rollback is to boot from the snapshot and then perform the rollback. See Section 7.3, “System rollback by booting from snapshots” for details.
Performing a rollback would also be possible by restoring all files from a
root file system snapshot as described below. However, this is not
recommended. You may restore single files, for example a configuration
file from the /etc
directory, but not the
complete list of files from the snapshot.
This restriction only affects snapshots taken from the root file system!
Start the
module from the section in YaST or by enteringyast2 snapper
.Choose the
from which to choose a snapshot.Select a timeline snapshot from which to restore a file and choose
. Timeline snapshots are of the type with a description value of .Select a file from the text box by clicking the file name. The difference between the snapshot version and the current system is shown. Activate the check box to select the file for restore. Do so for all files you want to restore.
Click
and confirm the action by clicking .
snapper
command #Get a list of timeline snapshots for a specific configuration by running the following command:
>
sudo
snapper -c CONFIG list -t single | grep timelineCONFIG needs to be replaced by an existing Snapper configuration. Use
snapper list-configs
to display a list.Get a list of changed files for a given snapshot by running the following command:
>
sudo
snapper -c CONFIG status SNAPSHOT_ID..0Replace SNAPSHOT_ID by the ID for the snapshot from which you want to restore the file(s).
Optionally list the differences between the current file version and the one from the snapshot by running
>
sudo
snapper -c CONFIG diff SNAPSHOT_ID..0 FILE NAMEIf you do not specify <FILE NAME>, the difference for all files are shown.
To restore one or more files, run
>
sudo
snapper -c CONFIG -v undochange SNAPSHOT_ID..0 FILENAME1 FILENAME2If you do not specify file names, all changed files will be restored.
7.3 System rollback by booting from snapshots #
The GRUB 2 version included on SUSE Linux Enterprise Server can boot from Btrfs snapshots.
Together with Snapper's rollback feature, this allows to recover a
misconfigured system. Only snapshots created for the default Snapper
configuration (root
) are bootable.
As of SUSE Linux Enterprise Server 15 SP3 system rollbacks are only supported if the default subvolume configuration of the root partition has not been changed.
When booting a snapshot, the parts of the file system included in the snapshot are mounted read-only; all other file systems and parts that are excluded from snapshots are mounted read-write and can be modified.
When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:
- Undoing changes
When undoing changes as described in Section 7.2, “Using Snapper to undo changes”, two snapshots are compared and the changes between these two snapshots are reverted. Using this method also allows to explicitly exclude selected files from being restored.
- Rollback
When doing rollbacks as described in the following, the system is reset to the state at which the snapshot was taken.
To do a rollback from a bootable snapshot, the following requirements must be met. When doing a default installation, the system is set up accordingly.
The root file system needs to be Btrfs. Booting from LVM volume snapshots is not supported.
The root file system needs to be on a single device. To check, run
sudo /sbin/btrfs filesystem show
. It needs to reportTotal devices 1
. If more than1
device is listed, your setup is not supported.Note: Directories excluded from snapshotsDirectories that are excluded from snapshots such as
/srv
(see Section 7.1.3, “Directories that are excluded from snapshots” for a full list) may reside on separate devices.The system needs to be bootable via the installed boot loader.
Only contents of the subvolume
/
will be rolled back. It is not possible to include other subvolumes.
To perform a rollback from a bootable snapshot, do as follows:
Boot the system. In the boot menu choose
and select the snapshot you want to boot. The list of snapshots is listed by date—the most recent snapshot is listed first.Log in to the system. Carefully check whether everything works as expected. Note that you cannot write to any directory that is part of the snapshot. Data you write to other directories will not get lost, regardless of what you do next.
Depending on whether you want to perform the rollback or not, choose your next step:
If the system is in a state where you do not want to do a rollback, reboot to boot into the current system state. You can then choose a different snapshot, or start the rescue system.
To perform the rollback, run
>
sudo
snapper rollbackand reboot afterward. On the boot screen, choose the default boot entry to reboot into the reinstated system. A snapshot of the file system status before the rollback is created. The default subvolume for root will be replaced with a fresh read-write snapshot. For details, see Section 7.3.1, “Snapshots after rollback”.
It is useful to add a description for the snapshot with the
-d
option. For example:New file system root since rollback on DATE TIME
If snapshots are not disabled during installation, an initial bootable
snapshot is created at the end of the initial system installation. You can
go back to that state at any time by booting this snapshot. The snapshot
can be identified by the description after installation
.
A bootable snapshot is also created when starting a system upgrade to a service pack or a new major release (provided snapshots are not disabled).
7.3.1 Snapshots after rollback #
Before a rollback is performed, a snapshot of the running file system is created. The description references the ID of the snapshot that was restored in the rollback.
Snapshots created by rollbacks receive the value number
for the Cleanup
attribute. The rollback snapshots are
therefore automatically deleted when the set number of snapshots is reached.
Refer to Section 7.7, “Automatic snapshot clean-up” for details.
If the snapshot contains important data, extract the data from the snapshot
before it is removed.
7.3.1.1 Example of rollback snapshot #
For example, after a fresh installation the following snapshots are available on the system:
#
snapper
--iso list Type | # | | Cleanup | Description | Userdata -------+---+ ... +---------+-----------------------+-------------- single | 0 | | | current | single | 1 | | | first root filesystem | single | 2 | | number | after installation | important=yes
After running sudo snapper rollback
snapshot
3
is created and contains the state of the system
before the rollback was executed. Snapshot 4
is
the new default Btrfs subvolume and thus the system after a reboot.
#
snapper
--iso list Type | # | | Cleanup | Description | Userdata -------+---+ ... +---------+-----------------------+-------------- single | 0 | | | current | single | 1 | | number | first root filesystem | single | 2 | | number | after installation | important=yes single | 3 | | number | rollback backup of #1 | important=yes single | 4 | | | |
7.3.2 Accessing and identifying snapshot boot entries #
To boot from a snapshot, reboot your machine and choose ↓ and ↑ to navigate and press Enter to activate the selected snapshot. Activating a snapshot from the boot menu does not reboot the machine immediately, but rather opens the boot loader of the selected snapshot.
. A screen listing all bootable snapshots opens. The most recent snapshot is listed first, the oldest last. Use the keysRefer to https://www.suse.com/support/kb/doc/?id=000020602 for more details.
Each snapshot entry in the boot loader follows a naming scheme which makes it possible to identify it easily:
[*]1OS2 (KERNEL3,DATE4TTIME5,DESCRIPTION6)
If the snapshot was marked | |
Operating system label. | |
Date in the format | |
Time in the format | |
This field contains a description of the snapshot. In case of a manually
created snapshot this is the string created with the option
|
It is possible to replace the default string in the description field of a snapshot with a custom string. This is for example useful if an automatically created description is not sufficient, or a user-provided description is too long. To set a custom string STRING for snapshot NUMBER, use the following command:
>
sudo
snapper modify --userdata "bootloader=STRING" NUMBER
The description should be no longer than 25 characters—everything that exceeds this size will not be readable on the boot screen.
7.3.3 Limitations #
A complete system rollback, restoring the complete system to the identical state as it was in when a snapshot was taken, is not possible.
7.3.3.1 Directories excluded from snapshots #
Root file system snapshots do not contain all directories. See Section 7.1.3, “Directories that are excluded from snapshots” for details and reasons. As a general consequence, data from these directories is not restored, resulting in the following limitations.
- Add-ons and third-party software may be unusable after a rollback
Applications and add-ons installing data in subvolumes excluded from the snapshot, such as
/opt
, may not work after a rollback, if others parts of the application data are also installed on subvolumes included in the snapshot. Re-install the application or the add-on to solve this problem.- File access problems
If an application had changed file permissions and/or ownership in between snapshot and current system, the application may not be able to access these files. Reset permissions and/or ownership for the affected files after the rollback.
- Incompatible data formats
If a service or an application has established a new data format in between snapshot and current system, the application may not be able to read the affected data files after a rollback.
- Subvolumes with a mixture of code and data
Subvolumes like
/srv
may contain a mixture of code and data. A rollback may result in non-functional code. A downgrade of the PHP version, for example, may result in broken PHP scripts for the Web server.- User data
If a rollback removes users from the system, data that is owned by these users in directories excluded from the snapshot, is not removed. If a user with the same user ID is created, this user will inherit the files. Use a tool like
find
to locate and remove orphaned files.
7.3.3.2 No rollback of boot loader data #
A rollback of the boot loader is not possible, since all
“stages” of the boot loader must fit together. This cannot be
guaranteed when doing rollbacks of /boot
.
7.4 Enabling Snapper in user home directories #
You may enable snapshots for users' /home
directories, which supports a number of use cases:
Individual users may manage their own snapshots and rollbacks.
System users, for example database, system, and network admins who want to track copies of configuration files, documentation, and so on.
Samba shares with home directories and Btrfs back-end.
Each user's directory is a Btrfs subvolume of /home
.
It is possible to set this up manually
(see Section 7.4.3, “Manually enabling snapshots in home directories”). However, a
more convenient way is to use pam_snapper
.
The pam_snapper
package installs the
pam_snapper.so
module and helper scripts, which
automate user creation and Snapper configuration.
pam_snapper
provides integration with the
useradd
command, pluggable
authentication modules (PAM), and Snapper. By default it creates snapshots
at user login and logout, and also creates time-based snapshots as some
users remain logged in for extended periods of time. You may change the
defaults using the normal Snapper commands and configuration files.
7.4.1 Installing pam_snapper and creating users #
The easiest way is to start with a new /home
directory formatted with Btrfs, and no existing users. Install
pam_snapper
:
#
zypper in pam_snapper
Add this line to /etc/pam.d/common-session
:
session optional pam_snapper.so
Use the /usr/lib/pam_snapper/pam_snapper_useradd.sh
script to create a new user and home directory. By default the script
performs a dry run. Edit the script to change
DRYRUN=1
to DRYRUN=0
. Now you
can create a new user:
#
/usr/lib/pam_snapper/pam_snapper_useradd.sh \
username group passwd=password
Create subvolume '/home/username'
useradd: warning: the home directory already exists.
Not copying any file from skel directory into it.
The files from /etc/skel
will be copied
into the user's home directory at their first login. Verify that
the user's configuration was created by listing your Snapper
configurations:
#
snapper list --all
Config: home_username, subvolume: /home/username
Type | # | Pre # | Date | User | Cleanup | Description | Userdata
-------+---+-------+------+------+---------+-------------+---------
single | 0 | | | root | | current |
Over time, this output will become populated with a list of snapshots, which the user can manage with the standard Snapper commands.
7.4.2 Removing users #
Remove users with the
/usr/lib/pam_snapper/pam_snapper_userdel.sh
script. By default it performs a dry run, so edit it to change
DRYRUN=1
to DRYRUN=0
. This
removes the user, the user's home subvolume, Snapper configuration,
and deletes all snapshots.
#
/usr/lib/pam_snapper/pam_snapper_userdel.sh username
7.4.3 Manually enabling snapshots in home directories #
These are the steps for manually setting up users' home directories
with Snapper. /home
must be formatted with Btrfs,
and the users not yet created.
#
btrfs subvol create /home/username#
snapper -c home_username create-config /home/username#
sed -i -e "s/ALLOW_USERS=\"\"/ALLOW_USERS=\"username\"/g" \ /etc/snapper/configs/home_username#
yast users add username=username home=/home/username password=password#
chown username.group /home/username#
chmod 755 /home/username/.snapshots
7.5 Creating and modifying Snapper configurations #
The way Snapper behaves is defined in a configuration file that is specific
for each partition or Btrfs
subvolume. These
configuration files reside under /etc/snapper/configs/
.
In case the root file system is big enough (approximately 12 GB), snapshots
are automatically enabled for the root file system /
upon installation. The corresponding default configuration is named
root
. It creates and manages the YaST and Zypper
snapshot. See Section 7.5.1.1, “Configuration data” for a list
of the default values.
As explained in Section 7.1, “Default setup”, enabling snapshots requires additional free space in the root file system. The amount depends on the amount of packages installed and the amount of changes made to the volume that is included in snapshots. The snapshot frequency and the number of snapshots that get archived also matter.
There is a minimum root file system size that is required to automatically
enable snapshots during the installation. Currently this size is
approximately 12 GB. This value may change in the future, depending on
architecture and the size of the base system. It depends on the values for
the following tags in the file /control.xml
from the
installation media:
<root_base_size> <btrfs_increase_percentage>
It is calculated with the following formula: ROOT_BASE_SIZE * (1 + BTRFS_INCREASE_PERCENTAGE/100)
Keep in mind that this value is a minimum size. Consider using more space for the root file system. As a rule of thumb, double the size you would use when not having enabled snapshots.
You may create your own configurations for other partitions formatted with
Btrfs
or existing subvolumes on a
Btrfs
partition. In the following example we will set up
a Snapper configuration for backing up the Web server data residing on a
separate, Btrfs
-formatted partition mounted at
/srv/www
.
After a configuration has been created, you can either use
snapper
itself or the YaST
module to restore files from these snapshots. In YaST you need to select
your , while you need to specify
your configuration for snapper
with the global switch
-c
(for example, snapper -c myconfig
list
).
To create a new Snapper configuration, run snapper
create-config
:
>
sudo
snapper -c www-data1 create-config /srv/www2
Name of configuration file. | |
Mount point of the partition or |
This command will create a new configuration file
/etc/snapper/configs/www-data
with reasonable default
values (taken from
/etc/snapper/config-templates/default
). Refer to
Section 7.5.1, “Managing existing configurations” for instructions on how to
adjust these defaults.
Default values for a new configuration are taken from
/etc/snapper/config-templates/default
. To use your own
set of defaults, create a copy of this file in the same directory and
adjust it to your needs. To use it, specify the -t
option
with the create-config command:
>
sudo
snapper -c www-data create-config -t MY_DEFAULTS /srv/www
7.5.1 Managing existing configurations #
The snapper
command offers several subcommands for managing
existing configurations. You can list, show, delete and modify them:
- Listing configurations
Use the subcommand
snapper list-configs
to get all existing configurations:>
sudo
snapper list-configs Config | Subvolume -------+---------- root | / usr | /usr local | /local- Showing a configuration
Use the subcommand
snapper -c CONFIG get-config
to display the specified configuration. Replace CONFIG with one of the configuration names shown bysnapper list-configs
. For more information about the configuration options, see Section 7.5.1.1, “Configuration data”.To display the default configuration, run:
>
sudo
snapper -c root get-config- Modifying a configuration
Use the subcommand
snapper -c CONFIG set-config OPTION=VALUE
to modify an option in the specified configuration. Replace CONFIG with one of the configuration names shown bysnapper list-configs
. Possible values for OPTION and VALUE are listed in Section 7.5.1.1, “Configuration data”.- Deleting a configuration
Use the subcommand
snapper -c CONFIG delete-config
to delete a configuration. Replace CONFIG with one of the configuration names shown bysnapper list-configs
.
7.5.1.1 Configuration data #
Each configuration contains a list of options that can be modified from
the command line. The following list provides details for each option. To
change a value, run snapper -c CONFIG
set-config
"KEY=VALUE"
.
ALLOW_GROUPS
,ALLOW_USERS
Granting permissions to use snapshots to regular users. See Section 7.5.1.2, “Using Snapper as regular user” for more information.
The default value is
""
.BACKGROUND_COMPARISON
Defines whether pre and post snapshots should be compared in the background after creation.
The default value is
"yes"
.EMPTY_*
Defines the clean-up algorithm for snapshots pairs with identical pre and post snapshots. See Section 7.7.3, “Cleaning up snapshot pairs that do not differ” for details.
FSTYPE
File system type of the partition. Do not change.
The default value is
"btrfs"
.NUMBER_*
Defines the clean-up algorithm for installation and admin snapshots. See Section 7.7.1, “Cleaning up numbered snapshots” for details.
QGROUP
/SPACE_LIMIT
Adds quota support to the clean-up algorithms. See Section 7.7.5, “Adding disk quota support” for details.
SUBVOLUME
Mount point of the partition or subvolume to snapshot. Do not change.
The default value is
"/"
.SYNC_ACL
If Snapper is used by regular users (see Section 7.5.1.2, “Using Snapper as regular user”), the users must be able to access the
.snapshot
directories and to read files within them. If SYNC_ACL is set toyes
, Snapper automatically makes them accessible using ACLs for users and groups from the ALLOW_USERS or ALLOW_GROUPS entries.The default value is
"no"
.TIMELINE_CREATE
If set to
yes
, hourly snapshots are created. Valid values:yes
,no
.The default value is
"no"
.TIMELINE_CLEANUP
/TIMELINE_LIMIT_*
Defines the clean-up algorithm for timeline snapshots. See Section 7.7.2, “Cleaning up timeline snapshots” for details.
7.5.1.2 Using Snapper as regular user #
By default Snapper can only be used by root
. However, there are
cases in which certain groups or users need to be able to create snapshots
or undo changes by reverting to a snapshot:
Web site administrators who want to take snapshots of
/srv/www
Users who want to take a snapshot of their home directory
For these purposes, you can create Snapper configurations that grant
permissions to users or/and groups. The corresponding
.snapshots
directory needs to be readable and
accessible by the specified users. The easiest way to achieve this is to
set the SYNC_ACL option to yes
.
Note that all steps in this procedure need to be run by root
.
If a Snapper configuration does not exist yet, create one for the partition or subvolume on which the user should be able to use Snapper. Refer to Section 7.5, “Creating and modifying Snapper configurations” for instructions. Example:
>
sudo
snapper --config web_data create /srv/wwwThe configuration file is created under
/etc/snapper/configs/CONFIG
, where CONFIG is the value you specified with-c/--config
in the previous step (for example/etc/snapper/configs/web_data
). Adjust it according to your needs. For more information, see Section 7.5.1, “Managing existing configurations”.Set values for
ALLOW_USERS
and/orALLOW_GROUPS
to grant permissions to users and/or groups, respectively. Multiple entries need to be separated by Space. To grant permissions to the userwww_admin
for example, run:>
sudo
snapper -c web_data set-config "ALLOW_USERS=www_admin" SYNC_ACL="yes"The given Snapper configuration can now be used by the specified user(s) and/or group(s). You can test it with the
list
command, for example:www_admin:~ >
snapper -c web_data list
7.6 Manually creating and managing snapshots #
Snapper is not restricted to creating and managing snapshots automatically by configuration; you can also create snapshot pairs (“before and after”) or single snapshots manually using either the command-line tool or the YaST module.
All Snapper operations are carried out for an existing configuration (see
Section 7.5, “Creating and modifying Snapper configurations” for details). You can only take
snapshots of partitions or volumes for which a configuration exists. By
default the system configuration (root
) is used.
To create or manage snapshots for your own configuration you need to
explicitly choose it. Use the
drop-down box in YaST or specify the -c
on the command
line (snapper -c MYCONFIG
COMMAND
).
7.6.1 Snapshot metadata #
Each snapshot consists of the snapshot itself and some metadata. When
creating a snapshot you also need to specify the metadata. Modifying a
snapshot means changing its metadata—you cannot modify its content.
Use snapper list
to show existing snapshots and their
metadata:
snapper --config home list
Lists snapshots for the configuration
home
. To list snapshots for the default configuration (root), usesnapper -c root list
orsnapper list
.snapper list -a
Lists snapshots for all existing configurations.
snapper list -t pre-post
Lists all pre and post snapshot pairs for the default (
root
) configuration.snapper list -t single
Lists all snapshots of the type
single
for the default (root
) configuration.
The following metadata is available for each snapshot:
Type: Snapshot type, see Section 7.6.1.1, “Snapshot types” for details. This data cannot be changed.
Number: Unique number of the snapshot. This data cannot be changed.
Pre Number: Specifies the number of the corresponding pre snapshot. For snapshots of type post only. This data cannot be changed.
Description: A description of the snapshot.
Userdata: An extended description where you can specify custom data in the form of a comma-separated key=value list:
reason=testing, project=foo
. This field is also used to mark a snapshot as important (important=yes
) and to list the user that created the snapshot (user=tux).Cleanup-Algorithm: Cleanup-algorithm for the snapshot, see Section 7.7, “Automatic snapshot clean-up” for details.
7.6.1.1 Snapshot types #
Snapper knows three different types of snapshots: pre, post, and single. Physically they do not differ, but Snapper handles them differently.
pre
Snapshot of a file system before a modification. Each
pre
snapshot corresponds to apost
snapshot. For example, this is used for the automatic YaST/Zypper snapshots.post
Snapshot of a file system after a modification. Each
post
snapshot corresponds to apre
snapshot. For example, this is used for the automatic YaST/Zypper snapshots.single
Stand-alone snapshot. For example, this is used for the automatic hourly snapshots. This is the default type when creating snapshots.
7.6.1.2 Cleanup algorithms #
Snapper provides three algorithms to clean up old snapshots. The
algorithms are executed in a daily
cron
job.
It is possible to define the
number of different types of snapshots to keep in the Snapper
configuration (see Section 7.5.1, “Managing existing configurations” for
details).
- number
Deletes old snapshots when a certain snapshot count is reached.
- timeline
Deletes old snapshots having passed a certain age, but keeps several hourly, daily, monthly, and yearly snapshots.
- empty-pre-post
Deletes pre/post snapshot pairs with empty diffs.
7.6.2 Creating snapshots #
To create a snapshot, run snapper create
or
click in the YaST module
. The following examples explain how to create
snapshots from the command line.
The YaST interface for Snapper is not explicitly described here but
provides equivalent functionality.
Always specify a meaningful description to later be able to
identify its purpose. You can also specify additional information via
the option --userdata
.
snapper create --from 17 --description "with package2"
Creates a stand-alone snapshot (type single) from an existing snapshot, which is specified by the snapshot's number from
snapper list
. (This applies to Snapper version 0.8.4 and newer.)snapper create --description "Snapshot for week 2 2014"
Creates a stand-alone snapshot (type single) for the default (
root
) configuration with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.snapper --config home create --description "Cleanup in ~tux"
Creates a stand-alone snapshot (type single) for a custom configuration named
home
with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.snapper --config home create --description "Daily data backup" --cleanup-algorithm timeline
>Creates a stand-alone snapshot (type single) for a custom configuration named
home
with a description. The snapshot will automatically be deleted when it meets the criteria specified for the timeline cleanup-algorithm in the configuration.snapper create --type pre --print-number --description "Before the Apache config cleanup" --userdata "important=yes"
Creates a snapshot of the type
pre
and prints the snapshot number. First command needed to create a pair of snapshots used to save a “before” and “after” state. The snapshot is marked as important.snapper create --type post --pre-number 30 --description "After the Apache config cleanup" --userdata "important=yes"
Creates a snapshot of the type
post
paired with thepre
snapshot number30
. Second command needed to create a pair of snapshots used to save a “before” and “after” state. The snapshot is marked as important.snapper create --command COMMAND --description "Before and after COMMAND"
Automatically creates a snapshot pair before and after running COMMAND. This option is only available when using snapper on the command line.
7.6.3 Modifying snapshot metadata #
Snapper allows you to modify the description, the cleanup algorithm, and the user data of a snapshot. All other metadata cannot be changed. The following examples explain how to modify snapshots from the command line. It should be easy to adopt them when using the YaST interface.
To modify a snapshot on the command line, you need to know its number. Use
snapper list
to display all snapshots
and their numbers.
The YaST
module already lists all snapshots. Choose one from the list and click .snapper modify --cleanup-algorithm "timeline"
10Modifies the metadata of snapshot 10 for the default (
root
) configuration. The cleanup algorithm is set totimeline
.snapper --config home modify --description "daily backup" -cleanup-algorithm "timeline" 120
Modifies the metadata of snapshot 120 for a custom configuration named
home
. A new description is set and the cleanup algorithm is unset.
7.6.4 Deleting snapshots #
To delete a snapshot with the YaST
module, choose a snapshot from the list and click .
To delete a snapshot with the command-line tool, you need to know its
number. Get it by running snapper list
. To delete a
snapshot, run snapper delete
NUMBER.
Deleting the current default subvolume snapshot is not allowed.
When deleting snapshots with Snapper, the freed space will be claimed by a
Btrfs process running in the background. Thus the visibility and the
availability of free space is delayed. In case you need space freed by
deleting a snapshot to be available immediately, use the option
--sync
with the delete command.
When deleting a pre
snapshot, you should always delete
its corresponding post
snapshot (and vice versa).
snapper delete 65
Deletes snapshot 65 for the default (
root
) configuration.snapper -c home delete 89 90
Deletes snapshots 89 and 90 for a custom configuration named
home
.snapper delete --sync 23
Deletes snapshot 23 for the default (
root
) configuration and makes the freed space available immediately.
Sometimes the Btrfs snapshot is present but the XML file containing the metadata for Snapper is missing. In this case the snapshot is not visible for Snapper and needs to be deleted manually:
btrfs subvolume delete /.snapshots/SNAPSHOTNUMBER/snapshot rm -rf /.snapshots/SNAPSHOTNUMBER
If you delete snapshots to free space on your hard disk, make sure to delete old snapshots first. The older a snapshot is, the more disk space it occupies.
Snapshots are also automatically deleted by a daily cron job. Refer to Section 7.6.1.2, “Cleanup algorithms” for details.
7.7 Automatic snapshot clean-up #
Snapshots occupy disk space and over time the amount of disk space occupied by the snapshots may become large. To prevent disks from running out of space, Snapper offers algorithms to automatically delete old snapshots. These algorithms differentiate between timeline snapshots and numbered snapshots (administration plus installation snapshot pairs). You can specify the number of snapshots to keep for each type.
In addition to that, you can optionally specify a disk space quota, defining the maximum amount of disk space the snapshots may occupy. It is also possible to automatically delete pre and post snapshots pairs that do not differ.
A clean-up algorithm is always bound to a single Snapper configuration, so you need to configure algorithms for each configuration. To prevent certain snapshots from being automatically deleted, refer to Can a snapshot be protected from deletion? .
The default setup (root
) is configured to do clean-up
for numbered snapshots and empty pre and post snapshot pairs. Quota support
is enabled—snapshots may not occupy more than 50% of the available
disk space of the root partition. Timeline snapshots are disabled by
default, therefore the timeline clean-up algorithm is also disabled.
7.7.1 Cleaning up numbered snapshots #
Cleaning up numbered snapshots—administration plus installation snapshot pairs—is controlled by the following parameters of a Snapper configuration.
NUMBER_CLEANUP
Enables or disables clean-up of installation and admin snapshot pairs. If enabled, snapshot pairs are deleted when the total snapshot count exceeds a number specified with
NUMBER_LIMIT
and/orNUMBER_LIMIT_IMPORTANT
and an age specified withNUMBER_MIN_AGE
. Valid values:yes
(enable),no
(disable).The default value is
"yes"
.Example command to change or set:
>
sudo
snapper -c CONFIG set-config "NUMBER_CLEANUP=no"NUMBER_LIMIT
/NUMBER_LIMIT_IMPORTANT
Defines how many regular and/or important installation and administration snapshot pairs to keep. Ignored if
NUMBER_CLEANUP
is set to"no"
.The default value is
"2-10"
forNUMBER_LIMIT
and"4-10"
forNUMBER_LIMIT_IMPORTANT
. The cleaning algorithms delete snapshots above the specified maximum value, without taking the snapshot and file system space into account. The algorithms also delete snapshots above the minimum value until the limits for the snapshot and file system are reached.Example command to change or set:
>
sudo
snapper -c CONFIG set-config "NUMBER_LIMIT=10"Important: Ranged compared to constant valuesIn case quota support is enabled (see Section 7.7.5, “Adding disk quota support”) the limit needs to be specified as a minimum-maximum range, for example
2-10
. If quota support is disabled, a constant value, for example10
, needs to be provided, otherwise cleaning-up will fail with an error.NUMBER_MIN_AGE
Defines the minimum age in seconds a snapshot must have before it can automatically be deleted. Snapshots younger than the value specified here will not be deleted, regardless of how many exist.
The default value is
"1800"
.Example command to change or set:
>
sudo
snapper -c CONFIG set-config "NUMBER_MIN_AGE=864000"
NUMBER_LIMIT
, NUMBER_LIMIT_IMPORTANT
and NUMBER_MIN_AGE
are always evaluated. Snapshots are
only deleted when all conditions are met.
If you always want to keep the number of snapshots defined with
NUMBER_LIMIT*
regardless of their age, set
NUMBER_MIN_AGE
to 0
.
The following example shows a configuration to keep the last 10 important and regular snapshots regardless of age:
NUMBER_CLEANUP=yes NUMBER_LIMIT_IMPORTANT=10 NUMBER_LIMIT=10 NUMBER_MIN_AGE=0
On the other hand, if you do not want to keep snapshots beyond a certain
age, set NUMBER_LIMIT*
to 0
and
provide the age with NUMBER_MIN_AGE
.
The following example shows a configuration to only keep snapshots younger than ten days:
NUMBER_CLEANUP=yes NUMBER_LIMIT_IMPORTANT=0 NUMBER_LIMIT=0 NUMBER_MIN_AGE=864000
7.7.2 Cleaning up timeline snapshots #
Cleaning up timeline snapshots is controlled by the following parameters of a Snapper configuration.
TIMELINE_CLEANUP
Enables or disables clean-up of timeline snapshots. If enabled, snapshots are deleted when the total snapshot count exceeds a number specified with
TIMELINE_LIMIT_*
and an age specified withTIMELINE_MIN_AGE
. Valid values:yes
,no
.The default value is
"yes"
.Example command to change or set:
>
sudo
snapper -c CONFIG set-config "TIMELINE_CLEANUP=yes"TIMELINE_LIMIT_DAILY
,TIMELINE_LIMIT_HOURLY
,TIMELINE_LIMIT_MONTHLY
,TIMELINE_LIMIT_WEEKLY
,TIMELINE_LIMIT_YEARLY
Number of snapshots to keep for hour, day, month, week, and year.
The default value for each entry is
"10"
, except forTIMELINE_LIMIT_WEEKLY
, which is set to"0"
by default.TIMELINE_MIN_AGE
Defines the minimum age in seconds a snapshot must have before it can automatically be deleted.
The default value is
"1800"
.
TIMELINE_CLEANUP="yes" TIMELINE_CREATE="yes" TIMELINE_LIMIT_DAILY="7" TIMELINE_LIMIT_HOURLY="24" TIMELINE_LIMIT_MONTHLY="12" TIMELINE_LIMIT_WEEKLY="4" TIMELINE_LIMIT_YEARLY="2" TIMELINE_MIN_AGE="1800"
This example configuration enables hourly snapshots which are
automatically cleaned up. TIMELINE_MIN_AGE
and
TIMELINE_LIMIT_*
are always both evaluated. In this
example, the minimum age of a snapshot before it can be deleted is set to
30 minutes (1800 seconds). Since we create hourly snapshots, this ensures
that only the latest snapshots are kept. If
TIMELINE_LIMIT_DAILY
is set to not zero, this means
that the first snapshot of the day is kept, too.
Hourly: The last 24 snapshots that have been made.
Daily: The first daily snapshot that has been made is kept from the last seven days.
Monthly: The first snapshot made on the last day of the month is kept for the last twelve months.
Weekly: The first snapshot made on the last day of the week is kept from the last four weeks.
Yearly: The first snapshot made on the last day of the year is kept for the last two years.
7.7.3 Cleaning up snapshot pairs that do not differ #
As explained in Section 7.1.2, “Types of snapshots”, whenever you run a YaST module or execute Zypper, a pre snapshot is created on start-up and a post snapshot is created when exiting. In case you have not made any changes there will be no difference between the pre and post snapshots. Such “empty” snapshot pairs can be automatically be deleted by setting the following parameters in a Snapper configuration:
EMPTY_PRE_POST_CLEANUP
If set to
yes
, pre and post snapshot pairs that do not differ will be deleted.The default value is
"yes"
.EMPTY_PRE_POST_MIN_AGE
Defines the minimum age in seconds a pre and post snapshot pair that does not differ must have before it can automatically be deleted.
The default value is
"1800"
.
7.7.4 Cleaning up manually created snapshots #
Snapper does not offer custom clean-up algorithms for manually created snapshots. However, you can assign the number or timeline clean-up algorithm to a manually created snapshot. If you do so, the snapshot will join the “clean-up queue” for the algorithm you specified. You can specify a clean-up algorithm when creating a snapshot, or by modifying an existing snapshot:
snapper create --description "Test" --cleanup-algorithm number
Creates a stand-alone snapshot (type single) for the default (root) configuration and assigns the
number
clean-up algorithm.snapper modify --cleanup-algorithm "timeline" 25
Modifies the snapshot with the number 25 and assigns the clean-up algorithm
timeline
.
7.7.5 Adding disk quota support #
In addition to the number and/or timeline clean-up algorithms described above, Snapper supports quotas. You can define what percentage of the available space snapshots are allowed to occupy. This percentage value always applies to the Btrfs subvolume defined in the respective Snapper configuration.
Btrfs quotas are applied to subvolumes, not to users. You may apply
disk space quotas to users and groups (for example, with the
quota
command) in addition to using Btrfs quotas.
If Snapper was enabled during the installation, quota support is
automatically enabled. In case you manually enable Snapper at a later point
in time, you can enable quota support by running snapper
setup-quota
. This requires a valid configuration (see
Section 7.5, “Creating and modifying Snapper configurations” for more information).
Quota support is controlled by the following parameters of a Snapper configuration.
QGROUP
The Btrfs quota group used by Snapper. If not set, run
snapper setup-quota
. If already set, only change if you are familiar withman 8 btrfs-qgroup
. This value is set withsnapper setup-quota
and should not be changed.SPACE_LIMIT
Limit of space snapshots are allowed to use in fractions of 1 (100%). Valid values range from 0 to 1 (0.1 = 10%, 0.2 = 20%, ...).
The following limitations and guidelines apply:
Quotas are only activated in addition to an existing number and/or timeline clean-up algorithm. If no clean-up algorithm is active, quota restrictions are not applied.
With quota support enabled, Snapper will perform two clean-up runs if required. The first run will apply the rules specified for number and timeline snapshots. Only if the quota is exceeded after this run, the quota-specific rules will be applied in a second run.
Even if quota support is enabled, Snapper will always keep the number of snapshots specified with the
NUMBER_LIMIT*
andTIMELINE_LIMIT*
values, even if the quota will be exceeded. It is therefore recommended to specify ranged values (MIN-MAX
) forNUMBER_LIMIT*
andTIMELINE_LIMIT*
to ensure the quota can be applied.If, for example,
NUMBER_LIMIT=5-20
is set, Snapper will perform a first clean-up run and reduce the number of regular numbered snapshots to 20. In case these 20 snapshots exceed the quota, Snapper will delete the oldest ones in a second run until the quota is met. A minimum of five snapshots will always be kept, regardless of the amount of space they occupy.
7.8 Showing exclusive disk space used by snapshots #
Snapshots share data, for efficient use of storage space, so using ordinary
commands like du
and df
won't measure
used disk space accurately. When you want to free up disk space on Btrfs
with quotas enabled, you need to know how much exclusive disk space is
used by each snapshot, rather than shared space. Snapper 0.6 and up reports
the used disk space for each snapshot in the
Used Space
column:
#
snapper --iso list
# | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata
----+--------+-------+---------------------+------+------------+---------+-----------------------+--------------
0 | single | | | root | | | current |
1* | single | | 2019-07-22 13:08:38 | root | 16.00 KiB | | first root filesystem |
2 | single | | 2019-07-22 14:21:05 | root | 14.23 MiB | number | after installation | important=yes
3 | pre | | 2019-07-22 14:26:03 | root | 144.00 KiB | number | zypp(zypper) | important=no
4 | post | 3 | 2019-07-22 14:26:04 | root | 112.00 KiB | number | | important=no
5 | pre | | 2019-07-23 08:19:36 | root | 128.00 KiB | number | zypp(zypper) | important=no
6 | post | 5 | 2019-07-23 08:19:43 | root | 80.00 KiB | number | | important=no
7 | pre | | 2019-07-23 08:20:50 | root | 256.00 KiB | number | yast sw_single |
8 | pre | | 2019-07-23 08:23:22 | root | 112.00 KiB | number | zypp(ruby.ruby2.5) | important=no
9 | post | 8 | 2019-07-23 08:23:35 | root | 64.00 KiB | number | | important=no
10 | post | 7 | 2019-07-23 08:24:05 | root | 16.00 KiB | number | |
The btrfs
command provides another view of space used by
snapshots:
#
btrfs qgroup show -p /
qgroupid rfer excl parent
-------- ---- ---- ------
0/5 16.00KiB 16.00KiB ---
[...]
0/272 3.09GiB 14.23MiB 1/0
0/273 3.11GiB 144.00KiB 1/0
0/274 3.11GiB 112.00KiB 1/0
0/275 3.11GiB 128.00KiB 1/0
0/276 3.11GiB 80.00KiB 1/0
0/277 3.11GiB 256.00KiB 1/0
0/278 3.11GiB 112.00KiB 1/0
0/279 3.12GiB 64.00KiB 1/0
0/280 3.12GiB 16.00KiB 1/0
1/0 3.33GiB 222.95MiB ---
The qgroupid
column displays the identification number for
each subvolume, assigning a qgroup level/ID combination.
The rfer
column displays the total amount of data
referred to in the subvolume.
The excl
column displays the exclusive data in each
subvolume.
The parent
column shows the parent qgroup of the subvolumes.
The final item, 1/0
, shows the totals for the parent
qgroup. In the above example, 222.95 MiB will be freed if all subvolumes
are removed. Run the following command to see which snapshots are associated
with each subvolume:
#
btrfs subvolume list -st /
ID gen top level path
-- --- --------- ----
267 298 266 @/.snapshots/1/snapshot
272 159 266 @/.snapshots/2/snapshot
273 170 266 @/.snapshots/3/snapshot
274 171 266 @/.snapshots/4/snapshot
275 287 266 @/.snapshots/5/snapshot
276 288 266 @/.snapshots/6/snapshot
277 292 266 @/.snapshots/7/snapshot
278 296 266 @/.snapshots/8/snapshot
279 297 266 @/.snapshots/9/snapshot
280 298 266 @/.snapshots/10/snapshot
Doing an upgrade from one service pack to another results in snapshots occupying a lot of disk space on the system subvolumes. Manually deleting these snapshots after they are no longer needed is recommended. See Section 7.6.4, “Deleting snapshots” for details.
7.9 Frequently asked questions #
- Q:
Why does Snapper never show changes in
/var/log
,/tmp
and other directories? For some directories we decided to exclude them from snapshots. See Section 7.1.3, “Directories that are excluded from snapshots” for a list and reasons. To exclude a path from snapshots we create a subvolume for that path.
- Q: Can I boot a snapshot from the boot loader?
Yes—refer to Section 7.3, “System rollback by booting from snapshots” for details.
- Q: Can a snapshot be protected from deletion?
Currently Snapper does not offer means to prevent a snapshot from being deleted manually. However, you can prevent snapshots from being automatically deleted by clean-up algorithms. Manually created snapshots (see Section 7.6.2, “Creating snapshots”) have no clean-up algorithm assigned unless you specify one with
--cleanup-algorithm
. Automatically created snapshots always either have thenumber
ortimeline
algorithm assigned. To remove such an assignment from one or more snapshots, proceed as follows:List all available snapshots:
>
sudo
snapper list -aMemorize the number of the snapshot(s) you want to prevent from being deleted.
Run the following command and replace the number placeholders with the number(s) you memorized:
>
sudo
snapper modify --cleanup-algorithm "" #1 #2 #nCheck the result by running
snapper list -a
again. The entry in the columnCleanup
should now be empty for the snapshots you modified.
- Q: Where can I get more information on Snapper?
See the Snapper home page at http://snapper.io/.
8 Live kernel patching with KLP #
This document describes the basic principles of the Kernel Live Patching (KLP) technology, and provides usage guidelines for the SLE Live Patching service.
KLP makes it possible to apply the latest security updates to Linux kernels without rebooting. This maximizes system uptime and availability, which is especially important for mission-critical systems.
The information provided in this document relates to the AMD64/Intel 64, POWER, and IBM Z architectures.
8.1 Advantages of Kernel Live Patching #
KLP offers several benefits.
Keeping a large number of servers automatically up to date is essential for organizations obtaining or maintaining certain compliance certifications. KLP can help achieve compliance, while reducing the need for costly maintenance windows.
Companies that work with service-level agreement contracts must guarantee a specific level of their system accessibility and uptime. Live patching makes it possible to patch systems without incurring downtime.
Since KLP is part of the standard system update mechanism, there is no need for specialized training or introduction of complicated maintenance routines.
8.2 Kernel Live Patching overview #
Kernel live patches are delivered as packages with modified code that are separate from the main kernel package. The live patches are cumulative, so the latest patch contains all fixes from the previous ones for the kernel package. Each kernel live package is tied to the exact kernel revision for which it is issued. The live patch package version number increases with every addition of fixes.
After a live patch is applied, the
lp-HASH
string is added to
the version of the running kernel as reported by the uname
-a
command.
>
uname -a
Linux sle15-sp3 5.3.18-150300.59.101-default #1 SMP \
Tue Nov 1 11:32:03 UTC 2022 (b2a976e/lp-cd28ef5) x86_64 x86_64 x86_64 GNU/Linux
To determine the kernel patching status, use the klp -v
patches
command.
Live patches contain only critical fixes, and they do not replace regular kernel updates that require a reboot. Consider live patches as temporary measures that protect the kernel until a proper kernel update and a reboot are performed.
The diagram below illustrates the overall relationship between live patches
and kernel updates. The list of CVEs and defect reports addressed by the
currently active live patch can be viewed using the klp -v
patches
command.
It is possible to have multiple versions of the kernel package installed along with their live patches. These packages do not conflict. You can install updated kernel packages along with live patches for the running kernel. In this case, you may be prompted to reboot the system. Users with SLE Live Patching subscriptions are eligible for technical support as long as there are live patch updates for the running kernel (see Section 8.5.1, “Checking expiration date of the live patch”).
With KLP activated, every kernel update comes with a live patch package.
This live patch does not contain any fixes and serves as a seed for future
live patches for the corresponding kernel. These empty seed patches are
called initial patches
.
8.2.1 Kernel Live Patching scope #
The scope of SLE Live Patching includes fixes for SUSE Common Vulnerability Scoring System (CVSS; SUSE CVSS is based on the CVSS v3.0 system) level 7+ vulnerabilities and bug fixes related to system stability or data corruption. However, it may not be technically feasible to create live patches for all fixes that fall under the specified categories. SUSE therefore reserves the right to skip fixes in situations where creating a kernel live patch is not possible for technical reasons. Currently, over 95% of qualifying fixes are released as live patches. For more information on CVSS (the base for the SUSE CVSS rating), see Common Vulnerability Scoring System SIG.
8.2.2 Kernel Live Patching limitations #
KLP involves replacing functions and gracefully handling replacement of interdependent function sets. This is done by redirecting calls to old code to updated code in a different memory location. Changes in data structures make the situation more complicated, as the data remain in place and cannot be extended or reinterpreted. While there are techniques that allow indirect alteration of data structures, some fixes cannot be converted to live patches. In this situation, a system restart is the only way to apply the fixes.
8.3 Activating Kernel Live Patching using YaST #
To activate KLP on your system, you need to have active SLES and SLE Live Patching subscriptions. Visit SUSE Customer Center to check the status of your subscriptions and obtain a registration code for the SLE Live Patching subscription.
To activate Kernel Live Patching on your system, follow these steps:
Run the
yast2 registration
command and click .Select
in the list of available extensions and click .Confirm the license terms and click
.Enter your SLE Live Patching registration code and click
.Check the
and selected . The patternsLive Patching
andSLE Live Patching Lifecycle Data
should be automatically selected for installation along with additional packages to satisfy dependencies.Click
to complete the installation. This will install the base Kernel Live Patching components on your system, the initial live patch, and the required dependencies.
8.4 Activating Kernel Live Patching from the command line #
To activate Kernel Live Patching, you need to have active SLES and SLES Live Patching subscriptions. Visit SUSE Customer Center to check the status of your subscriptions and obtain a registration code for the SLES Live Patching subscription.
Run
sudo SUSEConnect --list-extensions
. Note the exact activation command for SLES Live Patching. Example command output (abbreviated):$ SUSEConnect --list-extensions ... SUSE Linux Enterprise Live Patching 15 SP3 x86_64 Activate with: SUSEConnect -p sle-module-live-patching/15.3/x86_64 \ -r ADDITIONAL REGCODE
Activate SLES Live Patching using the obtained command followed by
-r LIVE_PATCHING_REGISTRATION_CODE
, for example:SUSEConnect -p sle-module-live-patching/15.3/x86_64 \ -r LIVE_PATCHING_REGISTRATION_CODE
Install the required packages and dependencies using the command
zypper install -t pattern lp_sles
At this point, the system has already been live-patched.
Here is how the process works behind the scenes: When the package installation system detects that there is an installed kernel that can be live-patched, and that there is a live patch for it in the software channel, the system selects the live patch for installation. The kernel then receives the live patch fixes as part of the package installation. The kernel gets live-patched even before the product installation is complete.
8.5 Performing Kernel Live Patching #
Kernel live patches are installed as part of regular system updates. However, there are several things you should be aware of.
The kernel is live-patched if a kernel-livepatch-* package has been installed for the running kernel. You can use the command
zypper se --details kernel-livepatch-*
to check what kernel live patch packages are installed on your system.When the kernel-default package is installed, the update manager prompts you to reboot the system. To prevent this message from appearing, you can filter out kernel updates from the patching operation. This can be done by adding package locks with Zypper. SUSE Manager also makes it possible to filter channel contents (see Live Patching with SUSE Manager).
You can check patching status using the
klp status
command. To examine installed patches, run theklp -v patches
command.Keep in mind that while there may be multiple kernel packages installed on the system, only one of them is running at any given time. Similarly, there may be multiple live patch packages installed, but only one live patch is loaded into the kernel.
The active live patch is included in the
initrd
. This means that in case of an unexpected reboot, the system comes up with the live patch fixes applied, so there is no need to perform patching again.
8.5.1 Checking expiration date of the live patch #
Make sure that the
lifecycle-data-sle-module-live-patching is installed,
then run the zypper lifecycle
command. You should see
expiration dates for live patches in the Package end of support if
different from product
section of the output.
Every live patch receives updates for one year from the release of the underlying kernel package. The Maintained kernels, patch updates and lifecycle page allows you to check expiration dates based on the running kernel version without installing the product extension.
8.6 Troubleshooting Kernel Live Patching issues #
8.6.1 Manual patch downgrade #
If you find the latest live patch problematic, you can downgrade the currently installed live patch back to its previous version. We recommend performing patch downgrade before the system starts exhibiting issues. Keep in mind that a system with kernel warnings or kernel error traces in the system log may not be suitable for the patch downgrade procedure. If you are unsure whether the system meets the requirements for a patch downgrade, contact SUSE Technical Support for help.
Identify the running live patch using the
klp -v patches
command. You can see the currently running patch on the line starting withRPM:
. For example:RPM: kernel-livepatch-5_3_18-24_29-default-2-2.1.x86_64
The
5_3_18-24_29-default
in the example above denotes the exact running kernel version.Use the command
zypper search -s kernel-livepatch-RUNNING_KERNEL_VERSION-default
to search for previous versions of the patch. The command returns a list of available package versions. Keep in mind that for every new live patch package release, the version number increases by one. Make sure that you choose the version number one release lower than the current one.Install the desired version with the command
zypper in --oldpackage kernel-livepatch-RUNNING_KERNEL_VERSION-default=DESIRED_VERSION
.
9 Transactional updates #
Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root file system is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not affect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the admin must decide if a reboot is more expensive than disturbing running services. If reboots are too expensive then do not use transactional updates.
Transactional updates are run daily by the
transactional-update
script. The script checks for
available updates. If there are any updates, it creates a new snapshot of
the root file system in the background, and then fetches updates from the
release channels. After the new snapshot is completely updated, it is
marked as active and will be the new default root file system after the next
reboot of the system. When transactional-update
is set to run
automatically (which is the default behavior) it also reboots the system.
Both the time that the update runs and the reboot maintenance window are
configurable.
Only packages that are part of the snapshot of the root file system can be updated. If packages contain files that are not part of the snapshot, the update could fail or break the system.
RPMs that require a license to be accepted cannot be updated.
9.1 Limitations of technology preview #
As a technology preview, there are certain limitations in functionality. The
following packages will not work with transactional-update
:
The nginx default index.html page may not be available
tomcat-webapps and tomcat-admin-webapps
phpMyAdmin
sca-appliance-*
mpi-selector
emacs works except for Emacs games
bind and bind-chrootenv
docbook*
sblim-sfcb*
texlive*
iso_ent
openjade
opensp
pcp
plymouth
postgresql-server-10
pulseaudio-gdm-hooks
smartmontools
The updater component of the system installer does not work with a read-only file system as it has no support for transactional updates.
Further considerations:
In general it is a good idea to minimize the time between updating the system and rebooting the machine.
Only one update can be applied at a time. Be sure to reboot after an update, and before the next update is applied.
update-alternatives
should not be run after a transactional update until the machine has been rebooted.Do not create new system users or system groups after a transactional update until after reboot. It is acceptable to create normal users and groups (UID > 1000, GID > 1000).
YaST is not yet aware of transactional updates. If a YaST module needs to install additional packages, this will not work. Normal system operations only modifying configuration files in
/etc
will work.For php7-fastcgi, you must manually create a symlink,
/srv/www/cgi-bin/php
, that points to/usr/bin/php-cgi
.ntpis part of the Legacy Module for migration from older SLES versions. It is not supported on a new SUSE Linux Enterprise Server installation, and has been replaced by chrony. If you continue to use ntp, a fresh installation is required to work correctly with transactional updates.
sblim-sfcb: The whole sblim ecosystem is incompatible with transactional update.
btrfs-defrag
from the btrfsmaintenance package does not work with a read-only root file system.For
btrfs-balance
, the variableBTRFS_BALANCE_MOUNTPOINTS
in/etc/sysconfig/btrfsmaintenance
must be changed from/
to/.snapshots
.For
btrfs-scrub
, the variableBTRFS_SCRUB_MOUNTPOINTS
in/etc/sysconfig/btrfsmaintenance
must be changed from/
to/.snapshots
.
9.2 Enabling transactional-update #
You must enable the Transactional Server Module during system installation, and then select the Transactional Server System Role. Installing any package from the Transactional Server Module later in a running system is NOT supported and may break the system.
Note that changing the subvolume layout of the root partition, or putting
sub-directories or subvolumes of the root partition on their own partitions
(except /home
, /var
,
/srv
, and /opt
) is not supported,
and will most likely break the system.
9.3 Managing automatic updates #
Automatic updates are controlled by a systemd.timer
that runs once per day. This applies all updates, and informs
rebootmgrd
that the machine should be rebooted. You may
adjust the time when the update runs, see systemd.timer(5). To adjust the
maintenance window, which is when rebootmgrd
reboots the
system, see rebootmgrd(8).
You can disable automatic transactional updates with this command:
#
systemctl --now disable transactional-update.timer
9.4 The transactional-update
command #
The transactional-update
command enables atomic installation
or removal of updates; updates are applied only
if all of them can be successfully installed.
transactional-update
creates a snapshot of your system
before the update is applied, and you can restore this snapshot. All changes become
active only after reboot.
--continue
The
--continue
option is for making multiple changes to an existing snapshot without rebooting.The default
transactional-update
behavior is to create a new snapshot from the current root file system. If you forget something, such as installing a new package, you have to reboot to apply your previous changes, runtransactional-update
again to install the forgotten package, and reboot again. You cannot run thetransactional-update
command multiple times without rebooting to add more changes to the snapshot, because that creates separate independent snapshots that do not include changes from the previous snapshots.Use the
--continue
option to make as many changes as you want without rebooting. A separate snapshot is made each time, and each snapshot contains all the changes you made in the previous snapshots, plus your new changes. Repeat this process as many times as you want, and when the final snapshot includes everything you want reboot the system, and your final snapshot becomes the new root file system.Another useful feature of the
--continue
option is you may select any existing snapshot as the base for your new snapshot. The following example demonstrates runningtransactional-update
to install a new package in a snapshot based on snapshot 13, and then running it again to install another package:#
transactional-update pkg install package_1
#
transactional-update --continue 13 pkg install package_2
The
--continue [num]
option callssnapper create --from
, see Section 7.6.2, “Creating snapshots”.cleanup
If the current root filesystem is identical to the active root filesystem (after a reboot, before
transactional-update
creates a new snapshot with updates), all old snapshots without a cleanup algorithm get a cleanup algorithm set. This ensures that old snapshots will be deleted by Snapper. (See the section about cleanup algorithms in snapper(8).) This also removes all unreferenced (and thus unused)/etc
overlay directories in/var/lib/overlay
:#
transactional-update cleanup
pkg in/install
Installs individual packages from the available channels using the
zypper install
command. This command can also be used to install Program Temporary Fix (PTF) RPM files.#
transactional-update pkg install package_name
or
#
transactional-update pkg install rpm1 rpm2
pkg rm/remove
Removes individual packages from the active snapshot using the
zypper remove
command. This command can also be used to remove PTF RPM files.#
transactional-update pkg remove package_name
pkg up/update
Updates individual packages from the active snapshot using the
zypper update
command. Only packages that are part of the snapshot of the base file system can be updated.#
transactional-update pkg update package_name
up/update
If there are new updates available, a new snapshot is created and
zypper up/update
updates the snapshot.#
transactional-update up
dup
If there are new updates available, a new snapshot is created and
zypper dup –no-allow-vendor-change
updates the snapshot. The snapshot is activated afterwards and becomes the new root file system after reboot.#
transactional-update dup
patch
If there are new updates available, a new snapshot is created and
zypper patch
updates the snapshot.#
transactional-update patch
rollback
This sets the default subvolume. On systems with a read-write file system
snapper rollback
is called. On a read-only file system and without any argument, the current system is set to a new default root file system. If you specify a number, that snapshot is used as the default root file system. On a read-only file system, it does not create any additional snapshots.#
transactional-update rollback snapshot_number
grub.cfg
This creates a new GRUB2 configuration. Sometimes it is necessary to adjust the boot configuration, for example adding additional kernel parameters. Edit /etc/default/grub, run
transactional-update grub.cfg
, and then reboot to activate the change. You must immediately reboot, or the new GRUB2 configuration will be overwritten with the default by the next transactional-update.#
transactional-update grub.cfg
reboot
This parameter triggers a reboot after the action is completed.
#
transactional-update dup reboot
--help
This prints a help screen with options and subcommands.
#
transactional-update --help
9.5 Troubleshooting #
If the upgrade fails, run supportconfig
to collect log
data. Provide the resulting files, including
/var/log/transactional-update.log
to SUSE Support.
10 Remote graphical sessions with VNC #
Virtual Network Computing (VNC) enables you to access a remote computer via a graphical desktop, and run remote graphical applications. VNC is platform-independent and accesses the remote machine from any operating system. This chapter describes how to connect to a VNC server with the desktop clients vncviewer and Remmina, and how to operate a VNC server.
SUSE Linux Enterprise Server supports two different kinds of VNC sessions: One-time sessions that “live” as long as the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated.
A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.
10.1 The vncviewer
client #
To connect to a VNC service provided by a server, a client is needed. The
default in SUSE Linux Enterprise Server is vncviewer
, provided by the
tigervnc
package.
10.1.1 Connecting using the vncviewer CLI #
To start your VNC viewer and initiate a session with the server, use the command:
>
vncviewer jupiter.example.com:1
Instead of the VNC display number you can also specify the port number with two colons:
>
vncviewer jupiter.example.com::5901
The actual display or port number you specify in the VNC client must be
the same as the display or port number picked by the
vncserver
command on the target machine. See
Section 10.4, “Configuring persistent VNC server sessions” for further info.
10.1.2 Connecting using the vncviewer GUI #
By running vncviewer
without specifying
--listen
or a host to connect to, it will show a window
to ask for connection details. Enter the host into the field like in Section 10.1.1, “Connecting using the vncviewer CLI”
and click .
10.1.3 Notification of unencrypted connections #
The VNC protocol supports different kinds of encrypted connections, not to be confused with password authentication. If a connection does not use TLS, the text “(Connection not encrypted!)” can be seen in the window title of the VNC viewer.
10.2 Remmina: the remote desktop client #
Remmina is a modern and feature rich remote desktop client. It supports several access methods, for example VNC, SSH, RDP, and Spice.
10.2.1 Installation #
To use Remmina, verify whether the remmina package is installed on your system, and install it if not. Remember to install the VNC plug-in for Remmina as well:
#
zypper in remmina remmina-plugin-vnc
10.2.2 Main window #
Run Remmina by entering the remmina
command.
The main application window shows the list of stored remote sessions. Here you can add and save a new remote session, quick-start a new session without saving it, start a previously saved session, or set Remmina's global preferences.
10.2.3 Adding remote sessions #
To add and save a new remote session, click in the top left of the main window. The window opens.
Complete the fields that specify your newly added remote session profile. The most important are:
- Name
Name of the profile. It will be listed in the main window.
- Protocol
The protocol to use when connecting to the remote session, for example VNC.
- Server
The IP or DNS address and display number of the remote server.
- User name, password
Credentials to use for remote authentication. Leave empty for no authentication.
- Color depth, quality
Select the best options according to your connection speed and quality.
Select the
tab to enter more specific settings.If the communication between the client and the remote server is not encrypted, activate
, otherwise the connection fails.Select the
tab for advanced SSH tunneling and authentication options.Confirm with
. Your new profile will be listed in the main window.10.2.4 Starting remote sessions #
You can either start a previously saved session, or quick-start a remote session without saving the connection details.
10.2.4.1 Quick-starting remote sessions #
To start a remote session quickly without adding and saving connection details, use the drop-down box and text box at the top of the main window.
Select the communication protocol from the drop-down box, for example 'VNC', then enter the VNC server DNS or IP address followed by a colon and a display number, and confirm with Enter.
10.2.4.2 Opening saved remote sessions #
To open a specific remote session, double-click it from the list of sessions.
10.2.4.3 Remote sessions window #
Remote sessions are opened in tabs of a separate window. Each tab hosts one session. The toolbar on the left of the window helps you manage the windows/sessions, such as toggle fullscreen mode, resize the window to match the display size of the session, send specific keystrokes to the session, take screenshots of the session, or set the image quality.
10.2.5 Editing, copying, and deleting saved sessions #
To edit a saved remote session, right-click its name in Remmina's main window and select . Refer to Section 10.2.3, “Adding remote sessions” for the description of the relevant fields.
To copy a saved remote session, right-click its name in Remmina's main window and select . In the window, change the name of the profile, optionally adjust relevant options, and confirm with .
To Delete a saved remote session, right-click its name in Remmina's main window and select . Confirm with in the next dialog.
10.2.6 Running remote sessions from the command line #
If you need to open a remote session from the command line or from a batch file without first opening the main application window, use the following syntax:
>
remmina -c profile_name.remmina
Remmina's profile files are stored in the
.local/share/remmina/
directory in your home
directory. To determine which profile file belongs to the session you want
to open, run Remmina, click the session name in the main window, and read
the path to the profile file in the window's status line at the bottom.
While Remmina is not running, you can rename the profile file to a more
reasonable file name, such as sle15.remmina
. You can
even copy the profile file to your custom directory and run it using the
remmina -c
command from there.
10.3 Configuring one-time sessions on the VNC server #
A one-time session is initiated by the remote client. It starts a graphical login screen on the server. This way you can choose the user which starts the session and, if supported by the login manager, the desktop environment. When you terminate the client connection to such a VNC session, all applications started within that session will be terminated, too. One-time VNC sessions cannot be shared, but it is possible to have multiple sessions on a single host at the same time.
Start
› › .Check
.Activate
if you plan to access the VNC session in a Web browser window.If necessary, also check
(for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via .Confirm your settings with
.In case not all needed packages are available yet, you need to approve the installation of missing packages.
Tip: Restart the display managerYaST makes changes to the display manager settings. You need to log out of your current graphical session and restart the display manager for the changes to take effect.
10.3.1 Available configurations #
The default configuration on SUSE Linux Enterprise Server serves sessions with a
resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are
available on ports 5901
for
“regular” VNC viewers (equivalent to VNC display
1
) and on port
5801
for Web browsers.
Other configurations can be made available on different ports, see Section 10.3.3, “Configuring one-time VNC sessions”.
VNC display numbers and X display numbers are independent in one-time sessions. A VNC display number is manually assigned to every configuration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the configurations, it automatically gets a free X display number.
By default, both the VNC client and server try to communicate securely via a self-signed SSL certificate, which is generated after installation. You can either use the default one, or replace it with your own. When using the self-signed certificate, you need to confirm its signature before the first connection—both in the VNC viewer and the Web browser.
Some VNC clients refuse to establish a secure connection via the default
self-signed certificate. For example, the Vinagre client verifies the
certification against the GnuTLS global trust store and fails if the
certificate is self-signed. In such a case, either use an encryption
method other than x509
, or generate a properly signed
certificate for the VNC server and import it to the client's system trust
store.
10.3.2 Initiating a one-time VNC session #
To connect to a one-time VNC session, a VNC viewer must be installed, see
also Section 10.1, “The vncviewer
client”. Alternatively use a
JavaScript-capable Web browser to view the VNC session by entering the
following URL: http://jupiter.example.com:5801
10.3.3 Configuring one-time VNC sessions #
You can skip this section, if you do not need or want to modify the default configuration.
One-time VNC sessions are started via the systemd
socket
xvnc.socket
. By default it offers six
configuration blocks: three for VNC viewers (vnc1
to
vnc3
), and three serving a JavaScript client
(vnchttpd1
to vnchttpd3
). By default
only vnc1
and vnchttpd1
are active.
To activate the VNC server socket at boot time, run the following command:
>
sudo
systemctl enable xvnc.socket
To start the socket immediately, run:
>
sudo
systemctl start xvnc.socket
The Xvnc
server can be configured via the
server_args
option. For a list of options, see
Xvnc --help
.
When adding custom configurations, make sure they are not using ports that are already in use by other configurations, other services, or existing persistent VNC sessions on the same host.
Activate configuration changes by entering the following command:
>
sudo
systemctl reload xvnc.socket
When activating Remote Administration as described in
Procedure 10.1, “Enabling one-time VNC sessions”, the ports
5801
and
5901
are opened in the firewall.
If the network interface serving the VNC sessions is protected by a
firewall, you need to manually open the respective ports when activating
additional ports for VNC sessions. See
Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls” for instructions.
10.4 Configuring persistent VNC server sessions #
A persistent session can be accessed from multiple clients simultaneously. This is ideal for demonstration purposes where one client has full access and all other clients have view-only access. Another use case are training sessions where the trainer might need access to the trainee's desktop.
To connect to a persistent VNC session, a VNC viewer must be installed.
Refer to Section 10.1, “The vncviewer
client” for more details. Alternatively
use a JavaScript-capable Web browser to view the VNC session by entering the
following URL: http://jupiter.example.com:5801
There are two types of persistent VNC sessions:
10.4.1 VNC session initiated using vncserver
#
This type of persistent VNC session is initiated on the server. The session and all applications started in this session run regardless of client connections until the session is terminated. Access to persistent sessions is protected by two possible types of passwords:
a regular password that grants full access or
an optional view-only password that grants a non-interactive (view-only) access.
A session can have multiple client connections of both kinds at once.
vncserver
#Open a shell and make sure you are logged in as the user that should own the VNC session.
If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the port used by your session in the firewall. If starting multiple sessions you may alternatively open a range of ports. See Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls” for details on how to configure the firewall.
vncserver
uses the ports5901
for display:1
,5902
for display:2
, and so on. For persistent sessions, the VNC display and the X display usually have the same number.To start a session with a resolution of 1024x768 pixel and with a color depth of 16-bit, enter the following command:
vncserver -alwaysshared -geometry 1024x768 -depth 16
The
vncserver
command picks an unused display number when none is given and prints its choice. Seeman 1 vncserver
for more options.
When running vncserver
for the first time, it asks for a
password for full access to the session. If needed, you can also provide a
password for view-only access to the session.
The password(s) you are providing here are also used for future sessions
started by the same user. They can be changed with the
vncpasswd
command.
Make sure to use strong passwords of significant length (eight or more characters). Do not share these passwords.
To terminate the session shut down the desktop environment that runs inside the VNC session from the VNC viewer as you would shut it down if it was a regular local X session.
If you prefer to manually terminate a session, open a shell on the VNC
server and make sure you are logged in as the user that owns the VNC
session you want to terminate. Run the following command to terminate the
session that runs on display :1
: vncserver
-kill :1
10.4.1.1 Configuring persistent VNC sessions #
Persistent VNC sessions can be configured by editing
$HOME/.vnc/xstartup
. By default this shell script
starts the same GUI/window manager it was started from. In SUSE Linux Enterprise Server
this will either be GNOME or IceWM. If you want to start your session
with a window manager of your choice, set the variable
WINDOWMANAGER
:
WINDOWMANAGER=gnome vncserver -geometry 1024x768 WINDOWMANAGER=icewm vncserver -geometry 1024x768
Persistent VNC sessions are configured in a single per-user configuration. Multiple sessions started by the same user will all use the same start-up and password files.
10.4.2 VNC session initiated using vncmanager
#
Start
› › .Activate
.Activate
if you plan to access the VNC session in a Web browser window.If necessary, also check
(for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via .Confirm your settings with
.In case not all needed packages are available yet, you need to approve the installation of missing packages.
Tip: Restart the display managerYaST makes changes to the display manager settings. You need to log out of your current graphical session and restart the display manager for the changes to take effect.
10.4.2.1 Configuring persistent VNC sessions #
After you enable the VNC session management as described in Procedure 10.3, “Enabling persistent VNC sessions”, you can normally connect to
the remote session with your favorite VNC viewer, such as
vncviewer
or Remmina. You will be presented with the
login screen. After you log in, the 'VNC' icon will appear in the system
tray of your desktop environment. Click the icon to open the window. If it does not appear or if your desktop
environment does not support icons in the system tray, run
vncmanager-controller
manually.
There are several settings that influence the VNC session's behavior:
This is equivalent to a one-time session. It is not visible to others and will be terminated after you disconnect from it. Refer to Section 10.3, “Configuring one-time sessions on the VNC server” for more information.
The session is visible to other users and keeps running even after you disconnect from it.
Here you can specify the name of the persistent session so that it is easily identified when reconnecting.
The session will be freely accessible without having to log in under user credentials.
You need to log in with a valid user name and password to access the session. Lists the valid user names in the
text box.Prevents multiple users from joining the session at the same time.
Allows multiple users to join the persistent session at the same time. Useful for remote presentations or training sessions.
Confirm with
.10.4.2.2 Joining persistent VNC sessions #
After you set up a persistent VNC session as described in Section 10.4.2.1, “Configuring persistent VNC sessions”, you can join it with your VNC viewer. After your VNC client connects to the server, you will be prompted to choose whether you want to create a new session, or join the existing one:
After you click the name of the existing session, you may be asked for login credentials, depending on the persistent session settings.
10.5 Configuring encryption on the VNC server #
If the VNC server is set up properly, all communication between the VNC server and the client is encrypted. The authentication happens at the beginning of the session; the actual data transfer only begins afterward.
Whether for a one-time or a persistent VNC session, security options are
configured via the -securitytypes
parameter of the
/usr/bin/Xvnc
command located on the
server_args
line. The -securitytypes
parameter selects both authentication method and encryption. It has the
following options:
- None, TLSNone, x509None
No authentication.
- VncAuth, TLSVnc, x509Vnc
Authentication using custom password.
- Plain, TLSPlain, x509Plain
Authentication using PAM to verify user's password.
- None, vncAuth, plain
No encryption.
- TLSNone, TLSVnc, TLSPlain
Anonymous TLS encryption. Everything is encrypted, but there is no verification of the remote host. So you are protected against passive attackers, but not against man-in-the-middle attackers.
- X509None, x509Vnc, x509Plain
TLS encryption with certificate. If you use a self-signed certificate, you will be asked to verify it on the first connection. On subsequent connections you will be warned only if the certificate changed. So you are protected against everything except man-in-the-middle on the first connection (similar to typical SSH usage). If you use a certificate signed by a certificate authority matching the machine name, then you get full security (similar to typical HTTPS usage).
TipSome VNC clients refuse to establish a secure connection via the default self-signed certificate. For example, the Vinagre client verifies the certification against the GnuTLS global trust store and fails if the certificate is self-signed. In such a case, either use an encryption method other than
x509
, or generate a properly signed certificate for the VNC server and import it to the client's system trust store.Tip: Path to certificate and keyWith X509 based encryption, you need to specify the path to the X509 certificate and the key with
-X509Cert
and-X509Key
options.
If you select multiple security types separated by comma, the first one supported and allowed by both client and server will be used. That way you can configure opportunistic encryption on the server. This is useful if you need to support VNC clients that do not support encryption.
On the client, you can also specify the allowed security types to prevent a downgrade attack if you are connecting to a server which you know has encryption enabled (although our vncviewer will warn you with the "Connection not encrypted!" message in that case).
10.6 Compatibility with Wayland #
The Remote Administration (VNC) feature relies on X11 and may result in an
empty screen if Wayland is enabled.
The display manager must be configured to use X11 instead of Wayland.
For gdm, edit /etc/gdm/custom.conf
.
In the [daemon]
section, add
WaylandEnable=false
to the configuration file.
When logging in, the user must choose an X11-compatible session as well.
If you wish to remove the Wayland option for GNOME, you can remove and lock
the gnome-session-wayland package.
11 File copying with RSync #
Today, a typical user has several computers: home and workplace machines, a laptop, a smartphone or a tablet. This makes the task of keeping files and documents in synchronization across multiple devices all the more important.
Before you start using a synchronization tool, you should familiarize yourself with its features and functionality. Make sure to back up your important files.
11.1 Conceptual overview #
For synchronizing a large amount of data over a slow network connection, Rsync offers a reliable method of transmitting only changes within files. This applies not only to text files but also binary files. To detect the differences between files, Rsync subdivides the files into blocks and computes check sums over them.
Detecting changes requires some computing power. So make sure that machines on both ends have enough resources, including RAM.
Rsync can be particularly useful when large amounts of data containing only minor changes need to be transmitted regularly. This is often the case when working with backups. Rsync can also be useful for mirroring staging servers that store complete directory trees of Web servers to a Web server in a DMZ.
Despite its name, Rsync is not a synchronization tool. Rsync is a tool that copies data only in one direction at a time. It does not and cannot do the reverse. If you need a bidirectional tool which can synchronize both source and destination, use Csync.
11.2 Basic syntax #
Rsync is a command-line tool that has the following basic syntax:
rsync [OPTION] SOURCE [SOURCE]... DEST
You can use Rsync on any local or remote machine, provided you have access and write permissions. It is possible to have multiple SOURCE entries. The SOURCE and DEST placeholders can be paths, URLs, or both.
Below are the most common Rsync options:
-v
Outputs more verbose text
-a
Archive mode; copies files recursively and preserves time stamps, user/group ownership, file permissions, and symbolic links
-z
Compresses the transmitted data
When working with Rsync, you should pay particular attention to trailing slashes. A trailing slash after the directory denotes the content of the directory. No trailing slash denotes the directory itself.
11.3 Copying files and directories locally #
The following description assumes that the current user has write
permissions to the directory /var/backup
. To copy a
single file from one directory on your machine to another path, use the
following command:
>
rsync
-avz backup.tar.xz /var/backup/
The file backup.tar.xz
is copied to
/var/backup/
; the absolute path will be
/var/backup/backup.tar.xz
.
Do not forget to add the trailing slash after the
/var/backup/
directory! If you do not insert the slash,
the file backup.tar.xz
is copied to
/var/backup
(file) not inside the
directory /var/backup/
!
Copying a directory is similar to copying a single file. The following
example copies the directory tux/
and
its content into the directory /var/backup/
:
>
rsync
-avz tux /var/backup/
Find the copy in the absolute path
/var/backup/tux/
.
11.4 Copying files and directories remotely #
The Rsync tool is required on both machines. To copy files from or to remote directories requires an IP address or a domain name. A user name is optional if your current user names on the local and remote machine are the same.
To copy the file file.tar.xz
from your local host to
the remote host
192.168.1.1
with
same users (being local and remote), use the following command:
>
rsync
-avz file.tar.xz tux@192.168.1.1:
Depending on what you prefer, these commands are also possible and equivalent:
>
rsync
-avz file.tar.xz 192.168.1.1:~>
rsync
-avz file.tar.xz 192.168.1.1:/home/tux
In all cases with standard configuration, you will be prompted to enter your
passphrase of the remote user. This command will copy
file.tar.xz
to the home directory of user tux
(usually /home/tux
).
Copying a directory remotely is similar to copying a directory locally. The
following example copies the directory
tux/
and its content into the remote
directory /var/backup/
on the
192.168.1.1
host:
>
rsync
-avz tux 192.168.1.1:/var/backup/
Assuming you have write permissions on the host
192.168.1.1
, you will
find the copy in the absolute path
/var/backup/tux
.
11.5 Configuring and using an rsync server #
Rsync can run as a daemon
(rsyncd
) listening on default
port 873 for incoming connections. This daemon can receive “copying
targets”.
The following description explains how to create an Rsync server on a
jupiter
host with a backup
target. This target can be used to store your backups. To create an Rsync
server, do the following:
On jupiter, create a directory to store all your backup files. In this example, we use
/var/backup
:#
mkdir
/var/backupSpecify ownership. In this case, the directory is owned by user
tux
in groupusers
:#
chown
tux.users /var/backupConfigure the rsyncd daemon.
We will separate the configuration file into a main file and some “modules” which hold your backup target. This makes it easier to add additional targets later. Global values can be stored in
/etc/rsyncd.d/*.inc
files, whereas your modules are placed in/etc/rsyncd.d/*.conf
files:Create a directory
/etc/rsyncd.d/
:#
mkdir
/etc/rsyncd.d/In the main configuration file
/etc/rsyncd.conf
, add the following lines:# rsyncd.conf main configuration file log file = /var/log/rsync.log pid file = /var/lock/rsync.lock &merge /etc/rsyncd.d 1 &include /etc/rsyncd.d 2
Create your module (your backup target) in the file
/etc/rsyncd.d/backup.conf
with the following lines:# backup.conf: backup module [backup] 1 uid = tux 2 gid = users 2 path = /var/backup 3 auth users = tux 4 secrets file = /etc/rsyncd.secrets 5 comment = Our backup target
The backup target. You can use any name you like. However, it is a good idea to name a target according to its purpose and use the same name in your
*.conf
file.Specifies the user name or group name that is used when the file transfer takes place.
Defines the path to store your backups (from Step 1).
Specifies a comma-separated list of allowed users. In its simplest form, it contains the user names that are allowed to connect to this module. In our case, only user
tux
is allowed.Specifies the path of a file that contains lines with user names and plain passwords.
Create the
/etc/rsyncd.secrets
file with the following content and replace PASSPHRASE:# user:passwd tux:PASSPHRASE
Make sure the file is only readable by
root
:#
chmod
0600 /etc/rsyncd.secrets
Start and enable the rsyncd daemon with:
#
systemctl
enable rsyncd#
systemctl
start rsyncdTest the access to your Rsync server:
>
rsync
jupiter::You should see a response that looks like this:
backup Our backup target
Otherwise, check your configuration file, firewall and network settings.
The above steps create an Rsync server that can now be used to store
backups. The example also creates a log file listing all connections. This
file is stored in /var/log/rsyncd.log
. This is useful
if you want to debug your transfers.
To list the content of your backup target, use the following command:
>
rsync -avz jupiter::backup
This command lists all files present in the directory
/var/backup
on the server. This request is also logged
in the log file /var/log/rsyncd.log
. To start an actual
transfer, provide a source directory. Use .
for the
current directory. For example, the following command copies the current
directory to your Rsync backup server:
>
rsync -avz . jupiter::backup
By default, Rsync does not delete files and directories when it runs. To
enable deletion, the additional option --delete
must be
stated. To ensure that no newer files are deleted, the option
--update
can be used instead. Any conflicts that arise must
be resolved manually.
11.6 More information #
- Csync
Bidirectional file synchronization tool, see https://csync.org/.
- RSnapshot
Creates incremental backups, see https://rsnapshot.org.
- Unison
A file synchronization tool similar to CSync but with a graphical interface, see https://github.com/bcpierce00/unison.
- Rear
A disaster recovery framework, see the Administration Guide of the SUSE Linux Enterprise High Availability, chapter Disaster Recovery with Rear (Relax-and-Recover).
Part II Booting a Linux system #
- 12 Introduction to the boot process
Booting a Linux system involves different components and tasks. After a firmware and hardware initialization process, which depends on the machine's architecture, the kernel is started by means of the boot loader GRUB 2. After this point, the boot process is completely controlled by the operating system and handled by
systemd
.systemd
provides a set of “targets” that boot configurations for everyday usage, maintenance or emergencies.- 13 UEFI (Unified Extensible Firmware Interface)
UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.
- 14 The boot loader GRUB 2
This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 12, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 13, UEFI (Unified Extensible Firmware Interface).
- 15 The
systemd
daemon systemd initializes the system. It has the process ID 1. systemd is started directly by the kernel and resists signal 9, which normally terminates processes. All other programs are started directly by systemd or by one of its child processes. systemd is a replacement for the System V init daemon and…
12 Introduction to the boot process #
Booting a Linux system involves different components and tasks. After a
firmware and hardware initialization process, which depends on the
machine's architecture, the kernel is started by means of the boot loader
GRUB 2. After this point, the boot process is completely controlled by the
operating system and handled by systemd
. systemd
provides a set of
“targets” that boot configurations for everyday usage,
maintenance or emergencies.
12.1 Terminology #
This chapter uses terms that can be interpreted ambiguously. To understand how they are used here, read the definitions below:
init
Two different processes are commonly named “init”:
The
initramfs
process mounting the root file systemThe operating system process that starts all other processes that is executed from the real root file system
In both cases, the
systemd
program is taking care of this task. It is first executed from theinitramfs
to mount the root file system. Once that has succeeded, it is re-executed from the root file system as the initial process. To avoid confusing these twosystemd
processes, we refer to the first process as init on initramfs and to the second one as systemd.-
initrd
/initramfs
An
initrd
(initial RAM disk) is an image file containing a root file system image which is loaded by the kernel and mounted from/dev/ram
as the temporary root file system. Mounting this file system requires a file system driver.Beginning with kernel 2.6.13, the initrd has been replaced by the
initramfs
(initial RAM file system), which does not require a file system driver to be mounted. SUSE Linux Enterprise Server exclusively uses aninitramfs
. However, since theinitramfs
is stored as/boot/initrd
, it is often called “initrd”. In this chapter we exclusively use the nameinitramfs
.
12.2 The Linux boot process #
The Linux boot process consists of several stages, each represented by a different component:
12.2.1 The initialization and boot loader phase #
During the initialization phase the machine's hardware is set up and the devices are prepared. This process differs significantly between hardware architectures.
SUSE Linux Enterprise Server uses the boot loader GRUB 2 on all architectures. Depending on the architecture and firmware, starting the GRUB 2 boot loader can be a multi-step process. The purpose of the boot loader is to load the kernel and the initial, RAM-based file system (initramfs). For more information about GRUB 2, refer to Chapter 14, The boot loader GRUB 2.
12.2.1.1 Initialization and boot loader phase on AArch64 and AMD64/Intel 64 #
After turning on the computer, the BIOS or the UEFI initializes the screen and keyboard, and tests the main memory. Up to this stage, the machine does not access any mass storage media. Subsequently, the information about the current date, time, and the most important peripherals are loaded from the CMOS values. When the boot media and its geometry are recognized, the system control passes from the BIOS/UEFI to the boot loader.
On a machine equipped with a traditional BIOS, only code from the first
physical 512-byte data sector (the Master Boot Record, MBR) of the boot
disk can be loaded. Only a minimal GRUB 2 fits into the MBR. Its sole
purpose is to load a GRUB 2 core image containing file system drivers from
the gap between the MBR and the first partition (MBR partition table) or
from the BIOS boot partition (GPT partition table). This image contains
file system drivers and therefore is able to access
/boot
located on the root file
system. /boot
contains additional modules for GRUB 2
core as well as the kernel and the initramfs image. Once it has access to
this partition, GRUB 2 loads the kernel and the initramfs image into
memory and hands control over to the kernel.
When booting a BIOS system from an encrypted file system that includes an
encrypted /boot
partition, you need to enter the
password for decryption twice. It is first needed by GRUB 2 to decrypt
/boot
and then for systemd
to mount the encrypted
volumes.
On machines with UEFI the boot process is much simpler than on machines
with a traditional BIOS. The firmware is able to read from a FAT formatted
system partition of disks with a GPT partition table. This EFI
system-partition (in the running system mounted as
/boot/efi
) holds enough space to host a fully-fledged
GRUB 2 which is directly loaded and executed by the firmware.
If the BIOS/UEFI supports network booting, it is also possible to configure a boot server that provides the boot loader. The system can then be booted via PXE. The BIOS/UEFI acts as the boot loader. It gets the boot image from the boot server and starts the system. This is completely independent of local hard disks.
12.2.1.2 Initialization and boot loader phase on IBM Z #
On IBM Z the boot process must be initialized by a boot loader
called zipl
(z initial program load). Although
zipl
supports reading from various file systems, it
does not support the SLE default file system (Btrfs) or booting from
snapshots. SUSE Linux Enterprise Server therefore uses a two-stage boot process that
ensures full Btrfs support at boot-time:
zipl
boots from the partition/boot/zipl
, which can be formatted with the Ext2, Ext3, Ext4, or XFS file system. This partition contains a minimal kernel and an initramfs that are loaded into memory. The initramfs contains a Btrfs driver (among others) and the boot loader GRUB 2. The kernel is started with a parameterinitgrub
, which tells it to start GRUB 2.The kernel mounts the root file system, so
/boot
becomes accessible. Now GRUB 2 is started from the initramfs. It reads its configuration from/boot/grub2/grub.cfg
and loads the final kernel and initramfs from/boot
. The new kernel now gets loaded via Kexec.
12.2.2 The kernel phase #
When the boot loader has passed on system control, the boot process is the
same on all architectures. The boot loader loads both the kernel and an
initial RAM-based file system (initramfs
) into
memory and the kernel takes over.
After the kernel has set up memory management and has detected the CPU type
and its features, it initializes the hardware and mounts the temporary root
file system from the memory that was loaded with the
initramfs
.
12.2.2.1 The initramfs
file #
initramfs
(initial RAM file system) is a small
cpio archive that the kernel can load into a RAM disk. It is located at
/boot/initrd
. It can be created with a tool called
dracut
—refer to man 8 dracut
for details.
The initramfs
provides a minimal Linux
environment that enables the execution of programs before the actual root
file system is mounted. This minimal Linux environment is loaded into
memory by BIOS or UEFI routines and does not have specific hardware
requirements other than sufficient memory. The
initramfs
archive must always provide an
executable named init
that executes the systemd
daemon on the root file system for the boot process to proceed.
Before the root file system can be mounted and the operating system can be
started, the kernel needs the corresponding drivers to access the device
on which the root file system is located. These drivers may include
special drivers for certain kinds of hard disks or even network drivers to
access a network file system. The needed modules for the root file system
are loaded by init
on
initramfs
. After the modules are loaded,
udev
provides the
initramfs
with the needed devices. Later in the
boot process, after changing the root file system, it is necessary to
regenerate the devices. This is done by the systemd
unit
systemd-udev-trigger.service
.
12.2.2.1.1 Regenerating the initramfs #
Because the initramfs
contains drivers, it needs
to be updated whenever a new version of one of its drivers is
available. This is done automatically when installing the package
containing the driver update. YaST or zypper will inform you about
this by showing the output of the command that generates the
initramfs
. However, there are some occasions
when you need to regenerate an initramfs
manually:
- Adding drivers because of hardware changes
If you need to change hardware, for example, hard disks, and this hardware requires different drivers to be in the kernel at boot time, you must update the
initramfs
file.Open or create
/etc/dracut.conf.d/10-DRIVER.conf
and add the following line (mind the leading whitespace):force_drivers+=" DRIVER1 "
Replace DRIVER1 with the module name of the driver. If you need to add more than one driver, list them space-separated:
force_drivers+=" DRIVER1 DRIVER2 "
Proceed with Procedure 12.1, “Generate an initramfs”.
- Moving system directories to a RAID or LVM
Whenever you move swap files, or system directories like
/usr
in a running system to a RAID or logical volume, you need to create aninitramfs
that contains support for software RAID or LVM drivers.To do so, create the respective entries in
/etc/fstab
and mount the new entries (for example withmount -a
and/orswapon -a
).Proceed with Procedure 12.1, “Generate an initramfs”.
- Adding disks to an LVM group or Btrfs RAID containing the root file system
Whenever you add (or remove) a disk to a logical volume group or a Btrfs RAID containing the root file system, you need to create an
initramfs
that contains support for the enlarged volume. Follow the instructions at Procedure 12.1, “Generate an initramfs”.Proceed with Procedure 12.1, “Generate an initramfs”.
- Changing kernel variables
If you change the values of kernel variables via the
sysctl
interface by editing related files (/etc/sysctl.conf
or/etc/sysctl.d/*.conf
), the change will be lost on the next system reboot. Even if you load the values withsysctl --system
at runtime, the changes are not saved into theinitramfs
file. You need to update it by proceeding as outlined in Procedure 12.1, “Generate an initramfs”.- Adding or removing swap devices, re-creating swap area
Whenever you add or remove a swap device, or re-create a swap area with a different UUID, update the initramfs as outlined in Procedure 12.1, “Generate an initramfs”. You may also need to update
GRUB_CMDLINE_*
variables that include theresume=
option in/etc/default/grub
, and then regenerate/boot/grub2/grub.cfg
as outlined in Section 14.2.1, “The file/boot/grub2/grub.cfg
”.
Note that all commands in the following procedure need to be executed
as the root
user.
Enter your
/boot
directory:#
cd /bootGenerate a new
initramfs
file withdracut
, replacing MY_INITRAMFS with a file name of your choice:#
dracut MY_INITRAMFSAlternatively, run
dracut -f
FILENAME to replace an existing init file.(Skip this step if you ran
dracut -f
in the previous step.) Create a symlink from theinitramfs
file you created in the previous step toinitrd
:#
ln -sf MY_INITRAMFSinitrd
On the IBM IBM Z architecture, additionally run
grub2-install
.
12.2.3 The init on initramfs phase #
The temporary root file system mounted by the kernel from the
initramfs
contains the executable systemd
(which
is called init
on
initramfs
in the following, also see Section 12.1, “Terminology”. This program performs all actions needed
to mount the proper root file system. It provides kernel functionality for
the needed file system and device drivers for mass storage controllers with
udev
.
The main purpose of init
on
initramfs
is to prepare the mounting of and access
to the real root file system. Depending on your system configuration,
init
on initramfs
is
responsible for the following tasks.
- Loading kernel modules
Depending on your hardware configuration, special drivers may be needed to access the hardware components of your computer (the most important component being your hard disk). To access the final root file system, the kernel needs to load the proper file system drivers.
- Providing block special files
The kernel generates device events depending on loaded modules.
udev
handles these events and generates the required special block files on a RAM file system in/dev
. Without those special files, the file system and other devices would not be accessible.- Managing RAID and LVM setups
If you configured your system to hold the root file system under RAID or LVM,
init
oninitramfs
sets up LVM or RAID to enable access to the root file system later.- Managing the network configuration
If you configured your system to use a network-mounted root file system (mounted via NFS),
init
must make sure that the proper network drivers are loaded and that they are set up to allow access to the root file system.If the file system resides on a network block device like iSCSI or SAN, the connection to the storage server is also set up by
init
oninitramfs
. SUSE Linux Enterprise Server supports booting from a secondary iSCSI target if the primary target is not available. For more details regarding configuration of the booting iSCSI target refer to Book “Storage Administration Guide”, Chapter 15 “Mass storage over IP networks: iSCSI”, Section 15.3.1 “Using YaST for the iSCSI initiator configuration”.
If the root file system fails to mount from within the boot environment, it must be checked and repaired before the boot can continue. The file system checker will be automatically started for Ext3 and Ext4 file systems. The repair process is not automated for XFS and Btrfs file systems, and the user is presented with information describing the options available to repair the file system. When the file system has been successfully repaired, exiting the boot environment will cause the system to retry mounting the root file system. If successful, the boot will continue normally.
12.2.3.1 The init on initramfs phase in the installation process #
When init
on initramfs
is called during the initial boot as part of the installation process, its
tasks differ from those mentioned above. Note that the installation system
also does not start systemd
from
initramfs
—these tasks are performed by
linuxrc
.
- Finding the installation medium
When starting the installation process, your machine loads an installation kernel and a special
init
containing the YaST installer. The YaST installer is running in a RAM file system and needs to have information about the location of the installation medium to access it for installing the operating system.- Initiating hardware recognition and loading appropriate kernel modules
As mentioned in Section 12.2.2.1, “The
initramfs
file”, the boot process starts with a minimum set of drivers that can be used with most hardware configurations. On AArch64, POWER, and AMD64/Intel 64 machines,linuxrc
starts an initial hardware scanning process that determines the set of drivers suitable for your hardware configuration. On IBM Z, a list of drivers and their parameters needs to be provided, for example via linuxrc or a parmfile.These drivers are used to generate a custom
initramfs
that is needed to boot the system. If the modules are not needed for boot but for coldplug, the modules can be loaded withsystemd
; for more information, see Section 15.6.4, “Loading kernel modules”.- Loading the installation system
When the hardware is properly recognized, the appropriate drivers are loaded. The
udev
program creates the special device files andlinuxrc
starts the installation system with the YaST installer.- Starting YaST
Finally,
linuxrc
starts YaST, which starts the package installation and the system configuration.
12.2.4 The systemd phase #
After the “real” root file system has been found, it is
checked for errors and mounted. If this is successful, the
initramfs
is cleaned and the systemd
daemon on
the root file system is executed. systemd
is Linux's system and service
manager. It is the parent process that is started as PID 1 and acts as an
init system which brings up and maintains user space services. See Chapter 15, The systemd
daemon for details.
13 UEFI (Unified Extensible Firmware Interface) #
UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.
UEFI is becoming more and more available on PC systems and thus is replacing the traditional PC-BIOS. UEFI, for example, properly supports 64-bit systems and offers secure booting (“Secure Boot”, firmware version 2.3.1c or better required), which is one of its most important features. Lastly, with UEFI a standard firmware will become available on all x86 platforms.
UEFI additionally offers the following advantages:
Booting from large disks (over 2 TiB) with a GUID Partition Table (GPT).
CPU-independent architecture and drivers.
Flexible pre-OS environment with network capabilities.
CSM (Compatibility Support Module) to support booting legacy operating systems via a PC-BIOS-like emulation.
For more information, see http://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface. The following sections are not meant as a general UEFI overview; these are only hints about how some features are implemented in SUSE Linux Enterprise Server.
13.1 Secure boot #
In the world of UEFI, securing the bootstrapping process means establishing a chain of trust. The “platform” is the root of this chain of trust; in the context of SUSE Linux Enterprise Server, the mainboard and the on-board firmware could be considered the “platform”. In other words, it is the hardware vendor, and the chain of trust flows from that hardware vendor to the component manufacturers, the OS vendors, etc.
The trust is expressed via public key cryptography. The hardware vendor puts a so-called Platform Key (PK) into the firmware, representing the root of trust. The trust relationship with operating system vendors and others is documented by signing their keys with the Platform Key.
Finally, security is established by requiring that no code will be executed by the firmware unless it has been signed by one of these “trusted” keys—be it an OS boot loader, some driver located in the flash memory of some PCI Express card or on disk, or be it an update of the firmware itself.
To use Secure Boot, you need to have your OS loader signed with a key trusted by the firmware, and you need the OS loader to verify that the kernel it loads can be trusted.
Key Exchange Keys (KEK) can be added to the UEFI key database. This way, you can use other certificates, as long as they are signed with the private part of the PK.
13.1.1 Implementation on SUSE Linux Enterprise Server #
Microsoft’s Key Exchange Key (KEK) is installed by default.
The Secure Boot feature is enabled by default on UEFI/x86_64 installations. You can find the
option in the tab of the dialog. It supports booting when the secure boot is activated in the firmware, while making it possible to boot when it is deactivated.The Secure Boot feature requires that a GUID Partitioning Table (GPT) replaces the old partitioning with a Master Boot Record (MBR). If YaST detects EFI mode during the installation, it will try to create a GPT partition. UEFI expects to find the EFI programs on a FAT-formatted EFI System Partition (ESP).
Supporting UEFI Secure Boot requires having a boot loader with a digital signature that the firmware recognizes as a trusted key. That key is trusted by the firmware a priori, without requiring any manual intervention.
There are two ways of getting there. One is to work with hardware vendors to have them endorse a SUSE key, which SUSE then signs the boot loader with. The other way is to go through Microsoft’s Windows Logo Certification program to have the boot loader certified and have Microsoft recognize the SUSE signing key (that is, have it signed with their KEK). By now, SUSE got the loader signed by UEFI Signing Service (that is Microsoft in this case).
At the implementation layer, SUSE uses the shim
loader which is installed by default. It is a smart solution that avoids
legal issues, and simplifies the certification and signing step
considerably. The shim
loader’s job is to load a
boot loader such as GRUB 2 and verify it; this boot loader in
turn will load kernels signed by a SUSE key only. SUSE provides this
functionality since SLE11 SP3 on fresh installations with UEFI Secure Boot
enabled.
There are two types of trusted users:
First, those who hold the keys. The Platform Key (PK) allows almost everything. The Key Exchange Key (KEK) allows all a PK can except changing the PK.
Second, anyone with physical access to the machine. A user with physical access can reboot the machine, and configure UEFI.
UEFI offers two types of variables to fulfill the needs of those users:
The first is the so-called “Authenticated Variables”, which can be updated from both within the boot process (the so-called Boot Services Environment) and the running OS. This can be done only when the new value of the variable is signed with the same key that the old value of the variable was signed with. And they can only be appended to or changed to a value with a higher serial number.
The second is the so-called “Boot Services Only Variables”. These variables are accessible to any code that runs during the boot process. After the boot process ends and before the OS starts, the boot loader must call the
ExitBootServices
call. After that, these variables are no longer accessible, and the OS cannot touch them.
The various UEFI key lists are of the first type, as this allows online updating, adding, and blacklisting of keys, drivers, and firmware fingerprints. It is the second type of variable, the “Boot Services Only Variable”, that helps to implement Secure Boot in a secure and open source-friendly manner, and thus compatible with GPLv3.
SUSE starts with shim
—a small and simple EFI
boot loader signed by SUSE and Microsoft.
This allows shim
to load and execute.
shim
then goes on to verify that the boot loader
it wants to load is trusted.
In a default situation shim
will use an
independent SUSE certificate embedded in its body. In addition,
shim
will allow to “enroll”
additional keys, overriding the default SUSE key. In the following, we call
them “Machine Owner Keys” or MOKs for short.
Next the boot loader will verify and then boot the kernel, and the kernel will do the same on the modules.
13.1.2 MOK (Machine Owner Key) #
To replace specific kernels, drivers, or other components that are part of
the boot process, you have to use Machine Owner Keys (MOKs). The
mokutil
tool can help you to manage MOKs.
You can create a MOK enrollment request with
mokutil
. The request is stored in a UEFI runtime
(RT) variable called MokNew
. During the next boot,
the shim
bootloader detects
MokNew
and loads
MokManager
, which presents you with several options.
You can use the and
options to add the key to the
MokList. Use the option to copy the key from
the MokNew
variable.
Enrolling a key from disk is usually done when the shim fails to
load grub2
and falls back to loading
MokManager. As MokNew
does not exist yet,
you have the option of locating the key on the UEFI partition.
13.1.3 Booting a custom kernel #
The following is based on https://en.opensuse.org/openSUSE:UEFI#Booting_a_custom_kernel.
Secure Boot does not prevent you from using a self-compiled kernel. You must sign it with your own certificate and make that certificate known to the firmware or MOK.
Create a custom X.509 key and certificate used for signing:
openssl req -new -x509 -newkey rsa:2048 -keyout key.asc \ -out cert.pem -nodes -days 666 -subj "/CN=$USER/"
For more information about creating certificates, see https://en.opensuse.org/openSUSE:UEFI_Image_File_Sign_Tools#Create_Your_Own_Certificate.
Package the key and the certificate as a PKCS#12 structure:
>
openssl pkcs12 -export -inkey key.asc -in cert.pem \ -name kernel_cert -out cert.p12Generate an NSS database for use with
pesign
:>
certutil -d . -NImport the key and the certificate contained in PKCS#12 into the NSS database:
>
pk12util -d . -i cert.p12“Bless” the kernel with the new signature using
pesign
:>
pesign -n . -c kernel_cert -i arch/x86/boot/bzImage \ -o vmlinuz.signed -sList the signatures on the kernel image:
>
pesign -n . -S -i vmlinuz.signedAt that point, you can install the kernel in
/boot
as usual. Because the kernel now has a custom signature the certificate used for signing needs to be imported into the UEFI firmware or MOK.Convert the certificate to the DER format for import into the firmware or MOK:
>
openssl x509 -in cert.pem -outform der -out cert.derCopy the certificate to the ESP for easier access:
>
sudo
cp cert.der /boot/efi/Use
mokutil
to launch the MOK list automatically.Import the certificate to MOK:
>
mokutil --root-pw --import cert.derThe
--root-pw
option enables usage of theroot
user directly.Check the list of certificates that are prepared to be enrolled:
>
mokutil --list-newReboot the system;
shim
should launch MokManager. You need to enter theroot
password to confirm the import of the certificate to the MOK list.Check if the newly imported key was enrolled:
>
mokutil --list-enrolled
Alternatively, this is the procedure if you want to launch MOK manually:
Reboot
In the GRUB 2 menu press the '
c
' key.Type:
chainloader $efibootdir/MokManager.efi boot
Select
.Navigate to the
cert.der
file and press Enter.Follow the instructions to enroll the key. Normally this should be pressing '
0
' and then 'y
' to confirm.Alternatively, the firmware menu may provide ways to add a new key to the Signature Database.
13.1.4 Using non-inbox drivers #
There is no support for adding non-inbox drivers (that is, drivers that do not come with SUSE Linux Enterprise Server) during installation with Secure Boot enabled. The signing key used for SolidDriver/PLDP is not trusted by default.
It is possible to install third party drivers during installation with Secure Boot enabled in two different ways. In both cases:
Add the needed keys to the firmware database via firmware/system management tools before the installation. This option depends on the specific hardware you are using. Consult your hardware vendor for more information.
Use a bootable driver ISO from https://drivers.suse.com/ or your hardware vendor to enroll the needed keys in the MOK list at first boot.
To use the bootable driver ISO to enroll the driver keys to the MOK list, follow these steps:
Burn the ISO image above to an empty CD/DVD medium.
Start the installation using the new CD/DVD medium, having the standard installation media at hand or a URL to a network installation server.
If doing a network installation, enter the URL of the network installation source on the boot command line using the
install=
option.If doing installation from optical media, the installer will first boot from the driver kit and then ask to insert the first installation disk of the product.
An initrd containing updated drivers will be used for installation.
For more information, see https://drivers.suse.com/doc/Usage/Secure_Boot_Certificate.html.
13.1.5 Features and limitations #
When booting in Secure Boot mode, the following features apply:
Installation to UEFI default boot loader location, a mechanism to keep or restore the EFI boot entry.
Reboot via UEFI.
Xen hypervisor will boot with UEFI when there is no legacy BIOS to fall back to.
UEFI IPv6 PXE boot support.
UEFI videomode support, the kernel can retrieve video mode from UEFI to configure KMS mode with the same parameters.
UEFI booting from USB devices is supported.
Since SUSE Linux Enterprise Server 15 SP3, Kexec and Kdump are supported in Secure Boot mode.
When booting in Secure Boot mode, the following limitations apply:
To ensure that Secure Boot cannot be easily circumvented, some kernel features are disabled when running under Secure Boot.
Boot loader, kernel, and kernel modules must be signed.
Hibernation (suspend on disk) is disabled.
Access to
/dev/kmem
and/dev/mem
is not possible, not even as root user.Access to the I/O port is not possible, not even as root user. All X11 graphical drivers must use a kernel driver.
PCI BAR access through sysfs is not possible.
custom_method
in ACPI is not available.debugfs for asus-wmi module is not available.
the
acpi_rsdp
parameter does not have any effect on the kernel.
13.2 More information #
https://www.uefi.org —UEFI home page where you can find the current UEFI specifications.
Blog posts by Olaf Kirch and Vojtěch Pavlík (the chapter above is heavily based on these posts):
https://en.opensuse.org/openSUSE:UEFI —UEFI with openSUSE.
14 The boot loader GRUB 2 #
This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 12, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 13, UEFI (Unified Extensible Firmware Interface).
14.1 Main differences between GRUB legacy and GRUB 2 #
The configuration is stored in different files.
More file systems are supported (for example, Btrfs).
Can directly read files stored on LVM or RAID devices.
The user interface can be translated and altered with themes.
Includes a mechanism for loading modules to support additional features, such as file systems, etc.
Automatically searches for and generates boot entries for other kernels and operating systems, such as Windows.
Includes a minimal Bash-like console.
14.2 Configuration file structure #
The configuration of GRUB 2 is based on the following files:
/boot/grub2/grub.cfg
This file contains the configuration of the GRUB 2 menu items. It replaces
menu.lst
used in GRUB Legacy.grub.cfg
should not be edited—it is automatically generated by the commandgrub2-mkconfig -o /boot/grub2/grub.cfg
./boot/grub2/custom.cfg
This optional file is directly sourced by
grub.cfg
at boot time and can be used to add custom items to the boot menu. Starting with SUSE Linux Enterprise Server 12 SP2 these entries are also parsed when usinggrub-once
./etc/default/grub
This file controls the user settings of GRUB 2 and normally includes additional environmental settings such as backgrounds and themes.
- Scripts under
/etc/grub.d/
The scripts in this directory are read during execution of the command
grub2-mkconfig -o /boot/grub2/grub.cfg
. Their instructions are integrated into the main configuration file/boot/grub/grub.cfg
./etc/sysconfig/bootloader
This configuration file holds certain basic settings like the boot loader type and whether to enable UEFI Secure Boot support.
/boot/grub2/x86_64-efi
,/boot/grub2/power-ieee1275
,/boot/grub2/s390x
These configuration files contain architecture-specific options.
GRUB 2 can be controlled in various ways. Boot entries from an existing
configuration can be selected from the graphical menu (splash screen). The
configuration is loaded from the file
/boot/grub2/grub.cfg
which is compiled from other
configuration files (see below). All GRUB 2 configuration files are
considered system files, and you need root
privileges to edit them.
After having manually edited GRUB 2 configuration files, you need to
run grub2-mkconfig -o /boot/grub2/grub.cfg
to
activate the changes. However, this is not necessary when changing the
configuration with YaST, because YaST automatically runs this
command.
14.2.1 The file /boot/grub2/grub.cfg
#
The graphical splash screen with the boot menu is based on the GRUB 2
configuration file /boot/grub2/grub.cfg
, which
contains information about all partitions or operating systems that can be
booted by the menu.
Every time the system is booted, GRUB 2 loads the menu file directly from
the file system. For this reason, GRUB 2 does not need to be re-installed
after changes to the configuration file. grub.cfg
is
automatically rebuilt with kernel installations or removals.
grub.cfg
is compiled from the file
/etc/default/grub
and scripts found in the
/etc/grub.d/
directory when running the command
grub2-mkconfig -o /boot/grub2/grub.cfg
. Therefore you should never
edit the file manually. Instead, edit the related source files or use the
YaST module to modify the configuration as
described in Section 14.3, “Configuring the boot loader with YaST”.
14.2.2 The file /etc/default/grub
#
More general options of GRUB 2 belong in this file, such as the time the menu is displayed, or the default OS to boot. To list all available options, see the output of the following command:
>
grep "export GRUB_DEFAULT" -A50 /usr/sbin/grub2-mkconfig | grep GRUB_
You can introduce custom variables and use them later in the scripts
found in the /etc/grub.d
directory.
After having edited /etc/default/grub
, update the
main configuration file with grub2-mkconfig -o
/boot/grub2/grub.cfg
.
All options specified in this file are general options that affect all
boot entries. Options specific to a Xen hypervisor include the
_XEN_
substring.
More complex options with spaces require quoting so that they are processed as one option. Such inner quotes need to be correctly escaped, for example:
GRUB_CMDLINE_LINUX_XEN="debug loglevel=9 log_buf_len=5M \"ddebug_query=file drivers/xen/xen-acpi-processor.c +p\""
GRUB_DEFAULT
Sets the boot menu entry that is booted by default. Its value can be a numeric value, the complete name of a menu entry, or “saved”.
GRUB_DEFAULT=2
boots the third (counted from zero) boot menu entry.GRUB_DEFAULT="2>0"
boots the first submenu entry of the third top-level menu entry.GRUB_DEFAULT="Example boot menu entry"
boots the menu entry with the title “Example boot menu entry”.GRUB_DEFAULT=saved
boots the entry specified by thegrub2-once
orgrub2-set-default
commands. Whilegrub2-reboot
sets the default boot entry for the next reboot only,grub2-set-default
sets the default boot entry until changed.grub2-editenv list
lists the next boot entry.GRUB_HIDDEN_TIMEOUT
Waits the specified number of seconds for the user to press a key. During the period no menu is shown unless the user presses a key. If no key is pressed during the time specified, the control is passed to
GRUB_TIMEOUT
.GRUB_HIDDEN_TIMEOUT=0
first checks whether Shift is pressed and shows the boot menu if yes, otherwise immediately boots the default menu entry. This is the default when only one bootable OS is identified by GRUB 2.GRUB_HIDDEN_TIMEOUT_QUIET
If
false
is specified, a countdown timer is displayed on a blank screen when theGRUB_HIDDEN_TIMEOUT
feature is active.GRUB_TIMEOUT
Time period in seconds the boot menu is displayed before automatically booting the default boot entry. If you press a key, the timeout is cancelled and GRUB 2 waits for you to make the selection manually.
GRUB_TIMEOUT=-1
causes the menu to be displayed until you select the boot entry manually.GRUB_CMDLINE_LINUX
Entries on this line are added at the end of the boot entries for normal and recovery modes. Use it to add kernel parameters to the boot entry.
GRUB_CMDLINE_LINUX_DEFAULT
Same as
GRUB_CMDLINE_LINUX
but the entries are appended in the normal mode only.GRUB_CMDLINE_LINUX_RECOVERY
Same as
GRUB_CMDLINE_LINUX
but the entries are appended in the recovery mode only.GRUB_CMDLINE_LINUX_XEN_REPLACE
This entry replaces the
GRUB_CMDLINE_LINUX
parameters for all Xen boot entries.GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT
Same as
GRUB_CMDLINE_LINUX_XEN_REPLACE
but it only replaces parameters ofGRUB_CMDLINE_LINUX_DEFAULT
.GRUB_CMDLINE_XEN
These entries are passed to the Xen hypervisor Xen menu entries for normal and recovery modes. For example:
GRUB_CMDLINE_XEN="loglvl=all guest_loglvl=all"
Tip: Xen hypervisor optionsFind a complete list of Xen hypervisor options in https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html
GRUB_CMDLINE_XEN_DEFAULT
Same as
GRUB_CMDLINE_XEN
but the entries are appended in the normal mode only.GRUB_TERMINAL
Enables and specifies an input/output terminal device. Can be
console
(PC BIOS and EFI consoles),serial
(serial terminal),ofconsole
(Open Firmware console), or the defaultgfxterm
(graphics-mode output). It is also possible to enable more than one device by quoting the required options, for example,GRUB_TERMINAL="console serial"
.GRUB_GFXMODE
The resolution used for the
gfxterm
graphical terminal. You can only use modes supported by your graphics card (VBE). The default is ‘auto’, which tries to select a preferred resolution. You can display the screen resolutions available to GRUB 2 by typingvideoinfo
in the GRUB 2 command line. The command line is accessed by typing C when the GRUB 2 boot menu screen is displayed.You can also specify a color depth by appending it to the resolution setting, for example,
GRUB_GFXMODE=1280x1024x24
.GRUB_BACKGROUND
Set a background image for the
gfxterm
graphical terminal. The image must be a file readable by GRUB 2 at boot time, and it must end with the.png
,.tga
,.jpg
, or.jpeg
suffix. If necessary, the image is scaled to fit the screen.GRUB_DISABLE_OS_PROBER
If this option is set to
true
, automatic searching for other operating systems is disabled. Only the kernel images in/boot/
and the options from your own scripts in/etc/grub.d/
are detected.SUSE_BTRFS_SNAPSHOT_BOOTING
If this option is set to
true
, GRUB 2 can boot directly into Snapper snapshots. For more information, see Section 7.3, “System rollback by booting from snapshots”.
For a complete list of options, see the GNU GRUB manual.
14.2.3 Scripts in /etc/grub.d
#
The scripts in this directory are read during execution of the command
grub2-mkconfig -o /boot/grub2/grub.cfg
. Their
instructions are incorporated into
/boot/grub2/grub.cfg
. The order of menu items in
grub.cfg
is determined by the order in which the
files in this directory are run. Files with a leading numeral are
executed first, beginning with the lowest number.
00_header
is run before
10_linux
, which would run before
40_custom
. If files with alphabetic names are
present, they are executed after the numerically named files. Only
executable files generate output to grub.cfg
during execution of grub2-mkconfig
. By default all
files in the /etc/grub.d
directory are executable.
grub.cfg
Because /boot/grub2/grub.cfg
is recompiled each
time grub2-mkconfig
is run, any custom content is
lost. To insert your lines directly into
/boot/grub2/grub.cfg
without losing them after
grub2-mkconfig
is run, insert them between
### BEGIN /etc/grub.d/90_persistent ###
and
### END /etc/grub.d/90_persistent ###
The 90_persistent
script ensures that such
content is preserved.
A list of the most important scripts follows:
00_header
Sets environmental variables such as system file locations, display settings, themes and previously saved entries. It also imports preferences stored in the
/etc/default/grub
. Normally you do not need to make changes to this file.10_linux
Identifies Linux kernels on the root device and creates relevant menu entries. This includes the associated recovery mode option if enabled. Only the latest kernel is displayed on the main menu page, with additional kernels included in a submenu.
30_os-prober
This script uses
os-prober
to search for Linux and other operating systems and places the results in the GRUB 2 menu. There are sections to identify specific other operating systems, such as Windows or macOS.40_custom
This file provides a simple way to include custom boot entries into
grub.cfg
. Make sure that you do not change theexec tail -n +3 $0
part at the beginning.
The processing sequence is set by the preceding numbers with the lowest number being executed first. If scripts are preceded by the same number the alphabetical order of the complete name decides the order.
/boot/grub2/custom.cfg
If you create /boot/grub2/custom.cfg
and fill it
with content, it is automatically included into
/boot/grub2/grub.cfg
right after
40_custom
at boot time.
14.2.4 Mapping between BIOS drives and Linux devices #
In GRUB Legacy, the device.map
configuration file
was used to derive Linux device names from BIOS drive numbers. The
mapping between BIOS drives and Linux devices cannot always be guessed
correctly. For example, GRUB Legacy would get a wrong order if the boot
sequence of IDE and SCSI drives is exchanged in the BIOS configuration.
GRUB 2 avoids this problem by using device ID strings (UUIDs) or file
system labels when generating grub.cfg
. GRUB 2
utilities create a temporary device map on the fly, which is normally
sufficient, particularly for single-disk systems.
However, if you need to override the GRUB 2's automatic device mapping
mechanism, create your custom mapping file
/boot/grub2/device.map
. The following example
changes the mapping to make DISK 3
the boot disk.
GRUB 2 partition numbers start with 1
and
not with 0
as in GRUB 2 Legacy.
(hd1) /dev/disk-by-id/DISK3 ID (hd2) /dev/disk-by-id/DISK1 ID (hd3) /dev/disk-by-id/DISK2 ID
14.2.6 Setting a boot password #
Even before the operating system is booted, GRUB 2 enables access to file systems. Users without root permissions can access files in your Linux system to which they have no access after the system is booted. To block this kind of access or to prevent users from booting certain menu entries, set a boot password.
If set, the boot password is required on every boot, which means the system does not boot automatically.
Proceed as follows to set a boot password. Alternatively use YaST ().
Encrypt the password using
grub2-mkpasswd-pbkdf2:
>
sudo
grub2-mkpasswd-pbkdf2 Password: **** Reenter password: **** PBKDF2 hash of your password is grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A...Paste the resulting string into the file
/etc/grub.d/40_custom
together with theset superusers
command.set superusers="root" password_pbkdf2 root grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A...
To import the changes into the main configuration file, run:
>
sudo
grub2-mkconfig -o /boot/grub2/grub.cfg
After you reboot, GRUB 2 prompts you for a user name and a password
when trying to boot a menu entry. Enter root
and the
password you typed during the grub2-mkpasswd-pbkdf2
command. If the credentials are correct, the system boots the
selected boot entry.
For more information, see https://www.gnu.org/software/grub/manual/grub.html#Security.
14.2.7 Authorized access to boot menu entries #
You can configure GRUB 2 to allow access to boot menu entries depending on the level of authorization. You can configure multiple user accounts protected with passwords and assign them access to different menu entries. To configure authorization in GRUB 2, follow these steps:
Create and encrypt one password for each user account you want to use in GRUB 2. Use the
grub2-mkpasswd-pbkdf2
command as described in Section 14.2.6, “Setting a boot password”.Delete the content of the
/etc/grub.d/10_linux
file and save it. This prevents outputting the default GRUB 2 menu entries.Edit the
/boot/grub2/custom.cfg
file and add custom menu entries manually. The following template is just an example, adjust it to better match your use case:set superusers=admin password admin ADMIN_PASSWORD password maintainer MAINTAINER_PASSWORD menuentry 'Operational mode' { insmod ext2 set root=hd0,1 echo 'Loading Linux ...' linux /boot/vmlinuz root=/dev/vda1 $GRUB_CMDLINE_LINUX_DEFAULT $GRUB_CMDLINE_LINUX mode=operation echo 'Loading Initrd ...' initrd /boot/initrd } menuentry 'Maintenance mode' --users maintainer { insmod ext2 set root=hd0,1 echo 'Loading Linux ...' linux /boot/vmlinuz root=/dev/vda1 $GRUB_CMDLINE_LINUX_DEFAULT $GRUB_CMDLINE_LINUX mode=maintenance echo 'Loading Initrd ...' initrd /boot/initrd }
Import the changes into the main configuration file:
>
sudo
grub2-mkconfig -o /boot/grub2/grub.cfg
In the above example:
The GRUB 2 menu has two entries,
and .If no user is specified, both boot menu entries are accessible, but no one can access GRUB 2 command line nor edit existing menu entries.
admin
user can access GRUB 2 command line and edit existing menu entries.maintenance
user can select the recovery menu item.
14.3 Configuring the boot loader with YaST #
The easiest way to configure general options of the boot loader in your SUSE Linux Enterprise Server system is to use the YaST module. In the , select › . The module shows the current boot loader configuration of your system and allows you to make changes.
Use the
tab to view and change settings related to type, location and advanced loader settings. You can choose whether to use GRUB 2 in standard or EFI mode.If you have an EFI system you can only install GRUB2-EFI, otherwise your system is no longer bootable.
To reinstall the boot loader, make sure to change a setting in YaST and then change it back. For example, to reinstall GRUB2-EFI, select
first and then immediately switch back to .Otherwise, the boot loader may only be partially reinstalled.
To use a boot loader other than the ones listed, select
. Read the documentation of your boot loader carefully before choosing this option.14.3.1 Boot loader location and boot code options #
The default location of the boot loader depends on the partition setup and
is either the Master Boot Record (MBR) or the boot sector of the
/
partition. To modify the location of the boot loader,
follow these steps:
Select the
tab and then choose one of the following options for :This installs the boot loader in the MBR of the disk containing the directory
/boot
. Usually this will be the disk mounted to/
, but if/boot
is mounted to a separate partition on a different disk, the MBR of that disk will be used.This installs the boot loader in the boot sector of the
/
partition.Use this option to specify the location of the boot loader manually.
Click
to apply the changes.
The
tab includes the following additional options:Activates the partition that contains the
/boot
directory. For POWER systems it activates the PReP partition. Use this option on systems with old BIOS and/or legacy operating systems because they may fail to boot from a non-active partition. It is safe to leave this option active.If MBR contains a custom 'non-GRUB' code, this option replaces it with a generic, operating system independent code. If you deactivate this option, the system may become unbootable.
Starts TrustedGRUB2, which supports trusted computing functionality (Trusted Platform Module (TPM)). For more information refer to https://github.com/Sirrix-AG/TrustedGRUB2.
The
section includes the following options:This is appropriate for traditional legacy BIOS booting.
This is appropriate for UEFI booting.
This is usually the best choice if you have an already working system.
In most cases YaST defaults to the appropriate choice.
14.3.2 Adjusting the disk order #
If your computer has more than one hard disk, you can specify the boot sequence of the disks. The first disk in the list is where GRUB 2 will be installed in the case of booting from MBR. It is the disk where SUSE Linux Enterprise Server is installed by default. The rest of the list is a hint for GRUB 2's device mapper (see Section 14.2.4, “Mapping between BIOS drives and Linux devices”).
The default value is usually valid for almost all deployments. If you change the boot order of disks wrongly, the system may become unbootable on the next reboot. For example, if the first disk in the list is not part of the BIOS boot order, and the other disks in the list have empty MBRs.
Open the
tab.Click
.If more than one disk is listed, select a disk and click
or to reorder the displayed disks.Click
two times to save the changes.
14.3.3 Configuring advanced options #
Advanced boot parameters can be configured via the
tab.14.3.3.1 tab #
Change the value of
by typing in a new value and clicking the appropriate arrow key with your mouse.When selected, the boot loader searches for other systems like Windows or other Linux installations.
Hides the boot menu and boots the default entry.
Select the desired entry from the “Default Boot Section” list. Note that the “>” sign in the boot entry name delimits the boot section and its subsection.
Protects the boot loader and the system with an additional password. For details on manual configuration, see Section 14.2.6, “Setting a boot password”. If this option is activated, the boot password is required on every boot, which means the system does not boot automatically. However, if you prefer the behavior of GRUB 1, additionally enable . With this setting, anybody is allowed to select a boot entry and boot the system, whereas the password for the GRUB 2
root
user is only required for modifying boot entries.
14.3.3.2 tab #
Specify optional kernel parameters here to enable/disable system features, add drivers, etc.
SUSE has released one or more kernel boot command line parameters for all software mitigations that have been deployed to prevent CPU side-channel attacks. Some of those may result in performance loss. Choose one the following options to strike a balance between security and performance, depending on your setting:
Enables all mitigations required for your CPU model, but does not protect against cross-CPU thread attacks. This setting may impact performance to some degree, depending on the workload. .
Provides the full set of available security mitigations. Enables all mitigations required for your CPU model. In addition, it disables Simultaneous Multithreading (SMT) to avoid side-channel attacks across multiple CPU threads. This setting may further impact performance, depending on the workload. .
Disables all mitigations. Side-channel attacks against your CPU are possible, depending on the CPU model. This setting has no impact on performance. .
Does not set any mitigation level. Specify your CPU mitigations manually by using the kernel command line options. .
When checked, the boot menu appears on a graphical splash screen rather than in a text mode. The resolution of the boot screen is set automatically by default, but you can manually set it via
. The graphical theme definition file can be specified with the file chooser. Only change this if you want to apply your own, custom-made theme.If your machine is controlled via a serial console, activate this option and specify which COM port to use at which speed. See
info grub
or http://www.gnu.org/software/grub/manual/grub.html#Serial-terminal
14.4 Differences in terminal usage on IBM Z #
On 3215 and 3270 terminals there are some differences and limitations on how to move the cursor and how to issue editing commands within GRUB 2.
14.4.1 Limitations #
- Interactivity
Interactivity is strongly limited. Typing often does not result in visual feedback. To see where the cursor is, type an underscore (_).
Note: 3270 compared to 3215The 3270 terminal is much better at displaying and refreshing screens than the 3215 terminal.
- Cursor movement
“Traditional” cursor movement is not possible. Alt, Meta, Ctrl and the cursor keys do not work. To move the cursor, use the key combinations listed in Section 14.4.2, “Key combinations”.
- Caret
The caret (^) is used as a control character. To type a literal ^ followed by a letter, type ^, ^, LETTER.
- Enter
The Enter key does not work, use ^–J instead.
14.4.2 Key combinations #
Common Substitutes: |
^–J |
engage (“Enter”) |
^–L |
abort, return to previous “state” | |
^–I |
tab completion (in edit and shell mode) | |
Keys Available in Menu Mode: |
^–A |
first entry |
^–E |
last entry | |
^–P |
previous entry | |
^–N |
next entry | |
^–G |
previous page | |
^–C |
next page | |
^–F |
boot selected entry or enter submenu (same as ^–J) | |
E |
edit selected entry | |
C |
enter GRUB-Shell | |
Keys Available in Edit Mode: |
^–P |
previous line |
^–N |
next line | |
^–B |
backward char | |
^–F |
forward char | |
^–A |
beginning of line | |
^–E |
end of line | |
^–H |
backspace | |
^–D |
delete | |
^–K |
kill line | |
^–Y |
yank | |
^–O |
open line | |
^–L |
refresh screen | |
^–X |
boot entry | |
^–C |
enter GRUB-Shell | |
Keys Available in Command Line Mode: |
^–P |
previous command |
^–N |
next command from history | |
^–A |
beginning of line | |
^–E |
end of line | |
^–B |
backward char | |
^–F |
forward char | |
^–H |
backspace | |
^–D |
delete | |
^–K |
kill line | |
^–U |
discard line | |
^–Y |
yank |
14.5 Helpful GRUB 2 commands #
grub2-mkconfig
Generates a new
/boot/grub2/grub.cfg
based on/etc/default/grub
and the scripts from/etc/grub.d/
.Example 14.1: Usage of grub2-mkconfig #grub2-mkconfig -o /boot/grub2/grub.cfg
Tip: Syntax checkRunning
grub2-mkconfig
without any parameters prints the configuration to STDOUT where it can be reviewed. Usegrub2-script-check
after/boot/grub2/grub.cfg
has been written to check its syntax.Important:grub2-mkconfig
cannot repair UEFI Secure Boot tablesIf you are using UEFI Secure Boot and your system is not reaching GRUB 2 correctly anymore, you may need to additionally reinstall the Shim and regenerate the UEFI boot table. To do so, use:
#
shim-install --config-file=/boot/grub2/grub.cfggrub2-mkrescue
Creates a bootable rescue image of your installed GRUB 2 configuration.
Example 14.2: Usage of grub2-mkrescue #grub2-mkrescue -o save_path/name.iso iso
grub2-script-check
Checks the given file for syntax errors.
Example 14.3: Usage of grub2-script-check #grub2-script-check /boot/grub2/grub.cfg
grub2-once
Set the default boot entry for the next boot only. To get the list of available boot entries use the
--list
option.Example 14.4: Usage of grub2-once #grub2-once number_of_the_boot_entry
Tip:grub2-once
helpCall the program without any option to get a full list of all possible options.
14.6 Rescue mode #
Rescue mode is a specific root
user session
for troubleshooting and repairing systems where the booting process
fails. It offers a single-user environment with local file systems and
core system services active. Network interfaces are not activated. To
enter the rescue mode, follow these steps.
Reboot the system. The boot screen appears, offering the GRUB 2 boot menu.
Select the menu entry to boot and press e to edit the boot line.
Append the following parameter to the line containing the kernel parameters:
systemd.unit=rescue.target
Press Ctrl+X to boot with these settings.
Enter the password for
root
.Make all the necessary changes.
Enter normal operating target again by entering
systemctl isolate multi-user.target
orsystemctl isolate graphical.target
at the command line.
14.7 More information #
Extensive information about GRUB 2 is available at https://www.gnu.org/software/grub/. Also refer to the
grub
info page. You can also
search for the keyword “GRUB 2” in the Technical Information
Search at https://www.suse.com/support to get
information about special issues.
15 The systemd
daemon #
systemd
initializes the system. It has the process ID 1. systemd
is
started directly by the kernel and resists signal 9, which normally
terminates processes. All other programs are started directly by
systemd
or by one of its child processes. systemd
is a replacement for
the System V init daemon and is fully compatible with System V init (by
supporting init scripts).
The main advantage of systemd
is that it considerably speeds up boot time
by parallelizing service starts. Furthermore, systemd
only starts a
service when it is really needed. Daemons are not started unconditionally
at boot time, but when being required for the first time. systemd
also
supports Kernel Control Groups (cgroups), creating snapshots, and restoring
the system state. For more details see
http://www.freedesktop.org/wiki/Software/systemd/.
15.1 The systemd
concept #
The following section explains the concept behind systemd
.
systemd
is a system and session manager for Linux, compatible with System V
and LSB init scripts.
The main features of systemd
include:
parallelization capabilities
socket and D-Bus activation for starting services
on-demand starting of daemons
tracking of processes using Linux cgroups
creating snapshots and restoring of the system state
maintains mount and automount points
implements an elaborate transactional dependency-based service control logic
15.1.1 Unit file #
A unit configuration file contains information about a service, a
socket, a device, a mount point, an automount point, a swap file or
partition, a start-up target, a watched file system path, a timer
controlled and supervised by systemd
, a temporary system state
snapshot, a resource management slice or a group of externally created
processes.
“Unit file” is a generic term used by systemd
for the
following:
Service. Information about a process (for example, running a daemon); file ends with .service
Targets. Used for grouping units and as synchronization points during start-up; file ends with .target
Sockets. Information about an IPC or network socket or a file system FIFO, for socket-based activation (like
inetd
); file ends with .socketPath. Used to trigger other units (for example, running a service when files change); file ends with .path
Timer. Information about a timer controlled, for timer-based activation; file ends with .timer
Mount point. Normally auto-generated by the fstab generator; file ends with .mount
Automount point. Information about a file system automount point; file ends with .automount
Swap. Information about a swap device or file for memory paging; file ends with .swap
Device. Information about a device unit as exposed in the sysfs/udev(7) device tree; file ends with .device
Scope / slice. A concept for hierarchically managing resources of a group of processes; file ends with .scope/.slice
For more information about systemd
unit files, see
http://www.freedesktop.org/software/systemd/man/systemd.unit.html
15.2 Basic usage #
The System V init system uses several commands to handle
services—the init scripts, insserv
,
telinit
and others. systemd
makes it easier to
manage services, because there is only one command to handle most service
related tasks: systemctl
. It uses the “command
plus subcommand” notation like git
or
zypper
:
systemctl GENERAL OPTIONS SUBCOMMAND SUBCOMMAND OPTIONS
See man 1 systemctl
for a complete manual.
If the output goes to a terminal (and not to a pipe or a file, for example), systemd
commands send long output to a pager by default.
Use the --no-pager
option to turn off paging mode.
systemd
also supports bash-completion, allowing you to enter the first letters of a subcommand and then press →|.
This feature is only available in the bash
shell and requires the installation of the package bash-completion
.
15.2.1 Managing services in a running system #
Subcommands for managing services are the same as for managing a service with System V init (start
, stop
, ...).
The general syntax for service management commands is as follows:
systemd
systemctl reload|restart|start|status|stop|... MY_SERVICE(S)
- System V init
rcMY_SERVICE(S) reload|restart|start|status|stop|...
systemd
allows you to manage several services in one go.
Instead of executing init scripts one after the other as with System V init, execute a command like the following:
>
sudo
systemctl start MY_1ST_SERVICE MY_2ND_SERVICE
To list all services available on the system:
>
sudo
systemctl list-unit-files --type=service
The following table lists the most important service management commands for systemd
and System V init:
Task |
|
System V init Command |
---|---|---|
Starting. |
start |
start |
Stopping. |
stop |
stop |
Restarting. Shuts down services and starts them afterward. If a service is not yet running, it is started. |
restart |
restart |
Restarting conditionally. Restarts services if they are currently running. Does nothing for services that are not running. |
try-restart |
try-restart |
Reloading.
Tells services to reload their configuration files without interrupting operation.
Use case: Tell Apache to reload a modified |
reload |
reload |
Reloading or restarting. Reloads services if reloading is supported, otherwise restarts them. If a service is not yet running, it is started. |
reload-or-restart |
n/a |
Reloading or restarting conditionally. Reloads services if reloading is supported, otherwise restarts them if currently running. Does nothing for services that are not running. |
reload-or-try-restart |
n/a |
Getting detailed status information.
Lists information about the status of services.
The |
status |
status |
Getting short status information. Shows whether services are active or not. |
is-active |
status |
15.2.2 Permanently enabling/disabling services #
The service management commands mentioned in the previous section let
you manipulate services for the current session. systemd
also lets
you permanently enable or disable services, so they are automatically
started when requested or are always unavailable. You can either do
this by using YaST, or on the command line.
15.2.2.1 Enabling/disabling services on the command line #
The following table lists enabling and disabling commands for
systemd
and System V init:
When enabling a service on the command line, it is not started
automatically. It is scheduled to be started with the next system
start-up or runlevel/target change. To immediately start a service
after having enabled it, explicitly run systemctl start
MY_SERVICE
or rc
MY_SERVICE start
.
Task |
|
System V init Command |
---|---|---|
Enabling. |
|
|
Disabling. |
|
|
Checking. Shows whether a service is enabled or not. |
|
|
Re-enabling. Similar to restarting a service, this command first disables and then enables a service. Useful to re-enable a service with its defaults. |
|
n/a |
Masking. After “disabling” a service, it can still be started manually. To disable a service, you need to mask it. Use with care. |
|
n/a |
Unmasking. A service that has been masked can only be used again after it has been unmasked. |
|
n/a |
15.3 System start and target management #
The entire process of starting the system and shutting it down is maintained by systemd
.
From this point of view, the kernel can be considered a background process to maintain all other processes and adjust CPU time and hardware access according to requests from other programs.
15.3.1 Targets compared to runlevels #
With System V init the system was booted into a so-called
“Runlevel”. A runlevel defines how the system is started
and what services are available in the running system. Runlevels are
numbered; the most commonly known ones are 0
(shutting down the system), 3
(multiuser with
network) and 5
(multiuser with network and display
manager).
systemd
introduces a new concept by using so-called “target
units”. However, it remains fully compatible with the runlevel
concept. Target units are named rather than numbered and serve specific
purposes. For example, the targets
local-fs.target
and
swap.target
mount local file systems and swap
spaces.
The target graphical.target
provides a
multiuser system with network and display manager capabilities and is
equivalent to runlevel 5. Complex targets, such as
graphical.target
act as “meta”
targets by combining a subset of other targets. Since systemd
makes
it easy to create custom targets by combining existing targets, it
offers great flexibility.
The following list shows the most important systemd
target units. For
a full list refer to man 7 systemd.special
.
systemd
target units #default.target
The target that is booted by default. Not a “real” target, but rather a symbolic link to another target like
graphic.target
. Can be permanently changed via YaST (see Section 15.4, “Managing services with YaST”). To change it for a session, use the kernel parametersystemd.unit=MY_TARGET.target
at the boot prompt.emergency.target
Starts a minimal emergency
root
shell on the console. Only use it at the boot prompt assystemd.unit=emergency.target
.graphical.target
Starts a system with network, multiuser support and a display manager.
halt.target
Shuts down the system.
mail-transfer-agent.target
Starts all services necessary for sending and receiving mails.
multi-user.target
Starts a multiuser system with network.
reboot.target
Reboots the system.
rescue.target
Starts a single-user
root
session without network. Basic tools for system administration are available. Therescue
target is suitable for solving multiple system problems, for example, failing logins or fixing issues with a display driver.
To remain compatible with the System V init runlevel system, systemd
provides special targets named
runlevelX.target
mapping
the corresponding runlevels numbered X.
To inspect the current target, use the command: systemctl
get-default
systemd
target units #
System V runlevel |
|
Purpose |
---|---|---|
0 |
|
System shutdown |
1, S |
|
Single-user mode |
2 |
|
Local multiuser without remote network |
3 |
|
Full multiuser with network |
4 |
|
Unused/User-defined |
5 |
|
Full multiuser with network and display manager |
6 |
|
System reboot |
systemd
ignores /etc/inittab
The runlevels in a System V init system are configured in
/etc/inittab
. systemd
does
not use this configuration. Refer to
Section 15.5.5, “Creating custom targets” for instructions on
how to create your own bootable target.
15.3.1.1 Commands to change targets #
Use the following commands to operate with target units:
Task |
|
System V init Command |
---|---|---|
Change the current target/runlevel |
|
|
Change to the default target/runlevel |
|
n/a |
Get the current target/runlevel |
With |
or
|
persistently change the default runlevel |
Use the Services Manager or run the following command:
|
Use the Services Manager or change the line
in |
Change the default runlevel for the current boot process |
Enter the following option at the boot prompt
|
Enter the desired runlevel number at the boot prompt. |
Show a target's/runlevel's dependencies |
“Requires” lists the hard dependencies (the ones that must be resolved), whereas “Wants” lists the soft dependencies (the ones that get resolved if possible). |
n/a |
15.3.2 Debugging system start-up #
systemd
offers the means to analyze the system start-up process.
You can review the list of all services and their status (rather than having to parse /var/log/
). systemd
also allows you to scan the start-up procedure to find out how much time each service start-up consumes.
15.3.2.1 Review start-up of services #
To review the complete list of services that have been started since booting the system, enter the command systemctl
.
It lists all active services like shown below (shortened).
To get more information on a specific service, use systemctl status MY_SERVICE
.
#
systemctl
UNIT LOAD ACTIVE SUB JOB DESCRIPTION
[...]
iscsi.service loaded active exited Login and scanning of iSC+
kmod-static-nodes.service loaded active exited Create list of required s+
libvirtd.service loaded active running Virtualization daemon
nscd.service loaded active running Name Service Cache Daemon
chronyd.service loaded active running NTP Server Daemon
polkit.service loaded active running Authorization Manager
postfix.service loaded active running Postfix Mail Transport Ag+
rc-local.service loaded active exited /etc/init.d/boot.local Co+
rsyslog.service loaded active running System Logging Service
[...]
LOAD = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB = The low-level unit activation state, values depend on unit type.
161 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.
To restrict the output to services that failed to start, use the --failed
option:
#
systemctl --failed
UNIT LOAD ACTIVE SUB JOB DESCRIPTION
apache2.service loaded failed failed apache
NetworkManager.service loaded failed failed Network Manager
plymouth-start.service loaded failed failed Show Plymouth Boot Screen
[...]
15.3.2.2 Debug start-up time #
To debug system start-up time, systemd
offers the systemd-analyze
command.
It shows the total start-up time, a list of services ordered by start-up time and can also generate an SVG graphic showing the time services took to start in relation to the other services.
- Listing the system start-up time
#
systemd-analyze Startup finished in 2666ms (kernel) + 21961ms (userspace) = 24628ms- Listing the services start-up time
#
systemd-analyze blame 15.000s backup-rpmdb.service 14.879s mandb.service 7.646s backup-sysconfig.service 4.940s postfix.service 4.921s logrotate.service 4.640s libvirtd.service 4.519s display-manager.service 3.921s btrfsmaintenance-refresh.service 3.466s lvm2-monitor.service 2.774s plymouth-quit-wait.service 2.591s firewalld.service 2.137s initrd-switch-root.service 1.954s ModemManager.service 1.528s rsyslog.service 1.378s apparmor.service [...]- Services start-up time graphics
#
systemd-analyze plot > jupiter.example.com-startup.svg
15.3.2.3 Review the complete start-up process #
The commands above list the services that are started and their start-up times.
For a more detailed overview, specify the following parameters at the boot prompt to instruct systemd
to create a verbose log of the complete start-up procedure.
systemd.log_level=debug systemd.log_target=kmsg
Now systemd
writes its log messages into the kernel ring buffer.
View that buffer with dmesg
:
>
dmesg -T | less
15.3.3 System V compatibility #
systemd
is compatible with System V, allowing you to still use existing System V init scripts.
However, there is at least one known issue where a System V init script does not work with systemd
out of the box: starting a service as a different user via su
or sudo
in init scripts will result in a failure of the script, producing an “Access denied” error.
When changing the user with su
or sudo
, a PAM session is started.
This session will be terminated after the init script is finished.
As a consequence, the service that has been started by the init script will also be terminated.
To work around this error, proceed as follows:
Create a service file wrapper with the same name as the init script plus the file name extension
.service
:[Unit] Description=DESCRIPTION After=network.target [Service] User=USER Type=forking1 PIDFile=PATH TO PID FILE1 ExecStart=PATH TO INIT SCRIPT start ExecStop=PATH TO INIT SCRIPT stop ExecStopPost=/usr/bin/rm -f PATH TO PID FILE1 [Install] WantedBy=multi-user.target2
Replace all values written in UPPERCASE LETTERS with appropriate values.
Start the daemon with
systemctl start APPLICATION
.
15.4 Managing services with YaST #
Basic service management can also be done with the YaST Services Manager module. It supports starting, stopping, enabling and disabling services. It also lets you show a service's status and change the default target. Start the YaST module with
› › .- Changing the
To change the target the system boots into, choose a target from the
drop-down box. The most often used targets are (starting a graphical login screen) and (starting the system in command line mode).- Starting or stopping a service
Select a service from the table. The
column shows whether it is currently running ( ) or not ( ). Toggle its status by choosing or .Starting or stopping a service changes its status for the currently running session. To change its status throughout a reboot, you need to enable or disable it.
- Defining service start-up behavior
Services can either be started automatically at boot time or manually. Select a service from the table. The
column shows whether it is currently started or . Toggle its status by choosing .To change a service status in the current session, you need to start or stop it as described above.
- View a status messages
To view the status message of a service, select it from the list and choose
. The output is identical to the one generated by the commandsystemctl
-l
status MY_SERVICE.
15.5 Customizing systemd
#
The following sections describe how to customize systemd
unit files.
15.5.1 Where are unit files stored? #
systemd
unit files shipped by SUSE are stored in
/usr/lib/systemd/
. Customized unit files and unit file
drop-ins are stored in
/etc/systemd/
.
When customizing systemd
, always use the directory
/etc/systemd/
instead of /usr/lib/systemd/
.
Otherwise your changes will be overwritten by the next update of systemd
.
15.5.2 Override with drop-in files #
Drop-in files (or drop-ins) are partial unit files that override only
specific settings of the unit file. Drop-ins have higher precedence over main configuration
files. The command
systemctl edit SERVICE
starts the default text editor and creates a directory with an empty
override.conf
file in
/etc/systemd/system/NAME.service.d/
. The
command also ensures that the running systemd
process is notified about the changes.
For example, to change the amount of time that the system waits for MariaDB to start, run
sudo systemctl edit mariadb.service
and edit the opened file to include
the modified lines only:
# Configures the time to wait for start-up/stop TimeoutSec=300
Adjust the TimeoutSec
value and save the changes. To enable the changes,
run sudo systemctl daemon-reload
.
For further information, refer to the man pages that can be evoked with
the man 1 systemctl
command.
If you use the --full
option in the systemctl edit --full
SERVICE
command, a copy of the original unit file is
created where you can modify specific options. We do not recommend such customization
because when the unit file is updated by SUSE, its changes are overridden by the
customized copy in the /etc/systemd/system/
directory. Moreover, if
SUSE provides updates to distribution drop-ins, they will override the copy of the unit
file created with --full
. To prevent this confusion and always have your
customization valid, use drop-ins.
15.5.3 Creating drop-in files manually #
Apart from using the systemctl edit
command, you can create drop-ins
manually to have more control over their priority. Such drop-ins let you extend both unit
and daemon configuration files without having to edit or override the files themselves.
They are stored in the following directories:
/etc/systemd/*.conf.d/
,/etc/systemd/system/*.service.d/
Drop-ins added and customized by system administrators.
/usr/lib/systemd/*.conf.d/
,/usr/lib/systemd/system/*.service.d/
Drop-ins installed by customization packages to override upstream settings. For example, SUSE ships systemd-default-settings.
See the man page man 5 systemd.unit
for the full
list of unit search paths.
For example, to disable the rate limiting that is enforced by the
default setting of
systemd-journald
, follow these steps:
Create a directory called
/etc/systemd/journald.conf.d
.>
sudo
mkdir /etc/systemd/journald.conf.dNoteThe directory name must follow the service name that you want to patch with the drop-in file.
In that directory, create a file
/etc/systemd/journald.conf.d/60-rate-limit.conf
with the option that you want to override, for example:>
cat /etc/systemd/journald.conf.d/60-rate-limit.conf
# Disable rate limiting RateLimitIntervalSec=0Save your changes and restart the service of the corresponding
systemd
daemon.>
sudo
systemctl restart systemd-journald
To avoid name conflicts between your drop-ins and files shipped by
SUSE, it is recommended to prefix all drop-ins with a two-digit
number and a dash, for example,
80-override.conf
.
The following ranges are reserved:
0-19
is reserved forsystemd
upstream.20-29
is reserved forsystemd
shipped by SUSE.30-39
is reserved for SUSE packages other thansystemd
.40-49
is reserved for third party packages.50
is reserved for unit drop-in files created withsystemctl set-property
.
Use a two-digit number above this range to ensure that none of the drop-ins shipped by SUSE can override your own drop-ins.
You can use systemctl cat $UNIT
to list and verify
which files are taken into account in the units configuration.
Because the configuration of systemd
components can be scattered
across different places on the file system, it might be hard to get a
global overview. To inspect the configuration of a systemd
component, use the following commands:
systemctl cat UNIT_PATTERN
prints configuration files related to one or moresystemd
units, for example:>
systemctl cat atd.servicesystemd-analyze cat-config DAEMON_NAME_OR_PATH
copies the contents of a configuration file and drop-ins for asystemd
daemon, for example:>
systemd-analyze cat-config systemd/journald.conf
15.5.4 Converting xinetd
services to systemd
#
Since the release of SUSE Linux Enterprise Server 15, the xinetd
infrastructure has been removed.
This section outlines how to convert existing custom xinetd
service files to systemd
sockets.
For each xinetd
service file, you need at least two systemd
unit files: the socket file (*.socket
) and an associated service file (*.service
).
The socket file tells systemd
which socket to create, and the service file tells systemd
which executable to start.
Consider the following example xinetd
service file:
#
cat /etc/xinetd.d/example
service example
{
socket_type = stream
protocol = tcp
port = 10085
wait = no
user = user
group = users
groups = yes
server = /usr/libexec/example/exampled
server_args = -auth=bsdtcp exampledump
disable = no
}
To convert it to systemd
, you need the following two matching files:
#
cat /usr/lib/systemd/system/example.socket
[Socket]
ListenStream=0.0.0.0:10085
Accept=false
[Install]
WantedBy=sockets.target
#
cat /usr/lib/systemd/system/example.service
[Unit]
Description=example
[Service]
ExecStart=/usr/libexec/example/exampled -auth=bsdtcp exampledump
User=user
Group=users
StandardInput=socket
For a complete list of the systemd
'socket' and 'service' file options, refer to the systemd.socket and systemd.service manual pages (man 5 systemd.socket
, man 5 systemd.service
).
15.5.5 Creating custom targets #
On System V init SUSE systems, runlevel 4 is unused to allow administrators to create their own runlevel configuration. systemd
allows you to create any number of custom targets.
It is suggested to start by adapting an existing target such as graphical.target
.
Copy the configuration file
/usr/lib/systemd/system/graphical.target
to/etc/systemd/system/MY_TARGET.target
and adjust it according to your needs.The configuration file copied in the previous step already covers the required (“hard”) dependencies for the target. To also cover the wanted (“soft”) dependencies, create a directory
/etc/systemd/system/MY_TARGET.target.wants
.For each wanted service, create a symbolic link from
/usr/lib/systemd/system
into/etc/systemd/system/MY_TARGET.target.wants
.When you have finished setting up the target, reload the
systemd
configuration to make the new target available:>
sudo
systemctl daemon-reload
15.6 Advanced usage #
The following sections cover advanced topics for system administrators.
For even more advanced systemd
documentation, refer to Lennart Pöttering's series about systemd
for administrators at http://0pointer.de/blog/projects.
15.6.1 Cleaning temporary directories #
systemd
supports cleaning temporary directories regularly.
The configuration from the previous system version is automatically migrated and active. tmpfiles.d
—which is responsible for managing temporary files—reads its configuration from /etc/tmpfiles.d/*.conf
, /run/tmpfiles.d/*.conf
, and /usr/lib/tmpfiles.d/*.conf
files.
Configuration placed in /etc/tmpfiles.d/*.conf
overrides related configurations from the other two directories (/usr/lib/tmpfiles.d/*.conf
is where packages store their configuration files).
The configuration format is one line per path containing action and path, and optionally mode, ownership, age and argument fields, depending on the action. The following example unlinks the X11 lock files:
Type Path Mode UID GID Age Argument r /tmp/.X[0-9]*-lock
To get the status the tmpfile timer:
>
sudo
systemctl status systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.timer - Daily Cleanup of Temporary Directories Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-clean.timer; static) Active: active (waiting) since Tue 2018-04-09 15:30:36 CEST; 1 weeks 6 days ago Docs: man:tmpfiles.d(5) man:systemd-tmpfiles(8) Apr 09 15:30:36 jupiter systemd[1]: Starting Daily Cleanup of Temporary Directories. Apr 09 15:30:36 jupiter systemd[1]: Started Daily Cleanup of Temporary Directories.
For more information on temporary files handling, see man 5 tmpfiles.d
.
15.6.2 System log #
Section 15.6.9, “Debugging services” explains how to view log messages for a given service.
However, displaying log messages is not restricted to service logs.
You can also access and query the complete log messages written by systemd
—the so-called “Journal”.
Use the command journalctl
to display the complete log messages starting with the oldest entries.
Refer to man 1 journalctl
for options such as applying filters or changing the output format.
15.6.3 Snapshots #
You can save the current state of systemd
to a named snapshot and later revert to it with the isolate
subcommand.
This is useful when testing services or custom targets, because it allows you to return to a defined state at any time.
A snapshot is only available in the current session and will automatically be deleted on reboot.
A snapshot name must end in .snapshot
.
- Create a snapshot
>
sudo
systemctl snapshot MY_SNAPSHOT.snapshot- Delete a snapshot
>
sudo
systemctl delete MY_SNAPSHOT.snapshot- View a snapshot
>
sudo
systemctl show MY_SNAPSHOT.snapshot- Activate a snapshot
>
sudo
systemctl isolate MY_SNAPSHOT.snapshot
15.6.4 Loading kernel modules #
With systemd
, kernel modules can automatically be loaded at boot time via a configuration file in /etc/modules-load.d
.
The file should be named MODULE.conf and have the following content:
# load module MODULE at boot time MODULE
In case a package installs a configuration file for loading a kernel module, the file gets installed to /usr/lib/modules-load.d
.
If two configuration files with the same name exist, the one in /etc/modules-load.d
tales precedence.
For more information, see the modules-load.d(5)
man page.
15.6.5 Performing actions before loading a service #
With System V init actions that need to be performed before loading a
service, needed to be specified in /etc/init.d/before.local
. This procedure is no longer supported with systemd
. If
you need to do actions before starting services, do the following:
- Loading kernel modules
Create a drop-in file in
/etc/modules-load.d
directory (seeman modules-load.d
for the syntax)- Creating Files or Directories, Cleaning-up Directories, Changing Ownership
Create a drop-in file in
/etc/tmpfiles.d
(seeman tmpfiles.d
for the syntax)- Other tasks
Create a system service file, for example,
/etc/systemd/system/before.service
, from the following template:[Unit] Before=NAME OF THE SERVICE YOU WANT THIS SERVICE TO BE STARTED BEFORE [Service] Type=oneshot RemainAfterExit=true ExecStart=YOUR_COMMAND # beware, executable is run directly, not through a shell, check the man pages # systemd.service and systemd.unit for full syntax [Install] # target in which to start the service WantedBy=multi-user.target #WantedBy=graphical.target
When the service file is created, you should run the following commands (as
root
):>
sudo
systemctl daemon-reload>
sudo
systemctl enable beforeEvery time you modify the service file, you need to run:
>
sudo
systemctl daemon-reload
15.6.6 Kernel control groups (cgroups) #
On a traditional System V init system, it is not always possible to match a process to the service that spawned it. Some services, such as Apache, spawn a lot of third-party processes (for example, CGI or Java processes), which themselves spawn more processes. This makes a clear assignment difficult or even impossible. Additionally, a service may not finish correctly, leaving certain children alive.
systemd
solves this problem by placing each service into its own
cgroup. cgroups are a kernel feature that allows aggregating processes
and all their children into hierarchical organized groups. systemd
names each cgroup after its service. Since a non-privileged process is
not allowed to “leave” its cgroup, this provides an
effective way to label all processes spawned by a service with the name
of the service.
To list all processes belonging to a service, use the command
systemd-cgls
, for example:
#
systemd-cgls --no-pager
├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 20
├─user.slice
│ └─user-1000.slice
│ ├─session-102.scope
│ │ ├─12426 gdm-session-worker [pam/gdm-password]
│ │ ├─15831 gdm-session-worker [pam/gdm-password]
│ │ ├─15839 gdm-session-worker [pam/gdm-password]
│ │ ├─15858 /usr/lib/gnome-terminal-server
[...]
└─system.slice
├─systemd-hostnamed.service
│ └─17616 /usr/lib/systemd/systemd-hostnamed
├─cron.service
│ └─1689 /usr/sbin/cron -n
├─postfix.service
│ ├─ 1676 /usr/lib/postfix/master -w
│ ├─ 1679 qmgr -l -t fifo -u
│ └─15590 pickup -l -t fifo -u
├─sshd.service
│ └─1436 /usr/sbin/sshd -D
[...]
See Book “System Analysis and Tuning Guide”, Chapter 10 “Kernel control groups” for more information about cgroups.
15.6.7 Terminating services (sending signals) #
As explained in Section 15.6.6, “Kernel control groups (cgroups)”, it is not always possible to assign a process to its parent service process in a System V init system. This makes it difficult to terminate a service and all of its children. Child processes that have not been terminated will remain as zombie processes.
systemd
's concept of confining each service into a cgroup makes it possible to clearly identify all child processes of a service and therefore allows you to send a signal to each of these processes.
Use systemctl kill
to send signals to services.
For a list of available signals refer to man 7 signals
.
- Sending
SIGTERM
to a service SIGTERM
is the default signal that is sent.>
sudo
systemctl kill MY_SERVICE- Sending SIGNAL to a service
Use the
-s
option to specify the signal that should be sent.>
sudo
systemctl kill -s SIGNAL MY_SERVICE- Selecting processes
By default the
kill
command sends the signal toall
processes of the specified cgroup. You can restrict it to thecontrol
or themain
process. The latter is, for example, useful to force a service to reload its configuration by sendingSIGHUP
:>
sudo
systemctl kill -s SIGHUP --kill-who=main MY_SERVICE
15.6.8 Important notes on the D-Bus service #
The D-Bus service is the message bus for communication between
systemd
clients and the systemd manager that is running as pid 1.
Even though dbus
is a
stand-alone daemon, it is an integral part of the init infrastructure.
Stopping dbus
or restarting it
in the running system is similar to an attempt to stop or restart PID
1. It breaks the systemd
client/server communication and makes most
systemd
functions unusable.
Therefore, terminating or restarting
dbus
is neither
recommended nor supported.
Updating the dbus
or
dbus
-related packages requires a reboot. When
in doubt whether a reboot is necessary, run the sudo zypper ps
-s
. If dbus
appears among the listed
services, you need to reboot the system.
Keep in mind that dbus
is updated even when
automatic updates are configured to skip the packages that require
reboot.
15.6.9 Debugging services #
By default, systemd
is not overly verbose. If a service was started
successfully, no output is produced. In case of a failure, a short
error message is displayed. However, systemctl
status
provides a means to debug the start-up and operation of a
service.
systemd
comes with its own logging mechanism (“The
Journal”) that logs system messages. This allows you to display
the service messages together with status messages. The
status
command works similar to
tail
and can also display the log messages in
different formats, making it a powerful debugging tool.
- Show service start-up failure
Whenever a service fails to start, use
systemctl status MY_SERVICE
to get a detailed error message:#
systemctl start apache2 Job failed. See system journal and 'systemctl status' for details.#
systemctl status apache2 Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: failed (Result: exit-code) since Mon, 04 Apr 2018 16:52:26 +0200; 29s ago Process: 3088 ExecStart=/usr/sbin/start_apache2 -D SYSTEMD -k start (code=exited, status=1/FAILURE) CGroup: name=systemd:/system/apache2.service Apr 04 16:52:26 g144 start_apache2[3088]: httpd2-prefork: Syntax error on line 205 of /etc/apache2/httpd.conf: Syntax error on li...alHost>- Show last N service messages
The default behavior of the
status
subcommand is to display the last ten messages a service issued. To change the number of messages to show, use the--lines=N
parameter:>
sudo
systemctl status chronyd>
sudo
systemctl --lines=20 status chronyd- Show service messages in append mode
To display a “live stream” of service messages, use the
--follow
option, which works liketail
-f
:>
sudo
systemctl --follow status chronyd- Messages output format
The
--output=MODE
parameter allows you to change the output format of service messages. The most important modes available are:short
The default format. Shows the log messages with a human readable time stamp.
verbose
Full output with all fields.
cat
Terse output without time stamps.
15.7 systemd
timer units #
Similar to cron, systemd
timer units provide a mechanism for scheduling jobs on Linux.
Although systemd
timer units serve the same purpose as cron, they offer several advantages.
Jobs scheduled using a timer unit can depend on other
systemd
services.Timer units are treated as regular
systemd
services, so can be managed withsystemctl
.Timers can be realtime and monotonic.
Time units are logged to the
systemd
journal, which makes it easier to monitor and troubleshoot them.
systemd
timer units are identified by the .timer
file name extension.
15.7.1 systemd
timer types #
Timer units can use monotonic and realtime timers.
Similar to cronjobs, realtime timers are triggered on calendar events. Realtime timers are defined using the option
OnCalendar
.Monotonic timers are triggered at a specified time elapsed from a certain starting point. The latter could be a system boot or system unit activation event. There are several options for defining monotonic timers including
OnBootSec
,OnUnitActiveSec
, andOnTypeSec
. Monotonic timers are not persistent, and they are reset after each reboot.
15.7.2 systemd
timers and service units #
Every timer unit must have a corresponding systemd
unit file it controls.
In other words, a .timer
file activates and manages the corresponding .service
file.
When used with a timer, the .service
file does not require an [Install]
section, as the service is managed by the timer.
15.7.3 Practical example #
To understand the basics of systemd
timer units, we set up a timer that triggers the foo.sh
shell script.
First step is to create a systemd
service unit that controls the shell script.
To do this, open a new text file for editing and add the following service unit definition:
[Unit] Description="Foo shell script" [Service] ExecStart=/usr/local/bin/foo.sh
Save the file under the name foo.service
in the directory /etc/systemd/system/
.
Next, open a new text file for editing and add the following timer definition:
[Unit] Description="Run foo shell script" [Timer] OnBootSec=5min OnUnitActiveSec=24h Unit=foo.service [Install] WantedBy=multi-user.target
The [Timer]
section in the example above specifies
what service to trigger (foo.service
) and when to
trigger it. In this case, the option OnBootSec
specifies a monotonic timer that triggers the service five minutes
after the system boot, while the option
OnUnitActiveSec
triggers the service 24 hours after
the service has been activated (that is, the timer triggers the service
once a day). Finally, the option WantedBy
specifies
that the timer should start when the system has reached the multi-user
target.
Instead of a monotonic timer, you can specify a real-time one using the
option OnCalendar
. The following realtime timer
definition triggers the related service unit once a week, starting on
Monday at 12:00.
[Timer] OnCalendar=weekly Persistent=true
The option Persistent=true
indicates that the service
is triggered immediately after the timer activation if the timer missed
the last start time (for example, because of the system being powered
off).
The option OnCalendar
can also be used to define
specific dates times for triggering a service using the following
format: DayOfWeek Year-Month-Day Hour:Minute:Second
.
The example below triggers a service at 5am every day:
OnCalendar=*-*-* 5:00:00
You can use an asterisk to specify any value, and commas to list possible values. Use two values separated by .. to indicate a contiguous range. The following example triggers a service at 6pm on Friday of every month:
OnCalendar=Fri *-*-1..7 18:00:00
To trigger a service at different times, you can specify several OnCalendar
entries:
OnCalendar=Mon..Fri 10:00 OnCalendar=Sat,Sun 22:00
In the example above, a service is triggered at 10am on week days and at 10pm on weekends.
When you are done editing the timer unit file, save it under the name foo.timer
in the /etc/systemd/system/
directory.
To check the correctness of the created unit files, run the following command:
>
sudo
systemd-analyze verify /etc/systemd/system/foo.*
If the command returns no output, the files have passed the verification successfully.
To start the timer, use the command sudo systemctl start foo.timer
.
To enable the timer on boot, run the command sudo systemctl enable foo.timer
.
15.7.4 Managing systemd
timers #
Since timers are treated as regular systemd
units, you can manage them using systemctl
.
You can start a timer with systemctl start
, enable a timer with systemctl enable
, and so on.
In addition to that, you can list all active timers using the command systemctl list-timers
.
To list all timers, including inactive ones, run the command systemctl list-timers --all
.
15.8 More information #
For more information on systemd
refer to the following online resources:
- Homepage
systemd
for administratorsLennart Pöttering, one of the
systemd
authors, has written a series of blog entries (13 at the time of writing this chapter). Find them at http://0pointer.de/blog/projects.
Part III System #
- 16 32-bit and 64-bit applications in a 64-bit system environment
SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. This chapter offers a brief overview of 32-bit support implementation on 64-bit SUSE Linux Enterprise Server platforms.
- 17
journalctl
: Query thesystemd
journal systemd
features its own logging system called journal. There is no need to run asyslog
-based service, as all system events are written to the journal.- 18
update-alternatives
: Managing multiple versions of commands and files Often, there are several versions of the same tool installed on a system. To give administrators a choice and to make it possible to install and use different versions side by side, the alternatives system allows managing such versions consistently.
- 19 Basic networking
Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.
- 20 Printer operation
SUSE® Linux Enterprise Server supports printing with many types of printers, including remote network printers. Printers can be configured manually or with YaST. For configuration instructions, refer to Book “Deployment Guide”, Chapter 20 “Setting up hardware components with YaST”, Section 20.3 “Set…
- 21 Graphical user interface
SUSE Linux Enterprise Server includes the X.org server and the GNOME desktop. This chapter describes the configuration of the graphical user interface for all users.
- 22 Accessing file systems with FUSE
FUSE is the acronym for Filesystem in Userspace. This means you can configure and mount a file system as an unprivileged user. Normally, you need to be
root
for this task. FUSE alone is a kernel module. Combined with plug-ins, it allows you to extend FUSE to access almost all file systems like remote SSH connections, ISO images, and more.- 23 Managing kernel modules
Although Linux is a monolithic kernel, it can be extended using kernel modules. These are special objects that can be inserted into the kernel and removed on demand. In practical terms, kernel modules make it possible to add and remove drivers and interfaces that are not included in the kernel itsel…
- 24 Dynamic kernel device management with
udev
The kernel can add or remove almost any device in a running system. Changes in the device state (whether a device is plugged in or removed) need to be propagated to user space. Devices need to be configured when they are plugged in and recognized. Users of a certain device need to be informed about …
- 25 Special system features
This chapter starts with information about various software packages, the virtual consoles and the keyboard layout. We talk about software components like
bash
,cron
andlogrotate
, because they were changed or enhanced during the last release cycles. Even if they are small or considered of minor importance, users should change their default behavior, because these components are often closely coupled with the system. The chapter concludes with a section about language and country-specific settings (I18N and L10N).- 26 Using NetworkManager
NetworkManager is the ideal solution for laptops and other portable computers. It supports state-of-the-art encryption types and standards for network connections, including connections to 802.1X protected networks. 802.1X is the “IEEE Standard for Local and Metropolitan Area Networks—Port-Based Net…
- 27 Power management
The features and hardware described in this chapter do not exist on IBM Z, making this chapter irrelevant for these platforms.
- 28 Persistent memory
This chapter contains additional information about using SUSE Linux Enterprise with non-volatile main memory, also known as Persistent Memory, comprising one or more NVDIMMs.
16 32-bit and 64-bit applications in a 64-bit system environment #
SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. This chapter offers a brief overview of 32-bit support implementation on 64-bit SUSE Linux Enterprise Server platforms.
SUSE Linux Enterprise Server for the 64-bit platforms POWER, IBM Z and AMD64/Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment “out-of-the-box.” The corresponding 32-bit platforms are POWER for POWER, and x86 for AMD64/Intel 64. This support means that you can continue to use your preferred 32-bit applications without waiting for a corresponding 64-bit port to become available. The current POWER system runs most applications in 32-bit mode, but you can run 64-bit applications.
SUSE Linux Enterprise Server does not support compilation of 32-bit applications. It only offers runtime support for 32-bit binaries.
16.1 Runtime support #
If an application is available for both 32-bit and 64-bit environments, installing both versions may cause problems. In such cases, decide on one version to install to avoid potential runtime errors.
An exception to this rule is PAM (pluggable authentication modules). SUSE Linux Enterprise Server uses PAM in the authentication process as a layer that mediates between user and application. Always install both PAM versions on 64-bit operating systems that also run 32-bit applications.
For correct execution, every application requires a range of libraries. Unfortunately, the names are identical for the 32-bit and 64-bit versions of these libraries. They must be differentiated from each other in another way.
To retain compatibility with 32-bit versions, 64-bit and
32-bit libraries are stored in the same location. The 32-bit
version of libc.so.6
is located under
/lib/libc.so.6
in both 32-bit and 64-bit
environments.
All 64-bit libraries and object files are located in directories called
lib64
. The 64-bit object files normally
found under /lib
and
/usr/lib
are now found under
/lib64
and /usr/lib64
. This means
that space is available for 32-bit libraries under /lib
and /usr/lib
, so the file name for both versions can
remain unchanged.
If the data content of 32-bit subdirectories under /lib
does not
depend on word size, they are not moved. This scheme conforms to LSB (Linux Standards Base)
and FHS (File System Hierarchy Standard).
16.2 Kernel specifications #
The 64-bit kernels for AMD64/Intel 64, POWER and IBM Z offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical to the ABI for the corresponding 32-bit kernel. This means that communication between both 32-bit and 64-bit applications with 64-bit kernels are identical.
The 32-bit system call emulation for 64-bit kernels does not support
all the APIs used by system programs. This depends on the platform. For this
reason, few applications, like lspci
, must be
compiled on non-POWER platforms as 64-bit programs to
function properly. On IBM Z, not all ioctls are available in the
32-bit kernel ABI.
A 64-bit kernel can only load 64-bit kernel modules. You must compile 64-bit modules specifically for 64-bit kernels. It is not possible to use 32-bit kernel modules with 64-bit kernels.
Some applications require separate kernel-loadable modules. If you intend to use a 32-bit application in a 64-bit system environment, contact the provider of the application and SUSE. Make sure that the 64-bit version of the kernel-loadable module and the 32-bit compiled version of the kernel API are available for this module.
17 journalctl
: Query the systemd
journal #
systemd
features its own logging system called
journal. There is no need to run a
syslog
-based service, as all system events are
written to the journal.
The journal itself is a system service managed by systemd
. Its full name is
systemd-journald.service
. It collects and stores logging
data by maintaining structured indexed journals based on logging information
received from the kernel, user processes, standard input, and system service errors. The systemd-journald
service is on
by default:
>
sudo
systemctl status systemd-journald systemd-journald.service - Journal Service Loaded: loaded (/usr/lib/systemd/system/systemd-journald.service; static) Active: active (running) since Mon 2014-05-26 08:36:59 EDT; 3 days ago Docs: man:systemd-journald.service(8) man:journald.conf(5) Main PID: 413 (systemd-journal) Status: "Processing requests..." CGroup: /system.slice/systemd-journald.service └─413 /usr/lib/systemd/systemd-journald [...]
17.1 Making the journal persistent #
The journal stores log data in /run/log/journal/
by
default. Because the /run/
directory is volatile by
nature, log data is lost at reboot. To make the log data persistent, create the
directory /var/log/journal/
and make sure it
has the correct access modes and ownership, so the systemd-journald service can store its
data. To switch to persistent logging, execute the following commands:
>
sudo
mkdir /var/log/journal>
sudo
systemd-tmpfiles --create --prefix=/var/log/journal>
sudo
journalctl --flush
Any log data stored in /run/log/journal/
will be flushed into
/var/log/journal/
.
17.2 journalctl
: Useful switches #
This section introduces several common useful options to enhance the default
journalctl
behavior. All switches are described in the
journalctl
manual page, man 1
journalctl
.
To show all journal messages related to a specific executable, specify the full path to the executable:
>
sudo
journalctl /usr/lib/systemd/systemd
- -f
Shows only the most recent journal messages, and prints new log entries as they are added to the journal.
Prints the messages and jumps to the end of the journal, so that the latest entries are visible within the pager.
- -r
Prints the messages of the journal in reverse order, so that the latest entries are listed first.
- -k
Shows only kernel messages. This is equivalent to the field match
_TRANSPORT=kernel
(see Section 17.3.3, “Filtering based on fields”).- -u
Shows only messages for the specified
systemd
unit. This is equivalent to the field match_SYSTEMD_UNIT=UNIT
(see Section 17.3.3, “Filtering based on fields”).>
sudo
journalctl -u apache2 [...] Jun 03 10:07:11 pinkiepie systemd[1]: Starting The Apache Webserver... Jun 03 10:07:12 pinkiepie systemd[1]: Started The Apache Webserver.
17.3 Filtering the journal output #
When called without switches, journalctl
shows the full
content of the journal, the oldest entries listed first. The output can be
filtered by specific switches and fields.
17.3.1 Filtering based on a boot number #
journalctl
can filter messages based on a specific
system boot. To list all available boots, run
>
sudo
journalctl --list-boots -1 097ed2cd99124a2391d2cffab1b566f0 Mon 2014-05-26 08:36:56 EDT—Fri 2014-05-30 05:33:44 EDT 0 156019a44a774a0bb0148a92df4af81b Fri 2014-05-30 05:34:09 EDT—Fri 2014-05-30 06:15:01 EDT
The first column lists the boot offset: 0
for the
current boot, -1
for the previous one,
-2
for the one prior to that, etc. The second column
contains the boot ID followed by the limiting time stamps of the specific
boot.
Show all messages from the current boot:
>
sudo
journalctl -b
If you need to see journal messages from the previous boot, add an offset parameter. The following example outputs the previous boot messages:
>
sudo
journalctl -b -1
Another way is to list boot messages based on the boot ID. For this purpose, use the _BOOT_ID field:
>
sudo
journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b
17.3.2 Filtering based on time interval #
You can filter the output of journalctl
by specifying
the starting and/or ending date. The date specification should be of the
format "2014-06-30 9:17:16". If the time part is omitted, midnight is
assumed. If seconds are omitted, ":00" is assumed. If the date part is
omitted, the current day is assumed. Instead of numeric expression, you can
specify the keywords "yesterday", "today", or "tomorrow". They refer to
midnight of the day before the current day, of the current day, or of the
day after the current day. If you specify "now", it refers to the current
time. You can also specify relative times prefixed with
-
or +
, referring to times before or
after the current time.
Show only new messages since now, and update the output continuously:
>
sudo
journalctl --since "now" -f
Show all messages since last midnight till 3:20am:
>
sudo
journalctl --since "today" --until "3:20"
17.3.3 Filtering based on fields #
You can filter the output of the journal by specific fields. The syntax of
a field to be matched is FIELD_NAME=MATCHED_VALUE
, such
as _SYSTEMD_UNIT=httpd.service
. You can specify multiple
matches in a single query to filter the output messages even more. See
man 7 systemd.journal-fields
for a list of default
fields.
Show messages produced by a specific process ID:
>
sudo
journalctl _PID=1039
Show messages belonging to a specific user ID:
# journalctl _UID=1000
Show messages from the kernel ring buffer (the same as
dmesg
produces):
>
sudo
journalctl _TRANSPORT=kernel
Show messages from the service's standard or error output:
>
sudo
journalctl _TRANSPORT=stdout
Show messages produced by a specified service only:
>
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service
If two different fields are specified, only entries that match both expressions at the same time are shown:
>
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1488
If two matches refer to the same field, all entries matching either expression are shown:
>
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service _SYSTEMD_UNIT=dbus.service
You can use the '+' separator to combine two expressions in a logical 'OR'. The following example shows all messages from the Avahi service process with the process ID 1480 together with all messages from the D-Bus service:
>
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service
17.4 Investigating systemd
errors #
This section introduces a simple example to illustrate how to find and fix
the error reported by systemd
during apache2
start-up.
Try to start the apache2 service:
# systemctl start apache2 Job for apache2.service failed. See 'systemctl status apache2' and 'journalctl -xn' for details.
Let us see what the service's status says:
>
sudo
systemctl status apache2 apache2.service - The Apache Webserver Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: failed (Result: exit-code) since Tue 2014-06-03 11:08:13 CEST; 7min ago Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND \ -k graceful-stop (code=exited, status=1/FAILURE)The ID of the process causing the failure is 11026.
Show the verbose version of messages related to process ID 11026:
>
sudo
journalctl -o verbose _PID=11026 [...] MESSAGE=AH00526: Syntax error on line 6 of /etc/apache2/default-server.conf: [...] MESSAGE=Invalid command 'DocumenttRoot', perhaps misspelled or defined by a module [...]Fix the typo inside
/etc/apache2/default-server.conf
, start the apache2 service, and print its status:>
sudo
systemctl start apache2 && systemctl status apache2 apache2.service - The Apache Webserver Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: active (running) since Tue 2014-06-03 11:26:24 CEST; 4ms ago Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND -k graceful-stop (code=exited, status=1/FAILURE) Main PID: 11263 (httpd2-prefork) Status: "Processing requests..." CGroup: /system.slice/apache2.service ├─11263 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11280 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11281 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11282 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11283 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] └─11285 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
17.5 Journald configuration #
The behavior of the systemd-journald service can be adjusted by modifying
/etc/systemd/journald.conf
. This section introduces
only basic option settings. For a complete file description, see
man 5 journald.conf
. Note that you need to restart the
journal for the changes to take effect with
>
sudo
systemctl restart systemd-journald
17.5.1 Changing the journal size limit #
If the journal log data is saved to a persistent location (see
Section 17.1, “Making the journal persistent”), it uses up to 10% of the file
system the /var/log/journal
resides on. For example,
if /var/log/journal
is located on a 30 GB
/var
partition, the journal may use up to 3 GB of the
disk space. To change this limit, change (and uncomment) the
SystemMaxUse
option:
SystemMaxUse=50M
17.5.2 Forwarding the journal to /dev/ttyX
#
You can forward the journal to a terminal device to inform you about system
messages on a preferred terminal screen, for example
/dev/tty12
. Change the following journald options to
ForwardToConsole=yes TTYPath=/dev/tty12
17.5.3 Forwarding the journal to syslog facility #
Journald is backward compatible with traditional syslog implementations
such as rsyslog
. Make sure the following is valid:
rsyslog is installed.
>
sudo
rpm -q rsyslog rsyslog-7.4.8-2.16.x86_64rsyslog service is enabled.
>
sudo
systemctl is-enabled rsyslog enabledForwarding to syslog is enabled in
/etc/systemd/journald.conf
.ForwardToSyslog=yes
17.6 Using YaST to filter the systemd
journal #
For an easy way of filtering the systemd journal (without dealing
with the journalctl syntax), you can use the YaST journal module. After
installing it with sudo zypper in yast2-journal
, start it
from YaST by selecting › . Alternatively, start it
from command line by entering sudo yast2 journal
.
The module displays the log entries in a table. The search box on top allows
you to search for entries that contain certain characters, similar to using
grep
. To filter the entries by date and time, unit, file,
or priority, click and set the respective
options.
17.7 Viewing logs in GNOME #
You can view the journal with GNOME Logs.
Start it from the application menu. To view system log messages, it
needs to be run as root, for example with xdg-su
gnome-logs
. This command can be executed when pressing
Alt–F2.
18 update-alternatives
: Managing multiple versions of commands and files #
Often, there are several versions of the same tool installed on a system. To give administrators a choice and to make it possible to install and use different versions side by side, the alternatives system allows managing such versions consistently.
18.1 Overview #
On SUSE Linux Enterprise Server, some programs perform the same or similar tasks. For example,
if Java 1.7 and Java 1.8 are both installed on the system, the alternatives system script
(update-alternatives
) is called from inside the RPM package.
By default, the alternatives system will refer to version 1.8: Higher versions also have a
higher priority. However, the administrator can change the default and
can point the generic name to version 1.7.
The following terminology is used in this chapter:
- Administrative directory
The default
/var/lib/rpm/alternatives
directory contains information about the current state of alternatives.- Alternative
The name of a specific file in the file system, which can be made accessible via a generic name using the alternatives system.
- Alternatives directory
The default
/etc/alternatives
directory containing symbolic links.- Generic name
A name (for example,
/usr/bin/edit
) that refers to one file out of several available using the alternatives system.- Link group
A set of related symbolic links that can be updated as a group.
- Master link
The link in a link group that determines how the other links in the group are configured.
- Slave link
A link in a link group controlled by the master link.
- Symbolic link (symlink)
A file that is a reference to another file in the same file system. The alternatives system uses symbolic links in the alternatives directory to switch between versions of a file.
Symbolic links in the alternatives directory can be modified by the administrator through the
update-alternatives
command.
The alternatives system provides the update-alternatives
command to
create, remove, maintain, and show information about symbolic links.
While these symbolic links usually point to commands, they can also point
to JAR archives, man pages, and other files.
Examples in this chapter use commands and man pages, but they are also
applicable to other file types.
The alternatives system uses the alternatives directory to collect links to possible alternatives. When a new package with an alternative is installed, the new alternative is added to the system. Whether the new package's alternative is selected as the default depends on its priority and on the mode that is set. Usually, packages with a higher version also have a higher priority. The alternatives system can operate in two modes:
Automatic mode. In this mode, the alternatives system ensures that the links in the group point to the highest priority alternatives appropriate for the group.
Manual mode. In this mode, the alternatives system does not make any changes to the system administrator's settings.
For example, the java
command has the following link
hierarchy in the alternatives system:
18.2 Use cases #
By default, the update-alternatives
script is called
from inside an RPM package. When a package is installed or removed, the
script takes care of all its symbolic links.
But you can run it manually from the command line for:
displaying the current alternatives for a generic name.
changing the defaults of an alternative.
creating a set of related files for an alternative.
18.3 Getting an overview of alternatives #
To retrieve the names of all configured alternatives, use:
>
ls /var/lib/alternatives
To get an overview of all configured alternatives and their values, use
>
sudo
update-alternatives --get-selections
asadmin auto /usr/bin/asadmin-2.7 awk auto /usr/bin/gawk chardetect auto /usr/bin/chardetect-3.6 dbus-launch auto /usr/bin/dbus-launch.x11 default-displaymanager auto /usr/lib/X11/displaymanagers/gdm [...]
18.4 Viewing details on specific alternatives #
The easiest way to check the alternatives is to follow the symbolic links of
your command.
For example, if you want to know what the java
command is referring to, use the following command:
>
readlink --canonicalize /usr/bin/java
/usr/lib64/jvm/jre-10-openjdk/bin/java
If you see the same path (in our example, it is
/usr/bin/java
),
there are no alternatives available for this command.
To see the full alternatives (including slaves), use the
--display
option:
>
sudo
update-alternatives --display java
java - auto mode link best version is /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java link currently points to /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java link java is /usr/bin/java slave java.1.gz is /usr/share/man/man1/java.1.gz slave jre is /usr/lib64/jvm/jre slave jre_exports is /usr/lib64/jvm-exports/jre slave keytool is /usr/bin/keytool slave keytool.1.gz is /usr/share/man/man1/keytool.1.gz slave orbd is /usr/bin/orbd slave orbd.1.gz is /usr/share/man/man1/orbd.1.gz [...]
18.5 Setting the default version of alternatives #
By default, commands in /usr/bin
refer to the
alternatives directory with the highest priority. For example,
by default, the command java
shows the following
version number:
>
java -version
openjdk version "10.0.1" 2018-04-17 OpenJDK Runtime Environment (build 10.0.1+10-suse-lp150.1.11-x8664) OpenJDK 64-Bit Server VM (build 10.0.1+10-suse-lp150.1.11-x8664, mixed mode)
To change the default java
command to refer
to a previous version, run:
>
sudo
update-alternatives --config java
root's password: There are 2 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/lib64/jvm/jre-10-openjdk/bin/java 2005 auto mode 1 /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java 1805 manual mode 2 /usr/lib64/jvm/jre-10-openjdk/bin/java 2005 manual mode 3 /usr/lib64/jvm/jre-11-openjdk/bin/java 0 manual mode Press <enter> to keep the current choice[*], or type selection number:
Depending on your system and installed versions, the exact Java version
number will be different.
After you have selected 1
, java
shows the following version number:
>
java -version
java version "1.8.0_171" OpenJDK Runtime Environment (IcedTea 3.8.0) (build 1.8.0_171-b11 suse-lp150.2.3.1-x86_64) OpenJDK 64-Bit Server VM (build 25.171-b11, mixed mode)
Also, keep in mind the following points:
When working in manual mode and installing another Java version, the alternatives system neither touches the links nor changes the generic name.
When working in automatic mode and installing another Java version, the alternatives system changes the Java master link and all slave links (as you can see in Section 18.4, “Viewing details on specific alternatives”). To check the master-slave relationships, use:
>
sudo
update-alternatives --display java
18.6 Installing custom alternatives #
This section describes how to set up custom alternatives on a system.
Do not install custom alternatives for python3.
/usr/bin/python3
does not have update alternatives and
always points to specific tested versions. Creating a custom python3
alternative pointing to a different version—such as python
3.11—breaks dependent system tools.
The example makes the following assumptions:
There are two scripts,
foo-2
andfoo-3
, with similar functionality.The scripts are stored in the
/usr/local/bin
directory to avoid any conflicts with the system tools in/usr/bin
.There is a master link
foo
that points to eitherfoo-2
orfoo-3
.
To provide alternatives on your system, follow these steps:
Copy your scripts into the
/usr/local/bin
directory.Make the scripts executable:
>
sudo
chmod +x /usr/local/bin/foo-{2,3}
Run
update-alternatives
for both scripts:>
sudo
update-alternatives --install \ /usr/local/bin/foo 1\ foo 2\ /usr/local/bin/foo-2 3\ 200 4>
sudo
update-alternatives --install \ /usr/local/bin/foo 1\ foo 2\ /usr/local/bin/foo-3 3\ 300 4The options after
--install
have the following meanings:The generic name. To avoid confusion, this is usually the script name without any version numbers.
The name of the master link. Must be the same.
The path to the original script(s) located in
/usr/local/bin
.The priority. We give
foo-2
a lower priority thanfoo-3
. It is good practice to use a significant number increase to separate priorities. For example, a priority of 200 forfoo-2
and 300 forfoo-3
.Check the master link:
>
sudo
update-alternatives --display foo
foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo /usr/local/bin/foo-2 - priority 200 /usr/local/bin/foo-3 - priority 300
After you completed the described steps, you can use the master link
/usr/local/bin/foo
.
If needed, you can install additional alternatives. To remove an alternative, use the following command:
>
sudo
update-alternatives --remove foo /usr/local/bin/foo-2
After this script has been removed, the alternatives system for the foo group looks like this:
>
sudo
update-alternatives --display foo
foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo /usr/local/bin/foo-3 - priority 300
18.7 Defining dependent alternatives #
If you have alternatives, the script itself is not enough. Most commands are not completely stand-alone: They usually ship with additional files, such as extensions, configurations, or man pages. To create alternatives which are dependent on a master link, use slave alternatives.
Let us assume we want to extend our example in Section 18.6, “Installing custom alternatives” and provide man pages and configuration files:
Two man pages,
foo-2.1.gz
andfoo-3.1.gz
stored in the/usr/local/man/man1
directory.Two configuration files,
foo-2.conf
andfoo-3.conf
, stored in/etc
.
Follow these steps to add the additional files to your alternatives:
Copy the configuration files into
/etc
:>
sudo
cp foo-{2,3}.conf /etc
Copy the man pages into the
/usr/local/man/man1
directory:>
sudo
cp foo-{2,3}.1.gz /usr/local/man/man1/
Add the slave links to the main scripts with the
--slave
option:>
sudo
update-alternatives --install \ /usr/local/bin/foo foo /usr/local/bin/foo-2 200 \ --slave /usr/local/man/man1/foo.1.gz \ foo.1.gz \ /usr/local/man/man1/foo-2.1.gz \ --slave /etc/foo.conf \ foo.conf \ /etc/foo-2.conf
>
sudo
update-alternatives --install \ /usr/local/bin/foo foo /usr/local/bin/foo-3 300 \ --slave /usr/local/man/man1/foo.1.gz \ foo.1.gz \ /usr/local/man/man1/foo-3.1.gz \ --slave /etc/foo.conf \ foo.conf \ /etc/foo-3.conf
Check the master link:
foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo slave foo.1.gz is /usr/local/man/man1/foo.1.gz slave foo.conf is /etc/foo.conf /usr/local/bin/foo-2 - priority 200 slave foo.1.gz: /usr/local/man/man1/foo-2.1.gz slave foo.conf: /etc/foo-2.conf /usr/local/bin/foo-3 - priority 300 slave foo.1.gz: /usr/local/man/man1/foo-3.1.gz slave foo.conf: /etc/foo-3.conf
If you change the links with update-alternatives --config foo
to foo-2
, then all slave links will change as well.
19 Basic networking #
Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.
Linux and other Unix operating systems use the TCP/IP protocol. It is not a single network protocol, but a family of network protocols that offer various services. The protocols listed in Several protocols in the TCP/IP protocol family are provided for exchanging data between two machines via TCP/IP. Networks combined by TCP/IP, comprising a worldwide network, are also called “the Internet.”
RFC stands for Request for Comments. RFCs are documents that describe various Internet protocols and implementation procedures for the operating system and its applications. The RFC documents describe the setup of Internet protocols. For more information about RFCs, see http://www.ietf.org/rfc.html.
- TCP
Transmission Control Protocol: a connection-oriented secure protocol. The data to transmit is first sent by the application as a stream of data and converted into the appropriate format by the operating system. The data arrives at the respective application on the destination host in the original data stream format it was initially sent. TCP determines whether any data has been lost or jumbled during the transmission. TCP is implemented wherever the data sequence matters.
- UDP
User Datagram Protocol: a connectionless, insecure protocol. The data to transmit is sent in the form of packets generated by the application. The order in which the data arrives at the recipient is not guaranteed and data loss is possible. UDP is suitable for record-oriented applications. It features a smaller latency period than TCP.
- ICMP
Internet Control Message Protocol: This is not a protocol for the end user, but a special control protocol that issues error reports and can control the behavior of machines participating in TCP/IP data transfer. In addition, it provides a special echo mode that can be viewed using the program ping.
- IGMP
Internet Group Management Protocol: This protocol controls machine behavior when implementing IP multicast.
As shown in Figure 19.1, “Simplified layer model for TCP/IP”, data exchange takes place in different layers. The actual network layer is the insecure data transfer via IP (Internet protocol). On top of IP, TCP (transmission control protocol) guarantees, to a certain extent, security of the data transfer. The IP layer is supported by the underlying hardware-dependent protocol, such as Ethernet.
The diagram provides one or two examples for each layer. The layers are ordered according to abstraction levels. The lowest layer is very close to the hardware. The uppermost layer, however, is almost a complete abstraction from the hardware. Every layer has its own special function. The special functions of each layer are mostly implicit in their description. The data link and physical layers represent the physical network used, such as Ethernet.
Almost all hardware protocols work on a packet-oriented basis. The data to transmit is collected into packets (it cannot be sent all at once). The maximum size of a TCP/IP packet is approximately 64 KB. Packets are normally quite smaller, as the network hardware can be a limiting factor. The maximum size of a data packet on an Ethernet is about fifteen hundred bytes. The size of a TCP/IP packet is limited to this amount when the data is sent over an Ethernet. If more data is transferred, more data packets need to be sent by the operating system.
For the layers to serve their designated functions, additional information regarding each layer must be saved in the data packet. This takes place in the header of the packet. Every layer attaches a small block of data, called the protocol header, to the front of each emerging packet. A sample TCP/IP data packet traveling over an Ethernet cable is illustrated in Figure 19.2, “TCP/IP ethernet packet”. The proof sum is located at the end of the packet, not at the beginning. This simplifies things for the network hardware.
When an application sends data over the network, the data passes through each layer, all implemented in the Linux kernel except the physical layer. Each layer is responsible for preparing the data so it can be passed to the next layer. The lowest layer is ultimately responsible for sending the data. The entire procedure is reversed when data is received. Like the layers of an onion, in each layer the protocol headers are removed from the transported data. Finally, the transport layer is responsible for making the data available for use by the applications at the destination. In this manner, one layer only communicates with the layer directly above or below it. For applications, it is irrelevant whether data is transmitted via a wireless or wired connection. Likewise, it is irrelevant for the data line which kind of data is transmitted, as long as packets are in the correct format.
19.1 IP addresses and routing #
The discussion in this section is limited to IPv4 networks. For information about IPv6 protocol, the successor to IPv4, refer to Section 19.2, “IPv6—the next generation Internet”.
19.1.1 IP addresses #
Every computer on the Internet has a unique 32-bit address. These 32 bits (or 4 bytes) are normally written as illustrated in the second row in Example 19.1, “Writing IP addresses”.
IP Address (binary): 11000000 10101000 00000000 00010100 IP Address (decimal): 192. 168. 0. 20
In decimal form, the four bytes are written in the decimal number system, separated by periods. The IP address is assigned to a host or a network interface. It can be used only once throughout the world. There are exceptions to this rule, but these are not relevant to the following passages.
The points in IP addresses indicate the hierarchical system. Until the 1990s, IP addresses were strictly categorized in classes. However, this system proved too inflexible and was discontinued. Now, classless routing (CIDR, classless interdomain routing) is used.
19.1.2 Netmasks and routing #
Netmasks are used to define the address range of a subnet. If two hosts are in the same subnet, they can reach each other directly. If they are not in the same subnet, they need the address of a gateway that handles all the traffic for the subnet. To check if two IP addresses are in the same subnet, simply “AND” both addresses with the netmask. If the result is identical, both IP addresses are in the same local network. If there are differences, the remote IP address, and thus the remote interface, can only be reached over a gateway.
To understand how the netmask works, look at
Example 19.2, “Linking IP addresses to the netmask”. The netmask consists of 32 bits
that identify how much of an IP address belongs to the network. All those
bits that are 1
mark the corresponding bit in the IP
address as belonging to the network. All bits that are 0
mark bits inside the subnet. This means that the more bits are
1
, the smaller the subnet is. Because the netmask always
consists of several successive 1
bits, it is also
possible to count the number of bits in the netmask. In
Example 19.2, “Linking IP addresses to the netmask” the first net with 24 bits could
also be written as 192.168.0.0/24
.
IP address (192.168.0.20): 11000000 10101000 00000000 00010100 Netmask (255.255.255.0): 11111111 11111111 11111111 00000000 --------------------------------------------------------------- Result of the link: 11000000 10101000 00000000 00000000 In the decimal system: 192. 168. 0. 0 IP address (213.95.15.200): 11010101 10111111 00001111 11001000 Netmask (255.255.255.0): 11111111 11111111 11111111 00000000 --------------------------------------------------------------- Result of the link: 11010101 10111111 00001111 00000000 In the decimal system: 213. 95. 15. 0
To give another example: all machines connected with the same Ethernet cable are usually located in the same subnet and are directly accessible. Even when the subnet is physically divided by switches or bridges, these hosts can still be reached directly.
IP addresses outside the local subnet can only be reached if a gateway is configured for the target network. In the most common case, there is only one gateway that handles all traffic that is external. However, it is also possible to configure several gateways for different subnets.
If a gateway has been configured, all external IP packets are sent to the appropriate gateway. This gateway then attempts to forward the packets in the same manner—from host to host—until it reaches the destination host or the packet's TTL (time to live) expires.
- Base Network Address
This is the netmask AND any address in the network, as shown in Example 19.2, “Linking IP addresses to the netmask” under
Result
. This address cannot be assigned to any hosts.- Broadcast Address
This could be paraphrased as: “Access all hosts in this subnet.” To generate this, the netmask is inverted in binary form and linked to the base network address with a logical OR. The above example therefore results in 192.168.0.255. This address cannot be assigned to any hosts.
- Local Host
The address
127.0.0.1
is assigned to the “loopback device” on each host. A connection can be set up to your own machine with this address and with all addresses from the complete127.0.0.0/8
loopback network as defined with IPv4. With IPv6 there is only one loopback address (::1
).
Because IP addresses must be unique all over the world, you cannot select random addresses. There are three address domains to use if you want to set up a private IP-based network. These cannot get any connection from the rest of the Internet, because they cannot be transmitted over the Internet. These address domains are specified in RFC 1597 and listed in Table 19.1, “Private IP address domains”.
Network/Netmask |
Domain |
---|---|
|
|
|
|
|
|
19.2 IPv6—the next generation Internet #
IPv6 is not supported by the CTC and IUCV network connections of the IBM Z hardware.
Because of the emergence of the World Wide Web (WWW), the Internet has experienced explosive growth, with an increasing number of computers communicating via TCP/IP in the past fifteen years. Since Tim Berners-Lee at CERN (http://public.web.cern.ch) invented the WWW in 1990, the number of Internet hosts has grown from a few thousand to about a hundred million.
As mentioned, an IPv4 address consists of only 32 bits. Also, quite a few IP addresses are lost—they cannot be used because of the way in which networks are organized. The number of addresses available in your subnet is two to the power of the number of bits, minus two. A subnet has, for example, 2, 6, or 14 addresses available. To connect 128 hosts to the Internet, for example, you need a subnet with 256 IP addresses, from which only 254 are usable, because two IP addresses are needed for the structure of the subnet itself: the broadcast and the base network address.
Under the current IPv4 protocol, DHCP or NAT (network address translation) are the typical mechanisms used to circumvent the potential address shortage. Combined with the convention to keep private and public address spaces separate, these methods can certainly mitigate the shortage. The problem with them lies in their configuration, which is a chore to set up and a burden to maintain. To set up a host in an IPv4 network, you need several address items, such as the host's own IP address, the subnetmask, the gateway address and maybe a name server address. All these items need to be known and cannot be derived from somewhere else.
With IPv6, both the address shortage and the complicated configuration should be a thing of the past. The following sections tell more about the improvements and benefits brought by IPv6 and about the transition from the old protocol to the new one.
19.2.1 Advantages #
The most important and most visible improvement brought by the newer protocol is the enormous expansion of the available address space. An IPv6 address is made up of 128 bit values instead of the traditional 32 bits. This provides for as many as several quadrillion IP addresses.
However, IPv6 addresses are not only different from their predecessors with regard to their length. They also have a different internal structure that may contain more specific information about the systems and the networks to which they belong. More details about this are found in Section 19.2.2, “Address types and structure”.
The following is a list of other advantages of the newer protocol:
- Autoconfiguration
IPv6 makes the network “plug and play” capable, which means that a newly set up system integrates into the (local) network without any manual configuration. The new host uses its automatic configuration mechanism to derive its own address from the information made available by the neighboring routers, relying on a protocol called the neighbor discovery (ND) protocol. This method does not require any intervention on the administrator's part and there is no need to maintain a central server for address allocation—an additional advantage over IPv4, where automatic address allocation requires a DHCP server.
Nevertheless if a router is connected to a switch, the router should send periodic advertisements with flags telling the hosts of a network how they should interact with each other. For more information, see RFC 2462 and the
radvd.conf(5)
man page, and RFC 3315.- Mobility
IPv6 makes it possible to assign several addresses to one network interface at the same time. This allows users to access several networks easily, something that could be compared with the international roaming services offered by mobile phone companies. When you take your mobile phone abroad, the phone automatically logs in to a foreign service when it enters the corresponding area, so you can be reached under the same number everywhere and can place an outgoing call, as you would in your home area.
- Secure communication
With IPv4, network security is an add-on function. IPv6 includes IPsec as one of its core features, allowing systems to communicate over a secure tunnel to avoid eavesdropping by outsiders on the Internet.
- Backward compatibility
Realistically, it would be impossible to switch the entire Internet from IPv4 to IPv6 at one time. Therefore, it is crucial that both protocols can coexist not only on the Internet, but also on one system. This is ensured by compatible addresses (IPv4 addresses can easily be translated into IPv6 addresses) and by using several tunnels. See Section 19.2.3, “Coexistence of IPv4 and IPv6”. Also, systems can rely on a dual stack IP technique to support both protocols at the same time, meaning that they have two network stacks that are completely separate, such that there is no interference between the two protocol versions.
- Custom tailored services through multicasting
With IPv4, some services, such as SMB, need to broadcast their packets to all hosts in the local network. IPv6 allows a much more fine-grained approach by enabling servers to address hosts through multicasting, that is by addressing several hosts as parts of a group. This is different from addressing all hosts through broadcasting or each host individually through unicasting. Which hosts are addressed as a group may depend on the concrete application. There are some predefined groups to address all name servers (the all name servers multicast group), for example, or all routers (the all routers multicast group).
19.2.2 Address types and structure #
As mentioned, the current IP protocol has two major limitations: there is an increasing shortage of IP addresses, and configuring the network and maintaining the routing tables is becoming a more complex and burdensome task. IPv6 solves the first problem by expanding the address space to 128 bits. The second one is mitigated by introducing a hierarchical address structure combined with sophisticated techniques to allocate network addresses, and multihoming (the ability to assign several addresses to one device, giving access to several networks).
When dealing with IPv6, it is useful to know about three different types of addresses:
- Unicast
Addresses of this type are associated with exactly one network interface. Packets with such an address are delivered to only one destination. Accordingly, unicast addresses are used to transfer packets to individual hosts on the local network or the Internet.
- Multicast
Addresses of this type relate to a group of network interfaces. Packets with such an address are delivered to all destinations that belong to the group. Multicast addresses are mainly used by certain network services to communicate with certain groups of hosts in a well-directed manner.
- Anycast
Addresses of this type are related to a group of interfaces. Packets with such an address are delivered to the member of the group that is closest to the sender, according to the principles of the underlying routing protocol. Anycast addresses are used to make it easier for hosts to find out about servers offering certain services in the given network area. All servers of the same type have the same anycast address. Whenever a host requests a service, it receives a reply from the server with the closest location, as determined by the routing protocol. If this server should fail for some reason, the protocol automatically selects the second closest server, then the third one, and so forth.
An IPv6 address is made up of eight four-digit fields, each representing 16
bits, written in hexadecimal notation. They are separated by colons
(:
). Any leading zero bytes within a given field may be
dropped, but zeros within the field or at its end may not. Another
convention is that more than four consecutive zero bytes may be collapsed
into a double colon. However, only one such ::
is
allowed per address. This kind of shorthand notation is shown in
Example 19.3, “Sample IPv6 address”, where all three lines represent the
same address.
fe80 : 0000 : 0000 : 0000 : 0000 : 10 : 1000 : 1a4 fe80 : 0 : 0 : 0 : 0 : 10 : 1000 : 1a4 fe80 : : 10 : 1000 : 1a4
Each part of an IPv6 address has a defined function. The first bytes form
the prefix and specify the type of address. The center part is the network
portion of the address, but it may be unused. The end of the address forms
the host part. With IPv6, the netmask is defined by indicating the length
of the prefix after a slash at the end of the address. An address, as shown
in Example 19.4, “IPv6 address specifying the prefix length”, contains the information that
the first 64 bits form the network part of the address and the last 64 form
its host part. In other words, the 64
means that the
netmask is filled with 64 1-bit values from the left. As with IPv4, the IP
address is combined with AND with the values from the netmask to determine
whether the host is located in the same subnet or in another one.
fe80::10:1000:1a4/64
IPv6 knows about several predefined types of prefixes. Some are shown in Various IPv6 prefixes.
00
IPv4 addresses and IPv4 over IPv6 compatibility addresses. These are used to maintain compatibility with IPv4. Their use still requires a router able to translate IPv6 packets into IPv4 packets. Several special addresses, such as the one for the loopback device, have this prefix as well.
2
or3
as the first digitAggregatable global unicast addresses. As is the case with IPv4, an interface can be assigned to form part of a certain subnet. Currently, there are the following address spaces:
2001::/16
(production quality address space) and2002::/16
(6to4 address space).fe80::/10
Link-local addresses. Addresses with this prefix should not be routed and should therefore only be reachable from within the same subnet.
fec0::/10
Site-local addresses. These may be routed, but only within the network of the organization to which they belong. In effect, they are the IPv6 equivalent of the current private network address space, such as
10.x.x.x
.ff
These are multicast addresses.
A unicast address consists of three basic components:
- Public topology
The first part (which also contains one of the prefixes mentioned above) is used to route packets through the public Internet. It includes information about the company or institution that provides the Internet access.
- Site topology
The second part contains routing information about the subnet to which to deliver the packet.
- Interface ID
The third part identifies the interface to which to deliver the packet. This also allows for the MAC to form part of the address. Given that the MAC is a globally unique, fixed identifier coded into the device by the hardware maker, the configuration procedure is substantially simplified. In fact, the first 64 address bits are consolidated to form the
EUI-64
token, with the last 48 bits taken from the MAC, and the remaining 24 bits containing special information about the token type. This also makes it possible to assign anEUI-64
token to interfaces that do not have a MAC, such as those based on PPP.
On top of this basic structure, IPv6 distinguishes between five different types of unicast addresses:
::
(unspecified)This address is used by the host as its source address when the interface is initialized for the first time (at which point, the address cannot yet be determined by other means).
::1
(loopback)The address of the loopback device.
- IPv4 compatible addresses
The IPv6 address is formed by the IPv4 address and a prefix consisting of 96 zero bits. This type of compatibility address is used for tunneling (see Section 19.2.3, “Coexistence of IPv4 and IPv6”) to allow IPv4 and IPv6 hosts to communicate with others operating in a pure IPv4 environment.
- IPv4 addresses mapped to IPv6
This type of address specifies a pure IPv4 address in IPv6 notation.
- Local addresses
There are two address types for local use:
- link-local
This type of address can only be used in the local subnet. Packets with a source or target address of this type should not be routed to the Internet or other subnets. These addresses contain a special prefix (
fe80::/10
) and the interface ID of the network card, with the middle part consisting of zero bytes. Addresses of this type are used during automatic configuration to communicate with other hosts belonging to the same subnet.- site-local
Packets with this type of address may be routed to other subnets, but not to the wider Internet—they must remain inside the organization's own network. Such addresses are used for intranets and are an equivalent of the private address space defined by IPv4. They contain a special prefix (
fec0::/10
), the interface ID, and a 16 bit field specifying the subnet ID. Again, the rest is filled with zero bytes.
As a completely new feature introduced with IPv6, each network interface normally gets several IP addresses, with the advantage that several networks can be accessed through the same interface. One of these networks can be configured completely automatically using the MAC and a known prefix with the result that all hosts on the local network can be reached when IPv6 is enabled (using the link-local address). With the MAC forming part of it, any IP address used in the world is unique. The only variable parts of the address are those specifying the site topology and the public topology, depending on the actual network in which the host is currently operating.
For a host to go back and forth between different networks, it needs at least two addresses. One of them, the home address, not only contains the interface ID but also an identifier of the home network to which it normally belongs (and the corresponding prefix). The home address is a static address and, as such, it does not normally change. Still, all packets destined to the mobile host can be delivered to it, regardless of whether it operates in the home network or somewhere outside. This is made possible by the completely new features introduced with IPv6, such as stateless autoconfiguration and neighbor discovery. In addition to its home address, a mobile host gets one or more additional addresses that belong to the foreign networks where it is roaming. These are called care-of addresses. The home network has a facility that forwards any packets destined to the host when it is roaming outside. In an IPv6 environment, this task is performed by the home agent, which takes all packets destined to the home address and relays them through a tunnel. On the other hand, those packets destined to the care-of address are directly transferred to the mobile host without any special detours.
19.2.3 Coexistence of IPv4 and IPv6 #
The migration of all hosts connected to the Internet from IPv4 to IPv6 is a gradual process. Both protocols will coexist for some time to come. The coexistence on one system is guaranteed where there is a dual stack implementation of both protocols. That still leaves the question of how an IPv6 enabled host should communicate with an IPv4 host and how IPv6 packets should be transported by the current networks, which are predominantly IPv4-based. The best solutions offer tunneling and compatibility addresses (see Section 19.2.2, “Address types and structure”).
IPv6 hosts that are more or less isolated in the (worldwide) IPv4 network can communicate through tunnels: IPv6 packets are encapsulated as IPv4 packets to move them across an IPv4 network. Such a connection between two IPv4 hosts is called a tunnel. To achieve this, packets must include the IPv6 destination address (or the corresponding prefix) and the IPv4 address of the remote host at the receiving end of the tunnel. A basic tunnel can be configured manually according to an agreement between the hosts' administrators. This is also called static tunneling.
However, the configuration and maintenance of static tunnels is often too labor-intensive to use them for daily communication needs. Therefore, IPv6 provides for three different methods of dynamic tunneling:
- 6over4
IPv6 packets are automatically encapsulated as IPv4 packets and sent over an IPv4 network capable of multicasting. IPv6 is tricked into seeing the whole network (Internet) as a huge local area network (LAN). This makes it possible to determine the receiving end of the IPv4 tunnel automatically. However, this method does not scale very well and is also hampered because IP multicasting is far from widespread on the Internet. Therefore, it only provides a solution for smaller corporate or institutional networks where multicasting can be enabled. The specifications for this method are laid down in RFC 2529.
- 6to4
With this method, IPv4 addresses are automatically generated from IPv6 addresses, enabling isolated IPv6 hosts to communicate over an IPv4 network. However, several problems have been reported regarding the communication between those isolated IPv6 hosts and the Internet. The method is described in RFC 3056.
- IPv6 tunnel broker
This method relies on special servers that provide dedicated tunnels for IPv6 hosts. It is described in RFC 3053.
19.2.4 Configuring IPv6 #
To configure IPv6, you normally do not need to make any changes on the
individual workstations. IPv6 is enabled by default. To disable or enable
IPv6 on an installed system, use the YaST modprobe
-i ipv6
as
root
. It is impossible to unload
the IPv6 module after it has been loaded.
Because of the autoconfiguration concept of IPv6, the network card is assigned an address in the link-local network. Normally, no routing table management takes place on a workstation. The network routers can be queried by the workstation, using the router advertisement protocol, for what prefix and gateways should be implemented. The radvd program can be used to set up an IPv6 router. This program informs the workstations which prefix to use for the IPv6 addresses and which routers. Alternatively, use zebra/quagga for automatic configuration of both addresses and routing.
For information about how to set up various types of tunnels using the
/etc/sysconfig/network
files, see the man page of
ifcfg-tunnel
(man ifcfg-tunnel
).
19.2.5 More information #
The above overview does not cover the topic of IPv6 comprehensively. For a more in-depth look at the newer protocol, refer to the following online documentation and books:
- https://pulse.internetsociety.org
The starting point for everything about IPv6.
- http://www.ipv6day.org
All information needed to start your own IPv6 network.
- http://www.ipv6-to-standard.org/
The list of IPv6-enabled products.
- http://www.bieringer.de/linux/IPv6/
Here, find the Linux IPv6-HOWTO and many links related to the topic.
- RFC 2460
The fundamental RFC about IPv6, see https://www.rfc-editor.org/rfc/rfc2460.
- IPv6 essentials
A book describing all the important aspects of the topic is IPv6 Essentials by Silvia Hagen (ISBN 0-596-00125-8).
19.3 Name resolution #
DNS assists in assigning an IP address to one or more names and assigning a name to an IP address. In Linux, this conversion is usually carried out by a special type of software known as bind. The machine that takes care of this conversion is called a name server. The names make up a hierarchical system in which each name component is separated by a period. The name hierarchy is, however, independent of the IP address hierarchy described above.
Consider a complete name, such as
jupiter.example.com
, written in the
format hostname.domain
. A full
name, called a fully qualified domain name (FQDN),
consists of a host name and a domain name
(example.com
). The latter
also includes the top level domain or TLD
(com
).
TLD assignment has become quite confusing for historical reasons.
Traditionally, three-letter domain names are used in the USA. In the rest of
the world, the two-letter ISO national codes are the standard. In addition
to that, longer TLDs were introduced in 2000 that represent certain spheres
of activity (for example, .info
,
.name
,
.museum
).
In the early days of the Internet (before 1990), the file
/etc/hosts
was used to store the names of all the
machines represented over the Internet. This quickly proved to be
impractical in the face of the rapidly growing number of computers connected
to the Internet. For this reason, a decentralized database was developed to
store the host names in a widely distributed manner. This database, similar
to the name server, does not have the data pertaining to all hosts in the
Internet readily available, but can dispatch requests to other name servers.
The top of the hierarchy is occupied by root name servers. These root name servers manage the top level domains and are run by the Network Information Center (NIC). Each root name server knows about the name servers responsible for a given top level domain. Information about top level domain NICs is available at http://www.internic.net.
DNS can do more than resolve host names. The name server also knows which host is receiving e-mails for an entire domain—the mail exchanger (MX).
For your machine to resolve an IP address, it must know about at least one name server and its IP address. Easily specify such a name server using YaST. The configuration of name server access with SUSE® Linux Enterprise Server is described in Section 19.4.1.4, “Configuring host name and DNS”. Setting up your own name server is described in Chapter 31, The domain name system.
The protocol whois
is closely related to DNS. With this
program, quickly find out who is responsible for a given domain.
The .local
top level domain is treated as link-local
domain by the resolver. DNS requests are send as multicast DNS requests
instead of normal DNS requests. If you already use the
.local
domain in your name server configuration, you
must switch this option off in /etc/host.conf
. For
more information, see the host.conf
manual page.
To switch off MDNS during installation, use
nomdns=1
as a boot parameter.
For more information on multicast DNS, see http://www.multicastdns.org.
19.4 Configuring a network connection with YaST #
There are many supported networking types on Linux. Most of them use different device names and the configuration files are spread over several locations in the file system. For a detailed overview of the aspects of manual network configuration, see Section 19.5, “Configuring a network connection manually”.
All network interfaces with link up (with a network cable connected) are automatically configured. Additional hardware can be configured any time on the installed system. The following sections describe the network configuration for all types of network connections supported by SUSE Linux Enterprise Server.
On IBM Z platforms, hotpluggable network cards are supported, but not their automatic network integration via DHCP (as is the case on the PC). After they have been detected, you need to manually configure the interface.
19.4.1 Configuring the network card with YaST #
To configure your Ethernet or Wi-Fi/Bluetooth card in YaST, select
› . After starting the module, YaST displays the dialog with four tabs: , , and .The Section 19.4.1.1, “Configuring global networking options”.
tab allows you to set general networking options such as the network setup method, IPv6, and general DHCP options. For more information, seeThe Section 19.4.1.3, “Configuring an undetected network card”. To change the configuration of an already configured card, see Section 19.4.1.2, “Changing the configuration of a network card”.
tab contains information about installed network interfaces and configurations. Any properly detected network card is listed with its name. You can manually configure new cards, remove or change their configuration in this dialog. To manually configure a card that was not automatically detected, seeThe Section 19.4.1.4, “Configuring host name and DNS”.
tab allows to set the host name of the machine and name the servers to be used. For more information, seeThe Section 19.4.1.5, “Configuring routing” for more information.
tab is used for the configuration of routing. See19.4.1.1 Configuring global networking options #
The
tab of the YaST module allows you to set important global networking options, such as the use of NetworkManager, IPv6 and DHCP client options. These settings are applicable for all network interfaces.NetworkManager is now provided by the SUSE Linux Enterprise Workstation Extension. To install NetworkManager, activate the Workstation Extension repository, and select the NetworkManager packages.
In the nm-applet
should be used to configure
network options and the ,
and tabs of the
module are disabled.
For more information
on NetworkManager, see the SUSE Linux Enterprise Desktop documentation.
In the
choose whether to use the IPv6 protocol. It is possible to use IPv6 together with IPv4. By default, IPv6 is enabled. However, in networks not using IPv6 protocol, response times can be faster with IPv6 protocol disabled. To disable IPv6, deactivate . If IPv6 is disabled, the kernel no longer loads the IPv6 module automatically. This setting will be applied after reboot.In the
configure options for the DHCP client. The must be different for each DHCP client on a single network. If left empty, it defaults to the hardware address of the network interface. However, if you are running several virtual machines using the same network interface and, therefore, the same hardware address, specify a unique free-form identifier here.
The AUTO
to
send the current host name (that is the one defined in
/etc/HOSTNAME
). Make the option field empty for not
sending any host name.
If you do not want to change the default route according to the information from DHCP, deactivate
.19.4.1.2 Changing the configuration of a network card #
To change the configuration of a network card, select a card from the list of the detected cards in
› in YaST and click . The dialog appears in which to adjust the card configuration using the , and tabs.19.4.1.2.1 Configuring IP addresses #
You can set the IP address of the network card or the way its IP address is determined in the
tab of the dialog. Both IPv4 and IPv6 addresses are supported. The network card can have (which is useful for bonding devices), a (IPv4 or IPv6) or a assigned via or or both.If using
, select whether to use (for IPv4), (for IPv6) or .If possible, the first network card with link that is available during the installation is automatically configured to use automatic address setup via DHCP.
On IBM Z platforms, DHCP-based address configuration is only supported with network cards that have a MAC address. This is only the case with OSA and OSA Express cards.
DHCP should also be used if you are using a DSL line but with no static IP assigned by the ISP (Internet Service Provider). If you decide to use DHCP, configure the details in
in the tab of the dialog of the YaST network card configuration module. If you have a virtual host setup where different hosts communicate through the same interface, an is necessary to distinguish them.DHCP is a good choice for client configuration but it is not ideal for server configuration. To set a static IP address, proceed as follows:
Select a card from the list of detected cards in the
tab of the YaST network card configuration module and click .In the
tab, choose .Enter the
. Both IPv4 and IPv6 addresses can be used. Enter the network mask in . If the IPv6 address is used, use for prefix length in format/64
.Optionally, you can enter a fully qualified
for this address, which will be written to the/etc/hosts
configuration file.Click
.To activate the configuration, click
.
During activation of a network interface, wicked
checks for a carrier and only applies the IP configuration when a link
has been detected. If you need to apply the configuration regardless of
the link status (for example, when you want to test a service listening to a
certain address), you can skip link detection by adding the variable
LINK_REQUIRED=no
to the configuration file of the
interface in /etc/sysconfig/network/ifcfg
.
Additionally, you can use the variable
LINK_READY_WAIT=5
to
specify the timeout for waiting for a link in seconds.
For more information about the ifcfg-*
configuration
files, refer to Section 19.5.2.5, “/etc/sysconfig/network/ifcfg-*
” and
man 5 ifcfg
.
If you use the static address, the name servers and default gateway are not configured automatically. To configure name servers, proceed as described in Section 19.4.1.4, “Configuring host name and DNS”. To configure a gateway, proceed as described in Section 19.4.1.5, “Configuring routing”.
19.4.1.2.2 Configuring multiple addresses #
A single network device can have multiple IP addresses called aliases or labels.
Aliases or labels work with IPv4 only. Using iproute2
network interfaces makes is possible to have one or more addresses.
To set additional addresses for your network card using YaST, proceed as follows:
Select a card from the list of detected cards in the
tab of the YaST dialog and click .In the
› tab, click .Enter
, , and . Note that IP aliases must be added with the/32
netmask. Do not include the interface name in the alias name.To activate the configuration, confirm the settings.
19.4.1.2.3 Changing the device name and udev rules #
It is possible to change the device name of the network card when it is used. It is also possible to determine whether the network card should be identified by udev via its hardware (MAC) address or via the bus ID. The latter option is preferable in large servers to simplify hotplugging of cards. To set these options with YaST, proceed as follows:
Select a card from the list of detected cards in the
tab of the YaST dialog and click .Go to the
tab. The current device name is shown in . Click .Select whether udev should identify the card by its
or . The current MAC address and bus ID of the card are shown in the dialog.To change the device name, check the
option and edit the name.To activate the configuration, confirm the settings.
19.4.1.2.4 Changing network card kernel driver #
For some network cards, several kernel drivers may be available. If the card is already configured, YaST allows you to select a kernel driver to be used from a list of available suitable drivers. It is also possible to specify options for the kernel driver. To set these options with YaST, proceed as follows:
Select a card from the list of detected cards in the
tab of the YaST Network Settings module and click .Go to the
tab.Select the kernel driver to be used in
. Enter any options for the selected driver in in the form=
=VALUE. If more options are used, they should be space-separated.To activate the configuration, confirm the settings.
19.4.1.2.5 Activating the network device #
If you use the method with wicked
, you can configure
your device to either start during boot, on cable connection, on card
detection, manually, or never. To change device start-up, proceed as
follows:
In YaST select a card from the list of detected cards in
› and click .In the
tab, select the desired entry from .Choose
to start the device during the system boot. With , the interface is watched for any existing physical connection. With , the interface is set when available. It is similar to the option, and only differs in that no error occurs if the interface is not present at boot time. Choose to control the interface manually withifup
. Choose to not start the device. The is similar to , but the interface does not shut down with thesystemctl stop network
command; thenetwork
service also cares about thewicked
service ifwicked
is active. Use this if you use an NFS or iSCSI root file system.To activate the configuration, confirm the settings.
On (diskless) systems where the root partition is mounted via network as an NFS share, you need to be careful when configuring the network device with which the NFS share is accessible.
When shutting down or rebooting the system, the default processing order is to turn off network connections, then unmount the root partition. With NFS root, this order causes problems as the root partition cannot be cleanly unmounted as the network connection to the NFS share is already not activated. To prevent the system from deactivating the relevant network device, open the network device configuration tab as described in Section 19.4.1.2.5, “Activating the network device” and choose in the pane.
19.4.1.2.6 Setting up maximum transfer unit size #
You can set a maximum transmission unit (MTU) for the interface. MTU refers to the largest allowed packet size in bytes. A higher MTU brings higher bandwidth efficiency. However, large packets can block up a slow interface for some time, increasing the lag for further packets.
In YaST select a card from the list of detected cards in
› and click .In the
tab, select the desired entry from the list.To activate the configuration, confirm the settings.
19.4.1.2.7 PCIe multifunction devices #
Multifunction devices that support LAN, iSCSI, and FCoE are supported.
The YaST FCoE client (yast2 fcoe-client
) shows the
private flags in additional columns to allow the user to select the device
meant for FCoE. The YaST network module (yast2 lan
)
excludes “storage only devices” for network configuration.
For more information about FCoE, see Book “Storage Administration Guide”, Chapter 16 “Fibre Channel storage over Ethernet networks: FCoE”, Section 16.3 “Managing FCoE services with YaST”.
19.4.1.2.8 Infiniband configuration for IP-over-InfiniBand (IPoIB) #
In YaST select the InfiniBand device in
› and click .In the
tab, select one of the (IPoIB) modes: (default) or .To activate the configuration, confirm the settings.
For more information about InfiniBand, see
/usr/src/linux/Documentation/infiniband/ipoib.txt
.
19.4.1.2.9 Configuring the firewall #
Without having to perform the detailed firewall setup as described in
Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4 “firewalld
”, you can determine the
basic firewall configuration for your device as part of the device setup.
Proceed as follows:
Open the YaST
› module. In the tab, select a card from the list of detected cards and click .Enter the
tab of the dialog.Determine the
to which your interface should be assigned. The following options are available:- Firewall disabled
This option is available only if the firewall is disabled and the firewall does not run. Only use this option if your machine is part of a greater network that is protected by an outer firewall.
- Automatically assign zone
This option is available only if the firewall is enabled. The firewall is running and the interface is automatically assigned to a firewall zone. The zone which contains the keyword
any
or the external zone will be used for such an interface.- Internal zone (unprotected)
The firewall is running, but does not enforce any rules to protect this interface. Use this option if your machine is part of a greater network that is protected by an outer firewall. It is also useful for the interfaces connected to the internal network, when the machine has more network interfaces.
- Demilitarized zone
A demilitarized zone is an additional line of defense in front of an internal network and the (hostile) Internet. Hosts assigned to this zone can be reached from the internal network and from the Internet, but cannot access the internal network.
- External zone
The firewall is running on this interface and fully protects it against other—presumably hostile—network traffic. This is the default option.
To activate the configuration, confirm the settings.
19.4.1.3 Configuring an undetected network card #
If a network card is not detected correctly, the card is not included in the list of detected cards. If you are sure that your system includes a driver for your card, you can configure it manually. You can also configure special network device types, such as bridge, bond, TUN or TAP. To configure an undetected network card (or a special device) proceed as follows:
In the
› › dialog in YaST click .In the
dialog, set the of the interface from the available options and . If the network card is a USB device, activate the respective check box and exit this dialog with . Otherwise, you can define the kernel to be used for the card and its , if necessary.In
, you can setethtool
options used byifup
for the interface. For information about available options, see theethtool
manual page.If the option string starts with a
-
(for example,-K INTERFACE_NAME rx on
), the second word in the string is replaced with the current interface name. Otherwise (for example,autoneg off speed 10
)ifup
adds-s INTERFACE_NAME
to the beginning.Click
.Configure any needed options, such as the IP address, device activation or firewall zone for the interface in the Section 19.4.1.2, “Changing the configuration of a network card”.
, , and tabs. For more information about the configuration options, seeIf you selected
as the device type of the interface, configure the wireless connection in the next dialog.To activate the new network configuration, confirm the settings.
19.4.1.4 Configuring host name and DNS #
If you did not change the network configuration during installation and the Ethernet card was already available, a host name was automatically generated for your computer and DHCP was activated. The same applies to the name service information your host needs to integrate into a network environment. If DHCP is used for network address setup, the list of domain name servers is automatically filled with the appropriate data. If a static setup is preferred, set these values manually.
To change the name of your computer and adjust the name server search list, proceed as follows:
Go to the
› tab in the module in YaST.Enter the
. Note that the host name is global and applies to all network interfaces.If you are using DHCP to get an IP address, the host name of your computer will be automatically set by the DHCP server. You should disable this behavior if you connect to different networks, because they may assign different host names and changing the host name at runtime may confuse the graphical desktop. To disable using DHCP to get an IP address deactivate
.In
, select the way the DNS configuration (name servers, search list, the content of the/run/netconfig/resolv.conf
file) is modified.If the
option is selected, the configuration is handled by thenetconfig
script which merges the data defined statically (with YaST or in the configuration files) with data obtained dynamically (from the DHCP client or NetworkManager). This default policy is usually sufficient.If the
option is selected,netconfig
is not allowed to modify the/run/netconfig/resolv.conf
file. However, this file can be edited manually.If the
option is selected, a string defining the merge policy should be specified. The string consists of a comma-separated list of interface names to be considered a valid source of settings. Except for complete interface names, basic wild cards to match multiple interfaces are allowed, as well. For example,eth* ppp?
will first target all eth and then all ppp0-ppp9 interfaces. There are two special policy values that indicate how to apply the static settings defined in the/etc/sysconfig/network/config
file:STATIC
The static settings need to be merged together with the dynamic settings.
STATIC_FALLBACK
The static settings are used only when no dynamic configuration is available.
For more information, see the man page of
netconfig
(8) (man 8 netconfig
).Enter the
and fill in the list. Name servers must be specified by IP addresses, such as 192.168.1.116, not by host names. Names specified in the tab are domain names used for resolving host names without a specified domain. If more than one is used, separate domains with commas or white space.To activate the configuration, confirm the settings.
It is also possible to edit the host name using YaST from the command
line. The changes made by YaST take effect immediately (which is not the
case when editing the /etc/HOSTNAME
file manually). To
change the host name, use the following command:
#
yast dns edit hostname=HOSTNAME
To change the name servers, use the following commands:
#
yast dns edit nameserver1=192.168.1.116#
yast dns edit nameserver2=192.168.1.117#
yast dns edit nameserver3=192.168.1.118
19.4.1.5 Configuring routing #
To make your machine communicate with other machines and other networks, routing information must be given to make network traffic take the correct path. If DHCP is used, this information is automatically provided. If a static setup is used, this data must be added manually.
In YaST go to
› .Enter the IP address of the
(IPv4 and IPv6 if necessary). The default gateway matches every possible destination, but if a routing table entry exists that matches the required address, this will be used instead of the default route via the Default Gateway.More entries can be entered in the
. Enter the network IP address, IP address and the . Select the through which the traffic to the defined network will be routed (the minus sign stands for any device). To omit any of these values, use the minus sign-
. To enter a default gateway into the table, usedefault
in the field.Note: Route prioritizationIf more default routes are used, it is possible to specify the metric option to determine which route has a higher priority. To specify the metric option, enter
- metric NUMBER
in . The lowest possible metric is 0. The route with the lowest metric has the highest priority and is used as default. If the network device is disconnected, its route will be removed and the next one will be used.If the system is a router, enable
and in the as needed.To activate the configuration, confirm the settings.
19.4.2 IBM Z: configuring network devices #
SUSE Linux Enterprise Server for IBM Z supports several types of network interfaces. YaST can be used to configure all of them.
19.4.2.1 The qeth-hsi device #
To add a qeth-hsi
(HiperSockets) interface to the
installed system, start the › module in YaST. Select
one of the devices marked to use as the READ
device address and click . Enter the device numbers
for the read, write and control channels (example device number format:
0.0.0800
). Then click next. In the dialog, specify the IP address and netmask for the
new interface and leave the network configuration by clicking
and .
19.4.2.2 The qeth-ethernet device #
To add a qeth-ethernet
(IBM OSA Express Ethernet Card)
interface to the installed system, start the ›
module in YaST. Select one of the devices marked to use as the READ device address and click
. Enter a device number for the read, write and
control channels (example device number format:
0.0.0700
). Enter the needed port name, port number (if
applicable) and some additional options, your IP address, and an appropriate
netmask. Leave the network configuration with and
.
19.4.2.3 The ctc device #
To add a ctc
(IBM parallel CTC Adapter) interface to the
installed system, start the › module in YaST. Select
one of the devices marked to use
as your read channel and click . Choose the
that fit your devices (usually this would
be ). Specify both your IP address and
the IP address of the remote partner. If needed, adjust the MTU size with
› . Leave the network configuration with
and .
The use of this interface is deprecated. This interface will not be supported in future versions of SUSE Linux Enterprise Server.
19.4.2.4 The lcs device #
To add an lcs
(IBM OSA-2 Adapter) interface to the
installed system, start the › module in YaST. Select
one of the devices marked and click
. Enter the needed port number, some additional
options, your IP address and an appropriate netmask. Leave the network
configuration with and .
19.4.2.5 The IUCV device #
To add an iucv
(IUCV) interface to the installed system,
start the › module in YaST. Select a device marked
and click . YaST prompts
you for the name of your IUCV partner ( ). Enter the
name (this entry is case-sensitive) and select .
Specify both the and the of your partner. If needed,
size on tab. Leave the network configuration with
and .
The use of this interface is deprecated. This interface will not be supported in future versions of SUSE Linux Enterprise Server.
19.5 Configuring a network connection manually #
Manual configuration of the network software should be the last alternative. Using YaST is recommended. However, this background information about the network configuration can also assist your work with YaST.
19.5.1 The wicked
network configuration #
The tool and library called wicked
provides a new
framework for network configuration.
One of the challenges with traditional network interface management is that different layers of network management get jumbled together into one single script, or at most two different scripts. These scripts interact with each other in a way that is not well defined. This leads to unpredictable issues, obscure constraints and conventions, etc. Several layers of special hacks for a variety of different scenarios increase the maintenance burden. Address configuration protocols are being used that are implemented via daemons like dhcpcd, which interact rather poorly with the rest of the infrastructure. Funky interface naming schemes that require heavy udev support are introduced to achieve persistent identification of interfaces.
The idea of wicked is to decompose the problem in several ways. None of them is entirely novel, but trying to put ideas from different projects together is hopefully going to create a better solution overall.
One approach is to use a client/server model. This allows wicked to define standardized facilities for things like address configuration that are well integrated with the overall framework. For example, using a specific address configuration, the administrator may request that an interface should be configured via DHCP or IPv4 zeroconf. In this case, the address configuration service simply obtains the lease from its server and passes it on to the wicked server process that installs the requested addresses and routes.
The other approach to decomposing the problem is to enforce the layering aspect. For any type of network interface, it is possible to define a dbus service that configures the network interface's device layer—a VLAN, a bridge, a bonding, or a paravirtualized device. Common functionality, such as address configuration, is implemented by joint services that are layered on top of these device specific services without having to implement them specifically.
The wicked framework implements these two aspects by using a variety of dbus services, which get attached to a network interface depending on its type. Here is a rough overview of the current object hierarchy in wicked.
Each network interface is represented via a child object of
/org/opensuse/Network/Interfaces
. The name of the
child object is given by its ifindex. For example, the loopback interface,
which usually gets ifindex 1, is
/org/opensuse/Network/Interfaces/1
, the first
Ethernet interface registered is
/org/opensuse/Network/Interfaces/2
.
Each network interface has a “class” associated with it, which
is used to select the dbus interfaces it supports. By default, each network
interface is of class netif
, and
wickedd
will automatically
attach all interfaces compatible with this class. In the current
implementation, this includes the following interfaces:
- org.opensuse.Network.Interface
Generic network interface functions, such as taking the link up or down, assigning an MTU, etc.
- org.opensuse.Network.Addrconf.ipv4.dhcp, org.opensuse.Network.Addrconf.ipv6.dhcp, org.opensuse.Network.Addrconf.ipv4.auto
Address configuration services for DHCP, IPv4 zeroconf, etc.
Beyond this, network interfaces may require or offer special configuration
mechanisms. For an Ethernet device, for example, you should be able to
control the link speed, offloading of checksumming, etc. To achieve this,
Ethernet devices have a class of their own, called
netif-ethernet
, which is a subclass of
netif
. As a consequence, the dbus interfaces assigned to
an Ethernet interface include all the services listed above, plus the
org.opensuse.Network.Ethernet
service available only to objects belonging to the netif-ethernet
class.
Similarly, there exist classes for interface types like bridges, VLANs, bonds, or infinibands.
How do you interact with an interface like VLAN (which is really a virtual network interface that
sits on top of an Ethernet device) that needs to be created
first? For this, wicked defines factory
interfaces, such as
org.opensuse.Network.VLAN.Factory
. Such a factory
interface offers a single function that lets you create an interface of the
requested type. These factory interfaces are attached to the
/org/opensuse/Network/Interfaces
list node.
19.5.1.1 wicked
architecture and features #
The wicked
service comprises several parts as depicted
in Figure 19.4, “wicked
architecture”.
wicked
architecture #
wicked
currently supports the following:
Configuration file back-ends to parse SUSE style
/etc/sysconfig/network
files.An internal configuration back-end to represent network interface configuration in XML.
Bring up and shutdown of “normal” network interfaces such as Ethernet or InfiniBand, VLAN, bridge, bonds, tun, tap, dummy, macvlan, macvtap, hsi, qeth, iucv, and wireless (currently limited to one wpa-psk/eap network) devices.
A built-in DHCPv4 client and a built-in DHCPv6 client.
The nanny daemon (enabled by default) helps to automatically bring up configured interfaces when the device is available (interface hotplugging) and set up the IP configuration when a link (carrier) is detected. See Section 19.5.1.3, “Nanny” for more information.
wicked
was implemented as a group of DBus services that are integrated with systemd. So the usualsystemctl
commands will apply towicked
.
19.5.1.2 Using wicked
#
On SUSE Linux Enterprise, wicked
runs by default. If you want to check
what is currently enabled and whether it is running, call:
systemctl status network
If wicked
is enabled, you will see something along these
lines:
wicked.service - wicked managed network interfaces Loaded: loaded (/usr/lib/systemd/system/wicked.service; enabled) ...
In case something different is running (for example, NetworkManager) and you want to
switch to wicked
, first stop what is running and then
enable wicked
:
systemctl is-active network && \ systemctl stop network systemctl enable --force wicked
This enables the wicked services, creates the
network.service
to wicked.service
alias link, and starts the network at the next boot.
Starting the server process:
systemctl start wickedd
This starts wickedd
(the main server) and associated
supplicants:
/usr/lib/wicked/bin/wickedd-auto4 --systemd --foreground /usr/lib/wicked/bin/wickedd-dhcp4 --systemd --foreground /usr/lib/wicked/bin/wickedd-dhcp6 --systemd --foreground /usr/sbin/wickedd --systemd --foreground /usr/sbin/wickedd-nanny --systemd --foreground
Then bringing up the network:
systemctl start wicked
Alternatively use the network.service
alias:
systemctl start network
These commands are using the default or system configuration sources as
defined in /etc/wicked/client.xml
.
To enable debugging, set WICKED_DEBUG
in
/etc/sysconfig/network/config
, for example:
WICKED_DEBUG="all"
Or, to omit some:
WICKED_DEBUG="all,-dbus,-objectmodel,-xpath,-xml"
Use the client utility to display interface information for all interfaces or the interface specified with IFNAME:
wicked show all wicked show IFNAME
In XML output:
wicked show-xml all wicked show-xml IFNAME
Bringing up one interface:
wicked ifup eth0 wicked ifup wlan0 ...
Because there is no configuration source specified, the wicked client
checks its default sources of configuration defined in
/etc/wicked/client.xml
:
firmware:
iSCSI Boot Firmware Table (iBFT)compat:
ifcfg
files—implemented for compatibility
Whatever wicked
gets from those sources for a given
interface is applied. The intended order of importance is
firmware
, then compat
—this may
be changed in the future.
For more information, see the wicked
man page.
19.5.1.3 Nanny #
Nanny is an event and policy driven daemon that is responsible for
asynchronous or unsolicited scenarios such as hotplugging devices. Thus the
nanny daemon helps with starting or restarting delayed or temporarily gone
devices. Nanny monitors device and link changes, and integrates new devices
defined by the current policy set. Nanny continues to set up even if
ifup
already exited because of specified timeout
constraints.
By default, the nanny daemon is active on the system. It is enabled in the
/etc/wicked/common.xml
configuration file:
<config> ... <use-nanny>true</use-nanny> </config>
This setting causes ifup and ifreload to apply a policy with the effective
configuration to the nanny daemon; then, nanny configures
wickedd
and thus ensures
hotplug support. It waits in the background for events or changes (such as
new devices or carrier on).
19.5.1.4 Bringing up multiple interfaces #
For bonds and bridges, it may make sense to define the entire device topology in one file (ifcfg-bondX), and bring it up in one go. wicked then can bring up the whole configuration if you specify the top level interface names (of the bridge or bond):
wicked ifup br0
This command automatically sets up the bridge and its dependencies in the appropriate order without the need to list the dependencies (ports, etc.) separately.
To bring up multiple interfaces in one command:
wicked ifup bond0 br0 br1 br2
Or also all interfaces:
wicked ifup all
19.5.1.5 Using tunnels with Wicked #
When you need to use tunnels with Wicked, the TUNNEL_DEVICE
is used for this. It permits to specify an optional device name to bind
the tunnel to the device. The tunneled packets will only be routed via this
device.
For more information, refer to man 5 ifcfg-tunnel
.
19.5.1.6 Handling incremental changes #
With wicked
, there is no need to actually take down an
interface to reconfigure it (unless it is required by the kernel). For
example, to add another IP address or route to a statically configured
network interface, add the IP address to the interface definition, and do
another “ifup” operation. The server will try hard to update
only those settings that have changed. This applies to link-level options
such as the device MTU or the MAC address, and network-level settings, such
as addresses, routes, or even the address configuration mode (for example,
when moving from a static configuration to DHCP).
Things get tricky of course with virtual interfaces combining several real devices such as bridges or bonds. For bonded devices, it is not possible to change certain parameters while the device is up. Doing that will result in an error.
However, what should still work, is the act of adding or removing the child devices of a bond or bridge, or choosing a bond's primary interface.
19.5.1.7 Wicked extensions: address configuration #
wicked
is designed to be extensible with shell scripts.
These extensions can be defined in the config.xml
file.
Currently, several classes of extensions are supported:
link configuration: these are scripts responsible for setting up a device's link layer according to the configuration provided by the client, and for tearing it down again.
address configuration: these are scripts responsible for managing a device's address configuration. Usually address configuration and DHCP are managed by
wicked
itself, but can be implemented by means of extensions.firewall extension: these scripts can apply firewall rules.
Typically, extensions have a start and a stop command, an optional “pid file”, and a set of environment variables that get passed to the script.
To illustrate how this is supposed to work, look at a firewall extension
defined in etc/server.xml
:
<dbus-service interface="org.opensuse.Network.Firewall"> <action name="firewallUp" command="/etc/wicked/extensions/firewall up"/> <action name="firewallDown" command="/etc/wicked/extensions/firewall down"/> <!-- default environment for all calls to this extension script --> <putenv name="WICKED_OBJECT_PATH" value="$object-path"/> <putenv name="WICKED_INTERFACE_NAME" value="$property:name"/> <putenv name="WICKED_INTERFACE_INDEX" value="$property:index"/> </dbus-service>
The extension is attached to the
<dbus-service>
tag and defines commands to execute for the actions of this interface.
Further, the declaration can define and initialize environment variables
passed to the actions.
19.5.1.8 Wicked extensions: configuration files #
You can extend the handling of configuration files with scripts as well.
For example, DNS updates from leases are ultimately handled by the
extensions/resolver
script, with behavior configured
in server.xml
:
<system-updater name="resolver"> <action name="backup" command="/etc/wicked/extensions/resolver backup"/> <action name="restore" command="/etc/wicked/extensions/resolver restore"/> <action name="install" command="/etc/wicked/extensions/resolver install"/> <action name="remove" command="/etc/wicked/extensions/resolver remove"/> </system-updater>
When an update arrives in wickedd
, the system
updater routines parse the lease and call the appropriate commands
(backup
, install
, etc.) in the
resolver script. This in turn configures the DNS settings using
/sbin/netconfig
, or by manually writing
/run/netconfig/resolv.conf
as a fallback.
19.5.2 Configuration files #
This section provides an overview of the network configuration files and explains their purpose and the format used.
19.5.2.1 /etc/wicked/common.xml
#
The /etc/wicked/common.xml
file contains common
definitions that should be used by all applications. It is sourced/included
by the other configuration files in this directory. Although you can use
this file to enable debugging across all
wicked
components, we recommend to use the file
/etc/wicked/local.xml
for this purpose. After applying
maintenance updates you might lose your changes as the
/etc/wicked/common.xml
might be overwritten. The
/etc/wicked/common.xml
file includes the
/etc/wicked/local.xml
in the default installation, thus
you typically do not need to modify the
/etc/wicked/common.xml
.
In case you want to disable nanny
by setting the
<use-nanny>
to false
, restart
the wickedd.service
and then run the following command to
apply all configurations and policies:
>
sudo
wicked ifup all
The wickedd
, wicked
, or
nanny
programs try to read
/etc/wicked/common.xml
if their own configuration
files do not exist.
19.5.2.2 /etc/wicked/server.xml
#
The file /etc/wicked/server.xml
is read by the
wickedd
server process at start-up. The file stores
extensions to the /etc/wicked/common.xml
. On top of
that this file configures handling of a resolver and receiving information
from addrconf
supplicants, for example DHCP.
We recommend to add changes required to this file into a separate file
/etc/wicked/server-local.xml
, that gets included by
/etc/wicked/server.xml
. By using a separate file
you avoid overwriting of your changes during maintenance updates.
19.5.2.3 /etc/wicked/client.xml
#
The /etc/wicked/client.xml
is used by the
wicked
command. The file specifies the location of a
script used when discovering devices managed by ibft and configures
locations of network interface configurations.
We recommend to add changes required to this file into a separate file
/etc/wicked/client-local.xml
, that gets included by
/etc/wicked/server.xml
. By using a separate file
you avoid overwriting of your changes during maintenance updates.
19.5.2.4 /etc/wicked/nanny.xml
#
The /etc/wicked/nanny.xml
configures types of link
layers. We recommend to add specific configuration into a separate file:
/etc/wicked/nanny-local.xml
to avoid losing the changes
during maintenance updates.
19.5.2.5 /etc/sysconfig/network/ifcfg-*
#
These files contain the traditional configurations for network interfaces.
wicked
and the ifcfg-*
files
wicked
reads these files if you specify the
compat:
prefix. According to the SUSE Linux Enterprise Server default
configuration in /etc/wicked/client.xml
,
wicked
tries these files before the XML configuration
files in /etc/wicked/ifconfig
.
The --ifconfig
switch is provided mostly for testing only.
If specified, default configuration sources defined in
/etc/wicked/ifconfig
are not applied.
The ifcfg-*
files include information such as the start
mode and the IP address. Possible parameters are described in the manual
page of ifup
. Additionally, most variables from the
dhcp
and wireless
files can be
used in the ifcfg-*
files if a general setting should
be used for only one interface. However, most of the
/etc/sysconfig/network/config
variables are global and
cannot be overridden in ifcfg
files. For example,
NETCONFIG_*
variables are global.
For configuring macvlan
and
macvtab
interfaces, see the
ifcfg-macvlan
and
ifcfg-macvtap
man pages. For example, for a macvlan
interface provide a ifcfg-macvlan0
with settings as
follows:
STARTMODE='auto' MACVLAN_DEVICE='eth0' #MACVLAN_MODE='vepa' #LLADDR=02:03:04:05:06:aa
For ifcfg.template
, see
Section 19.5.2.6, “/etc/sysconfig/network/config
, /etc/sysconfig/network/dhcp
, and /etc/sysconfig/network/wireless
”.
IBM Z
IBM Z does not support USB. The names of the interface files and
network aliases contain IBM Z-specific elements like
qeth
.
19.5.2.6 /etc/sysconfig/network/config
, /etc/sysconfig/network/dhcp
, and /etc/sysconfig/network/wireless
#
The file config
contains general settings for the
behavior of ifup
, ifdown
and
ifstatus
. dhcp
contains settings for
DHCP and wireless
for wireless LAN cards. The variables
in all three configuration files are commented. Some variables from
/etc/sysconfig/network/config
can also be used in
ifcfg-*
files, where they are given a higher priority.
The /etc/sysconfig/network/ifcfg.template
file lists
variables that can be specified in a per interface scope. However, most of
the /etc/sysconfig/network/config
variables are global
and cannot be overridden in ifcfg-files. For example,
NETWORKMANAGER
or
NETCONFIG_*
variables are global.
In SUSE Linux Enterprise 11, DHCPv6 used to work even on networks where IPv6 Router Advertisements (RAs) were not configured properly. Starting withSUSE Linux Enterprise 12, DHCPv6 requires that at least one of the routers on the network sends out RAs that indicate that this network is managed by DHCPv6.
For networks where the router cannot be configured correctly, the ifcfg
option allows the user to override this
behavior by specifying DHCLIENT6_MODE='managed'
in the
ifcfg
file.
You can also activate this workaround with a boot parameter in the
installation system:
ifcfg=eth0=dhcp6,DHCLIENT6_MODE=managed
19.5.2.7 /etc/sysconfig/network/routes
and /etc/sysconfig/network/ifroute-*
#
The static routing of TCP/IP packets is determined by the
/etc/sysconfig/network/routes
and
/etc/sysconfig/network/ifroute-*
files. All the static
routes required by the various system tasks can be specified in
/etc/sysconfig/network/routes
: routes to a host, routes
to a host via a gateway and routes to a network. For each interface that
needs individual routing, define an additional configuration file:
/etc/sysconfig/network/ifroute-*
. Replace the wild card
(*
) with the name of the interface. The entries in the
routing configuration files look like this:
# Destination Gateway Netmask Interface Options
The route's destination is in the first column. This column may contain the
IP address of a network or host or, in the case of
reachable name servers, the fully qualified network or
host name. The network should be written in CIDR notation (address with the
associated routing prefix-length) such as 10.10.0.0/16 for IPv4 or fc00::/7
for IPv6 routes. The keyword default
indicates that the
route is the default gateway in the same address family as the gateway. For
devices without a gateway use explicit 0.0.0.0/0 or ::/0 destinations.
The second column contains the default gateway or a gateway through which a host or network can be accessed.
The third column is deprecated; it used to contain the IPv4 netmask of the
destination. For IPv6 routes, the default route, or when using a
prefix-length (CIDR notation) in the first column, enter a dash
(-
) here.
The fourth column contains the name of the interface. If you leave it empty
using a dash (-
), it can cause unintended behavior in
/etc/sysconfig/network/routes
. For more information,
see the routes
man page.
An (optional) fifth column can be used to specify special options. For
details, see the routes
man page.
# --- IPv4 routes in CIDR prefix notation: # Destination [Gateway] - Interface 127.0.0.0/8 - - lo 204.127.235.0/24 - - eth0 default 204.127.235.41 - eth0 207.68.156.51/32 207.68.145.45 - eth1 192.168.0.0/16 207.68.156.51 - eth1 # --- IPv4 routes in deprecated netmask notation" # Destination [Dummy/Gateway] Netmask Interface # 127.0.0.0 0.0.0.0 255.255.255.0 lo 204.127.235.0 0.0.0.0 255.255.255.0 eth0 default 204.127.235.41 0.0.0.0 eth0 207.68.156.51 207.68.145.45 255.255.255.255 eth1 192.168.0.0 207.68.156.51 255.255.0.0 eth1 # --- IPv6 routes are always using CIDR notation: # Destination [Gateway] - Interface 2001:DB8:100::/64 - - eth0 2001:DB8:100::/32 fe80::216:3eff:fe6d:c042 - eth0
19.5.2.8 /var/run/netconfig/resolv.conf
#
The domain to which the host belongs is specified in
/var/run/netconfig/resolv.conf
(keyword
search
). Up to six domains with a total of 256
characters can be specified with the search
option.
When resolving a name that is not fully qualified, an attempt is made to
generate one by attaching the individual search
entries. Up to three name servers can be specified with the
nameserver
option, each on a line of its own.
Comments are preceded by hash mark or semicolon signs (#
or ;
). As an example, see
Example 19.6, “/var/run/netconfig/resolv.conf
”.
However, /etc/resolv.conf
should not be edited by
hand. It is generated by the netconfig
script and is a
symbolic link to /run/netconfig/resolv.conf
.
To define static DNS configuration without using YaST, edit the
appropriate variables manually in the
/etc/sysconfig/network/config
file:
NETCONFIG_DNS_STATIC_SEARCHLIST
list of DNS domain names used for host name lookup
NETCONFIG_DNS_STATIC_SERVERS
list of name server IP addresses to use for host name lookup
NETCONFIG_DNS_FORWARDER
the name of the DNS forwarder that needs to be configured, for example
bind
orresolver
NETCONFIG_DNS_RESOLVER_OPTIONS
arbitrary options that will be written to
/var/run/netconfig/resolv.conf
, for example:debug attempts:1 timeout:10
For more information, see the
resolv.conf
man page.NETCONFIG_DNS_RESOLVER_SORTLIST
list of up to 10 items, for example:
130.155.160.0/255.255.240.0 130.155.0.0
For more information, see the
resolv.conf
man page.
To disable DNS configuration using netconfig, set
NETCONFIG_DNS_POLICY=''
. For more information about
netconfig
, see the netconfig(8)
man page (man 8 netconfig
).
/var/run/netconfig/resolv.conf
## Our domain search example.com # # We use dns.example.com (192.168.1.116) as nameserver nameserver 192.168.1.116
19.5.2.9 /sbin/netconfig
#
netconfig
is a modular tool to manage additional network
configuration settings. It merges statically defined settings with settings
provided by autoconfiguration mechanisms as DHCP or PPP according to a
predefined policy. The required changes are applied to the system by calling
the netconfig modules that are responsible for modifying a configuration
file and restarting a service or a similar action.
netconfig
recognizes three main actions. The
netconfig modify
and netconfig remove
commands are used by daemons such as DHCP or PPP to provide or remove
settings to netconfig. Only the netconfig update
command
is available for the user:
modify
The
netconfig modify
command modifies the current interface and service specific dynamic settings and updates the network configuration. Netconfig reads settings from standard input or from a file specified with the--lease-file FILENAME
option and internally stores them until a system reboot (or the next modify or remove action). Already existing settings for the same interface and service combination are overwritten. The interface is specified by the-i INTERFACE_NAME
parameter. The service is specified by the-s SERVICE_NAME
parameter.remove
The
netconfig remove
command removes the dynamic settings provided by an editing action for the specified interface and service combination and updates the network configuration. The interface is specified by the-i INTERFACE_NAME
parameter. The service is specified by the-s SERVICE_NAME
parameter.update
The
netconfig update
command updates the network configuration using current settings. This is useful when the policy or the static configuration has changed. Use the-m MODULE_TYPE
parameter to update a specified service only (dns
,nis
, orntp
).
The netconfig policy and the static configuration settings are defined
either manually or using YaST in the
/etc/sysconfig/network/config
file. The dynamic
configuration settings provided by autoconfiguration tools such as DHCP or
PPP are delivered directly by these tools with the netconfig
modify
and netconfig remove
actions.
When NetworkManager is enabled, netconfig (in policy mode auto
)
uses only NetworkManager settings, ignoring settings from any other interfaces
configured using the traditional ifup method. If NetworkManager does not provide any
setting, static settings are used as a fallback. A mixed usage of NetworkManager and
the wicked
method is not supported.
For more information about netconfig
, see man 8
netconfig
.
19.5.2.10 /etc/hosts
#
In this file, shown in Example 19.7, “/etc/hosts
”, IP addresses
are assigned to host names. If no name server is implemented, all hosts to
which an IP connection will be set up must be listed here. For each host,
enter a line consisting of the IP address, the fully qualified host name,
and the host name into the file. The IP address must be at the beginning of
the line and the entries separated by blanks and tabs. Comments are always
preceded by the #
sign.
/etc/hosts
#127.0.0.1 localhost 192.168.2.100 jupiter.example.com jupiter 192.168.2.101 venus.example.com venus
19.5.2.11 /etc/networks
#
Here, network names are converted to network addresses. The format is
similar to that of the hosts
file, except the network
names precede the addresses. See Example 19.8, “/etc/networks
”.
/etc/networks
#loopback 127.0.0.0 localnet 192.168.0.0
19.5.2.12 /etc/host.conf
#
Name resolution—the translation of host and network names via the
resolver library—is controlled by this file. This
file is only used for programs linked to libc4 or libc5. For current glibc
programs, refer to the settings in /etc/nsswitch.conf
.
Each parameter must always be entered on a separate line. Comments are
preceded by a #
sign.
Table 19.2, “Parameters for /etc/host.conf” shows the parameters available. A
sample /etc/host.conf
is shown in
Example 19.9, “/etc/host.conf
”.
order hosts, bind |
Specifies in which order the services are accessed for the name resolution. Available arguments are (separated by blank spaces or commas): |
hosts: searches the
| |
bind: accesses a name server | |
nis: uses NIS | |
multi on/off |
Defines if a host entered in |
nospoof on spoofalert on/off |
These parameters influence the name server spoofing but do not exert any influence on the network configuration. |
trim domainname |
The specified domain name is separated from the host name after host
name resolution (as long as the host name includes the domain name).
This option is useful only if names from the local domain are in the
|
/etc/host.conf
## We have named running order hosts bind # Allow multiple address multi on
19.5.2.13 /etc/nsswitch.conf
#
The introduction of the GNU C Library 2.0 was accompanied by the
introduction of the Name Service Switch (NSS). Refer to
the nsswitch.conf(5)
man page and The GNU
C Library Reference Manual for details.
The order for queries is defined in the file
/etc/nsswitch.conf
. A sample
nsswitch.conf
is shown in
Example 19.10, “/etc/nsswitch.conf
”. Comments are preceded by
#
signs. In this example, the entry under the
hosts
database means that a request is sent to
/etc/hosts
(files
) via
DNS (see Chapter 31, The domain name system).
/etc/nsswitch.conf
#passwd: compat group: compat hosts: files dns networks: files dns services: db files protocols: db files rpc: files ethers: files netmasks: files netgroup: files nis publickey: files bootparams: files automount: files nis aliases: files nis shadow: compat
The “databases” available over NSS are listed in Table 19.3, “Databases available via /etc/nsswitch.conf”. The configuration options for NSS databases are listed in Table 19.4, “Configuration options for NSS “databases””.
|
Mail aliases implemented by |
|
Ethernet addresses. |
|
List of networks and their subnet masks. Only needed, if you use subnetting. |
|
User groups used by |
|
Host names and IP addresses, used by |
|
Valid host and user lists in the network for controlling access
permissions; see the |
|
Network names and addresses, used by |
|
Public and secret keys for Secure_RPC used by NFS and NIS+. |
|
User passwords, used by |
|
Network protocols, used by |
|
Remote procedure call names and addresses, used by
|
|
Network services, used by |
|
Shadow passwords of users, used by |
|
directly access files, for example, |
|
access via a database |
|
NIS, see also Book “Security and Hardening Guide”, Chapter 3 “Using NIS” |
|
can only be used as an extension for |
|
can only be used as an extension for |
19.5.2.14 /etc/nscd.conf
#
This file is used to configure nscd (name service cache daemon). See the
nscd(8)
and nscd.conf(5)
man pages. By default, the system entries of passwd
,
groups
and hosts
are cached by nscd. This is important for the
performance of directory services, like NIS and LDAP, because otherwise the
network connection needs to be used for every access to names, groups or
hosts.
If the caching for passwd
is activated, it usually takes
about fifteen seconds until a newly added local user is recognized. Reduce
this waiting time by restarting nscd with:
>
sudo
systemctl restart nscd
19.5.2.15 /etc/HOSTNAME
#
/etc/HOSTNAME
contains the fully qualified host name
(FQHN). The fully qualified host name is the host name with the domain name
attached. This file must contain only one line (in which the host name is
set). It is read while the machine is booting.
19.5.3 Testing the configuration #
Before you write your configuration to the configuration files, you can test
it. To set up a test configuration, use the ip
command.
To test the connection, use the ping
command.
The command ip
changes the network configuration directly
without saving it in the configuration file. Unless you enter your
configuration in the correct configuration files, the changed network
configuration is lost on reboot.
ifconfig
and route
are obsolete
The ifconfig
and route
tools are
obsolete. Use ip
instead. ifconfig
,
for example, limits interface names to 9 characters.
19.5.3.1 Configuring a network interface with ip
#
ip
is a tool to show and configure network devices,
routing, policy routing, and tunnels.
ip
is a very complex tool. Its common syntax is
ip
OPTIONS
OBJECT
COMMAND
. You can work with the
following objects:
- link
This object represents a network device.
- address
This object represents the IP address of device.
- neighbor
This object represents an ARP or NDISC cache entry.
- route
This object represents the routing table entry.
- rule
This object represents a rule in the routing policy database.
- maddress
This object represents a multicast address.
- mroute
This object represents a multicast routing cache entry.
- tunnel
This object represents a tunnel over IP.
If no command is given, the default command is used (usually
list
).
Change the state of a device with the command:
>
sudo
ip link set DEV_NAME
For example, to deactivate device eth0, enter
>
sudo
ip link set eth0 down
To activate it again, use
>
sudo
ip link set eth0 up
If you deactivate a device with
>
sudo
ip link set DEV_NAME down
it disables the network interface on a software level.
If you want to simulate losing the link as if the Ethernet cable is unplugged or the connected switch is turned off, run
>
sudo
ip link set DEV_NAME carrier off
For example, while ip link set
DEV_NAME down
drops all routes using
DEV_NAME, ip link set DEV carrier
off
does not. Be aware that carrier off
requires support from the network device driver.
To connect the device back to the physical network, run
>
sudo
ip link set DEV_NAME carrier on
After activating a device, you can configure it. To set the IP address, use
>
sudo
ip addr add IP_ADDRESS + dev DEV_NAME
For example, to set the address of the interface eth0 to 192.168.12.154/30
with standard broadcast (option brd
), enter
>
sudo
ip addr add 192.168.12.154/30 brd + dev eth0
To have a working connection, you must also configure the default gateway. To set a gateway for your system, enter
>
sudo
ip route add default via gateway_ip_address
To display all devices, use
>
sudo
ip link ls
To display the running interfaces only, use
>
sudo
ip link ls up
To print interface statistics for a device, enter
>
sudo
ip -s link ls DEV_NAME
To view additional useful information, specifically about virtual network devices, enter
>
sudo
ip -d link ls DEV_NAME
Moreover, to view network layer (IPv4, IPv6) addresses of your devices, enter
>
sudo
ip addr
In the output, you can find information about MAC addresses of your devices. To show all routes, use
>
sudo
ip route show
For more information about using ip
, enter
ip
help
or see the
man 8 ip
manual page. The help
option
is also available for all ip
subcommands, such as:
>
sudo
ip addr help
Find the ip
manual in
/usr/share/doc/packages/iproute2/ip-cref.pdf
.
19.5.3.2 Testing a connection with ping #
The ping
command is the standard tool for testing
whether a TCP/IP connection works. It uses the ICMP protocol to send a
small data packet, ECHO_REQUEST datagram, to the destination host,
requesting an immediate reply. If this works, ping
displays a message to that effect. This indicates that the network link is
functioning.
ping
does more than only test the function of the
connection between two computers: it also provides some basic information
about the quality of the connection. In
Example 19.11, “Output of the command ping”, you can see an example of the
ping
output. The second-to-last line contains
information about the number of transmitted packets, packet loss, and total
time of ping
running.
As the destination, you can use a host name or IP address, for example,
ping
example.com
or
ping
192.168.3.100
. The program sends
packets until you press
Ctrl–C.
If you only need to check the functionality of the connection, you can
limit the number of the packets with the -c
option. For
example to limit ping to three packets, enter
ping
-c 3 example.com
.
ping -c 3 example.com PING example.com (192.168.3.100) 56(84) bytes of data. 64 bytes from example.com (192.168.3.100): icmp_seq=1 ttl=49 time=188 ms 64 bytes from example.com (192.168.3.100): icmp_seq=2 ttl=49 time=184 ms 64 bytes from example.com (192.168.3.100): icmp_seq=3 ttl=49 time=183 ms --- example.com ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2007ms rtt min/avg/max/mdev = 183.417/185.447/188.259/2.052 ms
The default interval between two packets is one second. To change the
interval, ping provides the option -i
. For example, to
increase the ping interval to ten seconds, enter
ping
-i 10 example.com
.
In a system with multiple network devices, it is sometimes useful to send
the ping through a specific interface address. To do so, use the
-I
option with the name of the selected device, for
example, ping
-I wlan1
example.com
.
For more options and information about using ping, enter
ping
-h
or see the
ping (8)
man page.
For IPv6 addresses use the ping6
command. Note, to ping
link-local addresses, you must specify the interface with
-I
. The following command works, if the address is
reachable via eth1
:
ping6 -I eth1 fe80::117:21ff:feda:a425
19.5.4 Unit files and start-up scripts #
Apart from the configuration files described above, there are also systemd
unit files and various scripts that load the network services while the
machine is booting. These are started when the system is switched to the
multi-user.target
target. Some of these unit files
and scripts are described in Some unit files and start-up scripts for network programs. For
more information about systemd
, see
Chapter 15, The systemd
daemon and for more information about the
systemd
targets, see the man page of
systemd.special
(man
systemd.special
).
network.target
network.target
is the systemd target for networking, but its mean depends on the settings provided by the system administrator.For more information, see http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget/.
multi-user.target
multi-user.target
is the systemd target for a multiuser system with all required network services.rpcbind
Starts the rpcbind utility that converts RPC program numbers to universal addresses. It is needed for RPC services, such as an NFS server.
ypserv
Starts the NIS server.
ypbind
Starts the NIS client.
/etc/init.d/nfsserver
Starts the NFS server.
/etc/init.d/postfix
Controls the postfix process.
19.6 Basic router setup #
A router is a networking device that delivers and receives data (network packets) to or from more than one network back and forth. You often use a router to connect your local network to the remote network (Internet) or to connect local network segments. With SUSE Linux Enterprise Server you can build a router with features such as NAT (Network Address Translation) or advanced firewalling.
The following are basic steps to turn SUSE Linux Enterprise Server into a router.
Enable forwarding, for example in
/etc/sysctl.d/50-router.conf
net.ipv4.conf.all.forwarding = 1 net.ipv6.conf.all.forwarding = 1
Then provide a static IPv4 and IPv6 IP setup for the interfaces. Enabling forwarding disables several mechanisms, for example IPv6 does not accept an IPv6 RA (router advertisement) anymore, which also prevents the creation of a default route.
In many situations (for example, when you can reach the same network via more than one interface, or when VPN usually is used and already on “normal multi-home hosts”), you must disable the IPv4 reverse path filter (this feature does not currently exist for IPv6):
net.ipv4.conf.all.rp_filter = 0
You can also filter with firewall settings instead.
To accept an IPv6 RA (from the router on an external, uplink, or ISP interface) and create a default (or also a more specific) IPv6 route again, set:
net.ipv6.conf.${ifname}.accept_ra = 2 net.ipv6.conf.${ifname}.autoconf = 0
(Note: “
eth0.42
” needs to be written aseth0/42
in a dot-separated sysfs path.)
More router behavior and forwarding dependencies are described in https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt.
To provide IPv6 on your internal (DMZ) interfaces, and announce yourself as
an IPv6 router and “autoconf networks” to the clients, install
and configure radvd
in
/etc/radvd.conf
, for example:
interface eth0 { IgnoreIfMissing on; # do not fail if interface missed AdvSendAdvert on; # enable sending RAs AdvManagedFlag on; # IPv6 addresses managed via DHCPv6 AdvOtherConfigFlag on; # DNS, NTP... only via DHCPv6 AdvDefaultLifetime 3600; # client default route lifetime of 1 hour prefix 2001:db8:0:1::/64 # (/64 is default and required for autoconf) { AdvAutonomous off; # Disable address autoconf (DHCPv6 only) AdvValidLifetime 3600; # prefix (autoconf addr) is valid 1 h AdvPreferredLifetime 1800; # prefix (autoconf addr) is prefered 1/2 h } }
Configure the firewall to masquerade traffic with NAT from the LAN into the WAN and to block inbound traffic on the WAN interface:
>
sudo
firewall-cmd
--permanent --zone=external --change-interface=WAN_INTERFACE>
sudo
firewall-cmd
--permanent --zone=external --add-masquerade>
sudo
firewall-cmd
--permanent --zone=internal --change-interface=LAN_INTERFACE>
sudo
firewall-cmd
--reload
19.7 Setting up bonding devices #
For some systems, there is a desire to implement network connections that comply to more than the standard data security or availability requirements of a typical Ethernet device. In these cases, several Ethernet devices can be aggregated to a single bonding device.
The configuration of the bonding device is done by means of bonding module
options. The behavior is mainly affected by the mode of the bonding device.
By default, this is active-backup
which means
that a different slave device will become active if the active slave fails.
The following bonding modes are available:
- (balance-rr)
Packets are transmitted in round-robin fashion from the first to the last available interface. Provides fault tolerance and load balancing.
- (active-backup)
Only one network interface is active. If it fails, a different interface becomes active. This setting is the default for SUSE Linux Enterprise Server. Provides fault tolerance.
- (balance-xor)
Traffic is split between all available interfaces based on the following policy:
[(source MAC address XOR'd with destination MAC address XOR packet type ID) modulo slave count]
Requires support from the switch. Provides fault tolerance and load balancing.- (broadcast)
All traffic is broadcast on all interfaces. Requires support from the switch. Provides fault tolerance.
- (802.3ad)
Aggregates interfaces into groups that share the same speed and duplex settings. Requires
ethtool
support in the interface drivers, and a switch that supports and is configured for IEEE 802.3ad Dynamic link aggregation. Provides fault tolerance and load balancing.- (balance-tlb)
Adaptive transmit load balancing. Requires
ethtool
support in the interface drivers but not switch support. Provides fault tolerance and load balancing.- (balance-alb)
Adaptive load balancing. Requires
ethtool
support in the interface drivers but not switch support. Provides fault tolerance and load balancing.
For a more detailed description of the modes, see https://www.kernel.org/doc/Documentation/networking/bonding.txt.
Using bonding devices is only of interest for machines where you have multiple real network cards available. In most configurations, this means that you should use the bonding configuration only in Dom0. Only if you have multiple network cards assigned to a VM Guest system it may also be useful to set up the bond in a VM Guest.
There is a conflict with the tlb/alb bonding configuration and Power firmware. In short, the bonding driver in tlb/alb mode sends Ethernet Loopback packets with both the source and destination MAC addresses listed as the Virtual Ethernet MAC address. These packets are not supported by Power firmware. Therefore bonding modes 5 and 6 are unsupported by ibmveth.
To configure a bonding device, use the following procedure:
Run
› › .Use
and change the to . Proceed with .Select how to assign the IP address to the bonding device. Three methods are at your disposal:
No IP Address
Dynamic Address (with DHCP or Zeroconf)
Statically assigned IP Address
Use the method that is appropriate for your environment.
In the
tab, select the Ethernet devices that should be included into the bond by activating the related check box.Edit the
and choose a bonding mode.Make sure that the parameter
miimon=100
is added to the . Without this parameter, the data integrity is not checked regularly.Click
and leave YaST with to create the device.
19.7.1 Hotplugging of bonding slaves #
In specific network environments (such as High Availability), there are cases when you need to replace a bonding slave interface with another one. The reason may be a constantly failing network device. The solution is to set up hotplugging of bonding slaves.
The bond is configured as usual (according to man 5
ifcfg-bonding
), for example:
ifcfg-bond0 STARTMODE='auto' # or 'onboot' BOOTPROTO='static' IPADDR='192.168.0.1/24' BONDING_MASTER='yes' BONDING_SLAVE_0='eth0' BONDING_SLAVE_1='eth1' BONDING_MODULE_OPTS='mode=active-backup miimon=100'
The slaves are specified with STARTMODE=hotplug
and
BOOTPROTO=none
:
ifcfg-eth0 STARTMODE='hotplug' BOOTPROTO='none' ifcfg-eth1 STARTMODE='hotplug' BOOTPROTO='none'
BOOTPROTO=none
uses the ethtool
options (when provided), but does not set the link up on ifup
eth0
. The reason is that the slave interface is controlled by the
bond master.
STARTMODE=hotplug
causes the slave interface to join the
bond automatically when it is available.
The udev
rules in
/etc/udev/rules.d/70-persistent-net.rules
need to be
changed to match the device by bus ID (udev KERNELS
keyword equal to "SysFS BusID" as visible in hwinfo
--netcard
) instead of by MAC address. This allows replacement of
defective hardware (a network card in the same slot but with a different
MAC) and prevents confusion when the bond changes the MAC address of all its
slaves.
For example:
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", KERNELS=="0000:00:19.0", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
At boot time, the systemd network.service
does not
wait for the hotplug slaves, but for the bond to become ready, which
requires at least one available slave. When one of the slave interfaces gets
removed (unbind from NIC driver, rmmod
of the NIC driver
or true PCI hotplug remove) from the system, the kernel removes it from the
bond automatically. When a new card is added to the system (replacement of
the hardware in the slot), udev
renames it using
the bus-based persistent name rule to the name of the slave, and calls
ifup
for it. The ifup
call
automatically joins it into the bond.
19.8 Setting up team devices for Network Teaming #
The term “link aggregation” is the general term which describes combining (or aggregating) a network connection to provide a logical layer. Sometimes you find the terms “channel teaming”, “Ethernet bonding”, “port trunking”, etc. which are synonyms and refer to the same concept.
This concept is widely known as “bonding” and was originally integrated into the Linux kernel (see Section 19.7, “Setting up bonding devices” for the original implementation). The term Network Teaming is used to refer to the new implementation of this concept.
The main difference between bonding and Network Teaming is that teaming supplies a set of small kernel modules responsible for providing an interface for teamd instances. Everything else is handled in user space. This is different from the original bonding implementation which contains all of its functionality exclusively in the kernel. For a comparison refer to Table 19.5, “Feature comparison between bonding and team”.
Feature | Bonding | Team |
---|---|---|
broadcast, round-robin TX policy | yes | yes |
active-backup TX policy | yes | yes |
LACP (802.3ad) support | yes | yes |
hash-based TX policy | yes | yes |
user can set hash function | no | yes |
TX load-balancing support (TLB) | yes | yes |
TX load-balancing support for LACP | no | yes |
Ethtool link monitoring | yes | yes |
ARP link monitoring | yes | yes |
NS/NA (IPV6) link monitoring | no | yes |
RCU locking on TX/RX paths | no | yes |
port prio and stickiness | no | yes |
separate per-port link monitoring setup | no | yes |
multiple link monitoring setup | limited | yes |
VLAN support | yes | yes |
multiple device stacking | yes | yes |
Source: http://libteam.org/files/teamdev.pp.pdf |
Both implementations, bonding and Network Teaming, can be used in parallel. Network Teaming is an alternative to the existing bonding implementation. It does not replace bonding.
Network Teaming can be used for different use cases. The two most important use cases are explained later and involve:
Load balancing between different network devices.
Failover from one network device to another in case one of the devices should fail.
Currently, there is no YaST module to support creating a teaming device. You need to configure Network Teaming manually. The general procedure is shown below which can be applied for all your Network Teaming configurations:
Install the package libteam-tools:
>
sudo
zypper in libteam-tools
Create a configuration file under
/etc/sysconfig/network/
. Usually it will beifcfg-team0
. If you need more than one Network Teaming device, give them ascending numbers.This configuration file contains several variables which are explained in the man pages (see
man ifcfg
andman ifcfg-team
). An example configuration can be found in your system in the file/etc/sysconfig/network/ifcfg.template
.Remove the configuration files of the interfaces which will be used for the teaming device (usually
ifcfg-eth0
andifcfg-eth1
).It is recommended to make a backup and remove both files. Wicked will re-create the configuration files with the necessary parameters for teaming.
Optionally, check if everything is included in Wicked's configuration file:
>
sudo
wicked show-config
Start the Network Teaming device
team0
:>
sudo
wicked ifup team0
In case you need additional debug information, use the option
--debug all
after theall
subcommand.Check the status of the Network Teaming device. This can be done by the following commands:
Get the state of the teamd instance from Wicked:
>
sudo
wicked ifstatus --verbose team0
Get the state of the entire instance:
>
sudo
teamdctl team0 state
Get the systemd state of the teamd instance:
>
sudo
systemctl status teamd@team0
Each of them shows a slightly different view depending on your needs.
In case you need to change something in the
ifcfg-team0
file afterward, reload its configuration with:>
sudo
wicked ifreload team0
Do not use systemctl
for starting or
stopping the teaming device! Instead, use the wicked
command as shown above.
To completely remove the team device, use this procedure:
Stop the Network Teaming device
team0
:>
sudo
wicked ifdown team0
Rename the file
/etc/sysconfig/network/ifcfg-team0
to/etc/sysconfig/network/.ifcfg-team0
. Inserting a dot in front of the file name makes it “invisible” for wicked. If you really do not need the configuration anymore, you can also remove the file.Reload the configuration:
>
sudo
wicked ifreload all
19.8.1 Use case: load balancing with Network Teaming #
Load balancing is used to improve bandwidth. Use the following configuration
file to create a Network Teaming device with load balancing capabilities. Proceed
with Procedure 19.1, “General procedure” to set up the device. Check the
output with teamdctl
.
STARTMODE=auto 1 BOOTPROTO=static 2 IPADDRESS="192.168.1.1/24" 2 IPADDR6="fd00:deca:fbad:50::1/64" 2 TEAM_RUNNER="loadbalance" 3 TEAM_LB_TX_HASH="ipv4,ipv6,eth,vlan" TEAM_LB_TX_BALANCER_NAME="basic" TEAM_LB_TX_BALANCER_INTERVAL="100" TEAM_PORT_DEVICE_0="eth0" 4 TEAM_PORT_DEVICE_1="eth1" 4 TEAM_LW_NAME="ethtool" 5 TEAM_LW_ETHTOOL_DELAY_UP="10" 6 TEAM_LW_ETHTOOL_DELAY_DOWN="10" 6
Controls the start of the teaming device. The value of
In case you need to control the device yourself (and prevent it from
starting automatically), set | |
Sets a static IP address (here
If the Network Teaming device should use a dynamic IP address, set
| |
Sets | |
Specifies one or more devices which should be aggregated to create the Network Teaming device. | |
Defines a link watcher to monitor the state of subordinate devices. The
default value
If you need a higher confidence in the connection, use the
| |
Defines the delay in milliseconds between the link coming up (or down) and the runner being notified. |
19.8.2 Use case: failover with Network Teaming #
Failover is used to ensure high availability of a critical Network Teaming device by involving a parallel backup network device. The backup network device is running all the time and takes over if and when the main device fails.
Use the following configuration file to create a Network Teaming device with
failover capabilities. Proceed with Procedure 19.1, “General procedure” to
set up the device. Check the output with teamdctl
.
STARTMODE=auto 1 BOOTPROTO=static 2 IPADDR="192.168.1.2/24" 2 IPADDR6="fd00:deca:fbad:50::2/64" 2 TEAM_RUNNER=activebackup 3 TEAM_PORT_DEVICE_0="eth0" 4 TEAM_PORT_DEVICE_1="eth1" 4 TEAM_LW_NAME=ethtool 5 TEAM_LW_ETHTOOL_DELAY_UP="10" 6 TEAM_LW_ETHTOOL_DELAY_DOWN="10" 6
Controls the start of the teaming device. The value of
In case you need to control the device yourself (and prevent it from
starting automatically), set | |
Sets a static IP address (here
If the Network Teaming device should use a dynamic IP address, set
| |
Sets | |
Specifies one or more devices which should be aggregated to create the Network Teaming device. | |
Defines a link watcher to monitor the state of subordinate devices. The
default value
If you need a higher confidence in the connection, use the
| |
Defines the delay in milliseconds between the link coming up (or down) and the runner being notified. |
19.8.3 Use case: VLAN over team device #
VLAN is an abbreviation of Virtual Local Area Network. It allows the running of multiple logical (virtual) Ethernets over one single physical Ethernet. It logically splits the network into different broadcast domains so that packets are only switched between ports that are designated for the same VLAN.
The following use case creates two static VLANs on top of a team device:
vlan0
, bound to the IP address192.168.10.1
vlan1
, bound to the IP address192.168.20.1
Proceed as follows:
Enable the VLAN tags on your switch. To use load balancing for your team device, your switch needs to be capable of Link Aggregation Control Protocol (LACP) (802.3ad). Consult your hardware manual about the details.
Decide if you want to use load balancing or failover for your team device. Set up your team device as described in Section 19.8.1, “Use case: load balancing with Network Teaming” or Section 19.8.2, “Use case: failover with Network Teaming”.
In
/etc/sysconfig/network
create a fileifcfg-vlan0
with the following content:STARTMODE="auto" BOOTPROTO="static" 1 IPADDR='192.168.10.1/24' 2 ETHERDEVICE="team0" 3 VLAN_ID="0" 4 VLAN='yes'
Defines a fixed IP address, specified in
IPADDR
.Defines the IP address, here with its netmask.
Contains the real interface to use for the VLAN interface, here our team device (
team0
).Specifies a unique ID for the VLAN. Preferably, the file name and the
VLAN_ID
corresponds to the nameifcfg-vlanVLAN_ID
. In our caseVLAN_ID
is0
which leads to the file nameifcfg-vlan0
.Copy the file
/etc/sysconfig/network/ifcfg-vlan0
to/etc/sysconfig/network/ifcfg-vlan1
and change the following values:IPADDR
from192.168.10.1/24
to192.168.20.1/24
.VLAN_ID
from0
to1
.
Start the two VLANs:
#
wicked
ifup vlan0 vlan1Check the output of
ifconfig
:#
ifconfig
-a [...] vlan0 Link encap:Ethernet HWaddr 08:00:27:DC:43:98 inet addr:192.168.10.1 Bcast:192.168.10.255 Mask:255.255.255.0 inet6 addr: fe80::a00:27ff:fedc:4398/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:12 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:816 (816.0 b) vlan1 Link encap:Ethernet HWaddr 08:00:27:DC:43:98 inet addr:192.168.20.1 Bcast:192.168.20.255 Mask:255.255.255.0 inet6 addr: fe80::a00:27ff:fedc:4398/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:12 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:816 (816.0 b)
19.9 Software-defined networking with Open vSwitch #
Software-defined networking (SDN) means separating the system that controls where traffic is sent (the control plane) from the underlying system that forwards traffic to the selected destination (the data plane, also called the forwarding plane). This means that the functions previously fulfilled by a single, usually inflexible switch can now be separated between a switch (data plane) and its controller (control plane). In this model, the controller is programmable and can be very flexible and adapt quickly to changing network conditions.
Open vSwitch is software that implements a distributed virtual multilayer switch that is compatible with the OpenFlow protocol. OpenFlow allows a controller application to modify the configuration of a switch. OpenFlow is layered onto the TCP protocol and is implemented in a range of hardware and software. A single controller can thus drive multiple, very different switches.
19.9.1 Advantages of Open vSwitch #
Software-defined networking with Open vSwitch brings several advantages with it, especially when you used together with virtual machines:
Networking states can be identified easily.
Networks and their live state can be moved from one host to another.
Network dynamics are traceable and external software can be enabled to respond to them.
You can apply and manipulate tags in network packets to identify which machine they are coming from or going to and maintain other networking context. Tagging rules can be configured and migrated.
Open vSwitch implements the GRE protocol (Generic Routing Encapsulation). This allows you, for example, to connect private VM networks to each other.
Open vSwitch can be used on its own, but is designed to integrate with networking hardware and can control hardware switches.
19.9.2 Installing Open vSwitch #
Install Open vSwitch and supplementary packages:
#
zypper
install openvswitch openvswitch-switchIf you plan to use Open vSwitch together with the KVM hypervisor, additionally install tunctl . If you plan to use Open vSwitch together with the Xen hypervisor, additionally install openvswitch-kmp-xen .
Enable the Open vSwitch service:
#
systemctl
enable openvswitchEither restart the computer or use
systemctl
to start the Open vSwitch service immediately:#
systemctl
start openvswitchTo check whether Open vSwitch was activated correctly, use:
#
systemctl
status openvswitch
19.9.3 Overview of Open vSwitch daemons and utilities #
Open vSwitch consists of several components. Among them are a kernel module and various user space components. The kernel module is used for accelerating the data path, but is not necessary for a minimal Open vSwitch installation.
19.9.3.1 Daemons #
The central executables of Open vSwitch are its two daemons. When you start the
openvswitch
service, you are indirectly starting
them.
The main Open vSwitch daemon (ovs-vswitchd
) provides the
implementation of a switch. The Open vSwitch database daemon
(ovsdb-server
) serves the database that stores the
configuration and state of Open vSwitch.
19.9.3.2 Utilities #
Open vSwitch also comes with several utilities that help you work with it. The following list is not exhaustive, but instead describes important commands only.
ovsdb-tool
Create, upgrade, compact, and query Open vSwitch databases. Do transactions on Open vSwitch databases.
ovs-appctl
Configure a running
ovs-vswitchd
orovsdb-server
daemon.ovs-dpctl
,ovs-dpctl-top
Create, modify, visualize, and delete data paths. Using this tool can interfere with
ovs-vswitchd
also performing data path management. Therefore, it is often used for diagnostics only.ovs-dpctl-top
creates atop
-like visualization for data paths.ovs-ofctl
Manage any switches adhering to the OpenFlow protocol.
ovs-ofctl
is not limited to interacting with Open vSwitch.ovs-vsctl
Provides a high-level interface to the configuration database. It can be used to query and modify the database. In effect, it shows the status of
ovs-vswitchd
and can be used to configure it.
19.9.4 Creating a bridge with Open vSwitch #
The following example configuration uses the Wicked network service that is used by default on SUSE Linux Enterprise Server. To learn more about Wicked, see Section 19.5, “Configuring a network connection manually”.
When you have installed and started Open vSwitch, proceed as follows:
To configure a bridge for use by your virtual machine, create a file with content like this:
STARTMODE='auto'1 BOOTPROTO='dhcp'2 OVS_BRIDGE='yes'3 OVS_BRIDGE_PORT_DEVICE_1='eth0'4
Set up the bridge automatically when the network service is started.
The protocol to use for configuring the IP address.
Mark the configuration as an Open vSwitch bridge.
Choose which device/devices should be added to the bridge. To add more devices, append additional lines for each of them to the file:
OVS_BRIDGE_PORT_DEVICE_SUFFIX='DEVICE'
The SUFFIX can be any alphanumeric string. However, to avoid overwriting a previous definition, make sure the SUFFIX of each device is unique.
Save the file in the directory
/etc/sysconfig/network
under the nameifcfg-br0
. Instead of br0, you can use any name you want. However, the file name needs to begin withifcfg-
.To learn about further options, refer to the man pages of
ifcfg
(man 5 ifcfg
) andifcfg-ovs-bridge
(man 5 ifcfg-ovs-bridge
).Now start the bridge:
#
wicked
ifup br0When Wicked is done, it should output the name of the bridge and next to it the state
up
.
19.9.5 Using Open vSwitch directly with KVM #
After having created the bridge as described in Section 19.9.4, “Creating a bridge with Open vSwitch”, you can use Open vSwitch to manage the network access of virtual machines created with KVM/QEMU.
To be able to best use the capabilities of Wicked, make some further changes to the bridge configured before. Open the previously created
/etc/sysconfig/network/ifcfg-br0
and append a line for another port device:OVS_BRIDGE_PORT_DEVICE_2='tap0'
Additionally, set
BOOTPROTO
tonone
. The file should now look like this:STARTMODE='auto' BOOTPROTO='none' OVS_BRIDGE='yes' OVS_BRIDGE_PORT_DEVICE_1='eth0' OVS_BRIDGE_PORT_DEVICE_2='tap0'
The new port device tap0 will be configured in the next step.
Now add a configuration file for the tap0 device:
STARTMODE='auto' BOOTPROTO='none' TUNNEL='tap'
Save the file in the directory
/etc/sysconfig/network
under the nameifcfg-tap0
.Tip: Allowing other users to access the tap deviceTo be able to use this tap device from a virtual machine started as a user who is not
root
, append:TUNNEL_SET_OWNER=USER_NAME
To allow access for an entire group, append:
TUNNEL_SET_GROUP=GROUP_NAME
Finally, open the configuration for the device defined as the first
OVS_BRIDGE_PORT_DEVICE
. If you did not change the name, that should beeth0
. Therefore, open/etc/sysconfig/network/ifcfg-eth0
and make sure that the following options are set:STARTMODE='auto' BOOTPROTO='none'
If the file does not exist yet, create it.
Restart the bridge interface using Wicked:
#
wicked
ifreload br0This will also trigger a reload of the newly defined bridge port devices.
To start a virtual machine, use, for example:
#
qemu-kvm
\ -drive file=/PATH/TO/DISK-IMAGE1 \ -m 512 -net nic,vlan=0,macaddr=00:11:22:EE:EE:EE \ -net tap,ifname=tap0,script=no,downscript=no2For further information on the usage of KVM/QEMU, see Book “Virtualization Guide”.
19.9.6 Using Open vSwitch with libvirt
#
After having created the bridge as described before in
Section 19.9.4, “Creating a bridge with Open vSwitch”, you can add the bridge to an existing
virtual machine managed with libvirt
. Since libvirt
has some support for
Open vSwitch bridges already, you can use the bridge created in
Section 19.9.4, “Creating a bridge with Open vSwitch” without further changes to the networking
configuration.
Open the domain XML file for the intended virtual machine:
#
virsh
edit VM_NAMEReplace VM_NAME with the name of the desired virtual machine. This will open your default text editor.
Find the networking section of the document by looking for a section starting with
<interface type="...">
and ending in</interface>
.Replace the existing section with a networking section that looks somewhat like this:
<interface type='bridge'> <source bridge='br0'/> <virtualport type='openvswitch'/> </interface>
Important: Compatibility ofvirsh iface-*
and Virtual Machine Manager with Open vSwitchAt the moment, the Open vSwitch compatibility of
libvirt
is not exposed through thevirsh iface-*
tools and Virtual Machine Manager. If you use any of these tools, your configuration can break.You can now start or restart the virtual machine as usual.
For further information on the usage of libvirt
, see
Book “Virtualization Guide”.
19.9.7 More information #
For more information on SDN, refer to the documentation section of the Open vSwitch project Web site at https://docs.openvswitch.org/en/latest/#documentation.
20 Printer operation #
SUSE® Linux Enterprise Server supports printing with many types of printers, including remote network printers. Printers can be configured manually or with YaST. For configuration instructions, refer to Book “Deployment Guide”, Chapter 20 “Setting up hardware components with YaST”, Section 20.3 “Setting up a printer”. Both graphical and command line utilities are available for starting and managing print jobs. If your printer does not work as expected, refer to Section 20.8, “Troubleshooting”.
CUPS (Common Unix Printing System) is the standard print system in SUSE Linux Enterprise Server.
Printers can be distinguished by interface, such as USB or network, and printer language. When buying a printer, make sure that the printer has an interface that is supported (USB, Ethernet, or Wi-Fi) and a suitable printer language. Printers can be categorized on the basis of the following three classes of printer languages:
- PostScript printers
PostScript is the printer language in which most print jobs in Linux and Unix are generated and processed by the internal print system. If PostScript documents can be processed directly by the printer and do not need to be converted in additional stages in the print system, the number of potential error sources is reduced.
Currently PostScript is being replaced by PDF as the standard print job format. PostScript+PDF printers that can directly print PDF (in addition to PostScript) already exist. For traditional PostScript printers PDF needs to be converted to PostScript in the printing workflow.
- Standard printers (languages like PCL and ESC/p)
In the case of known printer languages, the print system can convert PostScript jobs to the respective printer language with Ghostscript. This processing stage is called interpreting. The best-known languages are PCL (which is mostly used by HP printers and their clones) and ESC/P (which is used by Epson printers). These printer languages are usually supported by Linux and produce an adequate print result. Linux may not be able to address some special printer functions. Except for HP and Epson, there are currently no printer manufacturers who develop Linux drivers and make them available to Linux distributors under an open source license.
- Proprietary printers (also called GDI printers)
These printers do not support any of the common printer languages. They use their own undocumented printer languages, which are subject to change when a new edition of a model is released. Usually only Windows drivers are available for these printers. See Section 20.8.1, “Printers without standard printer language support” for more information.
Before you buy a new printer, refer to the following sources to check how well the printer you intend to buy is supported:
- http://www.openprinting.org/printers
The OpenPrinting home page with the printer database. The database shows the latest Linux support status. However, a Linux distribution can only integrate the drivers available at production time. Accordingly, a printer currently rated as “perfectly supported” may not have had this status when the latest SUSE Linux Enterprise Server version was released. Thus, the databases may not necessarily indicate the correct status, but only provide an approximation.
- https://www.ghostscript.com
The Ghostscript Web page.
/usr/share/doc/packages/ghostscript/catalog.devices
List of built-in Ghostscript drivers.
20.1 The CUPS workflow #
The user creates a print job. The print job consists of the data to print plus information for the spooler. This includes the name of the printer or the name of the print queue, and optionally, information for the filter, such as printer-specific options.
At least one dedicated print queue exists for every printer. The spooler holds the print job in the queue until the desired printer is ready to receive data. When the printer is ready, the spooler sends the data through the filter and back-end to the printer.
The filter converts the data generated by the application that is printing (usually PostScript or PDF, but also ASCII, JPEG, etc.) into printer-specific data (PostScript, PCL, ESC/P, etc.). The features of the printer are described in the PPD files. A PPD file contains printer-specific options with the parameters needed to enable them on the printer. The filter system makes sure that options selected by the user are enabled.
If you use a PostScript printer, the filter system converts the data into printer-specific PostScript. This does not require a printer driver. If you use a non-PostScript printer, the filter system converts the data into printer-specific data. This requires a printer driver suitable for your printer. The back-end receives the printer-specific data from the filter then passes it to the printer.
20.2 Methods and protocols for connecting printers #
There are various possibilities for connecting a printer to the system. The configuration of CUPS does not distinguish between a local printer and a printer connected to the system over the network. For more information about the printer connection, read the article CUPS in a Nutshell at https://en.opensuse.org/SDB:CUPS_in_a_Nutshell.
IBM Z Printers and similar devices provided by the z/VM that connect locally with the IBM Z mainframes are not supported by CUPS. On these platforms, printing is only possible over the network. The cabling for network printers must be installed according to the instructions of the printer manufacturer.
When connecting the printer to the machine, do not forget that only USB devices can be plugged in or unplugged during operation. To avoid damaging your system or printer, shut down the system before changing any connections that are not USB.
20.3 Installing the software #
PPD (PostScript printer description) is the computer language that describes the properties, like resolution, and options, such as the availability of a duplex unit. These descriptions are required for using various printer options in CUPS. Without a PPD file, the print data would be forwarded to the printer in a “raw” state, which is usually not desired.
To configure a PostScript printer, the best approach is to get a suitable
PPD file. Many PPD files are available in the packages
manufacturer-PPDs
and
OpenPrintingPPDs-postscript
. See
Section 20.7.3, “PPD files in various packages” and
Section 20.8.2, “No suitable PPD file available for a PostScript printer”.
New PPD files can be stored in the directory
/usr/share/cups/model/
or added to the print system
with YaST as described in Book “Deployment Guide”, Chapter 20 “Setting up hardware components with YaST”, Section 20.3.1.1 “Adding drivers with YaST”.
Subsequently, the PPD file can be selected during the printer setup.
Be careful if a printer manufacturer wants you to install entire software packages. This kind of installation may result in the loss of the support provided by SUSE Linux Enterprise Server. Also, print commands may work differently and the system may no longer be able to address devices of other manufacturers. For this reason, the installation of manufacturer software is not recommended.
20.4 Network printers #
A network printer can support various protocols, some even concurrently. Although most of the supported protocols are standardized, some manufacturers modify the standard. Manufacturers then provide drivers for only a few operating systems. Unfortunately, Linux drivers are rarely provided. The current situation is such that you cannot act on the assumption that every protocol works smoothly in Linux. Therefore, you may need to experiment with various options to achieve a functional configuration.
CUPS supports the socket
,
LPD
, IPP
and
smb
protocols.
- socket
Socket refers to a connection in which the plain print data is sent directly to a TCP socket. Some socket port numbers that are commonly used are
9100
or35
. The device URI (uniform resource identifier) syntax is: socket://IP.OF.THE.PRINTER:PORT, for example:socket://192.168.2.202:9100/
.- LPD (line printer daemon)
The LPD protocol is described in RFC 1179. Under this protocol, some job-related data, such as the ID of the print queue, is sent before the actual print data is sent. Therefore, a print queue must be specified when configuring the LPD protocol. The implementations of diverse printer manufacturers are flexible enough to accept any name as the print queue. If necessary, the printer manual should indicate what name to use. LPT, LPT1, LP1 or similar names are often used. The port number for an LPD service is
515
. An example device URI islpd://192.168.2.202/LPT1
.- IPP (Internet printing protocol)
IPP is based on the HTTP protocol. With IPP, more job-related data is transmitted than with the other protocols. CUPS uses IPP for internal data transmission. The name of the print queue is necessary to configure IPP correctly. The port number for IPP is
631
. Example device URIs areipp://192.168.2.202/ps
andipp://192.168.2.202/printers/ps
.- SMB (Windows share)
CUPS also supports printing on printers connected to Windows shares. The protocol used for this purpose is SMB. SMB uses the port numbers
137
,138
and139
. Example device URIs aresmb://user:password@workgroup/smb.example.com/printer
,smb://user:password@smb.example.com/printer
, andsmb://smb.example.com/printer
.
The protocol supported by the printer must be determined before
configuration. If the manufacturer does not provide the needed information,
the command nmap
(which comes with the
nmap
package) can be used to ascertain the
protocol. nmap
checks a host for open ports. For example:
>
nmap -p 35,137-139,515,631,9100-10000 IP.OF.THE.PRINTER
20.5 Configuring CUPS with command line tools #
CUPS can be configured with command line tools like
lpinfo
, lpadmin
and
lpoptions
. You need a device URI consisting of a
back-end, such as USB, and parameters. To determine valid device URIs on
your system use the command lpinfo -v | grep ":/"
:
>
sudo
lpinfo -v | grep ":/" direct usb://ACME/FunPrinter%20XL network socket://192.168.2.253
With lpadmin
the CUPS server administrator can add,
remove or manage print queues. To add a print queue, use the following
syntax:
>
sudo
lpadmin -p QUEUE -v DEVICE-URI -P PPD-FILE -E
Then the device (-v
) is available as
QUEUE (-p
), using the specified
PPD file (-P
). This means that you must know the PPD file
and the device URI to configure the printer manually.
Do not use -E
as the first option. For all CUPS commands,
-E
as the first argument sets use of an encrypted
connection. To enable the printer, -E
must be used as shown
in the following example:
>
sudo
lpadmin -p ps -v usb://ACME/FunPrinter%20XL -P \ /usr/share/cups/model/Postscript.ppd.gz -E
The following example configures a network printer:
>
sudo
lpadmin -p ps -v socket://192.168.2.202:9100/ -P \ /usr/share/cups/model/Postscript-level1.ppd.gz -E
For more options of lpadmin
, see the man page of
lpadmin(8)
.
During printer setup, certain options are set as default. These options can be modified for every print job (depending on the print tool used). Changing these default options with YaST is also possible. Using command line tools, set default options as follows:
First, list all options:
>
sudo
lpoptions -p QUEUE -lExample:
Resolution/Output Resolution: 150dpi *300dpi 600dpi
The activated default option is identified by a preceding asterisk (
*
).Change the option with
lpadmin
:>
sudo
lpadmin -p QUEUE -o Resolution=600dpiCheck the new setting:
>
sudo
lpoptions -p QUEUE -l Resolution/Output Resolution: 150dpi 300dpi *600dpi
When a normal user runs lpoptions
, the settings are
written to ~/.cups/lpoptions
. However,
root
settings are written to
/etc/cups/lpoptions
.
20.6 Printing from the command line #
To print from the command line, enter lp -d
QUEUENAME FILENAME,
substituting the corresponding names for
QUEUENAME and
FILENAME.
Some applications rely on the lp
command for printing. In
this case, enter the correct command in the application's print dialog,
usually without specifying FILENAME, for example,
lp -d
QUEUENAME.
20.7 Special features in SUSE Linux Enterprise Server #
Several CUPS features have been adapted for SUSE Linux Enterprise Server. Some of the most important changes are covered here.
20.7.1 CUPS and firewall #
After completing a default installation of SUSE Linux Enterprise Server,
firewalld
is active and the network interfaces are configured to be in
the public
zone, which blocks incoming traffic.
When firewalld
is active, you may need to configure it to
allow clients to browse network printers by allowing
mdns
and ipp
through
the internal network zone. The public zone should never
expose printer queues.
(More
information about the firewalld
configuration is available in
Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4 “firewalld
” and at
https://en.opensuse.org/SDB:CUPS_and_SANE_Firewall_settings.)
20.7.1.1 CUPS client #
Normally, a CUPS client runs on a regular workstation located in a trusted
network environment behind a firewall. In this case it is recommended to
configure the network interface to be in the Internal
Zone
, so the workstation is reachable from within the network.
20.7.1.2 CUPS server #
If the CUPS server is part of a trusted network environment protected by a
firewall, the network interface should be configured to be in the
Internal Zone
of the firewall. It is not recommended to
set up a CUPS server in an untrusted network environment unless you ensure
that it is protected by special firewall rules and secure settings in
the CUPS configuration.
20.7.2 Browsing for network printers #
CUPS servers regularly announce the availability and status information of shared printers over the network. Clients can access this information to display a list of available printers in printing dialogs, for example. This is called “browsing”.
CUPS servers announce their print queues over the network either via the
traditional CUPS browsing protocol, or via Bonjour/DNS-SD. To enable browsing network print queues, the service
cups-browsed
needs to run on all
clients that print via CUPS servers.
cups-browsed
is not started by
default. To start it for the active session, use sudo systemctl
start cups-browsed
. To ensure it is automatically started after
booting, enable it with sudo systemctl enable
cups-browsed
on all clients.
In case browsing does not work after having started
cups-browsed
, the CUPS server(s)
probably announce the network print queues via Bonjour/DNS-SD. In this case
you need to additionally install the package
avahi
and start the associated
service with sudo systemctl start avahi-daemon
on all
clients.
See Section 20.7.1, “CUPS and firewall” for information
on allowing printer browsing through firewalld
.
20.7.3 PPD files in various packages #
The YaST printer configuration sets up the queues for CUPS using the PPD
files installed in /usr/share/cups/model
. To find the
suitable PPD files for the printer model, YaST compares the vendor and
model determined during hardware detection with the vendors and models in
all PPD files. For this purpose, the YaST printer configuration generates
a database from the vendor and model information extracted from the PPD
files.
The configuration using only PPD files and no other information sources has
the advantage that the PPD files in
/usr/share/cups/model
can be modified freely. For
example, if you have PostScript printers the PPD files can be copied
directly to /usr/share/cups/model
(if they do not
already exist in the manufacturer-PPDs
or
OpenPrintingPPDs-postscript
packages) to achieve
an optimum configuration for your printers.
Additional PPD files are provided by the following packages:
gutenprint
: the Gutenprint driver and its matching PPDssplix
: the SpliX driver and its matching PPDsOpenPrintingPPDs-ghostscript
: PPDs for Ghostscript built-in driversOpenPrintingPPDs-hpijs
: PPDs for the HPIJS driver for non-HP printers
20.8 Troubleshooting #
The following sections cover some of the most frequently encountered printer hardware and software problems and ways to solve or circumvent these problems. Among the topics covered are GDI printers, PPD files and port configuration. Common network printer problems, defective printouts, and queue handling are also addressed.
20.8.1 Printers without standard printer language support #
These printers do not support any common printer language and can only be addressed with special proprietary control sequences. Therefore they can only work with the operating system versions for which the manufacturer delivers a driver. GDI is a programming interface developed by Microsoft* for graphics devices. Usually the manufacturer delivers drivers only for Windows, and since the Windows driver uses the GDI interface these printers are also called GDI printers. The actual problem is not the programming interface, but that these printers can only be addressed with the proprietary printer language of the respective printer model.
Some GDI printers can be switched to operate either in GDI mode or in one of the standard printer languages. See the manual of the printer whether this is possible. Some models require special Windows software to do the switch (note that the Windows printer driver may always switch the printer back into GDI mode when printing from Windows). For other GDI printers there are extension modules for a standard printer language available.
Some manufacturers provide proprietary drivers for their printers. The disadvantage of proprietary printer drivers is that there is no guarantee that these work with the installed print system or that they are suitable for the various hardware platforms. In contrast, printers that support a standard printer language do not depend on a special print system version or a special hardware platform.
Instead of spending time trying to make a proprietary Linux driver work, it may be more cost-effective to purchase a printer which supports a standard printer language (preferably PostScript). This would solve the driver problem once and for all, eliminating the need to install and configure special driver software and obtain driver updates that may be required because of new developments in the print system.
20.8.2 No suitable PPD file available for a PostScript printer #
If the manufacturer-PPDs
or
OpenPrintingPPDs-postscript
packages do not
contain a suitable PPD file for a PostScript printer, it should be possible
to use the PPD file from the driver CD of the printer manufacturer or
download a suitable PPD file from the Web page of the printer manufacturer.
If the PPD file is provided as a zip archive (.zip) or a self-extracting
zip archive (.exe
), unpack it with
unzip
. First, review the license terms of the PPD file.
Then use the cupstestppd
utility to check if the PPD
file complies with “Adobe PostScript Printer Description File Format
Specification, version 4.3.” If the utility returns
“FAIL,” the errors in the PPD files are serious and are likely
to cause major problems. The problem spots reported by
cupstestppd
should be eliminated. If necessary, ask the
printer manufacturer for a suitable PPD file.
20.8.3 Network printer connections #
- Identifying network problems
Connect the printer directly to the computer. For test purposes, configure the printer as a local printer. If this works, the problems are related to the network.
- Checking the TCP/IP network
The TCP/IP network and name resolution must be functional.
- Checking a remote
lpd
Use the following command to test if a TCP connection can be established to
lpd
(port515
) on HOST:>
netcat -z HOST 515 && echo ok || echo failedIf the connection to
lpd
cannot be established,lpd
may not be active or there may be basic network problems.Provided that the respective
lpd
is active and the host accepts queries, run the following command asroot
to query a status report for QUEUE on remote HOST:#
echo -e "\004queue" \ | netcat -w 2 -p 722 HOST 515If
lpd
does not respond, it may not be active or there may be basic network problems. Iflpd
responds, the response should show why printing is not possible on thequeue
onhost
. If you receive a response like that shown in Example 20.1, “Error message fromlpd
”, the problem is caused by the remotelpd
.Example 20.1: Error message fromlpd
#lpd: your host does not have line printer access lpd: queue does not exist printer: spooling disabled printer: printing disabled
- Checking a remote
cupsd
A CUPS network server can broadcast its queues by default every 30 seconds on UDP port
631
. Accordingly, the following command can be used to test whether there is a broadcasting CUPS network server in the network. Make sure to stop your local CUPS daemon before executing the command.>
netcat -u -l -p 631 & PID=$! ; sleep 40 ; kill $PIDIf a broadcasting CUPS network server exists, the output appears as shown in Example 20.2, “Broadcast from the CUPS network server”.
Example 20.2: Broadcast from the CUPS network server #ipp://192.168.2.202:631/printers/queue
IBM Z Take into account that IBM Z Ethernet devices do not receive broadcasts by default.
The following command can be used to test if a TCP connection can be established to
cupsd
(port631
) on HOST:>
netcat -z HOST 631 && echo ok || echo failedIf the connection to
cupsd
cannot be established,cupsd
may not be active or there may be basic network problems.lpstat -h
HOST -l -t returns a (possibly very long) status report for all queues on HOST, provided the respectivecupsd
is active and the host accepts queries.The next command can be used to test if the QUEUE on HOST accepts a print job consisting of a single carriage-return character. Nothing should be printed. Possibly, a blank page may be ejected.
>
echo -en "\r" \ | lp -d queue -h HOST- Troubleshooting a Network Printer or Print Server Machine
Spoolers running in a print server machine sometimes cause problems when they need to deal with multiple print jobs. Since this is caused by the spooler in the print server machine, there no way to resolve this issue. As a work-around, circumvent the spooler in the print server machine by addressing the printer connected to the print server machine directly with the TCP socket. See Section 20.4, “Network printers”.
In this way, the print server machine is reduced to a converter between the various forms of data transfer (TCP/IP network and local printer connection). To use this method, you need to know the TCP port on the print server machine. If the printer is connected to the print server machine and turned on, this TCP port can usually be determined with the
nmap
utility from thenmap
package some time after the print server machine is powered up. For example,nmap
IP-address may deliver the following output for a print server machine:Port State Service 23/tcp open telnet 80/tcp open http 515/tcp open printer 631/tcp open cups 9100/tcp open jetdirect
This output indicates that the printer connected to the print server machine can be addressed via TCP socket on port
9100
. By default,nmap
only checks several commonly known ports listed in/usr/share/nmap/nmap-services
. To check all possible ports, use the commandnmap -p
FROM_PORT-TO_PORT IP_ADDRESS. This may take some time. For further information, refer to the man page ofnmap
.Enter a command like
>
echo -en "\rHello\r\f" | netcat -w 1 IP-address port cat file | netcat -w 1 IP-address portto send character strings or files directly to the respective port to test if the printer can be addressed on this port.
20.8.4 Defective printouts without error message #
For the print system, the print job is completed when the CUPS back-end completes the data transfer to the recipient (printer). If further processing on the recipient fails (for example, if the printer is not able to print the printer-specific data) the print system does not notice this. If the printer cannot print the printer-specific data, select a PPD file that is more suitable for the printer.
20.8.5 Disabled queues #
If the data transfer to the recipient fails entirely after several
attempts, the CUPS back-end, such as USB
or
socket
, reports an error to the print system (to
cupsd
). The back-end determines how many unsuccessful
attempts are appropriate until the data transfer is reported as impossible.
As further attempts would be in vain, cupsd
disables
printing for the respective queue. After eliminating the cause of the
problem, the system administrator must re-enable printing with the command
cupsenable
.
20.8.6 CUPS browsing: deleting print jobs #
If a CUPS network server broadcasts its queues to the client hosts via
browsing and a suitable local cupsd
is active on the
client hosts, the client cupsd
accepts print jobs from
applications and forwards them to the cupsd
on the
server. When cupsd
on the server accepts a print job, it
is assigned a new job number. Therefore, the job number on the client host
is different from the job number on the server. As a print job is usually
forwarded immediately, it cannot be deleted with the job number on the
client host This is because the client cupsd
regards the
print job as completed when it has been forwarded to the server
cupsd
.
To delete the print job on the server, use a
command such as lpstat -h cups.example.com -o
to determine the
job number on the server. This assumes that the server has not already
completed the print job (that is, sent it completely to the printer). Use
the obtained job
number to delete the print job on the server as follows:
>
cancel -h cups.example.com QUEUE-JOBNUMBER
20.8.7 Defective print jobs and data transfer errors #
If you switch the printer off or shut down the computer during the printing
process, print jobs remain in the queue. Printing resumes when the computer
(or the printer) is switched back on. Defective print jobs must be removed
from the queue with cancel
.
If a print job is corrupted or an error occurs in the communication between the host and the printer, the printer cannot process the data correctly and prints numerous sheets of paper with unintelligible characters. To fix the problem, follow these steps:
To stop printing, remove all paper from ink jet printers or open the paper trays of laser printers. High-quality printers have a button for canceling the current printout.
The print job may still be in the queue, because jobs are only removed after they are sent completely to the printer. Use
lpstat -o
orlpstat -h cups.example.com -o
to check which queue is currently printing. Delete the print job withcancel
QUEUE-JOBNUMBER orcancel -h cups.example.com
QUEUE-JOBNUMBER.Some data may still be transferred to the printer even though the print job has been deleted from the queue. Check if a CUPS back-end process is still running for the respective queue and terminate it.
Reset the printer completely by switching it off for some time. Then insert the paper and turn on the printer.
20.8.8 Debugging CUPS #
Use the following generic procedure to locate problems in CUPS:
Set
LogLevel debug
in/etc/cups/cupsd.conf
.Stop
cupsd
.Remove
/var/log/cups/error_log*
to avoid having to search through very large log files.Start
cupsd
.Repeat the action that led to the problem.
Check the messages in
/var/log/cups/error_log*
to identify the cause of the problem.
20.8.9 More information #
In-depth information about printing on SUSE Linux Enterprise Server is presented in the
openSUSE Support Database at https://en.opensuse.org/Portal:Printing. Solutions to many specific problems are presented in the
SUSE Knowledgebase (https://www.suse.com/support/). Locate the relevant articles
with a text search for CUPS
.
21 Graphical user interface #
SUSE Linux Enterprise Server includes the X.org server and the GNOME desktop. This chapter describes the configuration of the graphical user interface for all users.
21.1 X window system #
The X.org server is the de facto standard for implementing the X11 protocol. X is network-based, enabling applications started on one host to be displayed on another host connected over any kind of network (LAN or Internet).
Usually, the X Window System needs no configuration. The hardware is
dynamically detected during X start-up. The use of
xorg.conf
is therefore deprecated. If you still
need to specify custom options to change the way X behaves, you can
still do so by modifying configuration files under
/etc/X11/xorg.conf.d/
.
IBM Z does not have any input or output devices supported by X.Org. Therefore, none of the configuration procedures described in this section apply. More relevant information for IBM Z can be found in Book “Deployment Guide”, Chapter 5 “Installation on IBM Z and LinuxONE”.
Install the package xorg-docs
to
get more in-depth information about X11. man 5 xorg.conf
tells you more about the format of the manual configuration (if needed).
More information on the X11 development can be found on the project's home
page at http://www.x.org.
Drivers are found in xf86-video-*
packages, for
example xf86-video-ati
. Many of the drivers
delivered with these packages are described in detail in the related manual
page. For example, if you use the ati
driver, find more
information about this driver in man 4 ati
.
Information about third-party drivers is available in
/usr/share/doc/packages/<package_name>
.
For example, the documentation of x11-video-nvidiaG03
is available in
/usr/share/doc/packages/x11-video-nvidiaG04
after the package was installed.
21.2 Installing and configuring fonts #
Fonts in Linux can be categorized into two parts:
- Outline or vector fonts
Contains a mathematical description as drawing instructions about the shape of a glyph. As such, each glyph can be scaled to arbitrary sizes without loss of quality. Before such a font (or glyph) can be used, the mathematical descriptions need to be transformed into a raster (grid). This process is called font rasterization. Font hinting (embedded inside the font) improves and optimizes the rendering result for a particular size. Rasterization and hinting is done with the FreeType library.
Common formats under Linux are PostScript Type 1 and Type 2, TrueType, and OpenType.
- Bitmap or raster fonts
Consists of an array of pixels designed for a specific font size. Bitmap fonts are extremely fast and simple to render. However, compared to vector fonts, bitmap fonts cannot be scaled without losing quality. As such, these fonts are usually distributed in different sizes. These days, bitmap fonts are still used in the Linux console and sometimes in terminals.
Under Linux, Portable Compiled Format (PCF) or Glyph Bitmap Distribution Format (BDF) are the most common formats.
The appearance of these fonts can be influenced by two main aspects:
choosing a suitable font family,
rendering the font with an algorithm that achieves results comfortable for the receiver's eyes.
The last point is only relevant to vector fonts. Although the above two points are highly subjective, some defaults need to be created.
Linux font rendering systems consist of several libraries with different relations. The basic font rendering library is FreeType, which converts font glyphs of supported formats into optimized bitmap glyphs. The rendering process is controlled by an algorithm and its parameters (which may be subject to patent issues).
Every program or library which uses FreeType should consult the Fontconfig library. This library gathers font configuration from users and from the system. When a user amends their Fontconfig setting, this change will result in Fontconfig-aware applications.
More sophisticated OpenType shaping needed for scripts such as Arabic, Han or Phags-Pa and other higher level text processing is done using Harfbuzz or Pango.
21.2.1 Showing installed fonts #
To get an overview about which fonts are installed on your system, ask the
commands rpm
or fc-list
. Both will
give you a good answer, but may return a different list depending on system
and user configuration:
rpm
Invoke
rpm
to see which software packages containing fonts are installed on your system:>
rpm -qa '*fonts*'Every font package should satisfy this expression. However, the command may return some false positives like
fonts-config
(which is neither a font nor does it contain fonts).fc-list
Invoke
fc-list
to get an overview about what font families can be accessed, whether they are installed on the system or in your home:>
fc-list ':' familyNote: Commandfc-list
The command
fc-list
is a wrapper to the Fontconfig library. It is possible to query a lot of interesting information from Fontconfig—or, to be more precise, from its cache. Seeman 1 fc-list
for more details.
21.2.2 Viewing fonts #
If you want to know what an installed font family looks like, either use the
command ftview
(package
ft2demos
) or visit
http://fontinfo.opensuse.org/. For example, to display
the FreeMono font in 14 point, use ftview
like this:
>
ftview 14 /usr/share/fonts/truetype/FreeMono.ttf
If you need further information, go to http://fontinfo.opensuse.org/ to find out which styles (regular, bold, italic, etc.) and languages are supported.
21.2.3 Querying fonts #
To query which font is used when a pattern is given, use the
fc-match
command.
For example, if your pattern contains an already installed font,
fc-match
returns the file name, font family, and the
style:
>
fc-match 'Liberation Serif'
LiberationSerif-Regular.ttf: "Liberation Serif" "Regular"
If the desired font does not exist on your system, Fontconfig's matching rules take place and try to find the most similar fonts available. This means, your request is substituted:
>
fc-match 'Foo Family'
DejaVuSans.ttf: "DejaVu Sans" "Book"
Fontconfig supports aliases: a name is substituted with another family name. A typical example are the generic names such as “sans-serif”, “serif”, and “monospace”. These alias names can be substituted by real family names or even a preference list of family names:
>
for font in serif sans mono; do fc-match "$font" ; done
DejaVuSerif.ttf: "DejaVu Serif" "Book"
DejaVuSans.ttf: "DejaVu Sans" "Book"
DejaVuSansMono.ttf: "DejaVu Sans Mono" "Book"
The result may vary on your system, depending on which fonts are currently installed.
Fontconfig always returns a real family (if at least one is installed) according to the given request, as similar as possible. “Similarity” depends on Fontconfig's internal metrics and on the user's or administrator's Fontconfig settings.
21.2.4 Installing fonts #
To install a new font there are these major methods:
Manually install the font files such as
*.ttf
or*.otf
to a known font directory. If it needs to be system-wide, use the standard directory/usr/share/fonts
. For installation in your home directory, use~/.config/fonts
.If you want to deviate from the standard directories, Fontconfig allows you to choose another one. Let Fontconfig know by using the
<dir>
element, see Section 21.2.5.2, “Diving into fontconfig XML” for details.Install fonts using
zypper
. Lots of fonts are already available as a package, be it on your SUSE distribution or in the M17N:fonts repository. Add the repository to your list using the following command. For example, to add a repository for SUSE Linux Enterprise Server 15 SP3:>
sudo
zypper ar https://download.opensuse.org/repositories/M17N:/fonts/SLE_15/To search for your FONT_FAMILY_NAME use this command:
>
zypper se 'FONT_FAMILY_NAME*fonts'
21.2.5 Configuring the appearance of fonts #
Depending on the rendering medium, and font size, the result may be unsatisfactory. For example, an average monitor these days has a resolution of 100dpi which makes pixels too big and glyphs look clunky.
There are several algorithms available to deal with low resolutions, such as anti-aliasing (grayscale smoothing), hinting (fitting to the grid), or subpixel rendering (tripling resolution in one direction). These algorithms can also differ from one font format to another.
Via Fontconfig, it is possible to select a rendering algorithms for every font individually or for a set of fonts.
21.2.5.1 Configuring fonts via sysconfig
#
SUSE Linux Enterprise Server comes with a sysconfig
layer above
Fontconfig. This is a good starting point for experimenting with font
configuration. To change the default settings, edit the configuration file
/etc/sysconfig/fonts-config
. (or use the YaST
sysconfig module). After you have edited the file, run
fonts-config
:
>
sudo
/usr/sbin/fonts-config
Restart the application to make the effect visible. Keep in mind the following issues:
A few applications do need not to be restarted. For example, Firefox re-reads Fontconfig configuration from time to time. Newly created or reloaded tabs get new font configurations later.
The
fonts-config
script is called automatically after every package installation or removal (if not, it is a bug of the font software package).Every sysconfig variable can be temporarily overridden by the
fonts-config
command line option. Seefonts-config --help
for details.
There are several sysconfig variables which can be altered. See
man 1 fonts-config
or the help page of the YaST
sysconfig module. The following variables are examples:
- Usage of rendering algorithms
Consider
FORCE_HINTSTYLE
,FORCE_AUTOHINT
,FORCE_BW
,FORCE_BW_MONOSPACE
,USE_EMBEDDED_BITMAPS
andEMBEDDED_BITMAP_LANGAGES
- Preference lists of generic aliases
Use
PREFER_SANS_FAMILIES
,PREFER_SERIF_FAMILIES
,PREFER_MONO_FAMILIES
andSEARCH_METRIC_COMPATIBLE
The following list provides some configuration examples, sorted from the “most readable” fonts (more contrast) to “most beautiful” (more smoothed).
- Bitmap fonts
Prefer bitmap fonts via the
PREFER_*_FAMILIES
variables. Follow the example in the help section for these variables. Be aware that these fonts are rendered black and white, not smoothed and that bitmap fonts are available in several sizes only. Consider usingSEARCH_METRIC_COMPATIBLE="no"
to disable metric compatibility-driven family name substitutions.
- Scalable fonts rendered black and white
Scalable fonts rendered without antialiasing can result in a similar outcome to bitmap fonts, while maintaining font scalability. Use well hinted fonts like the Liberation families. Unfortunately, there is a lack of well hinted fonts though. Set the following variable to force this method:
FORCE_BW="yes"
- Monospaced fonts rendered black and white
Render monospaced fonts without antialiasing only, otherwise use default settings:
FORCE_BW_MONOSPACE="yes"
- Default settings
All fonts are rendered with antialiasing. Well hinted fonts will be rendered with the byte code interpreter (BCI) and the rest with autohinter (
hintstyle=hintslight
). Leave all relevant sysconfig variables to the default setting.- CFF fonts
Use fonts in CFF format. They can be considered also more readable than the default TrueType fonts given the current improvements in FreeType2. Try them out by following the example of
PREFER_*_FAMILIES
. Possibly make them more dark and bold with:SEARCH_METRIC_COMPATIBLE="no"
as they are rendered by
hintstyle=hintslight
by default. Also consider using:SEARCH_METRIC_COMPATIBLE="no"
- Autohinter exclusively
Even for a well hinted font, use FreeType2's autohinter. That can lead to thicker, sometimes fuzzier letter shapes with lower contrast. Set the following variable to activate this:
FORCE_AUTOHINTER="yes"
Use
FORCE_HINTSTYLE
to control the level of hinting.
21.2.5.2 Diving into fontconfig XML #
Fontconfig's configuration format is the eXtensible Markup
Language (XML). These few examples are not a complete reference,
but a brief overview. Details and other inspiration can be found in
man 5 fonts-conf
or in
/etc/fonts/conf.d/
.
The central Fontconfig configuration file is
/etc/fonts/fonts.conf
, which—along other
work—includes the whole /etc/fonts/conf.d/
directory. To customize Fontconfig, there are two places where you can
insert your changes:
System-wide changes. Edit the file
/etc/fonts/local.conf
(by default, it contains an emptyfontconfig
element).User-specific changes. Edit the file
~/.config/fontconfig/fonts.conf
. Place Fontconfig configuration files in the~/.config/fontconfig/conf.d/
directory.
User-specific changes overwrite any system-wide settings.
The file ~/.fonts.conf
is marked as deprecated and
should not be used anymore. Use
~/.config/fontconfig/fonts.conf
instead.
Every configuration file needs to have a fontconfig
element. As such, the minimal file looks like this:
<?xml version="1.0"?> <!DOCTYPE fontconfig SYSTEM "fonts.dtd"> <fontconfig> <!-- Insert your changes here --> </fontconfig>
If the default directories are not enough, insert the
dir
element with the respective directory:
<dir>/usr/share/fonts2</dir>
Fontconfig searches recursively for fonts.
Font-rendering algorithms can be chosen with following Fontconfig snippet (see Example 21.1, “Specifying rendering algorithms”):
<match target="font"> <test name="family"> <string>FAMILY_NAME</string> </test> <edit name="antialias" mode="assign"> <bool>true</bool> </edit> <edit name="hinting" mode="assign"> <bool>true</bool> </edit> <edit name="autohint" mode="assign"> <bool>false</bool> </edit> <edit name="hintstyle" mode="assign"> <const>hintfull</const> </edit> </match>
Various properties of fonts can be tested. For example, the
<test>
element can test for the font family (as
shown in the example), size interval, spacing, font format, and others.
When abandoning <test>
completely, all
<edit>
elements will be applied to every font
(global change).
- Rule 1
<alias> <family>Alegreya SC</family> <default> <family>serif</family> </default> </alias>
- Rule 2
<alias> <family>serif</family> <prefer> <family>Droid Serif</family> </prefer> </alias>
- Rule 3
<alias> <family>serif</family> <accept> <family>STIXGeneral</family> </accept> </alias>
The rules from Example 21.2, “Aliases and family name substitutions” create a prioritized family list (PFL). Depending on the element, different actions are performed:
<default>
from Rule 1This rule adds a
serif
family name at the end of the PFL.<prefer>
from Rule 2This rule adds “Droid Serif” just before the first occurrence of
serif
in the PFL, wheneverAlegreya SC
is in PFL.<accept>
from Rule 3This rule adds a “STIXGeneral” family name just after the first occurrence of the
serif
family name in the PFL.
Putting this together, when snippets occur in the order Rule 1 - Rule 2 - Rule 3 and the user requests “Alegreya SC”, then the PFL is created as depicted in Table 21.1, “Generating PFL from fontconfig rules”.
In Fontconfig's metrics, the family name has the highest priority over other patterns, like style, size, etc. Fontconfig checks which family is currently installed on the system. If “Alegreya SC” is installed, then Fontconfig returns it. If not, it asks for “Droid Serif”, etc.
Be careful. When the order of Fontconfig snippets is changed, Fontconfig can return different results, as depicted in Table 21.2, “Results from generating PFL from fontconfig rules with changed order”.
Think of the <default>
alias as a classification
or inclusion of this group (if not installed). As the example shows,
<default>
should always precede the
<prefer>
and <accept>
aliases of that group.
<default>
classification is not limited to the
generic aliases serif, sans-serif and monospace. See
/usr/share/fontconfig/conf.avail/30-metric-aliases.conf
for a complex example.
The following Fontconfig snippet in
Example 21.3, “Aliases and family name substitutions” creates a
serif
group. Every family in this group could substitute
others when a former font is not installed.
<alias> <family>Alegreya SC</family> <default> <family>serif</family> </default> </alias> <alias> <family>Droid Serif</family> <default> <family>serif</family> </default> </alias> <alias> <family>STIXGeneral</family> <default> <family>serif</family> </default> </alias> <alias> <family>serif</family> <accept> <family>Droid Serif</family> <family>STIXGeneral</family> <family>Alegreya SC</family> </accept> </alias>
Priority is given by the order in the <accept>
alias. Similarly, stronger <prefer>
aliases can be
used.
Example 21.2, “Aliases and family name substitutions” is expanded by Example 21.4, “Aliases and family names substitutions”.
- Rule 4
<alias> <family>serif</family> <accept> <family>Liberation Serif</family> </accept> </alias>
- Rule 5
<alias> <family>serif</family> <prefer> <family>DejaVu Serif</family> </prefer> </alias>
The expanded configuration from Example 21.4, “Aliases and family names substitutions” would lead to the following PFL evolution:
Order |
Current PFL |
---|---|
Request |
|
| |
| |
| |
| |
|
In case multiple
<accept>
declarations for the same generic name exist, the declaration that is parsed last “wins”. If possible, do not use<accept>
after user (/etc/fonts/conf.d/*-user.conf
) when creating a system-wide configuration.In case multiple
<prefer
declarations for the same generic name exist, the declaration that is parsed last “wins”. If possible, do not use<prefer>
before user in the system-wide configuration.Every
<prefer>
declaration overwrites<accept>
declarations for the same generic name. If the administrator wants to allow the user to use<accept>
and not only<prefer>
, the administrator should not use<prefer>
in the system-wide configuration. On the other hand, as users mostly use<prefer>
, this should not have any detrimental effect. We also see the use of<prefer>
in system-wide configurations.
21.3 GNOME configuration for administrators #
21.3.1 The dconf
system #
Configuration of the GNOME desktop is managed with
dconf
. It is a hierarchically structured database or
registry that allows users to modify their personal settings, and system
administrators to set default or mandatory values for all users.
dconf
replaces the gconf
system of
GNOME 2.
Use dconf-editor
to view the dconf
options with a graphical user interface. Use dconf
to
access and modify configuration options with the command line.
The GNOME Tweaks
tool provides an easy-to-use
user interface for additional configuration options beyond the
normal GNOME configuration. The tool can be started from the
GNOME application menu or from the command line with
gnome-tweak-tool
.
21.3.2 System-wide configuration #
Global dconf
configuration parameters can be set
in the /etc/dconf/db/
directory. This includes
the configuration for GDM or locking certain configuration options
for users.
Use the following procedure as an example to create a system-wide configuration:
Create a new directory that ends with a
.d
in/etc/dconf/db/
. This directory can contain an arbitrary amount of text files with configuration options. For this example, create the file/etc/dconf/db/network.d/00-proxy
with the following content:# This is a comment [system/proxy/http] host='10.0.0.1' enabled=true
Parse the new configuration directives into the dconf database format:
>
sudo
dconf update
Add the new
network
configuration database to the default user profile, by creating the file/etc/dconf/profile/user
. Then add the following content:system-db:network
The file
/etc/dconf/profile/user
is a GNOME default. Other profiles can be defined in the environment variableDCONF_PROFILE
.Optional: To lock the proxy configuration for users, create the file
/etc/dconf/db/network/locks/proxy
. Then add a line to this file with the keys that may not be changed:/system/proxy/http/host /system/proxy/http/enabled
You can use the graphical dconf-editor
to create a
profile with one user and then use dconf dump /
to list all configuration options. The configuration options can
then be stored in a global profile.
A detailed description of the global configuration is available at https://wiki.gnome.org/Projects/dconf/SystemAdministrators.
21.3.3 More information #
For more information, see http://help.gnome.org/admin/.
21.4 Switching between Intel and NVIDIA Optimus GPUs with SUSE Prime #
SUSE Prime is a tool for switching between onboard Intel graphical processing units (GPUs), and NVIDIA GPUs equipped with NVIDIA's "switchable graphics" Optimus technology. Optimus provides a mechanism for easily switching between an onboard Intel GPU and a discrete NVIDIA GPU. This is designed for running a laptop in a power-saving mode or at maximum performance: use the Intel GPU to save power, and the NVIDIA GPU for 3D applications.
SUSE Prime works only on systems running X11, not Wayland. If your system runs Wayland you must disable it and fall back to X11 if you wish to to use SUSE Prime (see Section 21.4.1, “Prerequisites”).
21.4.1 Prerequisites #
There must not be a /etc/X11/xorg.conf
file, and no
configuration files with active "ServerLayout", "Device", or "Screen"
sections in the /etc/X11/xorg.conf.d
directory.
SUSE Prime works only with X11. Use the loginctl
command to see if your system is using X11 or Wayland:
>
loginctl SESSION UID USER SEAT TTY 2 1000 tux seat0>
loginctl show-session 2|grep Type Type=x11
If your system uses Wayland, disable it by editing
/etc/gdm/custom.conf
and un-commenting
WaylandEnable=false
. Then reboot.
21.4.2 Installing and using SUSE Prime #
Your NVIDIA graphics card should already be installed and working. If it is not, see Section 21.4.3, “Installing NVIDIA drivers”.
Install the suse-prime package:
>
sudo
zypper install suse-prime
To switch your GPU run one of the following commands, then log out and log back in:
>
sudo
prime-select intel>
sudo
prime-select intel2>
sudo
prime-select nvidia
Use the intel
driver when it is the modesetting driver.
intel2
is for systems that use the
xf86-video-intel driver. You can get this information by
installing and running inxi:
>
inxi -G
Graphics: Device-1: Intel Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller
Display Server: x11(X.org 1.20.1 ) drivers: modesetting (unloaded: fbdev, vesa)
Resolution: 1920x1080@60.00hz
OpenGL: renderer: Mesa DRI Intel Haswell Desktop version: 4.5 Mesa 18.2.8
Which GPU is currently active?
>
sudo
/usr/sbin/prime-select get-current Driver configured: intel
21.4.3 Installing NVIDIA drivers #
If you need to identify your NVIDIA card so you know which driver to use, run the following command:
>
/sbin/lspci | grep VGA
Follow these steps to install the drivers with Zypper.
List the available driver packages:
>
sudo
zypper se nvidia
Then install the drivers for your NVIDIA graphics card:
>
sudo
zypper se packagename
22 Accessing file systems with FUSE #
FUSE is the acronym for Filesystem in Userspace.
This means you can configure and mount a file system as an unprivileged
user. Normally, you need to be
root
for this task. FUSE alone is
a kernel module. Combined with plug-ins, it allows you to extend FUSE to
access almost all file systems like remote SSH connections, ISO images, and
more.
22.1 Configuring FUSE #
Before you can use FUSE, you need to install the package
fuse
. Depending which file system
you want to use, you need additional plug-ins available as separate
packages.
Generally you do not need to configure FUSE. However, it is a good idea to
create a directory where all your mount points are combined. For example,
you can create a directory ~/mounts
and insert your
subdirectories for your different file systems there.
22.2 Mounting an NTFS partition #
NTFS, the New Technology File System, is the default file system of Windows. Since under normal circumstances the unprivileged user cannot mount NTFS block devices using the external FUSE library, the process of mounting a Windows partition described below requires root privileges.
Become
root
and install the packagentfs-3g
. It is available in SUSE Linux Enterprise Workstation Extension.Create a directory that is to be used as a mount point, for example
~/mounts/windows
.Find out which Windows partition you need. Use YaST and start the partitioner module to see which partition belongs to Windows, but do not modify anything. Alternatively, become
root
and execute/sbin/fdisk
-l
. Look for partitions with a partition type ofHPFS/NTFS
.Mount the partition in read-write mode. Replace the placeholder DEVICE with your respective Windows partition:
>
ntfs-3g /dev/DEVICE MOUNT POINTTo use your Windows partition in read-only mode, append
-o ro
:>
ntfs-3g /dev/DEVICE MOUNT POINT -o roThe command
ntfs-3g
uses the current user (UID) and group (GID) to mount the given device. If you want to set the write permissions to a different user, use the commandid
USER
to get the output of the UID and GID values. Set it with:#
id tux uid=1000(tux) gid=100(users) groups=100(users),16(dialout),33(video) ntfs-3g /dev/DEVICE MOUNT POINT -o uid=1000,gid=100Find additional options in the man page.
To unmount the resource, run fusermount -u
MOUNT POINT.
22.3 More information #
For more information, see the home page of FUSE at https://github.com/libfuse/libfuse.
23 Managing kernel modules #
Although Linux is a monolithic kernel, it can be extended using kernel modules. These are special objects that can be inserted into the kernel and removed on demand. In practical terms, kernel modules make it possible to add and remove drivers and interfaces that are not included in the kernel itself. Linux provides several commands for managing kernel modules.
23.1 Listing loaded modules with lsmod and modinfo #
Use the lsmod
command to view what kernel modules are
currently loaded. The output of the command may look as follows:
>
lsmod
Module Size Used by
snd_usb_audio 188416 2
snd_usbmidi_lib 36864 1 snd_usb_audio
hid_plantronics 16384 0
snd_rawmidi 36864 1 snd_usbmidi_lib
snd_seq_device 16384 1 snd_rawmidi
fuse 106496 3
nfsv3 45056 1
nfs_acl 16384 1 nfsv3
The output is divided into three columns. The Module
column lists the names
of the loaded modules, while the Size
column displays the size of each
module. The Used by
column shows the number of referring
modules and their names. Note that this list may be incomplete.
To view detailed information about a specific kernel module, use the
modinfo MODULE_NAME
command, where
MODULE_NAME is the name of the desired kernel
module. Note that the modinfo
binary resides in the
/sbin
directory that is not in the user's PATH
environment variable. This means that you must specify the full path to the
binary when running modinfo
command as a regular user:
>
/sbin/modinfo kvm
filename: /lib/modules/5.3.18-57-default/kernel/arch/x86/kvm/kvm.ko.xz
license: GPL
author: Qumranet
suserelease: SLE15-SP3
srcversion: 3D8FBA9060D4537359A06FC
depends: irqbypass
supported: yes
retpoline: Y
intree: Y
name: kvm
vermagic: 5.3.18-57-default SMP mod_unload modversions
23.2 Adding and removing kernel modules #
While it is possible to use insmod
and
rmmod
to add and remove kernel modules, it is recommended to use the
modprobe
tool instead. modprobe
offers several
important advantages, including automatic dependency resolution and
blacklisting.
When used without any parameters, the modprobe
command installs a specified kernel module. modprobe
must be run with root privileges:
>
sudo
modprobe acpi
To remove a kernel module, use the -r
parameter:
>
sudo
modprobe -r acpi
23.2.1 Loading kernel modules automatically on boot #
Instead of loading kernel modules manually, you can load them
automatically during the boot process using the
system-modules-load.service
service. To enable a
kernel module, add a .conf
file to the
/etc/modules-load.d/
directory. It is good practice
to give the configuration file the same name as the module, for example:
/etc/modules-load.d/rt2800usb.conf
The configuration file must contain the name of the desired kernel
module (for example, rt2800usb
).
The described technique allows you to load kernel modules without any
parameters. If you need to load a kernel module with specific options,
add a configuration file to the /etc/modprobe.d/
directory instead. The file must have the .conf
extension. The name of the file should adhere to the following naming convention:
priority-modulename.conf
, for example:
50-thinkfan.conf
. The configuration file must
contain the name of the kernel module and the desired parameters. You can use the
example command below to create a configuration file containing the name of the kernel module and its parameters:
>
echo "options thinkpad_acpi fan_control=1" | sudo tee /etc/modprobe.d/thinkfan.conf
Most kernel modules are loaded by the system automatically when a
device is detected or user space requests specific
functionality. Thus, adding modules manually to
/etc/modules-load.d/
is rarely required.
23.2.2 Blacklisting kernel modules with modprobe #
Blacklisting a kernel module prevents it from loading during the boot
process. This can be useful when you want to disable a module that you
suspect is causing problems on your system. Note that you can still load
blacklisted kernel modules manually using the
insmod
or modprobe
tools.
To blacklist a module, add the
blacklist MODULE_NAME
line
to the /etc/modprobe.d/50-blacklist.conf
file. For example:
blacklist nouveau
Run the mkinitrd
command as root to generate a new initrd
image, then reboot your machine. These steps can be performed using the following command:
>
su
echo "blacklist nouveau" >> /etc/modprobe.d/50-blacklist.conf && mkinitrd && reboot
To disable a kernel module temporarily only, blacklist it on-the-fly during the boot. To do this, press the E key when you see the boot screen. This drops you into a minimal editor that allows you to modify boot parameters. Locate the line that looks as follows:
linux /boot/vmlinuz...splash= silent quiet showopts
Add the
modprobe.blacklist=MODULE_NAME
command to the end of the line. For example:
linux /boot/vmlinuz...splash= silent quiet showopts modprobe.blacklist=nouveau
Press F10 or Ctrl–X to boot with the specified configuration.
To blacklist a kernel module permanently via GRUB, open the
/etc/default/grub
file for editing, and add the
modprobe.blacklist=MODULE_NAME
option to the GRUB_CMDLINE_LINUX
command. Then run the
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
command to enable
the changes.
24 Dynamic kernel device management with udev
#
The kernel can add or remove almost any device in a running system. Changes
in the device state (whether a device is plugged in or removed) need to be
propagated to user space. Devices need to be configured when they are
plugged in and recognized. Users of a certain device need to be informed
about any changes in this device's recognized state.
udev
provides the needed
infrastructure to dynamically maintain the device node files and symbolic
links in the /dev
directory.
udev
rules provide a way to plug
external tools into the kernel device event processing. This allows you to
customize udev
device handling by adding certain scripts to execute as part of kernel device
handling, or request and import additional data to evaluate during device
handling.
24.1 The /dev
directory #
The device nodes in the /dev
directory provide access
to the corresponding kernel devices. With
udev
, the /dev
directory reflects the current state of the kernel. Every kernel device has
one corresponding device file. If a device is disconnected from the system,
the device node is removed.
The content of the /dev
directory is kept on a
temporary file system and all files are rendered at every system start-up.
Manually created or modified files do not, by design, survive a reboot.
Static files and directories that should always be in the
/dev
directory regardless of the state of the
corresponding kernel device can be created with systemd-tmpfiles. The
configuration files are found in /usr/lib/tmpfiles.d/
and /etc/tmpfiles.d/
; for more information, see the
systemd-tmpfiles(8)
man page.
24.2 Kernel uevents
and udev
#
The required device information is exported by the
sysfs
file system. For every
device the kernel has detected and initialized, a directory with the device
name is created. It contains attribute files with device-specific
properties.
Every time a device is added or removed, the kernel sends a uevent to notify
udev
of the change. The
udev
daemon reads and parses all
rules from the /usr/lib/udev/rules.d/*.rules
and
/etc/udev/rules.d/*.rules
files at start-up and keeps
them in memory. If rules files are changed, added or removed, the daemon can
reload their in-memory representation with the command
udevadm control --reload
. For more details on
udev
rules and their syntax, refer
to Section 24.6, “Influencing kernel device event handling with udev
rules”.
Every received event is matched against the set of provides rules. The rules
can add or change event environment keys, request a specific name for the
device node to create, add symbolic links pointing to the node or add
programs to run after the device node is created. The driver core
uevents
are received from a kernel
netlink socket.
24.3 Drivers, kernel modules and devices #
The kernel bus drivers probe for devices. For every detected device, the
kernel creates an internal device structure while the driver core sends a
uevent to the udev
daemon. Bus
devices identify themselves by a specially-formatted ID, which tells what
kind of device it is. Usually these IDs consist of vendor and product ID and
other subsystem-specific values. Every bus has its own scheme for these IDs,
called MODALIAS
. The kernel takes the device information,
composes a MODALIAS
ID string from it and sends that string
along with the event. For a USB mouse, it looks like this:
MODALIAS=usb:v046DpC03Ed2000dc00dsc00dp00ic03isc01ip02
Every device driver carries a list of known aliases for devices it can
handle. The list is contained in the kernel module file itself. The program
depmod reads the ID lists and creates the file
modules.alias
in the kernel's
/lib/modules
directory for all currently available
modules. With this infrastructure, module loading is as easy as calling
modprobe
for every event that carries a
MODALIAS
key. If modprobe $MODALIAS
is
called, it matches the device alias composed for the device with the aliases
provided by the modules. If a matching entry is found, that module is
loaded. All this is automatically triggered by
udev
.
24.4 Booting and initial device setup #
All device events happening during the boot process before the
udev
daemon is running are lost,
because the infrastructure to handle these events resides on the root file
system and is not available at that time. To cover that loss, the kernel
provides a uevent
file located in the device directory
of every device in the sysfs
file system. By writing add
to that file, the kernel
resends the same event as the one lost during boot. A simple loop over all
uevent
files in /sys
triggers all
events again to create the device nodes and perform device setup.
As an example, a USB mouse present during boot may not be initialized by the
early boot logic, because the driver is not available at that time. The
event for the device discovery was lost and failed to find a kernel module
for the device. Instead of manually searching for connected
devices, udev
requests all device
events from the kernel after the root file system is available, so the event
for the USB mouse device runs again. Now it finds the kernel module on the
mounted root file system and the USB mouse can be initialized.
From user space, there is no visible difference between a device coldplug sequence and a device discovery during runtime. In both cases, the same rules are used to match and the same configured programs are run.
24.5 Monitoring the running udev
daemon #
The program udevadm monitor
can be used to visualize the
driver core events and the timing of the
udev
event processes.
UEVENT[1185238505.276660] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1 (usb) UDEV [1185238505.279198] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1 (usb) UEVENT[1185238505.279527] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0 (usb) UDEV [1185238505.285573] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0 (usb) UEVENT[1185238505.298878] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10 (input) UDEV [1185238505.305026] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10 (input) UEVENT[1185238505.305442] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/mouse2 (input) UEVENT[1185238505.306440] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/event4 (input) UDEV [1185238505.325384] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/event4 (input) UDEV [1185238505.342257] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10/mouse2 (input)
The UEVENT
lines show the events the kernel has sent over
netlink. The UDEV
lines show the finished
udev
event handlers. The timing is
printed in microseconds. The time between UEVENT
and
UDEV
is the time
udev
took to process this event or
the udev
daemon has delayed its
execution to synchronize this event with related and already running events.
For example, events for hard disk partitions always wait for the main disk
device event to finish, because the partition events may rely on the data
that the main disk event has queried from the hardware.
udevadm monitor --env
shows the complete event
environment:
ACTION=add DEVPATH=/devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10 SUBSYSTEM=input SEQNUM=1181 NAME="Logitech USB-PS/2 Optical Mouse" PHYS="usb-0000:00:1d.2-1/input0" UNIQ="" EV=7 KEY=70000 0 0 0 0 REL=103 MODALIAS=input:b0003v046DpC03Ee0110-e0,1,2,k110,111,112,r0,1,8,amlsfw
udev
also sends messages to syslog.
The default syslog priority that controls which messages are sent to syslog
is specified in the udev
configuration file /etc/udev/udev.conf
. The log
priority of the running daemon can be changed with udevadm control
--log_priority=
LEVEL/NUMBER.
24.6 Influencing kernel device event handling with udev
rules #
A udev
rule can match any property
the kernel adds to the event itself or any information that the kernel
exports to sysfs
. The rule can also request additional
information from external programs. Events are matched against all rules
provided in the directories /usr/lib/udev/rules.d/
(for default rules) and /etc/udev/rules.d
(system-specific configuration).
Every line in the rules file contains at least one key value pair. There are
two kinds of keys, match and assignment keys. If all match keys match their
values, the rule is applied and the assignment keys are assigned the
specified value. A matching rule may specify the name of the device node,
add symbolic links pointing to the node or run a specified program as part
of the event handling. If no matching rule is found, the default device node
name is used to create the device node. Detailed information about the rule
syntax and the provided keys to match or import data are described in the
udev
man page. The following
example rules provide a basic introduction to
udev
rule syntax. The example rules
are all taken from the udev
default
rule set /usr/lib/udev/rules.d/50-udev-default.rules
.
udev
rules ## console KERNEL=="console", MODE="0600", OPTIONS="last_rule" # serial devices KERNEL=="ttyUSB*", ATTRS{product}=="[Pp]alm*Handheld*", SYMLINK+="pilot" # printer SUBSYSTEM=="usb", KERNEL=="lp*", NAME="usb/%k", SYMLINK+="usb%k", GROUP="lp" # kernel firmware loader SUBSYSTEM=="firmware", ACTION=="add", RUN+="firmware.sh"
The console
rule consists of three keys: one match
key (KERNEL
) and two assign keys
(MODE
, OPTIONS
). The
KERNEL
match rule searches the device list for any items
of the type console
. Only exact matches are valid and
trigger this rule to be executed. The MODE
key assigns
special permissions to the device node, in this case, read and write
permissions to the owner of this device only. The OPTIONS
key makes this rule the last rule to be applied to any device of this type.
Any later rule matching this particular device type does not have any
effect.
The serial devices
rule is not available in
50-udev-default.rules
anymore, but it is still worth
considering. It consists of two match keys (KERNEL
and
ATTRS
) and one assign key (SYMLINK
).
The KERNEL
key searches for all devices of the
ttyUSB
type. Using the *
wild card,
this key matches several of these devices. The second match key,
ATTRS
, checks whether the product
attribute file in sysfs
for any ttyUSB
device contains a certain string. The assign key
(SYMLINK
) triggers the addition of a symbolic link to
this device under /dev/pilot
. The operator used in this
key (+=
) tells
udev
to additionally perform this
action, even if previous or later rules add other symbolic links. As this
rule contains two match keys, it is only applied if both conditions are met.
The printer
rule deals with USB printers and
contains two match keys which must both apply to get the entire rule applied
(SUBSYSTEM
and KERNEL
). Three assign
keys deal with the naming for this device type (NAME
),
the creation of symbolic device links (SYMLINK
) and the
group membership for this device type (GROUP
). Using the
*
wild card in the KERNEL
key makes it
match several lp
printer devices. Substitutions are used
in both, the NAME
and the SYMLINK
keys
to extend these strings by the internal device name. For example, the
symbolic link to the first lp
USB printer would read
/dev/usblp0
.
The kernel firmware loader
rule makes
udev
load additional firmware by an
external helper script during runtime. The SUBSYSTEM
match key searches for the firmware
subsystem. The
ACTION
key checks whether any device belonging to the
firmware
subsystem has been added. The
RUN+=
key triggers the execution of the
firmware.sh
script to locate the firmware that is to be
loaded.
Some general characteristics are common to all rules:
Each rule consists of one or more key value pairs separated by a comma.
A key's operation is determined by the operator.
udev
rules support several operators.Each given value must be enclosed by quotation marks.
Each line of the rules file represents one rule. If a rule is longer than one line, use
\
to join the different lines as you would do in shell syntax.udev
rules support a shell-style pattern that matches the*
,?
, and[]
patterns.udev
rules support substitutions.
24.6.1 Using operators in udev
rules #
Creating keys you can choose from several operators, depending on the type of key you want to create. Match keys will normally be used to find a value that either matches or explicitly mismatches the search value. Match keys contain either of the following operators:
==
Compare for equality. If the key contains a search pattern, all results matching this pattern are valid.
!=
Compare for non-equality. If the key contains a search pattern, all results matching this pattern are valid.
Any of the following operators can be used with assign keys:
=
Assign a value to a key. If the key previously consisted of a list of values, the key resets and only the single value is assigned.
+=
Add a value to a key that contains a list of entries.
:=
Assign a final value. Disallow any later change by later rules.
24.6.2 Using substitutions in udev
rules #
udev
rules support the use of
placeholders and substitutions. Use them in a similar fashion as you would
do in any other scripts. The following substitutions can be used with
udev
rules:
%r
,$root
The device directory,
/dev
by default.%p
,$devpath
The value of
DEVPATH
.%k
,$kernel
The value of
KERNEL
or the internal device name.%n
,$number
The device number.
%N
,$tempnode
The temporary name of the device file.
%M
,$major
The major number of the device.
%m
,$minor
The minor number of the device.
%s{ATTRIBUTE}
,$attr{ATTRIBUTE}
The value of a
sysfs
attribute (specified by ATTRIBUTE).%E{VARIABLE}
,$env{VARIABLE}
The value of an environment variable (specified by VARIABLE).
%c
,$result
The output of
PROGRAM
.%%
The
%
character.$$
The
$
character.
24.6.3 Using udev
match keys #
Match keys describe conditions that must be met before a
udev
rule can be applied. The
following match keys are available:
ACTION
The name of the event action, for example,
add
orremove
when adding or removing a device.DEVPATH
The device path of the event device, for example,
DEVPATH=/bus/pci/drivers/ipw3945
to search for all events related to the ipw3945 driver.KERNEL
The internal (kernel) name of the event device.
SUBSYSTEM
The subsystem of the event device, for example,
SUBSYSTEM=usb
for all events related to USB devices.ATTR{FILENAME}
sysfs
attributes of the event device. To match a string contained in thevendor
attribute file name, you could useATTR{vendor}=="On[sS]tream"
, for example.KERNELS
Let
udev
search the device path upward for a matching device name.SUBSYSTEMS
Let
udev
search the device path upward for a matching device subsystem name.DRIVERS
Let
udev
search the device path upward for a matching device driver name.ATTRS{FILENAME}
Let
udev
search the device path upward for a device with matchingsysfs
attribute values.ENV{KEY}
The value of an environment variable, for example,
ENV{ID_BUS}="ieee1394
to search for all events related to the FireWire bus ID.PROGRAM
Let
udev
execute an external program. To be successful, the program must return with exit code zero. The program's output, printed to STDOUT, is available to theRESULT
key.RESULT
Match the output string of the last
PROGRAM
call. Either include this key in the same rule as thePROGRAM
key or in a later one.
24.6.4 Using udev
assign keys #
In contrast to the match keys described above, assign keys do not describe
conditions that must be met. They assign values, names and actions to the
device nodes maintained by udev
.
NAME
The name of the device node to be created. After a rule has set a node name, all other rules with a
NAME
key for this node are ignored.SYMLINK
The name of a symbolic link related to the node to be created. Multiple matching rules can add symbolic links to be created with the device node. You can also specify multiple symbolic links for one node in one rule using the space character to separate the symbolic link names.
OWNER, GROUP, MODE
The permissions for the new device node. Values specified here overwrite anything that has been compiled in.
ATTR{KEY}
Specify a value to be written to a
sysfs
attribute of the event device. If the==
operator is used, this key is also used to match against the value of asysfs
attribute.ENV{KEY}
Tell
udev
to export a variable to the environment. If the==
operator is used, this key is also used to match against an environment variable.RUN
Tell
udev
to add a program to the list of programs to be executed for this device. Keep in mind to restrict this to very short tasks to avoid blocking further events for this device.LABEL
Add a label where a
GOTO
can jump to.GOTO
Tell
udev
to skip several rules and continue with the one that carries the label referenced by theGOTO
key.IMPORT{TYPE}
Load variables into the event environment such as the output of an external program.
udev
imports variables of several types. If no type is specified,udev
tries to determine the type itself based on the executable bit of the file permissions.program
tellsudev
to execute an external program and import its output.file
tellsudev
to import a text file.parent
tellsudev
to import the stored keys from the parent device.
WAIT_FOR_SYSFS
Tells
udev
to wait for the specifiedsysfs
file to be created for a certain device. For example,WAIT_FOR_SYSFS="ioerr_cnt"
informsudev
to wait until theioerr_cnt
file has been created.OPTIONS
The
OPTION
key may have several values:last_rule
tellsudev
to ignore all later rules.ignore_device
tellsudev
to ignore this event completely.ignore_remove
tellsudev
to ignore all later remove events for the device.all_partitions
tellsudev
to create device nodes for all available partitions on a block device.
24.7 Persistent device naming #
The dynamic device directory and the
udev
rules infrastructure make it
possible to provide stable names for all disk devices—regardless of
their order of recognition or the connection used for the device. Every
appropriate block device the kernel creates is examined by tools with
special knowledge about certain buses, drive types or file systems. Along
with the dynamic kernel-provided device node name,
udev
maintains classes of
persistent symbolic links pointing to the device:
/dev/disk |-- by-id | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B -> ../../sda | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part1 -> ../../sda1 | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part6 -> ../../sda6 | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part7 -> ../../sda7 | |-- usb-Generic_STORAGE_DEVICE_02773 -> ../../sdd | `-- usb-Generic_STORAGE_DEVICE_02773-part1 -> ../../sdd1 |-- by-label | |-- Photos -> ../../sdd1 | |-- SUSE10 -> ../../sda7 | `-- devel -> ../../sda6 |-- by-path | |-- pci-0000:00:1f.2-scsi-0:0:0:0 -> ../../sda | |-- pci-0000:00:1f.2-scsi-0:0:0:0-part1 -> ../../sda1 | |-- pci-0000:00:1f.2-scsi-0:0:0:0-part6 -> ../../sda6 | |-- pci-0000:00:1f.2-scsi-0:0:0:0-part7 -> ../../sda7 | |-- pci-0000:00:1f.2-scsi-1:0:0:0 -> ../../sr0 | |-- usb-02773:0:0:2 -> ../../sdd | |-- usb-02773:0:0:2-part1 -> ../../sdd1 `-- by-uuid |-- 159a47a4-e6e6-40be-a757-a629991479ae -> ../../sda7 |-- 3e999973-00c9-4917-9442-b7633bd95b9e -> ../../sda6 `-- 4210-8F8C -> ../../sdd1
24.8 Files used by udev
#
/sys/*
Virtual file system provided by the Linux kernel, exporting all currently known devices. This information is used by
udev
to create device nodes in/dev
/dev/*
Dynamically created device nodes and static content created with systemd-tmpfiles; for more information, see the
systemd-tmpfiles(8)
man page.
The following files and directories contain the crucial elements of the
udev
infrastructure:
/etc/udev/udev.conf
Main
udev
configuration file./etc/udev/rules.d/*
System-specific
udev
event matching rules. You can add custom rules here to modify or override the default rules from/usr/lib/udev/rules.d/*
.Files are parsed in alphanumeric order. Rules from files with a higher priority modify or override rules with lower priority. The lower the number, the higher the priority.
/usr/lib/udev/rules.d/*
Default
udev
event matching rules. The files in this directory are owned by packages and will be overwritten by updates. Do not add, remove or edit files here, use/etc/udev/rules.d
instead./usr/lib/udev/*
Helper programs called from
udev
rules./usr/lib/tmpfiles.d/
and/etc/tmpfiles.d/
Responsible for static
/dev
content.
24.9 More information #
For more information about the udev
infrastructure, refer to the following man pages:
udev
General information about
udev
, keys, rules and other important configuration issues.udevadm
udevadm
can be used to control the runtime behavior ofudev
, request kernel events, manage the event queue and provide simple debugging mechanisms.udevd
Information about the
udev
event managing daemon.
25 Special system features #
This chapter starts with information about various software packages, the
virtual consoles and the keyboard layout. We talk about software components
like bash
,
cron
and
logrotate
, because they were
changed or enhanced during the last release cycles. Even if they are small
or considered of minor importance, users should change their default
behavior, because these components are often closely coupled with the
system. The chapter concludes with a section about language and
country-specific settings (I18N and L10N).
25.1 Information about special software packages #
The following chapter provides basic information about the following tools: bash
, cron
, logrotate
, locate
, ulimit
and free
.
25.1.1 The bash
package and /etc/profile
#
Bash is the default system shell. When used as a login shell, it reads several initialization files. Bash processes them in the order they appear in this list:
/etc/profile
~/.profile
/etc/bash.bashrc
~/.bashrc
Make custom settings in ~/.profile
or
~/.bashrc
. To ensure the correct processing of these
files, it is necessary to copy the basic settings from
/etc/skel/.profile
or
/etc/skel/.bashrc
into the home directory of the user.
It is recommended to copy the settings from /etc/skel
after an update. Execute the following shell commands to prevent the loss of
personal adjustments:
>
mv ~/.bashrc ~/.bashrc.old>
cp /etc/skel/.bashrc ~/.bashrc>
mv ~/.profile ~/.profile.old>
cp /etc/skel/.profile ~/.profile
Then copy personal adjustments back from the *.old
files.
25.1.2 The cron package #
Use cron
to automatically run
commands in the background at predefined times. cron
uses specially formatted time tables, and
the tool comes with several default ones. Users can also specify custom
tables, if needed.
The cron tables are located in /var/spool/cron/tabs
.
/etc/crontab
serves as a systemwide cron table. Enter
the user name to run the command directly after the time table and before
the command. In Example 25.1, “Entry in /etc/crontab”,
root
is entered. Package-specific
tables, located in /etc/cron.d
, have the same format.
See the cron
man page (man cron
).
1-59/5 * * * * root test -x /usr/sbin/atrun && /usr/sbin/atrun
You cannot edit /etc/crontab
by calling the command
crontab -e
. This file must be loaded directly into an
editor, then modified and saved.
Several packages install shell scripts to the directories
/etc/cron.hourly
, /etc/cron.daily
,
/etc/cron.weekly
and
/etc/cron.monthly
, whose execution is controlled by
/usr/lib/cron/run-crons
.
/usr/lib/cron/run-crons
is run every 15 minutes from
the main table (/etc/crontab
). This guarantees that
processes that may have been neglected can be run at the proper time.
To run the hourly
, daily
or other
periodic maintenance scripts at custom times, remove the time stamp files
regularly using /etc/crontab
entries (see
Example 25.2, “/etc/crontab: remove time stamp files”, which removes the
hourly
one before every full hour, the
daily
one once a day at 2:14 a.m., etc.).
59 * * * * root rm -f /var/spool/cron/lastrun/cron.hourly 14 2 * * * root rm -f /var/spool/cron/lastrun/cron.daily 29 2 * * 6 root rm -f /var/spool/cron/lastrun/cron.weekly 44 2 1 * * root rm -f /var/spool/cron/lastrun/cron.monthly
Or you can set DAILY_TIME
in
/etc/sysconfig/cron
to the time at which
cron.daily
should start. The setting of
MAX_NOT_RUN
ensures that the daily tasks get triggered to
run, even if the user did not turn on the computer at the specified
DAILY_TIME
for a longer time. The maximum value of
MAX_NOT_RUN
is 14 days.
25.1.3 Stopping cron status messages #
To avoid the mail flood caused by cron status messages, the default value of
SEND_MAIL_ON_NO_ERROR
in
/etc/sysconfig/cron
is set to "no
"
for new installations. Even with this setting to "no
",
cron data output will still be sent to the MAILTO
address, as documented in the cron man page.
In the update case it is recommended to set these values according to your needs.
25.1.4 Log files: package logrotate #
There are several system services (daemons) that, along
with the kernel itself, regularly record the system status and specific
events onto log files. This way, the administrator can regularly check the
status of the system at a certain point in time, recognize errors or faulty
functions and troubleshoot them with pinpoint precision. These log files are
normally stored in /var/log
as specified by FHS and grow
on a daily basis. The logrotate
package helps
control the growth of these files. For more details refer to
Book “System Analysis and Tuning Guide”, Chapter 3 “System log files”, Section 3.3 “Managing log files with logrotate
”.
25.1.5 The locate
command #
locate
, a command for quickly finding files, is not
included in the standard scope of installed software. If desired, install
the package mlocate
, the successor of the package
findutils-locate
. The
updatedb
process is started
automatically every night or about 15 minutes after booting the system.
25.1.6 The ulimit
command #
With the ulimit
(user limits)
command, it is possible to set limits for the use of system resources and to
have these displayed. ulimit
is especially useful for
limiting available memory for applications. With this, an application can be
prevented from co-opting too much of the system resources and slowing or
even hanging up the operating system.
ulimit
can be used with various options. To limit memory
usage, use the options listed in Table 25.1, “ulimit
: Setting resources for the user”.
ulimit
: Setting resources for the user #
|
The maximum resident set size |
|
The maximum amount of virtual memory available to the shell |
|
The maximum size of the stack |
|
The maximum size of core files created |
|
All current limits are reported |
Systemwide default entries are set in /etc/profile
.
Editing this file directly is not recommended, because changes will be
overwritten during system upgrades. To customize systemwide profile
settings, use /etc/profile.local
. Per-user settings
should be made in
~USER/.profile
.
ulimit
: Settings in ~/.bashrc
## Limits maximum resident set size (physical memory): ulimit -m 98304 # Limits of virtual memory: ulimit -v 98304
Memory allocations must be specified in KB. For more detailed information,
see man bash
.
ulimit
support
Not all shells support ulimit
directives. PAM (for
example, pam_limits
) offers comprehensive adjustment
possibilities as an alternative to ulimit
.
25.1.7 The free
command #
The free
command displays the total amount of free and
used physical memory and swap space in the system and the buffers and
cache consumed by the kernel. The concept of available
RAM dates back to before the days of unified memory management.
The slogan free memory is bad memory applies well to
Linux. As a result, Linux has always made the effort to balance out caches
without actually allowing free or unused memory.
The kernel does not have direct knowledge of any applications or user data.
Instead, it manages applications and user data in a page
cache. If memory runs short, parts of it are written to the swap
partition or to files, from which they can initially be read using the
mmap
command (see man mmap
).
The kernel also contains other caches, such as the slab
cache, where the caches used for network access are stored. This
may explain the differences between the counters in
/proc/meminfo
. Most, but not all, of them can be
accessed via /proc/slabinfo
.
However, if your goal is to find out how much RAM is currently being used,
find this information in /proc/meminfo
.
25.1.8 Man pages and info pages #
For some GNU applications (such as tar), the man pages are no longer
maintained. For these commands, use the --help
option to
get a quick overview of the info pages, which provide more in-depth
instructions. Info
is GNU's hypertext system. Read an introduction to this system by entering
info
info
. Info pages can be viewed with
Emacs by entering emacs
-f info
or
directly in a console with info
. You can also use tkinfo,
xinfo or the help system to view info pages.
25.1.9 Selecting man pages using the man
command #
To read a man page enter man
MAN_PAGE. If a man page with the same name exists
in different sections, they will all be listed with the corresponding
section numbers. Select the one to display. If you do not enter a section
number within a few seconds, the first man page will be displayed.
To change this to the default system behavior, set
MAN_POSIXLY_CORRECT=1
in a shell initialization file such
as ~/.bashrc
.
25.1.10 Settings for GNU Emacs #
GNU Emacs is a complex work environment. The following sections cover the configuration files processed when GNU Emacs is started. More information is available at http://www.gnu.org/software/emacs/.
On start-up, Emacs reads several files containing the settings of the user,
system administrator and distributor for customization or preconfiguration.
The initialization file ~/.emacs
is installed to the
home directories of the individual users from /etc/skel
.
.emacs
, in turn, reads the file
/etc/skel/.gnu-emacs
. To customize the program, copy
.gnu-emacs
to the home directory (with cp
/etc/skel/.gnu-emacs ~/.gnu-emacs
) and make the desired settings
there.
.gnu-emacs
defines the file
~/.gnu-emacs-custom
as custom-file
.
If users make settings with the customize
options in
Emacs, the settings are saved to ~/.gnu-emacs-custom
.
With SUSE Linux Enterprise Server, the emacs
package installs the file site-start.el
in the directory
/usr/share/emacs/site-lisp
. The file
site-start.el
is loaded before the initialization file
~/.emacs
. Among other things,
site-start.el
ensures that special configuration files
distributed with Emacs add-on packages, such as
psgml
, are loaded automatically.
Configuration files of this type are located in
/usr/share/emacs/site-lisp
, too, and always begin with
suse-start-
. The local system administrator can specify
systemwide settings in default.el
.
More information about these files is available in the Emacs info file under
Init File: info:/emacs/InitFile
.
Information about how to disable the loading of these files (if necessary) is
also provided at this location.
The components of Emacs are divided into several packages:
The base package
emacs
.emacs-x11
(usually installed): the program with X11 support.emacs-nox
: the program without X11 support.emacs-info
: online documentation in info format.emacs-el
: the uncompiled library files in Emacs Lisp. These are not required at runtime.Numerous add-on packages can be installed if needed:
emacs-auctex
(LaTeX),psgml
(SGML and XML),gnuserv
(client and server operation) and others.
25.2 Virtual consoles #
Linux is a multiuser and multitasking system. The advantages of these features can be appreciated even on a stand-alone PC system. In text mode, there are six virtual consoles available. Switch between them using Alt–F1 through Alt–F6. The seventh console is reserved for X and the tenth console shows kernel messages.
To switch to a console from X without shutting it down, use Ctrl–Alt–F1 to Ctrl–Alt–F6. To return to X, press Alt–F7.
25.3 Keyboard mapping #
To standardize the keyboard mapping of programs, changes were made to the following files:
/etc/inputrc /etc/X11/Xmodmap /etc/skel/.emacs /etc/skel/.gnu-emacs /etc/skel/.vimrc /etc/csh.cshrc /etc/termcap /usr/share/terminfo/x/xterm /usr/share/X11/app-defaults/XTerm /usr/share/emacs/VERSION/site-lisp/term/*.el
These changes only affect applications that use terminfo
entries or whose configuration files are changed directly
(vi
, emacs
, etc.). Applications not
shipped with the system should be adapted to these defaults.
Under X, the compose key (multikey) can be enabled as explained in
/etc/X11/Xmodmap
.
Further settings are possible using the X Keyboard Extension (XKB).
Information about XKB is available in the documents listed in
/usr/share/doc/packages/xkeyboard-config
(part of the
xkeyboard-config
package).
25.4 Language and country-specific settings #
The system is, to a very large extent, internationalized and can be modified for local needs. Internationalization (I18N) allows specific localization (L10N). The abbreviations I18N and L10N are derived from the first and last letters of the words and, in between, the number of letters omitted.
Settings are made with LC_
variables defined in the
file /etc/sysconfig/language
. This refers not only to
native language support, but also to the categories
Messages (Language), Character Set,
Sort Order, Time and Date,
Numbers and Money. Each of these
categories can be defined directly with its own variable or indirectly with a
master variable in the file language
(see the
locale
man page).
RC_LC_MESSAGES
,RC_LC_CTYPE
,RC_LC_COLLATE
,RC_LC_TIME
,RC_LC_NUMERIC
,RC_LC_MONETARY
These variables are passed to the shell without the
RC_
prefix and represent the listed categories. The shell profiles concerned are listed below. The current setting can be shown with the commandlocale
.RC_LC_ALL
This variable, if set, overwrites the values of the variables already mentioned.
RC_LANG
If none of the previous variables are set, this is the fallback. By default, only
RC_LANG
is set. This makes it easier for users to enter their own values.ROOT_USES_LANG
This variable can be set to
yes
orctype
(default). If set toyes
,root
uses language and country-specific settings, otherwise the system administrator always works in a POSIX environment.
The variables can be set with the YaST sysconfig editor. The value of such a variable contains the language code, country code, encoding and modifier. The individual components are joined by special characters:
LANG=<language>[[_<COUNTRY>].<Encoding>[@<Modifier>]]
25.4.1 System-wide locale settings #
systemd
reads /etc/locale.conf
at early boot. The locale settings configured in this file are
inherited by every service or user, unless there are individual
settings.
Earlier versions of SUSE Linux Enterprise Server read locale settings from
/etc/sysconfig/language
,
/etc/sysconfig/keyboard
, and
/etc/sysconfig/console
.
Starting with SUSE Linux Enterprise Server
15 GA,
these files are considered obsolete.
systemd
does not read settings from these files anymore.
Instead, systemd
reads /etc/locale.conf
.
However, variables defined in /etc/sysconfig/language
will still be used: They override the system-wide locale and can be used to
define different locale settings for user shells (see Section 25.4.2, “Some examples”).
To set the system-wide locale, you can either:
Write your settings in
/etc/locale.conf
. Each line is a environment-like variable assignment (seeman 5 locale.conf
for a list of variables):LANG=de_DE.UTF-8
To fine-tune the settings, you can add additional variables, one variable per line.
Use the command
localectl
:#
localectl
set-locale LANG=de_DE.UTF-8Same here, you can also specify additional variables after the
localectl set-locale
command.
To keep backward compatibility with old systems during the update of the systemd package, all variables mentioned will be migrated from sysconfig to their final destinations if they are not already defined there.
25.4.2 Some examples #
You should always set the language and country codes together. Language settings follow the standard ISO 639 available at http://www.evertype.com/standards/iso639/iso639-en.html and http://www.loc.gov/standards/iso639-2/. Country codes are listed in ISO 3166, see http://en.wikipedia.org/wiki/ISO_3166.
It only makes sense to set values for which usable description files can be
found in /usr/lib/locale
. Additional description files
can be created from the files in /usr/share/i18n
using
the command localedef
. The description files are part of
the glibc-i18ndata
package. A description file for
en_US.UTF-8
(for English and United States) can be
created with:
localedef -i en_US -f UTF-8 en_US.UTF-8
-
LANG=en_US.UTF-8
This is the default setting if American English is selected during installation. If you selected another language, that language is enabled but still with UTF-8 as the character encoding.
-
LANG=en_US.ISO-8859-1
This sets the language to English, country to United States and the character set to
ISO-8859-1
. This character set does not support the Euro sign, but it can be useful sometimes for programs that have not been updated to supportUTF-8
. The string defining the charset (ISO-8859-1
in this case) is then evaluated by programs like Emacs.LANG=en_IE@euro
The above example explicitly includes the Euro sign in a language setting. This setting is obsolete now, as UTF-8 also covers the Euro symbol. It is only useful if an application supports ISO-8859-15 and not UTF-8.
Changes to /etc/sysconfig/language
are activated by the
following process chain:
For the Bash:
/etc/profile
reads/etc/profile.d/lang.sh
which, in turn, analyzes/etc/sysconfig/language
.For tcsh: At login,
/etc/csh.login
reads/etc/profile.d/lang.csh
which, in turn, analyzes/etc/sysconfig/language
.
This ensures that any changes to
/etc/sysconfig/language
are available at the next login
to the respective shell, without having to manually activate
them.
Users can override the system defaults by editing their
~/.bashrc
accordingly. For example, if you do not want
to use the system-wide en_US
for program messages,
include LC_MESSAGES=es_ES
so that messages are
displayed in Spanish instead.
25.4.3 Locale settings in ~/.i18n
#
If you are not satisfied with locale system defaults, change the settings in
~/.i18n
according to the Bash scripting syntax. Entries
in ~/.i18n
override system defaults from
/etc/sysconfig/language
. Use the same variable names
but without the RC_
namespace prefixes. For example, use
LANG
instead of RC_LANG
:
LANG=cs_CZ.UTF-8 LC_COLLATE=C
25.4.4 Settings for language support #
Files in the category Messages are, as a rule, only
stored in the corresponding language directory (like
en
) to have a fallback. If you set
LANG
to en_US
and the message
file in /usr/share/locale/en_US/LC_MESSAGES
does not
exist, it falls back to
/usr/share/locale/en/LC_MESSAGES
.
A fallback chain can also be defined, for example, for Breton to French or for Galician to Spanish to Portuguese:
LANGUAGE="br_FR:fr_FR"
LANGUAGE="gl_ES:es_ES:pt_PT"
If desired, use the Norwegian variants Nynorsk and Bokmål instead (with
additional fallback to no
):
LANG="nn_NO"
LANGUAGE="nn_NO:nb_NO:no"
or
LANG="nb_NO"
LANGUAGE="nb_NO:nn_NO:no"
Note that in Norwegian, LC_TIME
is also treated
differently.
One problem that can arise is a separator used to delimit groups of digits
not being recognized properly. This occurs if LANG
is set to only a two-letter language code like de
, but
the definition file glibc uses is located in
/usr/share/lib/de_DE/LC_NUMERIC
. Thus
LC_NUMERIC
must be set to de_DE
to make the separator definition visible to the system.
25.4.5 More information #
The GNU C Library Reference Manual, Chapter “Locales and Internationalization”. It is included in the package glibc-info.
Markus Kuhn, UTF-8 and Unicode FAQ for Unix/Linux, currently at https://www.cl.cam.ac.uk/~mgk25/unicode.html.
26 Using NetworkManager #
NetworkManager is the ideal solution for laptops and other portable computers. It supports state-of-the-art encryption types and standards for network connections, including connections to 802.1X protected networks. 802.1X is the “IEEE Standard for Local and Metropolitan Area Networks—Port-Based Network Access Control”. With NetworkManager, you need not worry about configuring network interfaces and switching between wired or wireless networks when you are on the move. NetworkManager can automatically connect to known wireless networks or manage several network connections in parallel—the fastest connection is then used as default. Furthermore, you can manually switch between available networks and manage your network connection using an applet in the system tray.
Instead of only one connection being active, multiple connections may be active at once. This enables you to unplug your laptop from an Ethernet and remain connected via a wireless connection.
NetworkManager is only supported by SUSE for desktop workloads with SLED or the
Workstation extension. All server certifications are done with
wicked
as the network configuration tool, and using NetworkManager may
invalidate them. NetworkManager is not supported by SUSE for server workloads.
26.1 Use cases for NetworkManager #
NetworkManager provides a sophisticated and intuitive user interface, which enables users to easily switch their network environment. However, NetworkManager is not a suitable solution in the following cases:
Your computer provides network services for other computers in your network, for example, it is a DHCP or DNS server.
Your computer is a Xen server or your system is a virtual system inside Xen.
26.2 Enabling or disabling NetworkManager #
On desktop and laptop computers, NetworkManager is enabled by default. You can disable and enable it at any time using the Network Settings module in YaST.
Run YaST and go to
› .The
dialog opens. Go to the tab.To configure and manage your network connections with NetworkManager:
In the
field, select .Click
and close YaST.Configure your network connections with NetworkManager as described in Section 26.3, “Configuring network connections”.
To deactivate NetworkManager and control the network with your own configuration:
In the
field, choose .Click
.Set up your network card with YaST using automatic configuration via DHCP or a static IP address.
Find a detailed description of the network configuration with YaST in Section 19.4, “Configuring a network connection with YaST”.
26.3 Configuring network connections #
After enabling NetworkManager in YaST, configure your network connections with the NetworkManager front-end available in GNOME. It shows tabs for all types of network connections, such as wired, wireless, mobile broadband, DSL, and VPN connections.
In previous SUSE Linux Enterprise Server releases, network connections were configured using an application called NetworkManager Connection Editor. This is no longer installed by default, because GNOME Control Center has fully replaced its configuration capabilities.
If you still need to use NetworkManager Connection Editor to configure network connections, install the NetworkManager-connection-editor package manually:
>
sudo
zypper install NetworkManager-connection-editor
To open the network configuration dialog in GNOME, open the settings menu via the status menu and click the
entry.
Depending on your system setup, you may not be allowed to configure
connections. In a secured environment, some options may be locked or
require root
permission. Ask your system administrator for details.
Open the NetworkManager configuration dialog.
To add a Connection:
Click the
icon in the lower left corner.Select your preferred connection type and follow the instructions.
When you are finished click
.After confirming your changes, the newly-configured network connection appears in the list of available networks in the Status Menu.
To edit a connection:
Select the entry to edit.
Click the gear icon to open the
dialog.Insert your changes and click
to save them.To make your connection available as a system connection go to the Section 26.4.1, “User and system connections”.
tab and set the check box . For more information about user and system connections, see
26.3.1 Managing wired network connections #
If your computer is connected to a wired network, use the NetworkManager applet to manage the connection.
Open the Status Menu and click
to change the connection details or to switch it off.To change the settings click
and then click the gear icon.To switch off all network connections, activate the
setting.
26.3.2 Managing wireless network connections #
Visible wireless networks are listed in the GNOME NetworkManager applet menu under
. The signal strength of each network is also shown in the menu. Encrypted wireless networks are marked with a shield icon.To connect to a visible wireless network, open the Status Menu and click
.Click
to enable it.Click
, select your Wi-Fi Network and click .If the network is encrypted, a configuration dialog opens. It shows the type of encryption the network uses and text boxes for entering the login credentials.
To connect to a network that does not broadcast its service set identifier (SSID or ESSID) and therefore cannot be detected automatically, open the Status Menu and click
.Click
to open the detailed settings menu.Make sure your Wi-Fi is enabled and click
.In the dialog that opens, enter the SSID or ESSID in
and set encryption parameters if necessary.
A wireless network that has been chosen explicitly will remain connected as long as possible. If a network cable is plugged in during that time, any connections that have been set to
will be connected, while the wireless connection remains up.26.3.3 Configuring your Wi-Fi/Bluetooth card as an access point #
If your Wi-Fi/Bluetooth card supports access point mode, you can use NetworkManager for the configuration.
Open the Status Menu and click
.Click
to open the detailed settings menu.Click
and follow the instructions.Use the credentials shown in the resulting dialog to connect to the hotspot from a remote machine.
26.3.4 NetworkManager and VPN #
NetworkManager supports several Virtual Private Network (VPN) technologies. For each technology, SUSE Linux Enterprise Server comes with a base package providing the generic support for NetworkManager. In addition to that, you also need to install the respective desktop-specific package for your applet.
- OpenVPN
To use this VPN technology, install:
NetworkManager-openvpn
NetworkManager-openvpn-gnome
- OpenConnect
To use this VPN technology, install:
NetworkManager-openconnect
NetworkManager-openconnect-gnome
- PPTP (point-to-point tunneling protocol)
To use this VPN technology, install:
NetworkManager-pptp
NetworkManager-pptp-gnome
The following procedure describes how to set up your computer as an OpenVPN client using NetworkManager. Setting up other types of VPNs works analogously.
Before you begin, make sure that the package
NetworkManager-openvpn-gnome
is
installed and all dependencies have been resolved.
Open the application
by clicking the status icons at the right end of the panel and clicking the icon. In the window , choose .Click the
icon.Select
and then .Choose the
type. Depending on the setup of your OpenVPN server, choose or .Insert the necessary values into the respective text boxes. For our example configuration, these are:
The remote endpoint of the VPN server
The user (only available when you have selected
)The password for the user (only available when you have selected
)/etc/openvpn/client1.crt
/etc/openvpn/ca.crt
/etc/openvpn/client1.key
Finish the configuration with
.To enable the connection, in the
panel of the application click the switch button. Alternatively, click the status icons at the right end of the panel, click the name of your VPN and then .
26.4 NetworkManager and security #
NetworkManager distinguishes two types of wireless connections: trusted and untrusted. A trusted connection is any network that you explicitly selected in the past. All others are untrusted. Trusted connections are identified by the name and MAC address of the access point. Using the MAC address ensures that you cannot use a different access point with the name of your trusted connection.
NetworkManager periodically scans for available wireless networks. If multiple trusted networks are found, the most recently used is automatically selected. NetworkManager waits for your selection in case if all networks are untrusted.
If the encryption setting changes but the name and MAC address remain the same, NetworkManager attempts to connect, but first you are asked to confirm the new encryption settings and provide any updates, such as a new key.
If you switch from using a wireless connection to offline mode, NetworkManager blanks the SSID or ESSID. This ensures that the card is disconnected.
26.4.1 User and system connections #
NetworkManager knows two types of connections: user
and
system
connections.
User connections require every user to authenticate in NetworkManager, which stores the user's credentials in their local GNOME keyring so they don't have to re-enter them every time they connect.
System connections are available to all users automatically. The first user to create the connection enters any necessary credentials, and then all other users have access without needing to know the credentials. The difference in configuring a user or system connection is a single checkbox, Section 26.3, “Configuring network connections”.
. For information on how to configure user or system connections with NetworkManager, refer to26.4.2 Storing passwords and credentials #
If you do not want to re-enter your credentials each time you want to connect to an encrypted network, you can use the GNOME Keyring Manager to store your credentials encrypted on the disk, secured by a master password.
26.4.3 Firewall zones #
firewalld
zones in NetworkManager #The firewall zones set general rules about which network connections are allowed. To configure the zone of firewalld for a wired connection, go to the Identity tab of the connection settings. To configure the zone of firewalld for a WiFi connection, go to the Security tab of the connection settings.
If you are in your home network, use the zone
home
. For public wireless networks, switch to
public
. If you are in a secure environment and
want to allow all connections, use the zone
trusted
.
For details about firewalld, see Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4 “firewalld
”.
26.5 Frequently asked questions #
In the following, find some frequently asked questions about configuring special network options with NetworkManager.
- 1. How to tie a connection to a specific device?
By default, connections in NetworkManager are device type-specific: they apply to all physical devices with the same type. If more than one physical device per connection type is available (for example, your machine is equipped with two Ethernet cards), you can tie a connection to a certain device.
To do this in GNOME, first look up the MAC address of your device (use the
available from the applet, or use the output of command line tools likenm-tool
orwicked show all
). Then start the dialog for configuring network connections and choose the connection you want to modify. On the or tab, enter the of the device and confirm your changes.
- 2. How to specify a certain access point in case multiple access points with the same ESSID are detected?
When multiple access points with different wireless bands (a/b/g/n) are available, the access point with the strongest signal is automatically chosen by default. To override this, use the
field when configuring wireless connections.The Basic Service Set Identifier (BSSID) uniquely identifies each Basic Service Set. In an infrastructure Basic Service Set, the BSSID is the MAC address of the wireless access point. In an independent (ad-hoc) Basic Service Set, the BSSID is a locally administered MAC address generated from a 46-bit random number.
Start the dialog for configuring network connections as described in Section 26.3, “Configuring network connections”. Choose the wireless connection you want to modify and click . On the tab, enter the BSSID.
- 3. How to share network connections with other computers?
The primary device (the device which is connected to the Internet) does not need any special configuration. However, you need to configure the device that is connected to the local hub or machine as follows:
Start the dialog for configuring network connections as described in Section 26.3, “Configuring network connections”. Choose the connection you want to modify and click . Switch to the tab and from the drop-down box, activate . That will enable IP traffic forwarding and run a DHCP server on the device. Confirm your changes in NetworkManager.
As the DCHP server uses port
67
, make sure that it is not blocked by the firewall: On the machine sharing the connections, start YaST and select › . Switch to the category. If is not already shown as , select from and click . Confirm your changes in YaST.
- 4. How to provide static DNS information with automatic (DHCP, PPP, VPN) addresses?
In case a DHCP server provides invalid DNS information (and/or routes), you can override it. Start the dialog for configuring network connections as described in Section 26.3, “Configuring network connections”. Choose the connection you want to modify and click . Switch to the tab, and from the drop-down box, activate . Enter the DNS information in the and fields. To click and activate the respective check box. Confirm your changes.
- 5. How to make NetworkManager connect to password protected networks before a user logs in?
Define a
system connection
that can be used for such purposes. For more information, refer to Section 26.4.1, “User and system connections”.
26.6 Troubleshooting #
Connection problems can occur. Some common problems related to NetworkManager include the applet not starting or a missing VPN option. Methods for resolving and preventing these problems depend on the tool used.
- NetworkManager desktop applet does not start
The applets starts automatically if the network is set up for NetworkManager control. If the applet does not start, check if NetworkManager is enabled in YaST as described in Section 26.2, “Enabling or disabling NetworkManager”. Then make sure that the NetworkManager-gnome package is also installed.
If the desktop applet is installed but is not running for some reason, start it manually with the command
nm-applet
.- NetworkManager applet does not include the VPN option
Support for NetworkManager, applets, and VPN for NetworkManager is distributed in separate packages. If your NetworkManager applet does not include the VPN option, check if the packages with NetworkManager support for your VPN technology are installed. For more information, see Section 26.3.4, “NetworkManager and VPN”.
- No network connection available
If you have configured your network connection correctly and all other components for the network connection (router, etc.) are also up and running, it sometimes helps to restart the network interfaces on your computer. To do so, log in to a command line as
root
and runsystemctl restart wickeds
.
26.7 More information #
More information about NetworkManager can be found on the following Web sites and directories:
- NetworkManager project page
https://gitlab.freedesktop.org/NetworkManager/NetworkManager
- Package documentation
Also check out the information in the following directories for the latest information about NetworkManager and the GNOME applet:
/usr/share/doc/packages/NetworkManager/
,/usr/share/doc/packages/NetworkManager-gnome/
.
27 Power management #
IBM Z The features and hardware described in this chapter do not exist on IBM Z, making this chapter irrelevant for these platforms.
Power management is especially important on laptop computers, but is also useful on other systems. ACPI (Advanced Configuration and Power Interface) is available on all modern computers (laptops, desktops, and servers). Power management technologies require suitable hardware and BIOS routines. Most laptops and many modern desktops and servers meet these requirements. It is also possible to control CPU frequency scaling to save power or decrease noise.
27.1 Power saving functions #
Power saving functions are not only significant for the mobile use of laptops, but also for desktop systems. The main functions and their use in ACPI are:
- Standby
Not supported.
- Suspend (to memory)
This mode writes the entire system state to the RAM. Subsequently, the entire system except the RAM is put to sleep. In this state, the computer consumes very little power. The advantage of this state is the possibility of resuming work at the same point within a few seconds without having to boot and restart applications. This function corresponds to the ACPI state
S3
.- Hibernation (suspend to disk)
In this operating mode, the entire system state is written to the hard disk and the system is powered off. There must be a swap partition at least as big as the RAM to write all the active data. Reactivation from this state takes about 30 to 90 seconds. The state prior to the suspend is restored. Some manufacturers offer useful hybrid variants of this mode, such as RediSafe in IBM Thinkpads. The corresponding ACPI state is
S4
. In Linux, suspend to disk is performed by kernel routines that are independent from ACPI.Note: Changed UUID for swap partitions when formatting viamkswap
Do not reformat existing swap partitions with
mkswap
if possible. Reformatting withmkswap
will change the UUID value of the swap partition. Either reformat via YaST (which will update/etc/fstab
) or adjust/etc/fstab
manually.- Battery monitor
ACPI checks the battery charge status and provides information about it. Additionally, it coordinates actions to perform when a critical charge status is reached.
- Automatic power-off
Following a shutdown, the computer is powered off. This is especially important when an automatic shutdown is performed shortly before the battery is empty.
- Processor speed control
In connection with the CPU, energy can be saved in three different ways: frequency and voltage scaling (also known as PowerNow! or Speedstep), throttling and putting the processor to sleep (C-states). Depending on the operating mode of the computer, these methods can also be combined.
27.2 Advanced configuration and power interface (ACPI) #
ACPI was designed to enable the operating system to set up and control the individual hardware components. ACPI supersedes both Power Management Plug and Play (PnP) and Advanced Power Management (APM). It delivers information about the battery, AC adapter, temperature, fan and system events, like “close lid” or “battery low.”
The BIOS provides tables containing information about the individual
components and hardware access methods. The operating system uses this
information for tasks like assigning interrupts or activating and
deactivating components. Because the operating system executes commands
stored into the BIOS, the functionality depends on the BIOS implementation.
The tables ACPI can detect and load are reported in journald. See
Chapter 17, journalctl
: Query the systemd
journal for more information on viewing the journal
log messages. See Section 27.2.2, “Troubleshooting” for more information
about troubleshooting ACPI problems.
27.2.1 Controlling the CPU performance #
The CPU can save energy in three ways:
Frequency and Voltage Scaling
Throttling the Clock Frequency (T-states)
Putting the Processor to Sleep (C-states)
Depending on the operating mode of the computer, these methods can be combined. Saving energy also means that the system heats up less and the fans are activated less frequently.
Frequency scaling and throttling are only relevant if the processor is busy, because the most economic C-state is applied anyway when the processor is idle. If the CPU is busy, frequency scaling is the recommended power saving method. Often the processor only works with a partial load. In this case, it can be run with a lower frequency. Usually, dynamic frequency scaling controlled by the kernel on-demand governor is the best approach.
Throttling should be used as the last resort, for example, to extend the battery operation time despite a high system load. However, some systems do not run smoothly when they are throttled too much. Moreover, CPU throttling does not make sense if the CPU has little to do.
For in-depth information, refer to Book “System Analysis and Tuning Guide”, Chapter 12 “Power management”.
27.2.2 Troubleshooting #
There are two different types of problems. On one hand, the ACPI code of the kernel may contain bugs that were not detected in time. In this case, a solution will be made available for download. More often, the problems are caused by the BIOS. Sometimes, deviations from the ACPI specification are purposely integrated in the BIOS to circumvent errors in the ACPI implementation of other widespread operating systems. Hardware components that have serious errors in the ACPI implementation are recorded in a blacklist that prevents the Linux kernel from using ACPI for these components.
The first thing to do when problems are encountered is to update the BIOS. If the computer does not boot, one of the following boot parameters may be helpful:
- pci=noacpi
Do not use ACPI for configuring the PCI devices.
- acpi=ht
Only perform a simple resource configuration. Do not use ACPI for other purposes.
- acpi=off
Disable ACPI.
Some newer machines (especially SMP systems and AMD64 systems) need ACPI for configuring the hardware correctly. On these machines, disabling ACPI can cause problems.
Sometimes, the machine is confused by hardware that is attached over USB or FireWire. If a machine refuses to boot, unplug all unneeded hardware and try again.
Monitor the boot messages of the system with the command dmesg
-T
| grep -2i acpi
(or all messages, because the
problem may not be caused by ACPI) after booting. If an error occurs while
parsing an ACPI table, the most important table—the DSDT
(Differentiated System Description Table)—can be
replaced with an improved version. In this case, the faulty DSDT of the
BIOS is ignored. The procedure is described in
Section 27.4, “Troubleshooting”.
In the kernel configuration, there is a switch for activating ACPI debug messages. If a kernel with ACPI debugging is compiled and installed, detailed information is issued.
If you experience BIOS or hardware problems, it is always advisable to contact the manufacturers. Especially if they do not always provide assistance for Linux, they should be confronted with the problems. Manufacturers will only take the issue seriously if they realize that an adequate number of their customers use Linux.
27.2.2.1 More information #
https://tldp.org/HOWTO/ACPI-HOWTO/ (detailed ACPI HOWTO, contains DSDT patches)
https://uefi.org/specifications (Advanced Configuration & Power Interface Specification)
https://01.org/linux-acpi (the Linux ACPI project)
27.3 Rest for the hard disk #
In Linux, the hard disk can be put to sleep entirely if it is not needed or
it can be run in a more economic or quieter mode. On modern laptops, you do
not need to switch off the hard disks manually, because they automatically
enter an economic operating mode whenever they are not needed. However, if
you want to maximize power savings, test some of the following methods,
using the hdparm
command.
It can be used to modify various hard disk settings. The option
-y
instantly switches the hard disk to the standby mode.
-Y
puts it to sleep. hdparm
-S
X causes the hard disk to be
spun down after a certain period of inactivity. Replace
X as follows: 0
disables this
mechanism, causing the hard disk to run continuously. Values from
1
to 240
are multiplied by 5
seconds. Values from 241
to 251
correspond to 1 to 11 times 30 minutes.
Internal power saving options of the hard disk can be controlled with the
option -B
. Select a value from 0
to
255
for maximum saving to maximum throughput. The result
depends on the hard disk used and is difficult to assess. To make a hard
disk quieter, use the option -M
. Select a value from
128
to 254
for quiet to fast.
Often, it is not so easy to put the hard disk to sleep. In Linux, numerous
processes write to the hard disk, waking it up repeatedly. Therefore, it is
important to understand how Linux handles data that needs to be written to
the hard disk. First, all data is buffered in the RAM. This buffer is
monitored by the pdflush
daemon.
When the data reaches a certain age limit or when the buffer is filled to a
certain degree, the buffer content is flushed to the hard disk. The buffer
size is dynamic and depends on the size of the memory and the system load.
By default, pdflush is set to short intervals to achieve maximum data
integrity. It checks the buffer every 5 seconds and writes the data to the
hard disk. The following variables are interesting:
/proc/sys/vm/dirty_writeback_centisecs
Contains the delay until a pdflush thread wakes up (in hundredths of a second).
/proc/sys/vm/dirty_expire_centisecs
Defines after which timeframe a dirty page should be written at latest. Default is
3000
, which means 30 seconds./proc/sys/vm/dirty_background_ratio
Maximum percentage of dirty pages until pdflush begins to write them. Default is
5
%./proc/sys/vm/dirty_ratio
When the dirty pages exceed this percentage of the total memory, processes are forced to write dirty buffers during their time slice instead of continuing to write.
Changes to the pdflush
daemon
settings can compromise data integrity.
Apart from these processes, journaling file systems, like
Btrfs
,
Ext3
,
Ext4
and others write their
metadata independently from pdflush
,
which also prevents the hard disk from spinning down.
Another important factor is the way active programs behave. For example, good editors regularly write hidden backups of the currently modified file to the hard disk, causing the disk to wake up. Features like this can be disabled at the expense of data integrity.
In this connection, the mail daemon postfix uses the variable
POSTFIX_LAPTOP
. If this variable is set to
yes
, postfix accesses the hard disk far less frequently.
27.4 Troubleshooting #
All error messages and alerts are logged in the system journal, which can be
queried with the command journalctl
(see
Chapter 17, journalctl
: Query the systemd
journal for more information). The following
sections cover the most common problems.
27.4.1 CPU frequency does not work #
Refer to the kernel sources to see if your processor is supported. You may
need a special kernel module or module option to activate CPU frequency
control. If the kernel-source
package is installed, this information is available in
/usr/src/linux/Documentation/cpu-freq/*
.
28 Persistent memory #
This chapter contains additional information about using SUSE Linux Enterprise with non-volatile main memory, also known as Persistent Memory, comprising one or more NVDIMMs.
28.1 Introduction #
Persistent memory is a new type of computer storage, combining speeds approaching those of dynamic RAM (DRAM) along with RAM's byte-by-byte addressability, plus the permanence of solid-state disks (SSDs).
SUSE currently supports the use of persistent memory with SUSE Linux Enterprise Server on machines with the AMD64/Intel 64 and POWER architectures.
Like conventional RAM, persistent memory is installed directly into motherboard memory slots. As such, it is supplied in the same physical form factor as RAM—as DIMMs. These are known as NVDIMMs: non-volatile dual inline memory modules.
Unlike RAM, though, persistent memory is also similar to flash-based SSDs in several ways. Both are based on forms of solid-state memory circuitry, but despite this, both provide non-volatile storage: Their contents are retained when the system is powered off or restarted. For both forms of medium, writing data is slower than reading it, and both support a limited number of rewrite cycles. Finally, also like SSDs, sector-level access to persistent memory is possible if that is more suitable for a particular application.
Different models use different forms of electronic storage medium, such as Intel 3D XPoint, or a combination of NAND-flash and DRAM. New forms of non-volatile RAM are also in development. This means that different vendors and models of NVDIMM offer different performance and durability characteristics.
Because the storage technologies involved are in an early stage of development, different vendors' hardware may impose different limitations. Thus, the following statements are generalizations.
Persistent memory is up to ten times slower than DRAM, but around a thousand times faster than flash storage. It can be rewritten on a byte-by-byte basis rather than flash memory's whole-sector erase-and-rewrite process. Finally, while rewrite cycles are limited, most forms of persistent memory can handle millions of rewrites, compared to the thousands of cycles of flash storage.
This has two important consequences:
It is not possible with current technology to run a system with only persistent memory and thus achieve completely non-volatile main memory. You must use a mixture of both conventional RAM and NVDIMMs. The operating system and applications will execute in conventional RAM, with the NVDIMMs providing very fast supplementary storage.
The performance characteristics of different vendors' persistent memory mean that it may be necessary for programmers to be aware of the hardware specifications of the NVDIMMs in a particular server, including how many NVDIMMs there are and in which memory slots they are fitted. This will obviously impact hypervisor use, migration of software between different host machines, and so on.
This new storage subsystem is defined in version 6 of the ACPI standard.
However, libnvdimm
supports pre-standard NVDIMMs and
they can be used in the same way.
Intel Optane DIMMs memory can be used in specific modes:
In App Direct Mode, the Intel Optane memory is used as fast persistent storage, an alternative to SSDs and NVMe devices. Data in this mode is kept when the system is powered off.
App Direct Mode has been supported since SLE 12 SP4.
In Memory Mode, the Intel Optane memory serves as a cost-effective, high-capacity alternative to DRAM. In this mode, separate DRAM DIMMs act as a cache for the most frequently accessed data while the Optane DIMMs memory provides large memory capacity. However, compared with DRAM-only systems, this mode is slower under random access workloads. If you run applications without Optane-specific enhancements that take advantage of this mode, memory performance may decrease. Data in this mode is lost when the system is powered off.
Memory Mode has been supported since SLE 15 SP1.
In Mixed Mode, the Intel Optane memory is partitioned, so it can serve in both modes simultaneously.
Mixed Mode has been supported since SLE 15 SP1.
For more detailed information about Intel Optane DC persistent memory, refer to https://www.intel.com/content/dam/support/us/en/documents/memory-and-storage/data-center-persistent-mem/Intel-Optane-DC-Persistent-Memory-Quick-Start-Guide.pdf.
28.2 Terms #
- Region
A region is a block of persistent memory that can be divided up into one or more namespaces. You cannot access the persistent memory of a region without first allocating it to a namespace.
- Namespace
A single contiguously-addressed range of non-volatile storage, comparable to NVM Express SSD namespaces, or to SCSI Logical Units (LUNs). Namespaces appear in the server's
/dev
directory as separate block devices. Depending on the method of access required, namespaces can either amalgamate storage from multiple NVDIMMs into larger volumes, or allow it to be partitioned into smaller volumes.- Mode
Each namespace also has a mode that defines which NVDIMM features are enabled for that namespace. Sibling namespaces of the same parent region will always have the same type, but might be configured to have different modes. Namespace modes include:
- devdax
Device-DAX mode. Creates a single-character device file (
/dev/daxX.Y
). Does not require file system creation.- fsdax
File system-DAX mode. Default if no other mode is specified. Creates a block device (
/dev/pmemX [.Y]
) which supports DAX forext4
orXFS
.- sector
For legacy file systems which do not checksum metadata. Suitable for small boot volumes. Compatible with other operating systems.
- raw
A memory disk without a label or metadata. Does not support DAX. Compatible with other operating systems.
Noteraw
mode is not supported by SUSE. It is not possible to mount file systems onraw
namespaces.
- Type
Each namespace and region has a type that defines the way in which the persistent memory associated with that namespace or region can be accessed. A namespace always has the same type as its parent region. There are two different types: Persistent Memory, which can be configured in two different ways, and the deprecated Block Mode.
- Persistent memory (PMEM)
PMEM storage offers byte-level access, just like RAM. Using PMEM, a single namespace can include multiple interleaved NVDIMMs, allowing them all to be used as a single device.
There are two ways to configure a PMEM namespace.
- PMEM with DAX
A PMEM namespace configured for Direct Access (DAX) means that accessing the memory bypasses the kernel's page cache and goes direct to the medium. Software can directly read or write every byte of the namespace separately.
- PMEM with block translation table (BTT)
A PMEM namespace configured to operate in BTT mode is accessed on a sector-by-sector basis, like a conventional disk drive, rather than the more RAM-like byte-addressable model. A translation table mechanism batches accesses into sector-sized units.
The advantage of BTT is data protection. The storage subsystem ensures that each sector is completely written to the underlying medium. If a sector cannot be completely written (that is, if the write operation fails for some reason), then the whole sector will be rolled back to its previous state. Thus a given sector cannot be partially written.
Additionally, access to BTT namespaces is cached by the kernel.
The drawback is that DAX is not possible for BTT namespaces.
- Block mode (BLK)
Block mode storage addresses each NVDIMM as a separate device. Its use is deprecated and no longer supported.
Apart from
devdax
namespaces, all other types must be formatted with a file system, just as with a conventional drive. SUSE Linux Enterprise Server supports theext2
,ext4
andXFS
file systems for this.- Direct access (DAX)
DAX allows persistent memory to be directly mapped into a process's address space, for example using the
mmap
system call.- DIMM physical address (DPA)
A memory address as an offset into a single DIMM's memory; that is, starting from zero as the lowest addressable byte on that DIMM.
- Label
Metadata stored on the NVDIMM, such as namespace definitions. This can be accessed using DSMs.
- Device-specific method (DSM)
ACPI method to access the firmware on an NVDIMM.
28.3 Use cases #
28.3.1 PMEM with DAX #
It is important to note that this form of memory access is not transactional. In the event of a power outage or other system failure, data may not be completely written into storage. PMEM storage is only suitable if the application can handle the situation of partially-written data.
28.3.1.1 Applications that benefit from large amounts of byte-addressable storage #
If the server will host an application that can directly use large amounts
of fast storage on a byte-by-byte basis, the programmer can use the mmap
system call to place blocks of persistent memory directly into the
application's address space, without using any additional system RAM.
28.3.1.2 Avoiding use of the kernel page cache #
Avoid using the kernel page cache if you wish to conserve the use of RAM for the page cache, and instead give it to your applications. For instance, non-volatile memory could be dedicated to holding virtual machine (VM) images. As these would not be cached, this would reduce the cache usage on the host, allowing more VMs per host.
28.3.2 PMEM with BTT #
This is useful when you want to use the persistent memory on a set of NVDIMMs as a disk-like pool of very fast storage. For example, placing the file system journal on PMEM with BTT increases the reliability of file system recovery after a power failure or other sudden interruption (see Section 28.5.3, “Creating a PMEM namespace with BTT”).
To applications, such devices just appear as very fast SSDs and can be used like any other storage device. For example, LVM can be layered on top of the persistent memory and will work as normal.
The advantage of BTT is that sector write atomicity is guaranteed, so even sophisticated applications that depend on data integrity will keep working. Media error reporting works through standard error-reporting channels.
28.4 Tools for managing persistent memory #
To manage persistent memory, it is necessary to install the
ndctl
package. This also installs the
libndctl
package, which provides a set of user-space
libraries to configure NVDIMMs.
These tools work via the libnvdimm
library, which
supports three types of NVDIMM:
PMEM
BLK
Simultaneous PMEM and BLK
The ndctl
utility has a helpful set of
man
pages, accessible with the command:
>
ndctl help subcommand
To see a list of available subcommands, use:
>
ndctl --list-cmds
The available subcommands include:
- version
Displays the current version of the NVDIMM support tools.
- enable-namespace
Makes the specified namespace available for use.
- disable-namespace
Prevents the specified namespace from being used.
- create-namespace
Creates a new namespace from the specified storage devices.
- destroy-namespace
Removes the specified namespace.
- enable-region
Makes the specified region available for use.
- disable-region
Prevents the specified region from being used.
- zero-labels
Erases the metadata from a device.
- read-labels
Retrieves the metadata of the specified device.
- list
Displays available devices.
- help
Displays information about using the tool.
28.5 Setting up persistent memory #
28.5.1 Viewing available NVDIMM storage #
The ndctl
list
command can be used to
list all available NVDIMMs in a system.
In the following example, the system has three NVDIMMs, which are in a single, triple-channel interleaved set.
#
ndctl list --dimms
[ { "dev":"nmem2", "id":"8089-00-0000-12325476" }, { "dev":"nmem1", "id":"8089-00-0000-11325476" }, { "dev":"nmem0", "id":"8089-00-0000-10325476" } ]
With a different parameter, ndctl
list
will also list the available regions.
Regions may not appear in numerical order.
Note that although there are only three NVDIMMs, they appear as four regions.
#
ndctl list --regions
[ { "dev":"region1", "size":68182605824, "available_size":68182605824, "type":"blk" }, { "dev":"region3", "size":202937204736, "available_size":202937204736, "type":"pmem", "iset_id":5903239628671731251 }, { "dev":"region0", "size":68182605824, "available_size":68182605824, "type":"blk" }, { "dev":"region2", "size":68182605824, "available_size":68182605824, "type":"blk" } ]
The space is available in two different forms: either as three separate 64 GB regions of type BLK, or as one combined 189 GB region of type PMEM which presents all the space on the three interleaved NVDIMMs as a single volume.
Note that the displayed value for available_size
is the
same as that for size
. This means that none of the space
has been allocated yet.
28.5.2 Configuring the storage as a single PMEM namespace with DAX #
For the first example, we will configure our three NVDIMMs into a single PMEM namespace with Direct Access (DAX).
The first step is to create a new namespace.
#
ndctl create-namespace --type=pmem --mode=fsdax --map=memory
{ "dev":"namespace3.0", "mode":"memory", "size":199764213760, "uuid":"dc8ebb84-c564-4248-9e8d-e18543c39b69", "blockdev":"pmem3" }
This creates a block device /dev/pmem3
, which supports
DAX. The 3
in the device name is inherited from the
parent region number, in this case region3
.
The --map=memory
option sets aside part of the PMEM
storage space on the NVDIMMs so that it can be used to allocate internal
kernel data structures called struct pages
. This allows
the new PMEM namespace to be used with features such as O_DIRECT
I/O
and RDMA
.
The reservation of some persistent memory for kernel data structures is why the resulting PMEM namespace has a smaller capacity than the parent PMEM region.
Next, we verify that the new block device is available to the operating system:
#
fdisk -l /dev/pmem3
Disk /dev/pmem3: 186 GiB, 199764213760 bytes, 390164480 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Before it can be used, like any other drive, it must be formatted. In this example, we format it with XFS:
#
mkfs.xfs /dev/pmem3
meta-data=/dev/pmem3 isize=256 agcount=4, agsize=12192640 blks = sectsz=4096 attr=2, projid32bit=1 = crc=0 finobt=0, sparse=0 data = bsize=4096 blocks=48770560, imaxpct=25 = sunit=0 swidth=0 blks naming =version 2 bsize=4096 ascii-ci=0 ftype=1 log =internal log bsize=4096 blocks=23813, version=2 = sectsz=4096 sunit=1 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0
Next, we can mount the new drive onto a directory:
#
mount -o dax /dev/pmem3 /mnt/pmem3
Then we can verify that we now have a DAX-capable device:
#
mount | grep dax
/dev/pmem3 on /mnt/pmem3 type xfs (rw,relatime,attr2,dax,inode64,noquota)
The result is that we now have a PMEM namespace formatted with the XFS file system and mounted with DAX.
Any mmap()
calls to files in that file system will
return virtual addresses that directly map to the persistent memory on our
NVDIMMs, completely bypassing the page cache.
Any fsync
or msync
calls on files in
that file system will still ensure that modified data has been fully
written to the NVDIMMs. These calls flush the processor cache lines
associated with any pages that have been modified in user space via
mmap
mappings.
28.5.2.1 Removing a namespace #
Before creating any other type of volume that uses the same storage, we must unmount and then remove this PMEM volume.
First, unmount it:
#
umount /mnt/pmem3
Then disable the namespace:
#
ndctl disable-namespace namespace3.0
disabled 1 namespace
Then delete it:
#
ndctl destroy-namespace namespace3.0
destroyed 1 namespace
28.5.3 Creating a PMEM namespace with BTT #
BTT provides sector write atomicity, which makes it a good choice when you need data protection, for example for Ext4 and XFS journals. If there is a power failure, the journals are protected and should be recoverable. The following examples show how to create a PMEM namespace with BTT in sector mode, and how to place the file system journal in this namespace.
#
ndctl create-namespace --type=pmem --mode=sector
{ "dev":"namespace3.0", "mode":"sector", "uuid":"51ab652d-7f20-44ea-b51d-5670454f8b9b", "sector_size":4096, "blockdev":"pmem3s" }
Next, verify that the new device is present:
#
fdisk -l /dev/pmem3s
Disk /dev/pmem3s: 188.8 GiB, 202738135040 bytes, 49496615 sectors Units: sectors of 1 * 4096 = 4096 bytes Sector size (logical/physical): 4096 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Like the DAX-capable PMEM namespace we previously configured, this BTT-capable PMEM namespace consumes all the available storage on the NVDIMMs.
The trailing s
in the device name
(/dev/pmem3s
) stands for
sector
and can be used to easily distinguish namespaces
that are configured to use the BTT.
The volume can be formatted and mounted as in the previous example.
The PMEM namespace shown here cannot use DAX. Instead it uses the BTT to provide sector write atomicity. On each sector write through the PMEM block driver, the BTT will allocate a new sector to receive the new data. The BTT atomically updates its internal mapping structures after the new data is fully written so the newly written data will be available to applications. If the power fails at any point during this process, the write will be completely lost and the application will have access to its old data, still intact. This prevents the condition known as "torn sectors".
This BTT-enabled PMEM namespace can be formatted and used with a file system
just like any other standard block device. It cannot be used with DAX.
However, mmap
mappings for files on this block device
will use the page cache.
28.5.4 Placing the file system journal on PMEM/BTT #
When you place the file system journal on a separate device, it must use the same file system block size as the file system. Most likely this is 4096, and you can find the block size with this command:
#
blockdev --getbsz /dev/sda3
The following example creates a new Ext4 journal on a separate NVDIMM device, creates the file system on a SATA device, then attaches the new file system to the journal:
#
mke2fs -b 4096 -O journal_dev /dev/pmem3s
#
mkfs.ext4 -J device=/dev/pmem3s /dev/sda3
The following example creates a new XFS file system on a SATA drive, and creates the journal on a separate NVDIMM device:
#
mkfs.xfs -l logdev=/dev/pmem3s /dev/sda3
See man 8 mkfs.ext4
and man 8 mkfs.ext4
for detailed information about options.
28.6 More information #
More about this topic can be found in the following list:
Contains instructions for configuring NVDIMM systems, information about testing, and links to specifications related to NVDIMM enabling. This site is developing as NVDIMM support in Linux is developing.
Information about configuring, using and programming systems with non-volatile memory under Linux and other operating systems. Covers the NVM Library (NVML), which aims to provide useful APIs for programming with persistent memory in user space.
LIBNVDIMM: Non-Volatile Devices
Aimed at kernel developers, this is part of the Documentation folder in the current Linux kernel tree. It talks about the different kernel modules involved in NVDIMM enablement, lays out some technical details of the kernel implementation, and talks about the
sysfs
interface to the kernel that is used by thendctl
tool.Utility library for managing the
libnvdimm
subsystem in the Linux kernel. Also contains user space libraries, as well as unit tests and documentation.
Part IV Services #
- 29 Service management with YaST
YaST provides a service manager for controlling the default system target, services, displaying service status, and reading the log file. New in SUSE Linux Enterprise Server 15 SP3 is YaST support for Systemd socket-based services activation, which configures services to start on demand.
- 30 Time synchronization with NTP
The NTP (network time protocol) mechanism is a protocol for synchronizing the system time over the network. First, a machine can obtain the time from a server that is a reliable time source. Second, a machine can itself act as a time source for other computers in the network. The goal is twofold—maintaining the absolute time and synchronizing the system time of all machines within a network.
- 31 The domain name system
DNS (domain name system) is needed to resolve the domain names and host names into IP addresses. In this way, the IP address 192.168.2.100 is assigned to the host name
jupiter
, for example. Before setting up your own name server, read the general information about DNS in Section 19.3, “Name resolution”. The following configuration examples refer to BIND, the default DNS server.- 32 DHCP
The purpose of the Dynamic Host Configuration Protocol (DHCP) is to assign network settings centrally (from a server) rather than configuring them locally on every workstation. A host configured to use DHCP does not have control over its own static address. It is enabled to configure itself completely and automatically according to directions from the server. If you use the NetworkManager on the client side, you do not need to configure the client. This is useful if you have changing environments and only one interface active at a time. Never use NetworkManager on a machine that runs a DHCP server.
- 33 SLP
Configuring a network client requires detailed knowledge about services provided over the network (such as printing or LDAP, for example). To make it easier to configure such services on a network client, the “service location protocol” (SLP) was developed. SLP makes the availability and configuration data of selected services known to all clients in the local network. Applications that support SLP can use this information to be configured automatically.
- 34 The Apache HTTP server
According to the surveys from http://www.netcraft.com/ and https://w3techs.com/, the Apache HTTP Server (Apache) is one of the world's most popular Web servers. Developed by the Apache Software Foundation (http://www.apache.org/), it is available for most operating systems. SUSE® Linux Enterprise Server includes Apache version 2.4. This chapter describes how to install, configure, and set up Apache. It also shows how to use additional modules, such as SSL, and how to troubleshoot Apache.
- 35 Setting up an FTP server with YaST
Using the YaST
module, you can configure your machine to function as an FTP (File Transfer Protocol) server. Anonymous and/or authenticated users can connect to your machine and download files using the FTP protocol. Depending on the configuration, they can also upload files to the FTP server. YaST uses vsftpd (Very Secure FTP Daemon).- 36 Squid caching proxy server
Squid is a widely-used caching proxy server for Linux and Unix platforms. This means that it stores requested Internet objects, such as data on a Web or FTP server, on a machine that is closer to the requesting workstation than the server. It can be set up in multiple hierarchies to assure optimal response times and low bandwidth usage, even in modes that are transparent to end users.
- 37 Web Based Enterprise Management using SFCB
29 Service management with YaST #
YaST provides a service manager for controlling the default system target, services, displaying service status, and reading the log file. New in SUSE Linux Enterprise Server 15 SP3 is YaST support for Systemd socket-based services activation, which configures services to start on demand.
Systemd supports starting services with socket-based activation, for starting
services on demand. These services have two unit types: service and socket.
For example, CUPS is controlled by cups.service
and
cups.socket
. YaST allows you to select the type of
service startup you want to use.
Figure 29.1, “YaST service manager” shows the options in the Start Mode drop-down menu: , , and . Select for socket-based activation. This opens a listening network socket, and the service starts when there is a request.
The man 5 systemd.socket
for detailed information on how
socket activation works.
30 Time synchronization with NTP #
The NTP (network time protocol) mechanism is a protocol for synchronizing the system time over the network. First, a machine can obtain the time from a server that is a reliable time source. Second, a machine can itself act as a time source for other computers in the network. The goal is twofold—maintaining the absolute time and synchronizing the system time of all machines within a network.
Maintaining an exact system time is important in many situations. The built-in hardware clock does often not meet the requirements of applications such as databases or clusters. Manual correction of the system time would lead to severe problems because, for example, a backward leap can cause malfunction of critical applications. Within a network, it is usually necessary to synchronize the system time of all machines, but manual time adjustment is a bad approach. NTP provides a mechanism to solve these problems. The NTP service continuously adjusts the system time with reliable time servers in the network. It further enables the management of local reference clocks, such as radio-controlled clocks.
Since SUSE Linux Enterprise Server 15, chrony
is the default implementation of NTP.
chrony
includes two parts; chronyd
is a daemon that can be started at
boot time and chronyc
is a command line interface program to monitor the
performance of chronyd
, and to change various operating parameters at
runtime.
Starting with SUSE Linux Enterprise Server 15.2, the YaST module for NTP client
configuration configures the systemd-timer instead of the cron daemon
to execute chrony
, when it is not configured to run as a daemon.
30.1 Configuring an NTP client with YaST #
The NTP daemon (chronyd
) coming with the chrony
package is preset to use the local computer hardware clock as a time
reference. The precision of the hardware clock heavily depends on its time
source. For example, an atomic clock or GPS receiver is a very precise time
source, while a common RTC chip is not a reliable time source. YaST
simplifies the configuration of an NTP client.
In the YaST NTP client configuration (
› ) window, you can specify when to start the NTP daemon, the type of the configuration source, and add custom time servers.30.1.1 NTP daemon start #
You can choose from three options for when to start the NTP daemon:
Select
, if you want to manually start thechrony
daemon.Select
to set the system time periodically without a permanently runningchrony
. You can set the .Select
to startchronyd
automatically when the system is booted. This setting is recommended.
30.1.2 Type of the configuration source #
In the
drop-down box, select either or . Set if your server uses only a fixed set of (public) NTP servers, while is better if your internal network offers NTP servers via DHCP.30.1.3 Configure time servers #
Time servers for the client to query are listed in the lower part of the
window. Modify this list as needed with , , and .Click
to add a new time server:In the
field, type the URL of the time server or pool of time servers with which you want to synchronize the machine time. After the URL is complete, click to verify that it points to a valid time source.Activate
to speed up the time synchronization by sending more requests at thechronyd
daemon start.Activate
to speed up the boot time on systems that start thechronyd
daemon automatically and may not have an Internet connection at boot time. This option is useful, for example, for laptops with network connections managed by NetworkManager.Confirm with
.
30.2 Manually configuring NTP in the network #
chrony
reads its configuration from the
/etc/chrony.conf
file. To keep the computer clock
synchronized, you need to tell chrony
what time servers to use. You can
use specific server names or IP addresses, for example:
0.suse.pool.ntp.org 1.suse.pool.ntp.org 2.suse.pool.ntp.org 3.suse.pool.ntp.org
You can also specify a pool name. Pool name resolves to several IP addresses:
pool pool.ntp.org
To synchronize time on multiple computers on the same network, we do not
recommend to synchronize all of them with an external server. A good
practice is to make one computer the time server which is synchronized with
an external time server, and the other computers act as its clients. Add a
local
directive to the server's
/etc/chrony.conf
to distinguish it from an
authoritative time server:
local stratum 10
To start chrony
, run:
systemctl start chronyd.service
After initializing chronyd
, it takes some time before the time is
stabilized and the drift file for correcting the local computer clock is
created. With the drift file, the systematic error of the hardware clock can
be computed when the computer is powered on. The correction is used
immediately, resulting in a higher stability of the system time.
To enable the service so that chrony
starts automatically at boot time,
run:
systemctl enable chronyd.service
yast-timesync.service
service
In addition to the chronyd.service
service, SLES includes yast-timesync.service
. yast-timesync.service
is triggered by a timer
every 5 minutes and runs chronyd
with the -q
option to
set the system time and exit. Because only one instance of chronyd
can be
running at any given time, do not enable or start both chronyd
-related
services at the same time.
30.3 Configure chronyd
at runtime using chronyc
#
You can use chronyc
to change the behavior of chronyd
at runtime. It
also generates status reports about the operation of chronyd
.
You can run chronyc
either in interactive or non-interactive mode. To
run chronyc
interactively, enter chronyc
on the command line. It
displays a prompt and waits for your command input. For example, to check
how many NTP sources are online or offline, run:
#
chronyc
chronyc> activity 200 OK 4 sources online 2 sources offline 1 sources doing burst (return to online) 1 sources doing burst (return to offline) 0 sources with unknown address
To exit chronyc
's prompt, enter quit
or
exit
.
If you do not need to use the interactive prompt, enter the command directly:
#
chronyc
activity
Changes made using chronyc
are not permanent. They will be lost after the
next chronyd
restart. For permanent changes, modify
/etc/chrony.conf
.
For a complete list of chronyc
commands, see its manual page (man
1 chronyc
).
30.4 Dynamic time synchronization at runtime #
Although chronyd
starts up normally on a system that boots without a network
connection, the tool cannot resolve the DNS names of the time servers
specified in the configuration file.
chronyd
keeps trying to resolve the time server names specified by the
server
, pool
, and peer
directives in an increasing time interval until it succeeds.
If the time server will not be reachable when chronyd
is started, you can
specify the offline
option:
server server_address offline
chronyd
will then not try to poll the server until it is enabled using the
following command:
#
chronyc online server_address
When the auto_offline
option is set, chronyd
assumes that
the time server has gone offline when two requests have been sent to it
without receiving a response. This option avoids the need to run the
'offline' command from chronyc
when disconnecting the network link.
30.5 Setting up a local reference clock #
The software package chrony
relies on other programs (such as
gpsd
) to access the timing data via the SHM or SOCK
driver. Use the refclock
directive in
/etc/chrony.conf
to specify a hardware reference clock
to be used as a time source. It has two mandatory parameters: a driver name
and a driver-specific parameter. The two parameters are followed by zero or
more refclock
options. chronyd
includes the following
drivers:
PPS - driver for the kernel 'pulse per second' API. For example:
refclock PPS /dev/pps0 lock NMEA refid GPS
SHM - NTP shared memory driver. For example:
refclock SHM 0 poll 3 refid GPS1 refclock SHM 1:perm=0644 refid GPS2
SOCK - Unix domain socket driver. For example:
refclock SOCK /var/run/chrony.ttyS0.sock
PHC - PTP hardware clock driver. For example:
refclock PHC /dev/ptp0 poll 0 dpoll -2 offset -37 refclock PHC /dev/ptp1:nocrossts poll 3 pps
For more information on individual drivers' options, see man 8
chrony.conf
.
30.6 Clock synchronization to an external time reference (ETR) #
Support for clock synchronization to an external time reference (ETR) is available. The external time reference sends an oscillator signal and a synchronization signal every 2**20 (2 to the power of 20) microseconds to keep TOD clocks of all connected servers synchronized.
For availability two ETR units can be connected to a machine. If the clock deviates for more than the sync-check tolerance all CPUs get a machine check that indicates that the clock is not synchronized. If this happens, all DASD I/O to XRC enabled devices is stopped until the clock is synchronized again.
The ETR support is activated via two sysfs
attributes;
run the following commands as root
:
echo 1 > /sys/devices/system/etr/etr0/online echo 1 > /sys/devices/system/etr/etr1/online
31 The domain name system #
DNS (domain name system) is needed to resolve the domain names and host
names into IP addresses. In this way, the IP address 192.168.2.100 is assigned to
the host name jupiter
, for example. Before setting up your
own name server, read the general information about DNS in
Section 19.3, “Name resolution”. The following configuration
examples refer to BIND, the default DNS server.
31.1 DNS terminology #
- Zone
The domain name space is divided into regions called zones. For example, if you have
example.com
, you have theexample
section (or zone) of thecom
domain.- DNS server
The DNS server is a server that maintains the name and IP information for a domain. You can have a primary DNS server for master zone, a secondary server for slave zone, or a slave server without any zones for caching.
- Master zone DNS server
The master zone includes all hosts from your network and a DNS server master zone stores up-to-date records for all the hosts in your domain.
- Slave zone DNS server
A slave zone is a copy of the master zone. The slave zone DNS server obtains its zone data with zone transfer operations from its master server. The slave zone DNS server responds authoritatively for the zone as long as it has valid (not expired) zone data. If the slave cannot obtain a new copy of the zone data, it stops responding for the zone.
- Forwarder
Forwarders are DNS servers to which your DNS server should send queries it cannot answer. To enable different configuration sources in one configuration,
netconfig
is used (see alsoman 8 netconfig
).- Record
The record is information about name and IP address. Supported records and their syntax are described in BIND documentation. Some special records are:
- NS record
An NS record tells name servers which machines are in charge of a given domain zone.
- MX record
The MX (mail exchange) records describe the machines to contact for directing mail across the Internet.
- SOA record
SOA (Start of Authority) record is the first record in a zone file. The SOA record is used when using DNS to synchronize data between multiple computers.
31.2 Installation #
To install a DNS server, start YaST and select
› . Choose › and select . Confirm the installation of the dependent packages to finish the installation process.Alternatively use the following command on the command line:
>
sudo
zypper in -t pattern dhcp_dns_server
31.3 Configuration with YaST #
Use the YaST DNS module to configure a DNS server for the local network. When starting the module for the first time, a wizard starts, prompting you to make a few decisions concerning administration of the server. Completing this initial setup produces a basic server configuration. Use the expert mode to deal with more advanced configuration tasks, such as setting up ACLs, logging, TSIG keys, and other options.
31.3.1 Wizard configuration #
The wizard consists of three steps or dialogs. At the appropriate places in the dialogs, you can enter the expert configuration mode.
When starting the module for the first time, the Figure 31.1, “DNS server installation: forwarder settings”, opens. The allows to set the following options:
dialog, shown inauto
, but here you can either set interface names or select from the two special policy namesSTATIC
andSTATIC_FALLBACK
.
In
, specify which service to use: , , or .For more information about all these settings, see
man 8 netconfig
.Figure 31.1: DNS server installation: forwarder settings #Forwarders are DNS servers to which your DNS server sends queries it cannot answer itself. Enter their IP address and click
.The Section 31.6, “Zone files”. For a new zone, provide a name for it in . To add a reverse zone, the name must end in
dialog consists of several parts and is responsible for the management of zone files, described in.in-addr.arpa
. Finally, select the (master, slave, or forward). See Figure 31.2, “DNS server installation: DNS zones”. Click to configure other settings of an existing zone. To remove a zone, click .Figure 31.2: DNS server installation: DNS zones #In the final dialog, you can open the DNS port in the firewall by clicking Figure 31.3, “DNS server installation: finish wizard”.
. Then decide whether to start the DNS server when booting ( or ). You can also activate LDAP support. SeeFigure 31.3: DNS server installation: finish wizard #
31.3.2 Expert configuration #
After starting the module, YaST opens a window displaying several configuration options. Completing it results in a DNS server configuration with the basic functions in place:
31.3.2.1 Start-up #
Under
, define whether the DNS server should be started when the booting the system or manually. To start the DNS server immediately, click . To stop the DNS server, click . To save the current settings, select . You can open the DNS port in the firewall with and modify the firewall settings with .By selecting
, the zone files are managed by an LDAP database. Any changes to zone data written to the LDAP database are picked up by the DNS server when it is restarted or prompted to reload its configuration.31.3.2.2 Forwarders #
If your local DNS server cannot answer a request, it tries to forward the
request to a man 8 netconfig
.
31.3.2.3 Basic options #
In this section, set basic server options. From the
menu, select the desired item then specify the value in the corresponding text box. Include the new entry by selecting .31.3.2.4 Logging #
To set what the DNS server should log and how, select
. Under , specify where the DNS server should write the log data. Use the system-wide log by selecting or specify a different file by selecting . In the latter case, additionally specify a name, the maximum file size in megabytes and the number of log file versions to store.Further options are available under every query to be logged, in which case the log file could grow extremely large. For this reason, it is not a good idea to enable this option for other than debugging purposes. To log the data traffic during zone updates between DHCP and DNS server, enable . To log the data traffic during a zone transfer from master to slave, enable . See Figure 31.4, “DNS server: logging”.
. Enabling causes31.3.2.5 ACLs #
Use this dialog to define ACLs (access control lists) to enforce access restrictions. After providing a distinct name under
, specify an IP address (with or without netmask) under in the following fashion:{ 192.168.1/24; }
The syntax of the configuration file requires that the address ends with a semicolon and is put into curly braces.
31.3.2.6 TSIG keys #
The main purpose of TSIGs (transaction signatures) is to secure communications between DHCP and DNS servers. They are described in Section 31.8, “Secure transactions”.
To generate a TSIG key, enter a distinctive name in the field labeled
and specify the file where the key should be stored ( ). Confirm your choices with .To use a previously created key, leave the
field blank and select the file where it is stored under . After that, confirm with .31.3.2.7 DNS zones (adding a slave zone) #
To add a slave zone, select
, choose the zone type , write the name of the new zone, and click .In the
sub-dialog under , specify the master from which the slave should pull its data. To limit access to the server, select one of the ACLs from the list.31.3.2.8 DNS zones (adding a master zone) #
To add a master zone, select example.com
that points to hosts in a subnet
192.168.1.0/24
, you should also add a reverse zone for
the IP-address range covered. By definition, this should be named
1.168.192.in-addr.arpa
.
31.3.2.9 DNS zones (editing a master zone) #
To edit a master zone, select
, select the master zone from the table, and click . The dialog consists of several pages: (the one opened first), , , , and .The basic dialog, shown in Figure 31.5, “DNS server: Zone Editor (Basics)”, lets you define settings for dynamic DNS and access options for zone transfers to clients and slave name servers. To permit the dynamic updating of zones, select and the corresponding TSIG key. The key must have been defined before the update action starts. To enable zone transfers, select the corresponding ACLs. ACLs must have been defined already.
In the
dialog, select whether to enable zone transfers. Use the listed ACLs to define who can download zones.- Zone Editor (NS Records)
The Figure 31.6, “DNS server: Zone Editor (NS Records)”.
dialog allows you to define alternative name servers for the zones specified. Make sure that your own name server is included in the list. To add a record, enter its name under then confirm with . SeeFigure 31.6: DNS server: Zone Editor (NS Records) #- Zone Editor (MX Records)
To add a mail server for the current zone to the existing list, enter the corresponding address and priority value. After doing so, confirm by selecting Figure 31.7, “DNS server: Zone Editor (MX Records)”.
. SeeFigure 31.7: DNS server: Zone Editor (MX Records) #- Zone Editor (SOA)
This page allows you to create SOA (start of authority) records. For an explanation of the individual options, refer to Example 31.6, “The /var/lib/named/example.com.zone file”. Changing SOA records is not supported for dynamic zones managed via LDAP.
Figure 31.8: DNS server: Zone Editor (SOA) #- Zone Editor (Records)
This dialog manages name resolution. In
, enter the host name then select its type. The type represents the main entry. The value for this should be an IP address (IPv4). Use for IPv6 addresses. is an alias. Use the types and for detailed or partial records that expand on the information provided in the and tabs. These three types resolve to an existingA
record. is for reverse zones. It is the opposite of anA
record, for example:hostname.example.com. IN A 192.168.0.1 1.0.168.192.in-addr.arpa IN PTR hostname.example.com.
31.3.2.9.1 Adding reverse zones #
To add a reverse zone, follow this procedure:
Start
› › .If you have not added a master forward zone, add it and
it.In the
tab, fill the corresponding and , then add the record with and confirm with . If YaST complains about a non-existing record for a name server, add it in the tab.Figure 31.9: Adding a record for a master zone #Back in the
window, add a reverse master zone.Figure 31.10: Adding a reverse zone #- Figure 31.11: Adding a reverse record #
Add a name server record if needed.
After adding a forward zone, go back to the main menu and select the reverse zone for editing. There in the tab
activate the check box and select your forward zone. That way, all changes to the forward zone are automatically updated in the reverse zone.31.4 Starting the BIND name server #
On a SUSE® Linux Enterprise Server system, the name server BIND (Berkeley
Internet Name Domain) comes preconfigured, so it can be started
right after installation without any problems. Normally, if you already have an Internet connection and entered
127.0.0.1
as the name server
address for localhost
in
/var/run/netconfig/resolv.conf
, you already have a working
name resolution without needing to know the DNS of the provider. BIND
carries out name resolution via the root name server, a notably slower
process. Normally, the DNS of the provider should be entered with its IP
address in the configuration file /etc/named.conf
under
forwarders
to ensure effective and secure name
resolution. If this works so far, the name server runs as a pure
caching-only name server. Only when you configure its
own zones it becomes a proper DNS. Find a simple example documented in
/usr/share/doc/packages/bind/config
.
Depending on the type of Internet connection or the network connection, the
name server information can automatically be adapted to the current
conditions. To do this, set the
NETCONFIG_DNS_POLICY
variable in the
/etc/sysconfig/network/config
file to
auto
.
However, do not set up an official domain until one is assigned to you by the responsible institution. Even if you have your own domain and it is managed by the provider, you are better off not using it, because BIND would otherwise not forward requests for this domain. The Web server at the provider, for example, would not be accessible for this domain.
To start the name server, enter the command systemctl start
named
as root
. Check
with systemctl status named
whether named (as the name
server process is called) has been started successfully. Test the name
server immediately on the local system with the host
or
dig
programs, which should return
localhost
as the default server
with the address 127.0.0.1
. If
this is not the case, /var/run/netconfig/resolv.conf
probably
contains an incorrect name server entry or the file does not exist. For the
first test, enter host
127.0.0.1
,
which should always work. If you get an error message, use
systemctl status named
to see whether the server is
actually running. If the name server does not start or behaves unexpectedly,
check the output of journalctl -e
.
To use the name server of the provider (or one already running on your
network) as the forwarder, enter the corresponding IP address or addresses
in the options
section under
forwarders
. The addresses included in
Example 31.1, “Forwarding options in named.conf” are examples only. Adjust these entries to your
own setup.
options { directory "/var/lib/named"; forwarders { 10.11.12.13; 10.11.12.14; }; listen-on { 127.0.0.1; 192.168.1.116; }; allow-query { 127/8; 192.168/16 }; notify no; };
The options
entry is followed by entries for the
zone, localhost
, and
0.0.127.in-addr.arpa
. The type
hint
entry under “.” should always be present. The
corresponding files do not need to be modified and should work as they are.
Also make sure that each entry is closed with a “;” and that
the curly braces are in the correct places. After changing the configuration
file /etc/named.conf
or the zone files, tell BIND to
reread them with systemctl reload named
. Achieve the same
by stopping and restarting the name server with systemctl restart
named
. Stop the server at any time by entering systemctl
stop named
.
31.5 The /etc/named.conf configuration file #
All the settings for the BIND name server itself are stored in the
/etc/named.conf
file. However, the zone data for the
domains to handle (consisting of the host names, IP addresses, and so on)
are stored in separate files in the /var/lib/named
directory. The details of this are described later.
/etc/named.conf
is roughly divided into two areas. One
is the options
section for general settings and the
other consists of zone
entries for the individual
domains. A logging
section and
acl
(access control list) entries are optional.
Comment lines begin with a #
sign or
//
. A minimal /etc/named.conf
is
shown in Example 31.2, “A basic /etc/named.conf”.
options { directory "/var/lib/named"; forwarders { 10.0.0.1; }; notify no; }; zone "localhost" in { type master; file "localhost.zone"; }; zone "0.0.127.in-addr.arpa" in { type master; file "127.0.0.zone"; }; zone "." in { type hint; file "root.hint"; };
31.5.1 Important configuration options #
- directory "FILENAME";
Specifies the directory in which BIND can find the files containing the zone data. Usually, this is
/var/lib/named
.- forwarders { IP-ADDRESS; };
Specifies the name servers (mostly of the provider) to which DNS requests should be forwarded if they cannot be resolved directly. Replace IP-ADDRESS with an IP address like
192.168.1.116
.- forward first;
Causes DNS requests to be forwarded before an attempt is made to resolve them via the root name servers. Instead of
forward first
,forward only
can be written to have all requests forwarded and none sent to the root name servers. This makes sense for firewall configurations.- listen-on port 53 { 127.0.0.1; IP-ADDRESS; };
Tells BIND on which network interfaces and port to accept client queries.
port 53
does not need to be specified explicitly, because53
is the default port. Enter127.0.0.1
to permit requests from the local host. If you omit this entry entirely, all interfaces are used by default.- listen-on-v6 port 53 {any; };
Tells BIND on which port it should listen for IPv6 client requests. The only alternative to
any
isnone
. As far as IPv6 is concerned, the server only accepts wild card addresses.- query-source address * port 53;
This entry is necessary if a firewall is blocking outgoing DNS requests. This tells BIND to post requests externally from port 53 and not from any of the high ports above 1024.
- query-source-v6 address * port 53;
Tells BIND which port to use for IPv6 queries.
- allow-query { 127.0.0.1; NET; };
Defines the networks from which clients can post DNS requests. Replace NET with address information like
192.168.2.0/24
. The/24
at the end is an abbreviated expression for the netmask (in this case255.255.255.0
).- allow-transfer ! *;;
Controls which hosts can request zone transfers. In the example, such requests are completely denied with
! *
. Without this entry, zone transfers can be requested from anywhere without restrictions.- statistics-interval 0;
In the absence of this entry, BIND generates several lines of statistical information per hour in the system's journal. Set it to 0 to suppress these statistics completely or set an interval in minutes.
- cleaning-interval 720;
This option defines at which time intervals BIND clears its cache. This triggers an entry in the system's journal each time it occurs. The time specification is in minutes. The default is 60 minutes.
- interface-interval 0;
BIND regularly searches the network interfaces for new or nonexistent interfaces. If this value is set to
0
, this is not done and BIND only listens at the interfaces detected at start-up. Otherwise, the interval can be defined in minutes. The default is sixty minutes.- notify no;
no
prevents other name servers from being informed when changes are made to the zone data or when the name server is restarted.
For a list of available options, read the manual page man 5
named.conf
.
31.5.2 Logging #
What, how, and where logging takes place can be extensively configured in BIND. Normally, the default settings should be sufficient. Example 31.3, “Entry to disable logging”, shows the simplest form of such an entry and completely suppresses any logging.
logging { category default { null; }; };
31.5.3 Zone entries #
zone "example.com" in { type master; file "example.com.zone"; notify no; };
After zone
, specify the name of the domain to
administer (example.com
)
followed by in
and a block of relevant options
enclosed in curly braces, as shown in Example 31.4, “Zone entry for example.com”. To
define a slave zone, switch the
type
to slave
and specify a
name server that administers this zone as master
(which,
in turn, may be a slave of another master), as shown in
Example 31.5, “Zone entry for example.net”.
zone "example.net" in { type slave; file "slave/example.net.zone"; masters { 10.0.0.1; }; };
The zone options:
- type master;
By specifying
master
, tell BIND that the zone is handled by the local name server. This assumes that a zone file has been created in the correct format.- type slave;
This zone is transferred from another name server. It must be used together with
masters
.- type hint;
The zone
.
of thehint
type is used to set the root name servers. This zone definition can be left as is.- file
example.com.zone
or file “slave/example.net.zone”; This entry specifies the file where zone data for the domain is located. This file is not required for a slave, because this data is pulled from another name server. To differentiate master and slave files, use the directory
slave
for the slave files.- masters { SERVER_IP_ADDRESS; };
This entry is only needed for slave zones. It specifies from which name server the zone file should be transferred.
- allow-update {! *; };
This option controls external write access, which would allow clients to make a DNS entry—something not normally desirable for security reasons. Without this entry, zone updates are not allowed. The above entry achieves the same because
! *
effectively bans any such activity.
31.6 Zone files #
Two types of zone files are needed. One assigns IP addresses to host names and the other does the reverse: it supplies a host name for an IP address.
The "."
has an important meaning in the zone files. If
host names are given without a final dot (.
), the zone
is appended. Complete host names specified with a full domain name must end
with a dot (.
) to avoid having the domain added to it
again. A missing or wrongly placed "." is probably the most frequent cause
of name server configuration errors.
The first case to consider is the zone file
example.com.zone
, responsible for the domain
example.com
, shown in
Example 31.6, “The /var/lib/named/example.com.zone file”.
$TTL 2D 1 example.com. IN SOA dns root.example.com. ( 2 2003072441 ; serial 3 1D ; refresh 4 2H ; retry 5 1W ; expiry 6 2D ) ; minimum 7 IN NS dns 8 IN MX 10 mail dns 9 gate IN A 192.168.5.1 10 IN A 10.0.0.1 dns IN A 192.168.1.116 mail IN A 192.168.3.108 jupiter IN A 192.168.2.100 venus IN A 192.168.2.101 saturn IN A 192.168.2.102 mercury IN A 192.168.2.103 ntp IN CNAME dns 11 dns6 IN A6 0 2002:c0a8:174::
| |
This is where the SOA (start of authority) control record begins:
| |
The | |
The | |
The | |
The | |
The last entry in the SOA record specifies the | |
The | |
The MX record specifies the mail server that accepts, processes, and
forwards e-mails for the domain | |
This and the following lines are the actual address records where one or more IP addresses are
assigned to host names. The names are listed here without a
Note: IPv6 syntax The IPv6 record has a slightly different syntax than IPv4. Because of the fragmentation possibility, it is necessary to provide information about missed bits before the address. To fill up the IPv6 address with the needed number of “0”, add two colons at the correct place in the address. pluto AAAA 2345:00C1:CA11::1234:5678:9ABC:DEF0 pluto AAAA 2345:00D2:DA11::1234:5678:9ABC:DEF0 | |
The alias |
The pseudo domain in-addr.arpa
is used for the reverse
lookup of IP addresses into host names. It is appended to the network part
of the address in reverse notation. So
192.168
is resolved into
168.192.in-addr.arpa
. See
Example 31.7, “Reverse lookup”.
$TTL 2D 1 168.192.in-addr.arpa. IN SOA dns.example.com. root.example.com. ( 2 2003072441 ; serial 1D ; refresh 2H ; retry 1W ; expiry 2D ) ; minimum IN NS dns.example.com. 3 1.5 IN PTR gate.example.com. 4 100.3 IN PTR www.example.com. 253.2 IN PTR cups.example.com.
$TTL defines the standard TTL that applies to all entries here. | |
The configuration file should activate reverse lookup for the network
See Example 31.6, “The /var/lib/named/example.com.zone file” for detail on the entries within this record. | |
This line specifies the name server responsible for this zone. This time,
however, the name is entered in its complete form with the domain and a
| |
This, and the following lines, are the pointer records hinting at the IP
addresses on the respective hosts. Only the last part of the IP address is
entered at the beginning of the line, without the |
Normally, zone transfers between different versions of BIND should be possible without any problems.
31.7 Dynamic update of zone data #
The term dynamic update refers to operations by which
entries in the zone files of a master server are added, changed, or deleted.
This mechanism is described in RFC 2136. Dynamic update is configured
individually for each zone entry by adding an optional
allow-update
or
update-policy
rule. Zones to update dynamically
should not be edited by hand.
Transmit the entries to update to the server with the command
nsupdate
. For the exact syntax of this command, check the
manual page for nsupdate (man
8
nsupdate
). For security reasons, any such update should be
performed using TSIG keys as described in Section 31.8, “Secure transactions”.
31.8 Secure transactions #
Secure transactions can be made with transaction signatures (TSIGs) based on shared secret keys (also called TSIG keys). This section describes how to generate and use such keys.
Secure transactions are needed for communication between different servers and for the dynamic update of zone data. Making the access control dependent on keys is much more secure than merely relying on IP addresses.
Generate a TSIG key with the following command (for details, see
man
tsig-keygen
):
>
sudo
tsig-keygen -a hmac-md5 host1-host2 > host1-host2.key
This creates a file with the name host1-host2.key
with
contents that may look as follows:
key "host1-host2" { | algorithm hmac-md5; secret "oHpBLgtcZso6wxnRTWdJMA=="; };
The file must be transferred to the remote host, preferably in a secure way
(using scp, for example). To enable a secure communication between
host1
and host2
, the key must be
included in the /etc/named.conf
file on both the local
and the remote
server.
key host1-host2 { algorithm hmac-md5; secret "ejIkuCyyGJwwuN3xAteKgg=="; };
/etc/named.conf
Make sure that the permissions of /etc/named.conf
are
properly restricted. The default for this file is 0640
,
with the owner being root
and the
group named
. As an alternative,
move the keys to an extra file with specially limited permissions, which is
then included from /etc/named.conf
. To include an
external file, use:
include "filename"
Replace filename
with an absolute path to your file with
keys.
To enable the server host1
to use the key for
host2
(which has the address 10.1.2.3
in this example), the server's /etc/named.conf
must
include the following rule:
server 10.1.2.3 { keys { host1-host2. ;}; };
Analogous entries must be included in the configuration files of
host2
.
Add TSIG keys for any ACLs (access control lists, not to be confused with file system ACLs) that are defined for IP addresses and address ranges to enable transaction security. The corresponding entry could look like this:
allow-update { key host1-host2. ;};
This topic is discussed in more detail in the BIND Administrator
Reference Manual under update-policy
.
31.9 DNS security #
DNSSEC, or DNS security, is described in RFC 2535. The tools available for DNSSEC are discussed in the BIND Manual.
A zone considered secure must have one or several zone keys associated with
it. These are generated with dnssec-keygen
, as are the
host keys. The DSA encryption algorithm is currently used to generate these
keys. The public keys generated should be included in the corresponding zone
file with an $INCLUDE
rule.
With the command dnssec-signzone
, you can create sets of
generated keys (keyset-
files), transfer them to the
parent zone in a secure manner, and sign them. This generates the files to
include for each zone in /etc/named.conf
.
31.10 More information #
For more information, see the BIND Administrator Reference
Manual from the
bind-doc
package, which is
installed under /usr/share/doc/packages/bind/arm
.
Consider additionally consulting the RFCs referenced by the manual and the
manual pages included with BIND.
/usr/share/doc/packages/bind/README.SUSE
contains
up-to-date information about BIND in SUSE Linux Enterprise Server.
32 DHCP #
The purpose of the Dynamic Host Configuration Protocol (DHCP) is to assign network settings centrally (from a server) rather than configuring them locally on every workstation. A host configured to use DHCP does not have control over its own static address. It is enabled to configure itself completely and automatically according to directions from the server. If you use the NetworkManager on the client side, you do not need to configure the client. This is useful if you have changing environments and only one interface active at a time. Never use NetworkManager on a machine that runs a DHCP server.
On IBM Z platforms, DHCP only works on interfaces using the OSA and OSA Express network cards. These cards are the only ones with a MAC, which is required for the DHCP autoconfiguration features.
One way to configure a DHCP server is to identify each client using the hardware address of its network card (which should usually be fixed), then supply that client with identical settings each time it connects to the server. DHCP can also be configured to assign addresses to each relevant client dynamically from an address pool set up for this purpose. In the latter case, the DHCP server tries to assign the same address to the client each time it receives a request, even over extended periods. This works only if the network does not have more clients than addresses.
DHCP makes life easier for system administrators. Any changes, even bigger ones, related to addresses and the network configuration in general can be implemented centrally by editing the server's configuration file. This is much more convenient than reconfiguring numerous workstations. It is also much easier to integrate machines, particularly new machines, into the network, because they can be given an IP address from the pool. Retrieving the appropriate network settings from a DHCP server is especially useful in case of laptops regularly used in different networks.
In this chapter, the DHCP server will run in the same subnet as the
workstations, 192.168.2.0/24
with
192.168.2.1
as gateway. It has
the fixed IP address 192.168.2.254
and
serves two address ranges,
192.168.2.10
to
192.168.2.20
and
192.168.2.100
to
192.168.2.200
.
A DHCP server supplies not only the IP address and the netmask, but also the host name, domain name, gateway, and name server addresses for the client to use. In addition to that, DHCP allows several parameters to be configured in a centralized way, for example, a time server from which clients may poll the current time or even a print server.
32.1 Configuring a DHCP server with YaST #
To install a DHCP server, start YaST and select
› . Choose › and select . Confirm the installation of the dependent packages to finish the installation process.The YaST DHCP module can be set up to store the server configuration locally (on the host that runs the DHCP server) or to have its configuration data managed by an LDAP server. To use LDAP, set up your LDAP environment before configuring the DHCP server.
For more information about LDAP, see Book “Security and Hardening Guide”, Chapter 5 “LDAP with 389 Directory Server”.
The YaST DHCP module (yast2-dhcp-server
) allows
you to set up your own DHCP server for the local network. The module can run
in wizard mode or expert configuration mode.
32.1.1 Initial configuration (wizard) #
When the module is started for the first time, a wizard starts, prompting you to make a few basic decisions concerning server administration. Completing this initial setup produces a very basic server configuration that should function in its essential aspects. The expert mode can be used to deal with more advanced configuration tasks. Proceed as follows:
Select the interface from the list to which the DHCP server should listen and click Figure 32.1, “DHCP server: card selection”.
and then . SeeNote: DHCP andfirewalld
Please note that the option
does not (yet) supportfirewalld
in SUSE Linux Enterprise Server 15 SP3. To manually open the DHCP port, run>
sudo
firewall-cmd --zone=public --permanent --add-service=dhcp
>
sudo
firewall-cmd --reload
Figure 32.1: DHCP server: card selection #Use the check box to determine whether your DHCP settings should be automatically stored by an LDAP server. In the text boxes, provide the network specifics for all clients the DHCP server should manage. These specifics are the domain name, address of a time server, addresses of the primary and secondary name server, addresses of a print and a WINS server (for a mixed network with both Windows and Linux clients), gateway address, and lease time. See Figure 32.2, “DHCP server: global settings”.
Figure 32.2: DHCP server: global settings #Configure how dynamic IP addresses should be assigned to clients. To do so, specify an IP range from which the server can assign addresses to DHCP clients. All these addresses must be covered by the same netmask. Also specify the lease time during which a client may keep its IP address without needing to request an extension of the lease. Optionally, specify the maximum lease time—the period during which the server reserves an IP address for a particular client. See Figure 32.3, “DHCP server: dynamic DHCP”.
Figure 32.3: DHCP server: dynamic DHCP #Define how the DHCP server should be started. Specify whether to start the DHCP server automatically when the system is booted or manually when needed (for example, for testing purposes). Click Figure 32.4, “DHCP server: start-up”.
to complete the configuration of the server. SeeFigure 32.4: DHCP server: start-up #Instead of using dynamic DHCP in the way described in the preceding steps, you can also configure the server to assign addresses in quasi-static fashion. Use the text boxes provided in the lower part to specify a list of the clients to manage in this way. Specifically, provide the Figure 32.5, “DHCP server: host management”.
and the to give to such a client, the , and the (token ring or Ethernet). Modify the list of clients, which is shown in the upper part with , , and . SeeFigure 32.5: DHCP server: host management #
32.1.2 DHCP server configuration (expert) #
In addition to the configuration method discussed earlier, there is also an expert configuration mode that allows you to change the DHCP server setup in every detail. Start the expert configuration by clicking Figure 32.4, “DHCP server: start-up”).
in the dialog (see- Chroot environment and declarations
In this first dialog, make the existing configuration editable by selecting Figure 32.6, “DHCP server: chroot jail and declarations”. After selecting , define the type of declaration to add. With , view the log file of the server, configure TSIG key management, and adjust the configuration of the firewall according to the setup of the DHCP server.
. An important feature of the behavior of the DHCP server is its ability to run in a chroot environment, or chroot jail, to secure the server host. If the DHCP server should ever be compromised by an outside attack, the attacker will still be in the chroot jail, which prevents them from accessing the rest of the system. The lower part of the dialog displays a tree view with the declarations that have already been defined. Modify these with , , and . Selecting takes you to additional expert dialogs. SeeFigure 32.6: DHCP server: chroot jail and declarations #- Selecting the declaration type
The Figure 32.7, “DHCP server: selecting a declaration type”).
of the DHCP server are made up of several declarations. This dialog lets you set the declaration types , , , , , and . This example shows the selection of a new subnet (seeFigure 32.7: DHCP server: selecting a declaration type #- Subnet configuration
This dialog allows you specify a new subnet with its IP address and netmask. In the middle part of the dialog, modify the DHCP server start options for the selected subnet using
, , and . To set up dynamic DNS for the subnet, select .Figure 32.8: DHCP server: configuring subnets #- TSIG key management
If you chose to configure dynamic DNS in the previous dialog, you can now configure the key management for a secure zone transfer. Selecting Figure 32.10, “DHCP server: interface configuration for dynamic DNS”).
takes you to another dialog in which to configure the interface for dynamic DNS (seeFigure 32.9: DHCP server: TSIG configuration #- Dynamic DNS: interface configuration
You can now activate dynamic DNS for the subnet by selecting Figure 32.8, “DHCP server: configuring subnets”). Selecting again returns to the original expert configuration dialog.
. After doing so, use the drop-down box to activate the TSIG keys for forward and reverse zones, making sure that the keys are the same for the DNS and the DHCP server. With , enable the automatic update and adjustment of the global DHCP server settings according to the dynamic DNS environment. Finally, define which forward and reverse zones should be updated per dynamic DNS, specifying the name of the primary name server for each of the two zones. Selecting returns to the subnet configuration dialog (seeFigure 32.10: DHCP server: interface configuration for dynamic DNS #Note:ignore client-updates
optionWhen enabling Dynamic DNS for a zone, YaST automatically adds the
ignore client-updates
option to improve client compatibility. The option can be disabled if it is not required.- Network interface configuration
To define the interfaces the DHCP server should listen to and to adjust the firewall configuration, select
› from the expert configuration dialog. From the list of interfaces displayed, select one or more that should be attended by the DHCP server. If clients in all subnets need to be able to communicate with the server and the server host also runs a firewall, adjust the firewall accordingly.Note: DHCP andfirewalld
Please note that the option
does not (yet) supportfirewalld
in SUSE Linux Enterprise Server 15 SP3. To manually open the DHCP port, run>
sudo
firewall-cmd --zone=public --permanent --add-service=dhcp
>
sudo
firewall-cmd --reload
Figure 32.11: DHCP server: network interface and firewall #
After completing all configuration steps, close the dialog with
. The server is now started with its new configuration.32.2 DHCP software packages #
Both the DHCP server and the DHCP clients are available for
SUSE Linux Enterprise Server. The DHCP server available is dhcpd
(published by the Internet Systems
Consortium).
On the client side, there is dhcp-client
(also from
ISC) and tools coming with the wicked
package.
By default, the wicked
tools are installed with the
services wickedd-dhcp4
and
wickedd-dhcp6
. Both are launched automatically on
each system boot to watch for a DHCP server. They do not need a
configuration file to do their job and work out of the box in most standard
setups. For more complex situations, use the ISC
dhcp-client
, which is controlled by means of the
configuration files /etc/dhclient.conf
and
/etc/dhclient6.conf
.
32.3 The DHCP server dhcpd #
The core of any DHCP system is the dynamic host configuration protocol
daemon. This server leases addresses and watches how
they are used, according to the settings defined in the configuration file
/etc/dhcpd.conf
. By changing the parameters and values
in this file, a system administrator can influence the program's behavior in
numerous ways. Look at the basic sample /etc/dhcpd.conf
file in Example 32.1, “The configuration file /etc/dhcpd.conf”.
default-lease-time 600; # 10 minutes max-lease-time 7200; # 2 hours option domain-name "example.com"; option domain-name-servers 192.168.1.116; option broadcast-address 192.168.2.255; option routers 192.168.2.1; option subnet-mask 255.255.255.0; subnet 192.168.2.0 netmask 255.255.255.0 { range 192.168.2.10 192.168.2.20; range 192.168.2.100 192.168.2.200; }
This simple configuration file should be sufficient to get the DHCP server to assign IP addresses in the network. Make sure that a semicolon is inserted at the end of each line, because otherwise dhcpd is not started.
The sample file can be divided into three sections. The first one defines
how many seconds an IP address is leased to a requesting client by default
(default-lease-time
) before it should apply for renewal.
This section also includes a statement of the maximum period for which a
machine may keep an IP address assigned by the DHCP server without applying
for renewal (max-lease-time
).
In the second part, some basic network parameters are defined on a global level:
The line
option domain-name
defines the default domain of your network.With the entry
option domain-name-servers
, specify up to three values for the DNS servers used to resolve IP addresses into host names and vice versa. Ideally, configure a name server on your machine or somewhere else in your network before setting up DHCP. That name server should also define a host name for each dynamic address and vice versa. To learn how to configure your own name server, read Chapter 31, The domain name system.The line
option broadcast-address
defines the broadcast address the requesting client should use.With
option routers
, set where the server should send data packets that cannot be delivered to a host on the local network (according to the source and target host address and the subnet mask provided). Usually, especially in smaller networks, this router is identical to the Internet gateway.With
option subnet-mask
, specify the netmask assigned to clients.
The last section of the file defines a network, including a subnet mask. To
finish, specify the address range that the DHCP daemon should use to assign
IP addresses to interested clients. In Example 32.1, “The configuration file /etc/dhcpd.conf”,
clients may be given any address between 192.168.2.10
and 192.168.2.20
or 192.168.2.100
and 192.168.2.200
.
After editing these few lines, you should be able to activate the DHCP
daemon with the command systemctl start dhcpd
. It will be
ready for use immediately. Use the command
rcdhcpd
check-syntax
to perform a brief syntax check. If you encounter any unexpected problems
with your configuration (the server aborts with an error or does not return
done
on start), you should be able to find out what has
gone wrong by looking for information either in the main system log that can
be queried with the command journalctl
(see
Chapter 17, journalctl
: Query the systemd
journal for more information).
On a default SUSE Linux Enterprise Server system, the DHCP daemon is started in a chroot
environment for security reasons. The configuration files must be copied to
the chroot environment so the daemon can find them. Normally, there is no
need to worry about this because the command systemctl start dhcpd
automatically copies the files.
32.3.1 Clients with fixed IP addresses #
DHCP can also be used to assign a predefined, static address to a specific client. Addresses assigned explicitly always take priority over dynamic addresses from the pool. A static address never expires in the way a dynamic address would, for example, if there were not enough addresses available and the server needed to redistribute them among clients.
To identify a client configured with a static address, dhcpd uses the
hardware address (which is a globally unique, fixed numerical code
consisting of six octet pairs) for the identification of all network
devices (for example, 00:30:6E:08:EC:80
). If the respective
lines, like the ones in Example 32.2, “Additions to the configuration file”, are added to
the configuration file of Example 32.1, “The configuration file /etc/dhcpd.conf”, the DHCP daemon
always assigns the same set of data to the corresponding client.
host jupiter { hardware ethernet 00:30:6E:08:EC:80; fixed-address 192.168.2.100; }
The name of the respective client (host
HOSTNAME, here jupiter
)
is entered in the first line and the MAC address in the second line. On
Linux hosts, find the MAC address with the command ip
link show
followed by the network device (for example,
eth0
). The output should contain something like
link/ether 00:30:6E:08:EC:80
In the preceding example, a client with a network card having the MAC
address 00:30:6E:08:EC:80
is assigned the IP address
192.168.2.100
and the host name
jupiter
automatically. The type of hardware to enter is
ethernet
in nearly all cases, although
token-ring
, which is often found on IBM systems, is also
supported.
32.3.2 The SUSE Linux Enterprise Server version #
To improve security, the SUSE Linux Enterprise Server version of the ISC's DHCP server
comes with the non-root/chroot patch by Ari Edelkind applied. This enables
dhcpd to run with the user ID
nobody
and run in a chroot
environment (/var/lib/dhcp
). To make this possible,
the configuration file dhcpd.conf
must be located in
/var/lib/dhcp/etc
. The init script automatically
copies the file to this directory when starting.
Control the server's behavior regarding this feature by means of entries in
the file /etc/sysconfig/dhcpd
. To run dhcpd without
the chroot environment, set the variable
DHCPD_RUN_CHROOTED
in
/etc/sysconfig/dhcpd
to “no”.
To enable dhcpd to resolve host names even from within the chroot environment, some other configuration files must be copied as well:
/etc/localtime
/etc/host.conf
/etc/hosts
/var/run/netconfig/resolv.conf
These files are copied to /var/lib/dhcp/etc/
when
starting the init script. Take these copies into account for any changes
that they require if they are dynamically modified by scripts like
/etc/ppp/ip-up
. However, there should be no need to
worry about this if the configuration file only specifies IP addresses
(instead of host names).
If your configuration includes additional files that should be copied into
the chroot environment, set these under the variable
DHCPD_CONF_INCLUDE_FILES
in the file
/etc/sysconfig/dhcpd
. To ensure that the DHCP logging
facility keeps working even after a restart of the syslog daemon, there is
an additional entry SYSLOGD_ADDITIONAL_SOCKET_DHCP
in the file /etc/sysconfig/syslog
.
32.4 More information #
More information about DHCP is available at the Web site of the
Internet Systems Consortium
(https://www.isc.org/dhcp/). Information is
also available in the dhcpd
, dhcpd.conf
,
dhcpd.leases
, and dhcp-options
man pages.
33 SLP #
Configuring a network client requires detailed knowledge about services provided over the network (such as printing or LDAP, for example). To make it easier to configure such services on a network client, the “service location protocol” (SLP) was developed. SLP makes the availability and configuration data of selected services known to all clients in the local network. Applications that support SLP can use this information to be configured automatically.
SUSE® Linux Enterprise Server supports installation using installation sources provided with SLP and contains many system services with integrated support for SLP. You can use SLP to provide networked clients with central functions, such as an installation server, file server, or print server on your system. Services that offer SLP support include cupsd, login, ntp, openldap2-client, postfix, rpasswd, rsyncd, saned, sshd (via fish), vnc, and ypserv.
All packages necessary to use SLP services on a network client are installed
by default. However, if you want to provide services via
SLP, check that the openslp-server
package is
installed.
33.1 The SLP front-end slptool
#
slptool
is a command line tool to query and register SLP
services. The query functions are useful for diagnostic purposes. The most
important slptool
subcommands are listed below.
slptool
--help
lists all available
options and functions.
- findsrvtypes
List all service types available on the network.
>
slptool findsrvtypes service:install.suse:nfs service:install.suse:ftp service:install.suse:http service:install.suse:smb service:ssh service:fish service:YaST.installation.suse:vnc service:smtp service:domain service:management-software.IBM:hardware-management-console service:rsync service:ntp service:ypserv- findsrvs SERVICE_TYPE
List all servers providing SERVICE_TYPE
>
slptool findsrvs service:ntp service:ntp://ntp.example.com:123,57810 service:ntp://ntp2.example.com:123,57810- findattrs SERVICE_TYPE//HOST
List attributes for SERVICE_TYPE on HOST
>
slptool findattrs service:ntp://ntp.example.com (owner=tux),(email=tux@example.com)- register SERVICE type//HOST:PORT "(ATTRIBUTE=VALUE),(ATTRIBUTE=VALUE)"
Registers SERVICE_TYPE on HOST with an optional list of attributes
slptool register service:ntp://ntp.example.com:57810 \ "(owner=tux),(email=tux@example.com)"
- deregister SERVICE_TYPE//host
Deregisters SERVICE_TYPE on HOST
slptool deregister service:ntp://ntp.example.com
For more information run slptool --help
.
33.2 Providing services via SLP #
To provide SLP services, the SLP daemon
(slpd
) must be running. Like most
system services in SUSE Linux Enterprise Server,
slpd
is controlled by means of a
separate start script. After the installation, the daemon is inactive by
default. To activate it for the current session, run sudo systemctl
start slpd
. If slpd
should
be activated on system start-up, run sudo systemctl enable
slpd
.
Many applications in SUSE Linux Enterprise Server have integrated SLP support via the
libslp
library. If a service has not been compiled with
SLP support, use one of the following methods to make it available via SLP:
- Static registration with
/etc/slp.reg.d
Create a separate registration file for each new service. The following example registers a scanner service:
## Register a saned service on this system ## en means english language ## 65535 disables the timeout, so the service registration does ## not need refreshes service:scanner.sane://$HOSTNAME:6566,en,65535 watch-port-tcp=6566 description=SANE scanner daemon
The most important line in this file is the service URL, which begins with
service:
. This contains the service type (scanner.sane
) and the address under which the service is available on the server. $HOSTNAME is automatically replaced with the full host name. The name of the TCP port on which the relevant service can be found follows, separated by a colon. Then enter the language in which the service should appear and the duration of registration in seconds. These should be separated from the service URL by commas. Set the value for the duration of registration between0
and65535
.0
prevents registration.65535
removes all restrictions.The registration file also contains the two variables
watch-port-tcp
anddescription
.watch-port-tcp
links the SLP service announcement to whether the relevant service is active by havingslpd
check the status of the service. The second variable contains a more precise description of the service that is displayed in suitable browsers.Tip: YaST and SLPSome services brokered by YaST, such as an installation server or YOU server, perform this registration automatically when you activate SLP in the module dialogs. YaST then creates registration files for these services.
- Static registration with
/etc/slp.reg
The only difference between this method and the procedure with
/etc/slp.reg.d
is that all services are grouped within a central file.- Dynamic registration with
slptool
If a service needs to be registered dynamically without the need of configuration files, use the slptool command line utility. The same utility can also be used to deregister an existing service offering without restarting
slpd
. See Section 33.1, “The SLP front-endslptool
” for details.
33.2.1 Setting up an SLP installation server #
Announcing the installation data via SLP within your network makes the network installation much easier, since the installation data such as IP address of the server or the path to the installation media are automatically required via SLP query. Refer to Book “Deployment Guide”, Chapter 16 “Setting up a network installation source” for instructions.
33.3 More information #
- RFC 2608, 2609, 2610
RFC 2608 generally deals with the definition of SLP. RFC 2609 deals with the syntax of the service URLs used in greater detail and RFC 2610 deals with DHCP via SLP.
- http://www.openslp.org
The home page of the OpenSLP project.
/usr/share/doc/packages/openslp
This directory contains the documentation for SLP coming with the
openslp-server
package, including aREADME.SUSE
containing the SUSE Linux Enterprise Server details, the RFCs, and two introductory HTML documents. Programmers who want to use the SLP functions will find more information in the Programmers Guide that is included in theopenslp-devel
package that is provided with the SUSE Software Development Kit.
34 The Apache HTTP server #
According to the surveys from http://www.netcraft.com/ and https://w3techs.com/, the Apache HTTP Server (Apache) is one of the world's most popular Web servers. Developed by the Apache Software Foundation (http://www.apache.org/), it is available for most operating systems. SUSE® Linux Enterprise Server includes Apache version 2.4. This chapter describes how to install, configure, and set up Apache. It also shows how to use additional modules, such as SSL, and how to troubleshoot Apache.
34.1 Quick start #
With this section, quickly set up and start Apache. You must be root
to install and configure Apache.
34.1.1 Requirements #
Make sure the following requirements are met before trying to set up the Apache Web server:
The machine's network is configured properly. For more information about this topic, refer to Chapter 19, Basic networking.
The machine's exact system time is maintained by synchronizing with a time server. This is necessary because parts of the HTTP protocol depend on the correct time. See Chapter 30, Time synchronization with NTP to learn more about this topic.
The latest security updates are installed. If in doubt, run a YaST Online Update.
The default Web server port (
80
) is opened in the firewall. For this, configurefirewalld
to allow the servicehttp
in the public zone. See Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4.3 “Configuring the firewall on the command line” for details.
34.1.2 Installation #
Apache on SUSE Linux Enterprise Server is not installed by default. To install it with a standard, predefined configuration that runs “out of the box”, proceed as follows:
Start YaST and select
› .Choose
› and select .Confirm the installation of the dependent packages to finish the installation process.
34.1.3 Start #
You can start Apache automatically at boot time or start it manually.
To make sure that Apache is automatically started during boot in the
targets multi-user.target
and
graphical.target
, execute the following command:
>
sudo
systemctl enable apache2.service
For more information about the systemd
targets in SUSE Linux Enterprise Server and a
description of the YaST , refer to
Section 15.4, “Managing services with YaST”.
To manually start Apache using the shell, run systemctl start
apache2.service
.
If you do not receive error messages when starting Apache, this usually indicates that the Web server is running. To test this:
Start a browser and open http://localhost/.
If Apache is up and running, you get a test page stating “It works!”.
If you do not see this page, refer to Section 34.9, “Troubleshooting”.
Now that the Web server is running, you can add your own documents, adjust the configuration according to your needs, or add functionality by installing modules.
34.2 Configuring Apache #
SUSE Linux Enterprise Server offers two configuration options:
Manual configuration offers a higher level of detail, but lacks the convenience of the YaST GUI.
Most configuration changes require a reload (some also a restart) of Apache
to take effect. Manually reload Apache with systemctl reload
apache2.service
or use one of the restart options as described in
Section 34.3, “Starting and stopping Apache”.
If you configure Apache with YaST, this can be taken care of automatically if you set Section 34.2.3.2, “HTTP server configuration”.
to as described in34.2.1 Apache configuration files #
This section gives an overview of the Apache configuration files. If you use YaST for configuration, you do not need to touch these files—however, the information might be useful for you to switch to manual configuration later on.
Apache configuration files can be found in two different locations:
34.2.1.1 /etc/sysconfig/apache2
#
/etc/sysconfig/apache2
controls some global settings
of Apache, like modules to load, additional configuration files to
include, flags with which the server should be started, and flags that
should be added to the command line. Every configuration option in this
file is extensively documented and therefore not mentioned here. For a
general-purpose Web server, the settings in
/etc/sysconfig/apache2
should be sufficient for any
configuration needs.
34.2.1.2 /etc/apache2/
#
/etc/apache2/
hosts all configuration files for
Apache. In the following, the purpose of each file is explained. Each file
includes several configuration options (also called
directives). Every configuration option in these
files is extensively documented and therefore not mentioned here.
The Apache configuration files are organized as follows:
/etc/apache2/ | |- charset.conv |- conf.d/ | | | |- *.conf | |- default-server.conf |- errors.conf |- global.conf |- httpd.conf |- listen.conf |- loadmodule.conf |- magic |- mime.types |- mod_*.conf |- protocols.conf |- server-tuning.conf |- ssl-global.conf |- ssl.* |- sysconfig.d | | | |- global.conf | |- include.conf | |- loadmodule.conf . . | |- uid.conf |- vhosts.d | |- *.conf
charset.conv
Specifies which character sets to use for different languages. Do not edit this file.
conf.d/*.conf
Configuration files added by other modules. These configuration files can be included into your virtual host configuration where needed. See
vhosts.d/vhost.template
for examples. By doing so, you can provide different module sets for different virtual hosts.default-server.conf
Global configuration for all virtual hosts with reasonable defaults. Instead of changing the values, overwrite them with a virtual host configuration.
errors.conf
Defines how Apache responds to errors. To customize these messages for all virtual hosts, edit this file. Otherwise overwrite these directives in your virtual host configurations.
global.conf
General configuration of the main Web server process, such as the access path, error logs, or the level of logging.
httpd.conf
The main Apache server configuration file. Avoid changing this file. It primarily contains include statements and global settings. Overwrite global settings in the pertinent configuration files listed here. Change host-specific settings (such as document root) in your virtual host configuration.
listen.conf
Binds Apache to specific IP addresses and ports. Name-based virtual hosting is also configured here. For details, see Section 34.2.2.1.1, “Name-based virtual hosts”.
magic
Data for the mime_magic module that helps Apache automatically determine the MIME type of an unknown file. Do not change this file.
mime.types
MIME types known by the system (this actually is a link to
/etc/mime.types
). Do not edit this file. If you need to add MIME types not listed here, add them tomod_mime-defaults.conf
.mod_*.conf
Configuration files for the modules that are installed by default. Refer to Section 34.4, “Installing, activating, and configuring modules” for details. Note that configuration files for optional modules reside in the directory
conf.d
.protocols.conf
Configuration directives for serving pages over HTTP2 connection.
server-tuning.conf
Contains configuration directives for the different MPMs (see Section 34.4.4, “Multiprocessing modules”) and general configuration options that control Apache's performance. Properly test your Web server when making changes here.
ssl-global.conf
andssl.*
Global SSL configuration and SSL certificate data. Refer to Section 34.6, “Setting up a secure Web server with SSL” for details.
sysconfig.d/*.conf
Configuration files automatically generated from
/etc/sysconfig/apache2
. Do not change any of these files—edit/etc/sysconfig/apache2
instead. Do not put other configuration files in this directory.uid.conf
Specifies under which user and group ID Apache runs. Do not change this file.
vhosts.d/*.conf
Your virtual host configuration should be located here. The directory contains template files for virtual hosts with and without SSL. Every file in this directory ending with
.conf
is automatically included in the Apache configuration. Refer to Section 34.2.2.1, “Virtual host configuration” for details.
34.2.2 Configuring Apache manually #
Configuring Apache manually involves editing plain text configuration files
as user root
.
34.2.2.1 Virtual host configuration #
The term virtual host refers to Apache's ability to serve multiple universal resource identifiers (URIs) from the same physical machine. This means that several domains, such as www.example.com and www.example.net, are run by a single Web server on one physical machine.
It is common practice to use virtual hosts to save administrative effort (only a single Web server needs to be maintained) and hardware expenses (each domain does not require a dedicated server). Virtual hosts can be name based, IP based, or port based.
To list all existing virtual hosts, use the command
apache2ctl
-S
. This outputs a list
showing the default server and all virtual hosts together with their IP
addresses and listening ports. Furthermore, the list also contains an
entry for each virtual host showing its location in the configuration
files.
Virtual hosts can be configured via YaST as described in
Section 34.2.3.1.4, “Virtual hosts” or
by manually editing a configuration file. By default, Apache in
SUSE Linux Enterprise Server is prepared for one configuration file per virtual host in
/etc/apache2/vhosts.d/
. All files in this directory
with the extension .conf
are automatically included
to the configuration. A basic template for a virtual host is provided in
this directory (vhost.template
or
vhost-ssl.template
for a virtual host with SSL
support).
It is recommended to always create a virtual host configuration file, even if your Web server only hosts one domain. By doing so, you not only have the domain-specific configuration in one file, but you can always fall back to a working basic configuration by simply moving, deleting, or renaming the configuration file for the virtual host. For the same reason, you should also create separate configuration files for each virtual host.
When using name-based virtual hosts it is recommended to set up a default
configuration that will be used when a domain name does not match a
virtual host configuration. The default virtual host is the one whose
configuration is loaded first. Since the order of the configuration files
is determined by file name, start the file name of the default virtual
host configuration with an underscore character (_
) to
make sure it is loaded first (for example:
_default_vhost.conf
).
The
<VirtualHost>
</VirtualHost>
block holds the information that applies to a particular domain. When
Apache receives a client request for a defined virtual host, it uses the
directives enclosed in this section. Almost all directives can be used in
a virtual host context. See
http://httpd.apache.org/docs/2.4/mod/quickreference.html
for further information about Apache's configuration directives.
34.2.2.1.1 Name-based virtual hosts #
With name-based virtual hosts, more than one Web site is served per IP
address. Apache uses the host field in the HTTP header that is sent by
the client to connect the request to a matching
ServerName
entry of one of the virtual host
declarations. If no matching ServerName
is
found, the first specified virtual host is used as a default.
The first step is to create a <VirtualHost>
block for each different name-based host that you want to serve. Inside
each <VirtualHost>
block, you will need at
minimum a ServerName
directive to designate which host
is served and a DocumentRoot
directive to show where
in the file system the content for that host resides.
VirtualHost
entries #<VirtualHost *:80> # This first-listed virtual host is also the default for *:80 ServerName www.example.com ServerAlias example.com DocumentRoot /srv/www/htdocs/domain </VirtualHost> <VirtualHost *:80> ServerName other.example.com DocumentRoot /srv/www/htdocs/otherdomain </VirtualHost>
The opening VirtualHost
tag takes the IP address
(or fully qualified domain name) as an argument in a name-based virtual
host configuration. A port number directive is optional.
The wild card * is also allowed as a substitute for the IP address. When using IPv6 addresses, the address must be included in square brackets.
VirtualHost
directives #<VirtualHost 192.168.3.100:80> ... </VirtualHost> <VirtualHost 192.168.3.100> ... </VirtualHost> <VirtualHost *:80> ... </VirtualHost> <VirtualHost *> ... </VirtualHost> <VirtualHost [2002:c0a8:364::]> ... </VirtualHost>
34.2.2.1.2 IP-based virtual hosts #
This alternative virtual host configuration requires the setup of multiple IP addresses for a machine. One instance of Apache hosts several domains, each of which is assigned a different IP.
The physical server must have one IP address for each IP-based virtual host. If the machine does not have multiple network cards, virtual network interfaces (IP aliasing) can also be used.
The following example shows Apache running on a machine with the IP
192.168.3.100
, hosting two domains
on the additional IP addresses 192.168.3.101
and 192.168.3.102
. A separate
VirtualHost
block is needed for every virtual
server.
VirtualHost
directives #<VirtualHost 192.168.3.101> ... </VirtualHost> <VirtualHost 192.168.3.102> ... </VirtualHost>
Here, VirtualHost
directives are only specified
for interfaces other than 192.168.3.100
. When a
Listen
directive is also configured for
192.168.3.100
, a separate IP-based virtual host must
be created to answer HTTP requests to that interface—otherwise the
directives found in the default server configuration
(/etc/apache2/default-server.conf
) are applied.
34.2.2.1.3 Basic virtual host configuration #
At least the following directives should be in each virtual host
configuration to set up a virtual host. See
/etc/apache2/vhosts.d/vhost.template
for more
options.
ServerName
The fully qualified domain name under which the host should be addressed.
DocumentRoot
Path to the directory from which Apache should serve files for this host. For security reasons, access to the entire file system is forbidden by default, so you must explicitly unlock this directory within a
Directory
container.ServerAdmin
E-mail address of the server administrator. This address is, for example, shown on error pages Apache creates.
ErrorLog
The error log file for this virtual host. Although it is not necessary to create separate error log files for each virtual host, it is common practice to do so, because it makes the debugging of errors much easier.
/var/log/apache2/
is the default directory for Apache's log files.CustomLog
The access log file for this virtual host. Although it is not necessary to create separate access log files for each virtual host, it is common practice to do so, because it allows the separate analysis of access statistics for each host.
/var/log/apache2/
is the default directory for Apache's log files.
As mentioned above, access to the whole file system is forbidden by
default for security reasons. Therefore, explicitly unlock the
directories in which you have placed the files Apache should
serve—for example the DocumentRoot
:
<Directory "/srv/www/www.example.com/htdocs"> Require all granted </Directory>
Require all granted
In previous versions of Apache, the statement Require all
granted
was expressed as:
Order allow,deny Allow from all
This old syntax is still supported by the
mod_access_compat
module.
The complete configuration file looks like this:
VirtualHost
configuration #<VirtualHost 192.168.3.100> ServerName www.example.com DocumentRoot /srv/www/www.example.com/htdocs ServerAdmin webmaster@example.com ErrorLog /var/log/apache2/www.example.com_log CustomLog /var/log/apache2/www.example.com-access_log common <Directory "/srv/www/www.example.com/htdocs"> Require all granted </Directory> </VirtualHost>
34.2.3 Configuring Apache with YaST #
To configure your Web server with YaST, start YaST and select Section 34.2.3.2, “HTTP server configuration”.
› . When starting the module for the first time, the starts, prompting you to make a few basic decisions concerning administration of the server. After having finished the wizard, the dialog starts each time you call the module. For more information, see34.2.3.1 HTTP server wizard #
The HTTP Server Wizard consists of five steps. In the last step of the dialog, you may enter the expert configuration mode to make even more specific settings.
34.2.3.1.1 Network device selection #
Here, specify the network interfaces and ports Apache uses to listen for
incoming requests. You can select any combination of existing network
interfaces and their respective IP addresses. Ports from all three ranges
(well-known ports, registered ports, and dynamic or private ports) that are
not reserved by other services can be used. The default setting is to
listen on all network interfaces (IP addresses) on port
80
.
Check
to open the ports in the firewall that the Web server listens on. This is necessary to make the Web server available on the network, which can be a LAN, WAN, or the public Internet. Keeping the port closed is only useful in test situations where no external access to the Web server is necessary. If you have multiple network interfaces, click to specify on which interface(s) the port(s) should be opened.Click
to continue with the configuration.34.2.3.1.2 Modules #
The Section 34.2.3.2.2, “Server modules”. Click to advance to the next dialog.
configuration option allows for the activation or deactivation of the script languages that the Web server should support. For the activation or deactivation of other modules, refer to34.2.3.1.3 Default host #
This option pertains to the default Web server. As explained in Section 34.2.2.1, “Virtual host configuration”, Apache can serve multiple virtual hosts from a single physical machine. The first declared virtual host in the configuration file is commonly called the default host. Each virtual host inherits the default host's configuration.
To edit the host settings (also called directives), select the appropriate entry in the table then click . To add new directives, click . To delete a directive, select it and click .
Here is list of the default settings of the server:
Document Root
Path to the directory from which Apache serves files for this host.
/srv/www/htdocs
is the default location.Alias
Using
Alias
directives, URLs can be mapped to physical file system locations. This means that a certain path even outside theDocument Root
in the file system can be accessed via a URL aliasing that path.The default SUSE Linux Enterprise Server
Alias
/icons
points to/usr/share/apache2/icons
for the Apache icons displayed in the directory index view.ScriptAlias
Similar to the
Alias
directive, theScriptAlias
directive maps a URL to a file system location. The difference is thatScriptAlias
designates the target directory as a CGI location, meaning that CGI scripts should be executed in that location.Directory
With
Directory
settings, you can enclose a group of configuration options that will only apply to the specified directory.Access and display options for the directories
/srv/www/htdocs
,/usr/share/apache2/icons
and/srv/www/cgi-bin
are configured here. It should not be necessary to change the defaults.Include
With include, additional configuration files can be specified. Two
Include
directives are already preconfigured:/etc/apache2/conf.d/
is the directory containing the configuration files that come with external modules. With this directive, all files in this directory ending in.conf
are included. With the second directive,/etc/apache2/conf.d/apache2-manual.conf
, theapache2-manual
configuration file is included.Server Name
This specifies the default URL used by clients to contact the Web server. Use a fully qualified domain name (FQDN) to reach the Web server at
http://FQDN/
or its IP address. You cannot choose an arbitrary name here—the server must be “known” under this name.Server Administrator E-Mail
E-mail address of the server administrator. This address is, for example, shown on error pages Apache creates.
After finishing with the
step, click to continue with the configuration.34.2.3.1.4 Virtual hosts #
In this step, the wizard displays a list of already configured virtual hosts (see Section 34.2.2.1, “Virtual host configuration”). If you have not made manual changes prior to starting the YaST HTTP wizard, no virtual host is present.
To add a host, click DocumentRoot
), and the . is used to determine
how a host is identified (name based or IP based). Specify the name or IP
address with
Clicking
advances to the second part of the virtual host configuration dialog.
In part two of the virtual host configuration you can specify whether to
enable CGI scripts and which directory to use for these scripts. It is also
possible to enable SSL. If you do so, you must specify the path to the
certificate as well. See Section 34.6.2, “Configuring Apache with SSL”
for details on SSL and certificates. With the option, you can specify which file to display when the
client requests a directory (by default, index.html
).
Add one or more file names (space-separated) to change this.
With , the content of the users public
directories
(~USER/public_html/
) is
made available on the server under
http://www.example.com/~USER
.
It is not possible to add virtual hosts at will. If using name-based virtual hosts, each host name must be resolved on the network. If using IP-based virtual hosts, you can assign only one host to each IP address available.
34.2.3.1.5 Summary #
This is the final step of the wizard. Here, determine how and when the Apache server is started: when booting or manually. Also see a short summary of the configuration made so far. If you are satisfied with your settings, click Section 34.2.3.2, “HTTP server configuration”.
to complete configuration. To change something, click until you have reached the desired dialog. Clicking opens the dialog described in34.2.3.2 HTTP server configuration #
The
dialog also lets you make even more adjustments to the configuration than the wizard (which only runs if you configure your Web server for the first time). It consists of four tabs described in the following. No configuration option you change here is effective immediately—you always must confirm your changes with to make them effective. Clicking leaves the configuration module and discards your changes.34.2.3.2.1 Listen ports and addresses #
In 80
. You should always check
, because otherwise the Web server
is not reachable from outside. Keeping the port closed is only useful in
test situations where no external access to the Web server is necessary. If
you have multiple network interfaces, click to specify on which interface(s) the port(s) should be
opened.
With Section 34.3, “Starting and stopping Apache”. These commands are effective immediately and their log messages are also displayed immediately.
, watch either the access log file or the error log file. This is useful if you want to test your configuration. The log file opens in a separate window from which you can also restart or reload the Web server. For details, see34.2.3.2.2 Server modules #
You can change the status (enabled or disabled) of Apache2 modules by clicking Section 34.4, “Installing, activating, and configuring modules”.
. Click to add a new module that is already installed but not yet listed. Learn more about modules in34.2.3.2.3 Main host or hosts #
These dialogs are identical to the ones already described. Refer to Section 34.2.3.1.3, “Default host” and Section 34.2.3.1.4, “Virtual hosts”.
34.3 Starting and stopping Apache #
If configured with YaST as described in
Section 34.2.3, “Configuring Apache with YaST”, Apache is started at boot
time in the multi-user.target
and
graphical.target
. You can change this behavior
using YaST's or with the
systemctl
command line tool (systemctl
enable
or systemctl disable
).
To start, stop, or manipulate Apache on a running system, use either the
systemctl
or the apachectl
commands as
described below.
For general information about systemctl
commands, refer
to Section 15.2.1, “Managing services in a running system”.
systemctl status apache2.service
Checks if Apache is started.
systemctl start apache2.service
Starts Apache if it is not already running.
systemctl stop apache2.service
Stops Apache by terminating the parent process.
systemctl restart apache2.service
Stops and then restarts Apache. Starts the Web server if it was not running before.
systemctl try-restart apache2.service
Stops then restarts Apache only if it is already running.
systemctl reload apache2.service
Stops the Web server by advising all forked Apache processes to first finish their requests before shutting down. As each process dies, it is replaced by a newly started one, resulting in a complete “restart” of Apache.
Tip: Restarting Apache in production environmentsThis command allows activating changes in the Apache configuration without causing connection break-offs.
systemctl stop apache2.service
Stops the Web server after a defined period of time configured with
GracefulShutdownTimeout
to ensure that existing requests can be finished.apachectl configtest
Checks the syntax of the configuration files without affecting a running Web server. Because this check is forced every time the server is started, reloaded, or restarted, it is usually not necessary to run the test explicitly (if a configuration error is found, the Web server is not started, reloaded, or restarted).
apachectl status
andapachectl fullstatus
Dumps a short or full status screen, respectively. Requires the module
mod_status
to be enabled and a text-based browser (such aslinks
orw3m
) to be installed. In addition to that,STATUS
must be added toAPACHE_SERVER_FLAGS
in the file/etc/sysconfig/apache2
.
If you specify additional flags to the commands, these are passed through to the Web server.
34.4 Installing, activating, and configuring modules #
The Apache software is built in a modular fashion: all functionality except
some core tasks are handled by modules. This has progressed so far that even
HTTP is processed by a module (http_core
).
Apache modules can be compiled into the Apache binary at build time or be dynamically loaded at runtime. Refer to Section 34.4.2, “Activation and deactivation” for details of how to load modules dynamically.
Apache modules are organized into the following categories:
- Base modules
Base modules are compiled into Apache by default. Apache in SUSE Linux Enterprise Server has only
mod_so
(needed to load other modules) andhttp_core
compiled in. All others are available as shared objects: rather than being included in the server binary itself, they can be included at runtime.- Extension modules
In general, modules labeled as extensions are included in the Apache software package, but are usually not compiled into the server statically. In SUSE Linux Enterprise Server, they are available as shared objects that can be loaded into Apache at runtime.
- External modules
Modules labeled external are not included in the official Apache distribution. However, SUSE Linux Enterprise Server provides several of them.
- Multiprocessing modules (MPMs)
MPMs are responsible for accepting and handling requests to the Web server, representing the core of the Web server software.
34.4.1 Module installation #
If you have done a default installation as described in
Section 34.1.2, “Installation”, the following
modules are already installed: all base and extension modules, the
multiprocessing module Prefork MPM, and the external module
mod_python
.
You can install additional external modules by starting YaST and choosing
apache
. Among other packages, the
results list contains all available external Apache modules.
34.4.2 Activation and deactivation #
Activate or deactivate particular modules either manually or with YaST. In YaST, script language modules (PHP 7 and Python) need to be enabled or disabled with the module configuration described in Section 34.2.3.1, “HTTP server wizard”. All other modules can be enabled or disabled as described in Section 34.2.3.2.2, “Server modules”.
If you prefer to activate or deactivate the modules manually, use the
commands a2enmod
MODULE or
a2dismod
MODULE,
respectively. a2enmod -l
outputs a list of all currently
active modules.
If you have activated external modules manually, make sure to load their
configuration files in all virtual host configurations. Configuration
files for external modules are located under
/etc/apache2/conf.d/
and are loaded in
/etc/apache2/default-server.conf
by default. For more
fine-grained control you can comment out the inclusion in
/etc/apache2/default-server.conf
and add it to
specific virtual hosts only. See
/etc/apache2/vhosts.d/vhost.template
for examples.
34.4.3 Base and extension modules #
All base and extension modules are described in detail in the Apache documentation. Only a brief description of the most important modules is available here. Refer to http://httpd.apache.org/docs/2.4/mod/ to learn details about each module.
mod_actions
Provides methods to execute a script whenever a certain MIME type (such as
application/pdf
), a file with a specific extension (like.rpm
), or a certain request method (such asGET
) is requested. This module is enabled by default.mod_alias
Provides
Alias
andRedirect
directives with which you can map a URL to a specific directory (Alias
) or redirect a requested URL to another location. This module is enabled by default.mod_auth*
The authentication modules provide different authentication methods: basic authentication with
mod_auth_basic
or digest authentication withmod_auth_digest
.mod_auth_basic
andmod_auth_digest
must be combined with an authentication provider module,mod_authn_*
(for example,mod_authn_file
for text file–based authentication) and with an authorization modulemod_authz_*
(for example,mod_authz_user
for user authorization).More information about this topic is available in the Authentication HOWTO at http://httpd.apache.org/docs/2.4/howto/auth.html.
mod_auth_openidc
mod_auth_openidc
the only certified way to use OpenID Connect with the Apache HTTP server. (See https://openid.net/developers/certified/.)mod_autoindex
Autoindex generates directory listings when no index file (for example,
index.html
) is present. The look and feel of these indexes is configurable. This module is enabled by default. However, directory listings are disabled by default via theOptions
directive—overwrite this setting in your virtual host configuration. The default configuration file for this module is located at/etc/apache2/mod_autoindex-defaults.conf
.mod_cgi
mod_cgi
is needed to execute CGI scripts. This module is enabled by default.mod_deflate
Using this module, Apache can be configured to compress given file types on the fly before delivering them.
mod_dir
mod_dir
provides theDirectoryIndex
directive with which you can configure which files are automatically delivered when a directory is requested (index.html
by default). It also provides an automatic redirect to the correct URL when a directory request does not contain a trailing slash. This module is enabled by default.mod_env
Controls the environment that is passed to CGI scripts or SSI pages. Environment variables can be set or unset or passed from the shell that invoked the
httpd
process. This module is enabled by default.mod_expires
With
mod_expires
, you can control how often proxy and browser caches refresh your documents by sending anExpires
header. This module is enabled by default.mod_http2
With
mod_http2
, Apache gains support for the HTTP/2 protocol. It can be enabled by specifyingProtocols h2 http/1.1
in aVirtualHost
.mod_include
mod_include
lets you use Server Side Includes (SSI), which provide a basic functionality to generate HTML pages dynamically. This module is enabled by default.mod_info
Provides a comprehensive overview of the server configuration under http://localhost/server-info/. For security reasons, you should always limit access to this URL. By default only
localhost
is allowed to access this URL.mod_info
is configured at/etc/apache2/mod_info.conf
.mod_log_config
With this module, you can configure the look of the Apache log files. This module is enabled by default.
mod_mime
The mime module ensures that a file is delivered with the correct MIME header based on the file name's extension (for example
text/html
for HTML documents). This module is enabled by default.mod_negotiation
Necessary for content negotiation. See http://httpd.apache.org/docs/2.4/content-negotiation.html for more information. This module is enabled by default.
mod_rewrite
Provides the functionality of
mod_alias
, but offers more features and flexibility. Withmod_rewrite
, you can redirect URLs based on multiple rules, request headers, and more.mod_setenvif
Sets environment variables based on details of the client's request, such as the browser string the client sends, or the client's IP address. This module is enabled by default.
mod_spelling
mod_spelling
attempts to automatically correct typographical errors in URLs, such as capitalization errors.mod_ssl
Enables encrypted connections between Web server and clients. See Section 34.6, “Setting up a secure Web server with SSL” for details. This module is enabled by default.
mod_status
Provides information on server activity and performance under http://localhost/server-status/. For security reasons, you should always limit access to this URL. By default, only
localhost
is allowed to access this URL.mod_status
is configured at/etc/apache2/mod_status.conf
.mod_suexec
mod_suexec
lets you run CGI scripts under a different user and group. This module is enabled by default.mod_userdir
Enables user-specific directories available under
~USER/
. TheUserDir
directive must be specified in the configuration. This module is enabled by default.
34.4.4 Multiprocessing modules #
SUSE Linux Enterprise Server provides two different multiprocessing modules (MPMs) for use with Apache:
34.4.4.1 Prefork MPM #
The prefork MPM implements a non-threaded, preforking Web server. It makes the Web server behave similarly to Apache version 1.x. In this version it isolates each request and handles it by forking a separate child process. Thus problematic requests cannot affect others, avoiding a lockup of the Web server.
While providing stability with this process-based approach, the prefork MPM consumes more system resources than its counterpart, the worker MPM. The prefork MPM is considered the default MPM for Unix-based operating systems.
This document assumes Apache is used with the prefork MPM.
34.4.4.2 Worker MPM #
The worker MPM provides a multi-threaded Web server. A thread is a “lighter” form of a process. The advantage of a thread over a process is its lower resource consumption. Instead of only forking child processes, the worker MPM serves requests by using threads with server processes. The preforked child processes are multi-threaded. This approach makes Apache perform better by consuming fewer system resources than the prefork MPM.
One major disadvantage is the stability of the worker MPM: if a thread becomes corrupt, all threads of a process can be affected. In the worst case, this may result in a server crash. Especially when using the Common Gateway Interface (CGI) with Apache under heavy load, internal server errors might occur because of threads being unable to communicate with system resources. Another argument against using the worker MPM with Apache is that not all available Apache modules are thread-safe and thus cannot be used with the worker MPM.
Not all available PHP modules are thread-safe. Using the worker MPM with
mod_php
is strongly discouraged.
34.4.5 External modules #
Find a list of all external modules shipped with SUSE Linux Enterprise Server here. Find the module's documentation in the listed directory.
mod_apparmor
Adds support to Apache to provide AppArmor confinement to individual CGI scripts handled by modules like
mod_php7
.Package Name: apache2-mod_apparmor
More Information: Book “Security and Hardening Guide” mod_php7
PHP is a server-side, cross-platform HTML embedded scripting language.
Package Name: apache2-mod_php7
Configuration File: /etc/apache2/conf.d/php7.conf
mod_python
mod_python
allows embedding Python within the Apache HTTP server for a considerable boost in performance and added flexibility in designing Web-based applications.Package Name: apache2-mod_python
More Information: /usr/share/doc/packages/apache2-mod_python
mod_security
mod_security
provides a Web application firewall to protect Web applications from a range of attacks. It also enables HTTP traffic monitoring and real-time analysis.Package Name: apache2-mod_security2
Configuration File: /etc/apache2/conf.d/mod_security2.conf
More Information: /usr/share/doc/packages/apache2-mod_security2
Documentation: http://modsecurity.org/documentation/
34.4.6 Compilation #
Apache can be extended by advanced users by writing custom modules. To
develop modules for Apache or compile third-party modules, the package
apache2-devel
is required along with the
corresponding development tools. apache2-devel
also contains the apxs2
tools, which are necessary for
compiling additional modules for Apache.
apxs2
enables the compilation and installation of
modules from source code (including the required changes to the
configuration files), which creates dynamic shared
objects (DSOs) that can be loaded into Apache at runtime.
The apxs2
binaries are located under
/usr/sbin
:
/usr/sbin/apxs2
—suitable for building an extension module that works with any MPM. The installation location is/usr/lib64/apache2
./usr/sbin/apxs2-prefork
—suitable for prefork MPM modules. The installation location is/usr/lib64/apache2-prefork
./usr/sbin/apxs2-worker
—suitable for worker MPM modules. The installation location is/usr/lib64/apache2-worker
.
Install and activate a module from source code with the following commands:
>
sudo
cd /path/to/module/source>
sudo
apxs2 -cia MODULE.c
where -c
compiles the module, -i
installs
it, and -a
activates it. Other options of
apxs2
are described in the
apxs2(1)
man page.
34.5 Enabling CGI scripts #
Apache's Common Gateway Interface (CGI) lets you create dynamic content with programs or scripts usually called CGI scripts. CGI scripts can be written in any programming language. Usually, script languages such as PHP are used.
To enable Apache to deliver content created by CGI scripts,
mod_cgi
needs to be activated.
mod_alias
is also needed. Both modules are enabled
by default. Refer to Section 34.4.2, “Activation and deactivation” for
details on activating modules.
Allowing the server to execute CGI scripts is a potential security hole. Refer to Section 34.8, “Avoiding security problems” for additional information.
34.5.1 Apache configuration #
In SUSE Linux Enterprise Server, the execution of CGI scripts is only allowed in the
directory /srv/www/cgi-bin/
. This location is already
configured to execute CGI scripts. If you have created a virtual host
configuration (see
Section 34.2.2.1, “Virtual host configuration”) and want to
place your scripts in a host-specific directory, you must unlock and
configure this directory.
ScriptAlias /cgi-bin/ "/srv/www/www.example.com/cgi-bin/"1 <Directory "/srv/www/www.example.com/cgi-bin/"> Options +ExecCGI2 AddHandler cgi-script .cgi .pl3 Require all granted4 </Directory>
Tells Apache to handle all files within this directory as CGI scripts. | |
Enables CGI script execution | |
Tells the server to treat files with the extensions .pl and .cgi as CGI scripts. Adjust according to your needs. | |
The |
34.5.2 Running an example script #
CGI programming differs from "regular" programming in that the CGI programs
and scripts must be preceded by a MIME-Type header such as
Content-type: text/html
. This header is sent to the
client, so it understands what kind of content it receives. Secondly, the
script's output must be something the client, usually a Web browser,
understands—HTML usually, or plain text or images, for example.
A simple test script available under
/usr/share/doc/packages/apache2/test-cgi
is part of
the Apache package. It outputs the content of some environment variables as
plain text. Copy this script to either
/srv/www/cgi-bin/
or the script directory of your
virtual host (/srv/www/www.example.com/cgi-bin/
) and name it
test.cgi
. Edit the file to have
#!/bin/sh
as the first line.
Files accessible by the Web server should be owned by the user
root
. For additional information
see Section 34.8, “Avoiding security problems”. Because the Web server runs
with a different user, the CGI scripts must be world-executable and
world-readable. Change into the CGI directory and use the command
chmod 755 test.cgi
to apply the proper permissions.
Now call http://localhost/cgi-bin/test.cgi
or
http://www.example.com/cgi-bin/test.cgi
. You should see the
“CGI/1.0 test script report”.
34.5.3 CGI troubleshooting #
If you do not see the output of the test program but an error message instead, check the following:
Have you reloaded the server after having changed the configuration? If not, reload with
systemctl reload apache2.service
.If you have configured your custom CGI directory, is it configured properly? If in doubt, try the script within the default CGI directory
/srv/www/cgi-bin/
and call it withhttp://localhost/cgi-bin/test.cgi
.Are the file permissions correct? Change into the CGI directory and execute
ls -l test.cgi
. The output should start with-rwxr-xr-x 1 root root
Make sure that the script does not contain programming errors. If you have not changed
test.cgi
, this should not be the case, but if you are using your own programs, always make sure that they do not contain programming errors.
34.6 Setting up a secure Web server with SSL #
Whenever sensitive data, such as credit card information, is transferred
between Web server and client, it is desirable to have a secure, encrypted
connection with authentication. mod_ssl
provides
strong encryption using the secure sockets layer (SSL) and transport layer
security (TLS) protocols for HTTP communication between a client and the Web
server. Using TLS/SSL, a private connection between Web server and client is
established. Data integrity is ensured and client and server can
authenticate each other.
For this purpose, the server sends an SSL certificate that holds information proving the server's valid identity before any request to a URL is answered. In turn, this guarantees that the server is the uniquely correct end point for the communication. Additionally, the certificate generates an encrypted connection between client and server that can transport information without the risk of exposing sensitive, plain-text content.
mod_ssl
does not implement the TLS/SSL protocols
itself, but acts as an interface between Apache and an SSL library. In
SUSE Linux Enterprise Server, the OpenSSL library is used. OpenSSL is automatically
installed with Apache.
The most visible effect of using mod_ssl
with
Apache is that URLs are prefixed with https://
instead of
http://
.
34.6.1 Creating an SSL certificate #
To use TLS/SSL with the Web server, you need to create an SSL certificate. This certificate is needed for the authorization between Web server and client, so that each party can clearly identify the other party. To ensure the integrity of the certificate, it must be signed by a party every user trusts.
There are three types of certificates you can create: a “dummy” certificate for testing purposes only, a self-signed certificate for a defined circle of users that trust you, and a certificate signed by an independent, publicly-known certificate authority (CA).
Creating a certificate is a two step process. First, a private key for the certificate authority is generated then the server certificate is signed with this key.
To learn more about concepts and definitions of TLS/SSL, refer to https://httpd.apache.org/docs/2.4/ssl/ssl_intro.html.
34.6.1.1 Creating a “dummy” certificate #
To generate a dummy certificate, call the script
/usr/bin/gensslcert
. It creates or overwrites the files
listed below. Use gensslcert
's optional switches to
fine-tune the certificate. Call /usr/bin/gensslcert
-h
for more information.
/etc/apache2/ssl.crt/ca.crt
/etc/apache2/ssl.crt/server.crt
/etc/apache2/ssl.key/server.key
/etc/apache2/ssl.csr/server.csr
A copy of ca.crt
is also placed at
/srv/www/htdocs/CA.crt
for download.
A dummy certificate should never be used on a production system. Only use it for testing purposes.
34.6.1.2 Creating a self-signed certificate #
If you are setting up a secure Web server for an intranet or for a defined circle of users, it is probably sufficient if you sign a certificate with your own certificate authority (CA). Note that visitors to such a site will see a warning like “this is an untrusted site”, as Web browsers do not recognize self-signed certificates.
Only use a self-signed certificate on a Web server that is accessed by people who know and trust you as a certificate authority. It is not recommended to use such a certificate for a public shop, for example.
First you need to generate a certificate signing request (CSR). You are
going to use openssl
, with PEM
as
the certificate format. During this step, you will be asked for a
passphrase, and to answer several questions. Remember the passphrase you
enter as you will need it in the future.
>
sudo
openssl req -new > new.cert.csr Generating a 1024 bit RSA private key ..++++++ .........++++++ writing new private key to 'privkey.pem' Enter PEM pass phrase:1 Verifying - Enter PEM pass phrase:2 ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [AU]:3 State or Province Name (full name) [Some-State]:4 Locality Name (eg, city) []:5 Organization Name (eg, company) [Internet Widgits Pty Ltd]:6 Organizational Unit Name (eg, section) []:7 Common Name (for example server FQDN, or YOUR name) []:8 Email Address []:9 Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []:10 An optional company name []:11
Fill in your passphrase. | |
Fill it in once more (and remember it). | |
Fill in your 2 letter country code, such as | |
Fill in the name of the state where you live. | |
Fill in the city name, such as | |
Fill in the name of the organization you work for. | |
Fill in your organization unit, or leave blank if you have none. | |
Fill in either the domain name of the server, or your first and last name. | |
Fill in your work e-mail address. | |
Leave the challenge password empty, otherwise you will need to enter it every time you restart the Apache Web server. | |
Fill in the optional company name, or leave blank. |
Now you can generate the certificate. You are going to use
openssl
again, and the format of the certificate is the
default PEM
.
Export the private part of the key to
new.cert.key
. You will be prompted for the passphrase you entered when creating the certificate signing request (CSR).>
sudo
openssl rsa -in privkey.pem -out new.cert.keyGenerate the public part of the certificate according to the information you filled out in the signing request. The
-days
option specifies the length of time before the certificate expires. You can revoke a certificate, or replace one before it expires.>
sudo
openssl x509 -in new.cert.csr -out new.cert.cert -req \ -signkey new.cert.key -days 365Copy the certificate files to the relevant directories, so that the Apache server can read them. Make sure that the private key
/etc/apache2/ssl.key/server.key
is not world-readable, while the public PEM certificate/etc/apache2/ssl.crt/server.crt
is.>
sudo
cp new.cert.cert /etc/apache2/ssl.crt/server.crt>
sudo
cp new.cert.key /etc/apache2/ssl.key/server.key
The last step is to copy the public certificate file from
/etc/apache2/ssl.crt/server.crt
to a location where
your users can access it to incorporate it into the list of known and
trusted CAs in their Web browsers. Otherwise a browser complains that the
certificate was issued by an unknown authority.
34.6.1.3 Getting an officially signed certificate #
There are several official certificate authorities that sign your certificates. The certificate is signed by a trustworthy third party, so can be fully trusted. Publicly operating secure Web servers usually have an officially signed certificate. A list of the most used Certificate Authorities (CAs) is available at https://en.wikipedia.org/wiki/Certificate_authority#Providers.
When requesting an officially signed certificate, you do not send a certificate to the CA. Instead, issue a Certificate Signing Request (CSR). To create a CSR, run the following command:
>
openssl req -new -newkey rsa:2048 -nodes -keyout newkey.pem -out newreq.pem
You are asked to enter a distinguished name. This requires you to answer a few questions, such as country name or organization name. Enter valid data—everything you enter here later shows up in the certificate and is checked. You do not need to answer every question. If one does not apply to you or you want to leave it blank, use “.”. Common name is the name of the CA itself—choose a significant name, such as My company CA. Last, a challenge password and an alternative company name must be entered.
Find the CSR in the directory from which you called the script. The file
is named newreq.pem
.
34.6.2 Configuring Apache with SSL #
The default port for TLS/SSL requests on the Web server side is 443. There is no conflict between a “regular” Apache listening on port 80 and an TLS/SSL-enabled Apache listening on port 443. In fact, HTTP and HTTPS can be run with the same Apache instance. Usually separate virtual hosts are used to dispatch requests to port 80 and port 443 to separate virtual servers.
Do not forget to open the firewall for SSL-enabled Apache on port 443.
This can be done with firewalld
as described in
Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4.3 “Configuring the firewall on the command line”.
The SSL module is enabled by default in the global server configuration.
In case it has been disabled on your host, activate it with the following
command: a2enmod ssl
. To finally enable SSL, the server
needs to be started with the flag “SSL”. To do so, call
a2enflag SSL
(case-sensitive!). If you have chosen to
encrypt your server certificate with a password, you should also increase
the value for APACHE_TIMEOUT
in
/etc/sysconfig/apache2
, so you have enough time to
enter the passphrase when Apache starts. Restart the server to make these
changes active. A reload is not sufficient.
The virtual host configuration directory contains a template
/etc/apache2/vhosts.d/vhost-ssl.template
with
SSL-specific directives that are extensively documented. Refer to
Section 34.2.2.1, “Virtual host configuration” for the general
virtual host configuration.
To get started, copy the template to
/etc/apache2/vhosts.d/MYSSL-HOST.conf
and edit it. Adjusting the values for the following directives should be
sufficient:
DocumentRoot
ServerName
ServerAdmin
ErrorLog
TransferLog
34.6.2.1 Name-based virtual hosts and SSL #
By default it is not possible to run multiple SSL-enabled virtual hosts on a server with only one IP address. Name-based virtual hosting requires that Apache knows which server name has been requested. The problem with SSL connections is, that such a request can only be read after the SSL connection has already been established (by using the default virtual host). As a result, users will receive a warning message stating that the certificate does not match the server name.
SUSE Linux Enterprise Server comes with an extension to the SSL protocol called Server Name Indication (SNI) addresses this issue by sending the name of the virtual domain as part of the SSL negotiation. This enables the server to “switch” to the correct virtual domain early and present the browser the correct certificate.
SNI is enabled by default on SUSE Linux Enterprise Server. To enable Name-Based Virtual
Hosts for SSL, configure the server as described in
Section 34.2.2.1.1, “Name-based virtual hosts”
(note that you need to use port 443
rather than port
80
with SSL).
SNI must also be supported on the client side. However, SNI is supported by most browsers, except for certain older browsers. For more information, see https://en.wikipedia.org/wiki/Server_Name_Indication#Support.
To configure handling of non-SNI capable browsers, use the directive
SSLStrictSNIVHostCheck
. When set to
on
in the server configuration, non-SNI capable
browser will be rejected for all virtual hosts. When set to
on
within a VirtualHost
directive, access to this particular host will be rejected.
When set to off
in the server configuration, the
server will behave as if not having SNI support. SSL requests will be
handled by the first virtual host defined (for port
443).
34.7 Running multiple Apache instances on the same server #
Running multiple Apache instances on the same server has several advantages over running multiple virtual hosts (see Section 34.2.2.1, “Virtual host configuration”):
When a virtual host needs to be disabled for some time, you need to change the Web server configuration and restart it so that the change takes effect.
In case of problems with one virtual host, you need to restart all of them.
You can run the default Apache instance as usual:
>
sudo
systemctl start apache2.service
It reads the default /etc/sysconfig/apache2
file. If
the file is not present, or it is present but it does not set the
APACHE_HTTPD_CONF
variable, it reads
/etc/apache2/httpd.conf
.
To activate another Apache instance, run:
>
sudo
systemctl start apache2@INSTANCE_NAME
For example:
>
sudo
systemctl start apache2@example_web.org
By default, the instance uses
/etc/apache2@example_web.org/httpd.conf
as a main
configuration file, which can be overwritten by setting
APACHE_HTTPD_CONF
in
/etc/sysconfig/apache2@example_web.org
.
An example to set up an additional instance of Apache follows. Note that you
need to execute all the commands as root
.
Create a new configuration file based on
/etc/sysconfig/apache2
, for example/etc/sysconfig/apache2@example_web.org
:>
sudo
cp /etc/sysconfig/apache2 /etc/sysconfig/apache2@example_web.orgEdit the file
/etc/sysconfig/apache2@example_web.org
and change the line containingAPACHE_HTTPD_CONF
to
APACHE_HTTPD_CONF="/etc/apache2/httpd@example_web.org.conf"
Create the file
/etc/apache2/httpd@example_web.org.conf
based on/etc/apache2/httpd.conf
.>
sudo
cp /etc/apache2/httpd.conf /etc/apache2/httpd@example_web.org.confEdit
/etc/apache2/httpd@example_web.org.conf
and changeInclude /etc/apache2/listen.conf
to
Include /etc/apache2/listen@example_web.org.conf
Review all the directives and change them to fit your needs. You will probably want to change
Include /etc/apache2/global.conf
and create new
global@example_web.org.conf
for each instance. We suggest to changeErrorLog /var/log/apache2/error_log
to
ErrorLog /var/log/apache2/error@example_web.org_log
to have separate logs for each instance.
Create
/etc/apache2/listen@example_web.org.conf
based on/etc/apache2/listen.conf
.>
sudo
cp /etc/apache2/listen.conf /etc/apache2/listen@example_web.org.confEdit
/etc/apache2/listen@example_web.org.conf
and changeListen 80
to the port number you want the new instance to run on, for example 82:
Listen 82
To run the new Apache instance over a secured protocol (see Section 34.6, “Setting up a secure Web server with SSL”), change also the line
Listen 443
for example to
Listen 445
Start the new Apache instance:
>
sudo
systemctl start apache2@example_web.orgCheck if the server is running by pointing your Web browser at
http://server_name:82
. If you previously changed the name of the error log file for the new instance, you can check it:>
sudo
tail -f /var/log/apache2/error@example_web.org_log
Here are several points to consider when setting up more Apache instances on the same server:
The file
/etc/sysconfig/apache2@INSTANCE_NAME
can include the same variables as/etc/sysconfig/apache2
, including module loading and MPM setting.The default Apache instance does not need to be running while other instances run.
The Apache helper utilities
a2enmod
,a2dismod
andapachectl
operate on the default Apache instance if not specified otherwise with theHTTPD_INSTANCE
environment variable. The following example>
sudo
export HTTPD_INSTANCE=example_web.org>
sudo
a2enmod access_compat>
sudo
a2enmod status>
sudo
apachectl startwill add
access_compat
andstatus
modules to theAPACHE_MODULES
variable of/etc/sysconfig/apache2@example_web.org
, and then start theexample_web.org
instance.
34.8 Avoiding security problems #
A Web server exposed to the public Internet requires an ongoing administrative effort. It is inevitable that security issues appear, both related to the software and to accidental misconfiguration. Here are some tips for how to deal with them.
34.8.1 Up-to-date software #
If there are vulnerabilities found in the Apache software, a security advisory will be issued by SUSE. It contains instructions for fixing the vulnerabilities, which in turn should be applied when possible. The SUSE security announcements are available from the following locations:
Web page. https://www.suse.com/support/security/
Mailing list archive. https://lists.opensuse.org/archives/list/security-announce@lists.opensuse.org/
List of security announcements. https://www.suse.com/support/update/
34.8.2 DocumentRoot permissions #
By default in SUSE Linux Enterprise Server, the DocumentRoot
directory /srv/www/htdocs
and the CGI directory
/srv/www/cgi-bin
belong to the user and group
root
. You should not change these permissions. If
the directories are writable for all, any user can place files into them.
These files might then be executed by Apache with the permissions of
wwwrun
, which may give the user unintended access
to file system resources. Use subdirectories of
/srv/www
to place the
DocumentRoot
and CGI directories for your virtual
hosts and make sure that directories and files belong to user and group
root
.
34.8.3 File system access #
By default, access to the whole file system is denied in
/etc/apache2/httpd.conf
. You should never overwrite
these directives, but specifically enable access to all directories Apache
should be able to read. For details, see
Section 34.2.2.1.3, “Basic virtual host configuration”.
In doing so, ensure that no critical files, such as password or system
configuration files, can be read from the outside.
34.8.4 CGI scripts #
Interactive scripts in PHP, SSI, or any other programming language can essentially run arbitrary commands and therefore present a general security issue. Scripts that will be executed from the server should only be installed from sources the server administrator trusts—allowing users to run their own scripts is generally not a good idea. It is also recommended to do security audits for all scripts.
To make the administration of scripts as easy as possible, it is common
practice to limit the execution of CGI scripts to specific directories
instead of globally allowing them. The directives
ScriptAlias
and Option
ExecCGI
are used for configuration. The SUSE Linux Enterprise Server default
configuration does not allow execution of CGI scripts from everywhere.
All CGI scripts run as the same user, so different scripts can potentially conflict with each other. The module suEXEC lets you run CGI scripts under a different user and group.
34.8.5 User directories #
When enabling user directories (with mod_userdir
or mod_rewrite
) you should strongly consider not
allowing .htaccess
files, which would allow users to
overwrite security settings. At least you should limit the user's
engagement by using the directive AllowOverRide
.
In SUSE Linux Enterprise Server, .htaccess
files are enabled by
default, but the user is not allowed to overwrite any
Option
directives when using
mod_userdir
(see the
/etc/apache2/mod_userdir.conf
configuration file).
34.9 Troubleshooting #
If Apache does not start, the Web page is not accessible, or users cannot connect to the Web server, it is important to find the cause of the problem. Here are some typical places to look for error explanations and important things to check:
- Output of the
apache2.service
subcommand: Instead of starting and stopping the Web server with the binary
/usr/sbin/apache2ctl
, rather use thesystemctl
commands instead (described in Section 34.3, “Starting and stopping Apache”).systemctl status apache2.service
is verbose about errors, and it even provides tips and hints for fixing configuration errors.- Log files and verbosity
In case of both fatal and nonfatal errors, check the Apache log files for causes, mainly the error log file located at
/var/log/apache2/error_log
by default. Additionally, you can control the verbosity of the logged messages with theLogLevel
directive if more detail is needed in the log files.Tip: A simple testWatch the Apache log messages with the command
tail -F /var/log/apache2/MY_ERROR_LOG
. Then runsystemctl restart apache2.service
. Now, try to connect with a browser and check the output.- Firewall and ports
A common mistake is to not open the ports for Apache in the firewall configuration of the server. If you configure Apache with YaST, there is a separate option available to take care of this specific issue (see Section 34.2.3, “Configuring Apache with YaST”). If you are configuring Apache manually, open firewall ports for HTTP and HTTPS via YaST's firewall module.
If the error cannot be tracked down with any of these, check the online Apache bug database at http://httpd.apache.org/bug_report.html. Additionally, the Apache user community can be reached via a mailing list available at http://httpd.apache.org/userslist.html.
34.10 More information #
The package apache2-doc
contains the complete
Apache manual in various localizations for local installation and reference.
It is not installed by default—the quickest way to install it is to
use the command zypper in apache2-doc
. Having been
installed, the Apache manual is available at
http://localhost/manual/. You may also access it on the
Web at http://httpd.apache.org/docs-2.4/. SUSE-specific
configuration hints are available in the directory
/usr/share/doc/packages/apache2/README.*
.
34.10.1 Apache 2.4 #
For a list of new features in Apache 2.4, refer to http://httpd.apache.org/docs/2.4/new_features_2_4.html. Information about upgrading from version 2.2 to 2.4 is available at http://httpd.apache.org/docs-2.4/upgrading.html.
34.10.2 Apache modules #
More information about external Apache modules that are briefly described in Section 34.4.5, “External modules” is available at the following locations:
mod_apparmor
mod_php7
http://www.php.net/manual/en/install.unix.apache2.php
You can obtain detailed information about
mod_php7
configuration in its well-commented main configuration file/etc/php7/apache2/php.ini
.mod_python
mod_security
34.10.3 Development #
More information about developing Apache modules or about getting involved in the Apache Web server project are available at the following locations:
- Apache developer information
- Apache developer documentation
34.10.4 Miscellaneous sources #
If you experience difficulties specific to Apache in SUSE Linux Enterprise Server, take a look at the Technical Information Search at https://www.suse.com/support. The history of Apache is provided at https://httpd.apache.org/ABOUT_APACHE.html. This page also explains why the server is called Apache.
35 Setting up an FTP server with YaST #
Using the YaST
module, you can configure your machine to function as an FTP (File Transfer Protocol) server. Anonymous and/or authenticated users can connect to your machine and download files using the FTP protocol. Depending on the configuration, they can also upload files to the FTP server. YaST uses vsftpd (Very Secure FTP Daemon).
If the YaST FTP Server module is not available in your system, install the
yast2-ftp-server
package. (For
managing the FTP server from the command line, see
Section 4.4.3.7, “yast ftp-server”.)
To configure the FTP server using YaST, follow these steps:
Open the YaST control center and choose
› or run theyast2 ftp-server
command asroot
.If there is not any FTP server installed in your system, you will be asked which server to install when the YaST FTP Server module starts. Choose the vsftpd server and confirm the dialog.
In the Section 35.1, “Starting the FTP server”.
dialog, configure the options for starting of the FTP server. For more information, seeIn the Section 35.2, “FTP general settings”.
dialog, configure FTP directories, welcome message, file creation masks and other parameters. For more information, seeIn the Section 35.3, “FTP performance settings”.
dialog, set the parameters that affect the load on the FTP server. For more information, seeIn the Section 35.4, “Authentication”.
dialog, set whether the FTP server should be available for anonymous and/or authenticated users. For more information, seeIn the Section 35.5, “Expert settings”.
dialog, configure the operation mode of the FTP server, SSL connections and firewall settings. For more information, seeClick
to save the configurations.
35.1 Starting the FTP server #
In the
frame of the dialog set the way the FTP server is started up. You can choose between starting the server automatically during the system boot and starting it manually. If the FTP server should be started only after an FTP connection request, choose .The current status of the FTP server is shown in the
frame of the dialog. Start the FTP server by clicking . To stop the server, click . After having changed the settings of the server click . Your configurations will be saved by leaving the configuration module with .35.2 FTP general settings #
In the
frame of the dialog you can set the which is shown after connecting to the FTP server.If you check the
option, all local users will be placed in a chroot jail in their home directory after login. This option has security implications, especially if the users have upload permission or shell access, so be careful enabling this option.If you check the
option, all FTP requests and responses are logged.
You can limit permissions of files created by anonymous and/or authenticated
users with umask. Set the file creation mask for anonymous users in
man 1p umask
).
In the /srv/ftp
. Note that
vsftpd does not allow this directory to be writable for all users. The
subdirectory upload
with write permissions for
anonymous users is created instead.
35.3 FTP performance settings #
In the
dialog set the parameters which affect the load on the FTP server. is the maximum time (in minutes) the remote client may spend between FTP commands. In case of longer inactivity, the remote client is disconnected. determines the maximum number of clients which can be connected from a single IP address. determines the maximum number of clients which may be connected. Any additional clients will get an error message.
The maximum data transfer rate (in KB/s) is set in 0
, which means unlimited data transfer
rate.
35.4 Authentication #
In the
frame of the dialog, you can set which users are allowed to access your FTP server. You can choose between the following options: granting access to anonymous users only, to authenticated users only (with accounts on the system) or to both types of users.To allow users to upload files to the FTP server, check
in the frame of the dialog. Here you can allow uploading or creating directories even for anonymous users by checking the respective box.If a vsftpd server is used and you want anonymous users to be able to upload files or create directories, a subdirectory with writing permissions for all users needs to be created in the anonymous FTP directory.
35.5 Expert settings #
An FTP server can run in active or in passive mode. By default the server runs in passive mode. To switch into active mode, deselect the
option in the dialog. You can also change the range of ports on the server used for the data stream by tweaking the and options.If you want encrypted communication between clients and the server, you can
. Check the versions of the protocol to be supported and specify the RSA certificate to be used for SSL encrypted connections.If your system is protected by a firewall, check
to enable a connection to the FTP server.35.6 More information #
For more information about the FTP server read the manual pages of
vsftpd
and vsftpd.conf
.
36 Squid caching proxy server #
Squid is a widely-used caching proxy server for Linux and Unix platforms. This means that it stores requested Internet objects, such as data on a Web or FTP server, on a machine that is closer to the requesting workstation than the server. It can be set up in multiple hierarchies to assure optimal response times and low bandwidth usage, even in modes that are transparent to end users.
Squid acts as a caching proxy server. It redirects object requests from clients (in this case, from Web browsers) to the server. When the requested objects arrive from the server, it delivers the objects to the client and keeps a copy of them in the hard disk cache. An advantage of caching is that several clients requesting the same object can be served from the hard disk cache. This enables clients to receive the data much faster than from the Internet. This procedure also reduces the network traffic.
Along with actual caching, Squid offers a wide range of features:
Distributing load over intercommunicating hierarchies of proxy servers
Defining strict access control lists for all clients accessing the proxy server
Allowing or denying access to specific Web pages using other applications
Generating statistics about frequently-visited Web pages for the assessment of surfing habits
Squid is not a generic proxy server. It normally proxies only HTTP connections. It supports the protocols FTP, Gopher, SSL, and WAIS, but it does not support other Internet protocols, such as the news protocol, or video conferencing protocols. Because Squid only supports the UDP protocol to provide communication between different caches, many multimedia programs are not supported.
36.1 Some facts about proxy servers #
As a caching proxy server, Squid can be used in several ways. When combined with a firewall, it can help with security. Multiple proxies can be used together. It can also determine what types of objects should be cached and for how long.
36.1.1 Squid and security #
It is possible to use Squid together with a firewall to secure internal networks from the outside. The firewall denies all clients access to external services except Squid. All Web connections must be established by the proxy server. With this configuration, Squid completely controls Web access.
If the firewall configuration includes a demilitarized zone (DMZ), the proxy server should operate within this zone. Section 36.6, “Configuring a transparent proxy” describes how to implement a transparent proxy. This simplifies the configuration of the clients, because in this case, they do not need any information about the proxy server.
36.1.2 Multiple caches #
Several instances of Squid can be configured to exchange objects between them. This reduces the total system load and increases the chances of retrieving an object from the local network. It is also possible to configure cache hierarchies, so a cache can forward object requests to sibling caches or to a parent cache—causing it to request objects from another cache in the local network, or directly from the source.
Choosing the appropriate topology for the cache hierarchy is very important, because it is not desirable to increase the overall traffic on the network. For a very large network, it would make sense to configure a proxy server for every subnet and connect them to a parent proxy server, which in turn is connected to the caching proxy server of the ISP.
All this communication is handled by ICP (Internet cache protocol) running on top of the UDP protocol. Data transfers between caches are handled using HTTP (hypertext transmission protocol) based on TCP.
To find the most appropriate server from which to request objects, a cache
sends an ICP request to all sibling proxies. The sibling proxies answer
these requests via ICP responses. If the object was detected, they use the
code HIT
, if not, they use MISS
.
If multiple HIT
responses were found, the proxy server
decides from which server to download, depending on factors such as which
cache sent the fastest answer or which one is closer. If no satisfactory
responses are received, the request is sent to the parent cache.
To avoid duplication of objects in different caches in the network, other ICP protocols are used, such as CARP (cache array routing protocol) or HTCP (hypertext cache protocol). The more objects maintained in the network, the greater the possibility of finding the desired object.
36.1.3 Caching Internet objects #
Many objects available in the network are not static, such as dynamically generated pages and TLS/SSL-encrypted content. Objects like these are not cached because they change each time they are accessed.
To determine how long objects should remain in the cache, objects are assigned one of several states. Web and proxy servers find out the status of an object by adding headers to these objects, such as “Last modified” or “Expires” and the corresponding date. Other headers specifying that objects must not be cached can be used as well.
Objects in the cache are normally replaced, because of a lack of free disk space, using algorithms such as LRU (last recently used). This means that the proxy expunges those objects that have not been requested for the longest time.
36.2 System requirements #
System requirements largely depend on the maximum network load that the system must bear. Therefore, examine load peaks, as during those times, load might be more than four times the day's average. When in doubt, slightly overestimate the system's requirements. Having Squid working close to the limit of its capabilities can lead to a severe loss in quality of service. The following sections point to system factors in order of significance:
RAM size
CPU speed/physical CPU cores
Size of the disk cache
Hard disks/SSDs and their architecture
36.2.1 RAM #
The amount of memory (RAM) required by Squid directly correlates with the number of objects in the cache. Random access memory is much faster than a hard disk/SSD. Therefore, it is very important to have sufficient memory for the Squid process, because system performance is dramatically reduced if the swap disk is used.
Squid also stores cache object references and frequently requested objects in the main memory to speed up retrieval of this data. In addition to that, there is other data that Squid needs to keep in memory, such as a table with all the IP addresses handled, an exact domain name cache, the most frequently requested objects, access control lists, buffers, and more.
36.2.2 CPU #
Squid is tuned to work best with lower processor core counts (4–8 physical cores), with each providing high performance. Technologies providing virtual cores such as hyperthreading can hurt performance.
To make the best use of multiple CPU cores, it is necessary to set up multiple worker threads writing to different caching devices. By default, multi-core support is mostly disabled.
36.2.3 Size of the disk cache #
In a small cache, the probability of a HIT
(finding the
requested object already located there) is small, because the cache is
easily filled and less requested objects are replaced by newer ones. If,
for example, 1 GB is available for the cache and the users use up only
10 MB per day surfing, it would take more than one hundred days to
fill the cache.
The easiest way to determine the necessary cache size is to consider the maximum transfer rate of the connection. With a 1 Mbit/s connection, the maximum transfer rate is 128 KB/s. If all this traffic ended up in the cache, in one hour it would add up to 460 MB. Assuming that all this traffic is generated in only eight working hours, it would reach 3.6 GB in one day. Because the connection is normally not used to its upper volume limit, it can be assumed that the total data volume handled by the cache is approximately 2 GB. Hence, in this example, 2 GB of disk space is required for Squid to keep one day's worth of browsing data cached.
36.2.4 Hard disk/SSD architecture #
Speed plays an important role in the caching process, so this factor deserves special attention. For hard disks/SSDs, this parameter is described as random seek time or random read performance, measured in milliseconds. Because the data blocks that Squid reads from or writes to the hard disk/SSD tend to be small, the seek time/read performance of the hard disk/SSD is more important than its data throughput.
For use as a proxy server, hard disks with high rotation speeds or SSDs are the best choice. When using hard disks, it can be better to use multiple smaller hard disks, each with a single cache directory to avoid excessive read times.
Using a RAID system allows increasing reliability at expense of speed. However, for performance reasons, avoid (software) RAID5 and similar settings.
File system choice is usually not decisive. However, using the mount option
noatime
can improve performance—Squid provides its
own time stamps and thus does not need the file system to track access
times.
36.3 Basic usage of Squid #
If not already installed, install the package squid .
squid
is not among the packages installed by
default on SUSE® Linux Enterprise Server.
Squid is already preconfigured in SUSE Linux Enterprise Server, you can start it directly
after the installation. To ensure a smooth start-up, the network should be
configured in a way that at least one name server and the Internet can be
reached. Problems can arise if a dial-up connection is used with a dynamic
DNS configuration. In this case, at least the name server should be
specified, because Squid does not start if it does not detect a DNS server
in /var/run/netconfig/resolv.conf
.
36.3.1 Starting Squid #
To start Squid, use:
>
sudo
systemctl start squid
If you want Squid to start when the system boots up, enable the service
with systemctl enable squid
.
36.3.2 Checking whether Squid is working #
To check whether Squid is running, choose one of the following ways:
Using
systemctl
:>
systemctl status squid
The output of this command should indicate that Squid is
loaded
andactive (running)
.Using Squid itself:
>
sudo
squid -k check | echo $?
The output of this command should be
0
, but may contain additional warnings or messages.
To test the functionality of Squid on the local system, choose one of the following ways:
To test, you can use
squidclient
, a command-line tool that can output the response to a Web request, similar towget
orcurl
.Unlike those tools,
squidclient
will automatically connect to the default proxy setup of Squid,localhost:3128
. However, if you changed the configuration of Squid, you need to configuresquidclient
to use different settings using command line options. For more information, seesquidclient --help
.Example 36.1: A request withsquidclient
#>
squidclient http://www.example.org
HTTP/1.1 200 OK Cache-Control: max-age=604800 Content-Type: text/html Date: Fri, 22 Jun 2016 12:00:00 GMT Expires: Fri, 29 Jun 2016 12:00:00 GMT Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT Server: ECS (iad/182A) Vary: Accept-Encoding X-Cache: HIT x-ec-custom-error: 1 Content-Length: 1270 X-Cache: MISS from moon1 X-Cache-Lookup: MISS from moon:3128 Via: 1.1 moon (squid/3.5.16)2 Connection: close <!doctype html> <html> <head> <title>Example domain</title> [...] </body> </html>The output shown in Example 36.1, “A request with
squidclient
” can be split into two parts:The protocol headers of the response: the lines before the blank line.
The actual content of the response: the lines after the blank line.
To verify that Squid is used, refer to the selected header lines:
The value of the header
X-Cache
tells you that the requested document was not in the Squid cache (MISS
) of the computermoon
.The example above contains two
X-Cache
lines. You can ignore the firstX-Cache
header. It is produced by the internal caching software of the originating Web server.The value of the header
Via
tells you the HTTP version, the name of the computer, and the version of Squid in use.Using a browser: Set up
localhost
as the proxy and3128
as the port. You can then load a page and check the response headers in the panel of the browser's Inspector or Developer Tools. The headers should be reproduced similarly to the way shown in Example 36.1, “A request withsquidclient
”.
To allow users from the local system and other systems to access Squid and
the Internet, change the entry in the configuration files
/etc/squid/squid.conf
from http_access deny
all
to http_access allow all
. However, in doing
so, consider that Squid is made completely accessible to anyone by this
action. Therefore, define ACLs (access control lists) that control access
to the proxy server. After modifying the configuration file, Squid must be
reloaded or restarted. For more information on ACLs, see
Section 36.5.2, “Options for access controls”.
If Squid quits after a short period of time even though it was started
successfully, check whether there is a faulty name server entry or whether
the /var/run/netconfig/resolv.conf
file is missing.
Squid logs the cause of a start-up failure in the file
/var/log/squid/cache.log
.
36.3.3 Stopping, reloading, and restarting Squid #
To reload Squid, choose one of the following ways:
Using
systemctl
:>
sudo
systemctl
reload squidor
>
sudo
systemctl
restart squidUsing YaST:
In the Squid module, click the
button.
To stop Squid, choose one of the following ways:
Using
systemctl
:>
sudo
systemctl
stop squidUsing YaST
In the Squid module click the
. button.
Shutting down Squid can take a while, because Squid waits up to half a
minute before dropping the connections to the clients and writing its data
to the disk (see shutdown_lifetime
option in
/etc/squid/squid.conf
),
Terminating Squid with kill
or
killall
can damage the cache. To be able to restart
Squid, damaged caches must be deleted.
36.3.4 Removing Squid #
Removing Squid from the system does not remove the cache hierarchy and log
files. To remove these, delete the /var/cache/squid
directory manually.
36.3.5 Local DNS server #
Setting up a local DNS server makes sense even if it does not manage its own domain. It then simply acts as a caching-only name server and is also able to resolve DNS requests via the root name servers without requiring any special configuration (see Section 31.4, “Starting the BIND name server”). How this can be done depends on whether you chose dynamic DNS during the configuration of the Internet connection.
- Dynamic DNS
Normally, with dynamic DNS, the DNS server is set by the provider during the establishment of the Internet connection and the local
/var/run/netconfig/resolv.conf
file is adjusted automatically. This behavior is controlled in the/etc/sysconfig/network/config
file with theNETCONFIG_DNS_POLICY
sysconfig variable. SetNETCONFIG_DNS_POLICY
to""
with the YaST sysconfig editor.Then, add the local DNS server in the
/var/run/netconfig/resolv.conf
file with the IP address127.0.0.1
forlocalhost
. This way, Squid can always find the local name server when it starts.To make the provider's name server accessible, specify it in the configuration file
/etc/named.conf
underforwarders
along with its IP address. With dynamic DNS, this can be achieved automatically when establishing the connection by setting the sysconfig variableNETCONFIG_DNS_POLICY
toauto
.- Static DNS
With static DNS, no automatic DNS adjustments take place while establishing a connection, so there is no need to change any sysconfig variables. However, you must specify the local DNS server in the file
/var/run/netconfig/resolv.conf
as described in Dynamic DNS. Additionally, the provider's static name server must be specified manually in the/etc/named.conf
file underforwarders
along with its IP address.
If you have a firewall running, make sure DNS requests can pass it.
36.4 The YaST Squid module #
The YaST Squid module contains the following tabs:
Specifies how Squid is started and which Firewall port is open on which interfaces.
Define all ports where Squid will listen for HTTP requests from clients.
Defines how Squid treats objects in the cache.
Defines settings in regard to cache memory, maximum and minimum object size, and more.
Defines the top-level directory where Squid stores all cache swap files.
Controls the access to the Squid server via ACL groups.
Define paths to access, cache, and cache store log files in addition with connection timeouts and client lifetime.
Sets language and mail address of administrator.
36.5 The Squid configuration file #
All Squid proxy server settings are made in the
/etc/squid/squid.conf
file. To start Squid for the
first time, no changes are necessary in this file, but external clients are
initially denied access. The proxy is available for
localhost
. The default port
is 3128
. The preinstalled configuration file
/etc/squid/squid.conf
provides detailed information
about the options and many examples.
Many entries are commented and therefore begin with the comment character
#
. The relevant specifications can be found at the end of
the line. The given values usually correlate with the default values, so
removing the comment signs without changing any of the parameters usually
has no effect. If possible, leave the commented lines as they are and insert
the options along with the modified values in the line below. This way, the
default values may easily be recovered and compared with the changes.
If you have updated from an earlier Squid version, it is recommended to
edit the new /etc/squid/squid.conf
and only apply the
changes made in the previous file.
Sometimes, Squid options are added, removed, or modified. Therefore, if you
try to use the old squid.conf
, Squid might stop
working properly.
36.5.1 General configuration options #
The following is a list of a selection of configuration options for Squid.
It is not exhaustive. The Squid package contains a full, lightly documented
list of options in /etc/squid/squid.conf.documented
.
http_port PORT
This is the port on which Squid listens for client requests. The default port is
3128
, but8080
is also common.cache_peer HOST_NAME TYPE PROXY_PORT ICP_PORT
This option allows creating a network of caches that work together. The cache peer is a computer that also hosts a network cache and stands in a relationship to your own. The type of relationship is specified as the TYPE. The type can either be
parent
orsibling
.As the HOST_NAME, specify the name or IP address of the proxy server to use. For PROXY_PORT, specify the port number for use in a browser (usually
8080
). Set ICP_PORT to7
or, if the ICP port of the parent is not known and its use is irrelevant to the provider, to0
.To make Squid behave like a Web browser instead of like a proxy server, prohibit the use of the ICP protocol. You can do so by appending the options
default
andno-query
.cache_mem SIZE
This option defines the amount of memory Squid can use for very popular replies. The default is
8 MB
. This does not specify the memory usage of Squid and may be exceeded.cache_dir STORAGE_TYPE CACHE_DIRECTORY CACHE_SIZE LEVEL_1_DIRECTORIES LEVEL_2_DIRECTORIES
The option
cache_dir
defines the directory for the disk cache. In the default configuration on SUSE Linux Enterprise Server, Squid does not create a disk cache.The placeholder STORAGE_TYPE can be one of the following:
Directory-based storage types:
ufs
,aufs
(the default),diskd
. All three are variations of the storage formatufs
. However, whileufs
runs as part of the core Squid thread,aufs
runs in a separate thread, anddiskd
uses a separate process. This means that the latter two types avoid blocking Squid because of disk I/O.Database-based storage systems:
rock
. This storage format relies on a single database file, in which each object takes up one or more memory units of a fixed size (“slots”).
In the following, only the parameters for storage types based on
ufs
will be discussed.rock
has somewhat different parameters.The CACHE_DIRECTORY is the directory for the disk cache. By default, that is
/var/cache/squid
. CACHE_SIZE is the maximum size of that directory in megabytes; by default, this is set to 100 MB. Set it to between 50% and a maximum of 80% of available disk space.The final two values, LEVEL_1_DIRECTORIES and LEVEL_2_DIRECTORIES specify how many subdirectories are created in the CACHE_DIRECTORY. By default, 16 subdirectories are created at the first level below CACHE_DIRECTORY and 256 within each of these. These values should only be increased with caution, because creating too many directories can lead to performance problems.
If you have several disks that share a cache, specify several
cache_dir
lines.cache_access_log LOG_FILE
,cache_log LOG_FILE
,cache_store_log LOG_FILE
These three options specify the paths where Squid logs all its actions. Normally, nothing needs to be changed here. If Squid is burdened by heavy usage, it might make sense to distribute the cache and the log files over several disks.
client_netmask NETMASK
This option allows masking IP addresses of clients in the log files by applying a subnet mask. For example, to set the last digit of the IP address to
0
, specify255.255.255.0
.ftp_user E-MAIL
This option allows setting the password that Squid should use for anonymous FTP login. Specify a valid e-mail address here, because some FTP servers check these for validity.
cache_mgr E-MAIL
If it unexpectedly crashes, Squid sends a message to this e-mail address. The default is webmaster.
logfile_rotate VALUE
If you run
squid
-k rotate
,squid
can rotate log files. The files are numbered in this process and, after reaching the specified value, the oldest file is overwritten. The default value is10
which rotates log files with the numbers 0 to 9.However, on SUSE Linux Enterprise Server, rotating log files is performed automatically using
logrotate
and the configuration file/etc/logrotate.d/squid
.append_domain DOMAIN
Use append_domain to specify which domain to append automatically when none is given. Usually, your own domain is specified here, so specifying www in the browser accesses your own Web server.
forwarded_for STATE
If this option is set to
on
, it adds a line to the header similar to this:X-Forwarded-For: 192.168.0.1
If you set this option to
off
, Squid removes the IP address and the system name of the client from HTTP requests.negative_ttl TIME
,negative_dns_ttl TIME
If these options are set, Squid will cache some types of failures, such as
404
responses. It will then refuse to issue new requests, even if the resource would be available then.By default,
negative_ttl
is set to0
,negative_dns_ttl
is set to1 minutes
. This means that negative responses to Web requests are not cached by default, while negative responses to DNS requests are cached for 1 minute.never_direct allow ACL_NAME
To prevent Squid from taking requests directly from the Internet, use the option
never_direct
to force connection to another proxy server. This must have previously been specified incache_peer
. Ifall
is specified as the ACL_NAME, all requests are forwarded directly to theparent
. This can be necessary, for example, if you are using a provider that dictates the use of its proxies or denies its firewall direct Internet access.
36.5.2 Options for access controls #
Squid provides a detailed system for controlling the access to the proxy
server. These Access Control Lists (ACL) are lists with rules that are
processed sequentially. ACLs must be defined before they can be used. Some
default ACLs, such as all
and
localhost
, already exist. However, the mere definition
of an ACL does not mean that it is actually applied. This only happens when
there is a corresponding http_access
rule.
The syntax for the option acl
is as follows:
acl ACL_NAME TYPE DATA
The placeholders within this syntax stand for the following:
The name ACL_NAME can be chosen arbitrarily.
For TYPE, select from a variety of different options which can be found in the
ACCESS CONTROLS
section in the/etc/squid/squid.conf
file.The specification for DATA depends on the individual ACL type, for example host names, IP addresses, or URLs, and can also be read from a file.
To add rules in the YaST squid module, open the module and click the
tab. Click under the ACL Groups list and enter the name of your rule, the type, and its parameters.For more information on types of ACL rules, see the Squid documentation at http://www.squid-cache.org/Versions/v3/3.5/cfgman/acl.html.
acl mysurfers srcdomain .example.com 1 acl teachers src 192.168.1.0/255.255.255.0 2 acl students src 192.168.7.0-192.168.9.0/255.255.255.0 3 acl lunch time MTWHF 12:00-15:00 4
This ACL defines | |
This ACL defines | |
This ACL defines | |
This ACL defines |
- http_access allow ACL_NAME
http_access
defines who is allowed to use the proxy server and who can access what on the Internet. For this, ACLs must be defined.localhost
andall
have already been defined above for which you can deny or allow access viadeny
orallow
. A list containing any number ofhttp_access
entries can be created, processed from top to bottom. Depending on which occurs first, access is allowed or denied to the respective URL. The last entry should always behttp_access deny all
. In the following example,localhost
has free access to everything while all other hosts are denied access completely:http_access allow localhost http_access deny all
In another example using these rules, the group
teachers
always has access to the Internet. The groupstudents
only has access between Monday and Friday during lunch time:http_access deny localhost http_access allow teachers http_access allow students lunch time http_access deny all
For readability, within the configuration file
/etc/squid/squid.conf
, specify allhttp_access
options as a block.url_rewrite_program PATH
With this option, specify a URL rewriter.
auth_param basic program PATH
If users must be authenticated on the proxy server, set a corresponding program, such as
/usr/sbin/pam_auth
. When accessingpam_auth
for the first time, the user sees a login window in which they need to specify a user name and a password. In addition, you need an ACL, so only clients with a valid login can use the Internet:acl password proxy_auth REQUIRED http_access allow password http_access deny all
In the
acl proxy_auth
option, usingREQUIRED
means that all valid user names are accepted.REQUIRED
can also be replaced with a list of permitted user names.ident_lookup_access allow ACL_NAME
With this option, have an ident request run to find each user's identity for all clients defined by an ACL of the type
src
. Alternatively, use this for all clients, apply the predefined ACLall
as the ACL_NAME.All clients covered by
ident_lookup_access
must run an ident daemon. On Linux, you can usepidentd
(package pidentd ) as the ident daemon. For other operating systems, free software is usually available. To ensure that only clients with a successful ident lookup are permitted, define a corresponding ACL:acl identhosts ident REQUIRED http_access allow identhosts http_access deny all
In the
acl identhosts ident
option, usingREQUIRED
means that all valid user names are accepted.REQUIRED
can also be replaced with a list of permitted user names.Using
ident
can slow down access time, because ident lookups are repeated for each request.
36.6 Configuring a transparent proxy #
A transparent proxy intercepts and answers the requests of the Web browser, so the Web browser receives the requested pages without knowing where they are coming from. As the name indicates, the entire process is transparent to the user.
The usual way of working with proxy servers is as follows: the Web browser sends requests to a certain port of the proxy server and the proxy always provides these required objects, regardless of whether they are in its cache. However, in some cases the transparent proxy mode of Squid makes sense:
If, for security reasons, it is recommended that all clients use a proxy server to surf the Internet.
If all clients must use a proxy server, regardless of whether they are aware of it.
If the proxy server in a network is moved, but the existing clients need to retain their old configuration.
In
/etc/squid/squid.conf
, on the line of the optionhttp_port
add the parametertransparent
. You should then have 2 lines:http_port 3128 http_port 3128 transparent
Restart Squid:
>
sudo
systemctl restart squid
Set up the firewall to redirect HTTP traffic to the port given in
http_proxy
. In the example above it is port 3128. Then reload the firewall configuration. This assumes that the zoneinternal
is assigned to your LAN interface.>
sudo
firewall-cmd
--permanent --zone=internal \ --add-forward-port=port=80:proto=tcp:toport=3128:toaddr=LAN_IP>
sudo
firewall-cmd
--permanent --zone=internal --add-port=3128/tcp>
sudo
firewall-cmd
--reloadReplace LAN_IP with the IP address of your LAN interface or the interface Squid is listening on.
To verify that everything is working properly, check the Squid log files in
/var/log/squid/access.log
.
36.7 Using the Squid cache manager CGI interface (cachemgr.cgi
) #
The Squid cache manager CGI interface (cachemgr.cgi
) is
a CGI utility for displaying statistics about the memory usage of a running
Squid process. It is also a convenient way to manage the cache and view
statistics without logging the server.
cachemgr.cgi
#Make sure the Apache Web server is running on your system. Configure Apache as described in Chapter 34, The Apache HTTP server. In particular, see Section 34.5, “Enabling CGI scripts”. To check whether Apache is already running, use:
>
sudo
systemctl status apache2
If
inactive
is shown, you can start Apache with the SUSE Linux Enterprise Server default settings:>
sudo
systemctl start apache2
Now enable
cachemgr.cgi
in Apache. To do so, create a configuration file for aScriptAlias
.Create the file in the directory
/etc/apache2/conf.d
and name itcachemgr.conf
. In it, add the following:ScriptAlias /squid/cgi-bin/ /usr/lib64/squid/ <Directory "/usr/lib64/squid/"> Options +ExecCGI AddHandler cgi-script .cgi Require host HOST_NAME </Directory>
Replace HOST_NAME with the host name of the computer you want to access
cachemgr.cgi
from. This allows only your computer to accesscachemgr.cgi
. To allow access from anywhere, useRequire all granted
instead.If Squid and your Apache Web server run on the same computer, there should be no changes that need to be made to
/etc/squid/squid.conf
. However, verify that/etc/squid/squid.conf
contains the following lines:http_access allow manager localhost http_access deny manager
These lines allow you to access the manager interface from your own computer (
localhost
) but not from elsewhere.If Squid and your Apache Web server run on different computers, you need to add extra rules to allow access from the CGI script to Squid. Define an ACL for your server (replace WEB_SERVER_IP with the IP address of your Web server):
acl webserver src WEB_SERVER_IP/255.255.255.255
Make sure the following rules are in the configuration file. Compared to the default configuration, only the rule in the middle is new. However, the sequence is important.
http_access allow manager localhost http_access allow manager webserver http_access deny manager
(Optional) Optionally, you can configure one or more passwords for
cachemgr.cgi
. This also allows access to more actions such as closing the cache remotely or viewing more information about the cache. For this, configure the optionscache_mgr
andcachemgr_passwd
with one or more password for the manager and a list of allowed actions.For example, to explicitly enable viewing the index page, the menu, 60-minute average of counters without authentication, to enable toggling offline mode using the password
secretpassword
, and to completely disable everything else, use the following configuration:cache_mgr user cachemgr_passwd none index menu 60min cachemgr_passwd secretpassword offline_toggle cachemgr_passwd disable all
cache_mgr
defines a user name.cache_mgr
defines which actions are allowed using which password.The keywords
none
anddisable
are special:none
removes the need for a password,disable
disables functionality outright.The full list of actions can be best seen after logging in to
cachemgr.cgi
. To find out how the operation needs to be referenced in the configuration file, see the string after&operation=
in the URL of the action page.all
is a special keyword meaning all actions.Reload Squid and Apache after the configuration file changes:
>
sudo
systemctl reload squid
To view the statistics, go to the
cachemgr.cgi
page that you set up before. For example, it could behttp://webserver.example.org/squid/cgi-bin/cachemgr.cgi
.Choose the right server, and, if set, specify user name and password. Then click
and browse through the different statistics.
36.8 Cache report generation with Calamaris #
Calamaris is a Perl script used to generate reports of cache activity in
ASCII or HTML format. It works with native Squid access log files. The
Calamaris home page is located at
http://cord.de/calamaris-english. This tool does not
belong to the SUSE Linux Enterprise Server default installation scope—to use it,
install the calamaris
package.
Log in as root
, then enter:
#
cat access1.log [access2.log access3.log] | calamaris OPTIONS > reportfile
When using more than one log file, make sure they are chronologically
ordered, with older files listed first. This can be achieved by either
listing the files one after the other as in the example above, or by using
access{1..3}.log
.
calamaris
takes the following options:
-a
output all available reports
-w
output as HTML report
-l
include a message or logo in report header
More information about the various options can be found in the program's
manual page with man
calamaris
.
A typical example is:
#
cat access.log.{10..1} access.log | calamaris -a -w \
> /usr/local/httpd/htdocs/Squid/squidreport.html
This puts the report in the directory of the Web server. Apache is required to view the reports.
36.9 More information #
Visit the home page of Squid at http://www.squid-cache.org/. Here, find the “Squid User Guide” and a very extensive collection of FAQs on Squid.
In addition, mailing lists are available for Squid at http://www.squid-cache.org/Support/mailing-lists.html.
37 Web Based Enterprise Management using SFCB #
37.1 Introduction and basic concept #
SUSE® Linux Enterprise Server (SLES) provides a collection of open standards based tools for the unified management of disparate computing systems and environments. Our enterprise solutions implement the standards proposed by the Distributed Management Task Force. The following paragraphs describe their basic components.
Distributed Management Task Force, Inc (DMTF) is the industry organization which leads the development of management standards for enterprise and Internet environments. Their goal is to unify management standards and initiatives, and to enable more integrated, cost effective and interoperable management solutions. DMTF standards provide common system management components for control and communication. Their solutions are independent of platforms and technologies. Web Based Enterprise Management and the Common Information Model are two of their key technologies.
Web Based Enterprise Management (WBEM) is a set of management and Internet standard technologies. WBEM was developed to unify the management of enterprise computing environments. It provides the ability for the industry to deliver a well-integrated collection of management tools using Web technologies. WBEM consists of the following standards:
A data model: the Common Information Model (CIM) standard
An encoding specification: CIM-XML Encoding Specification
A transport mechanism: CIM operations over HTTP
The Common Information Model is a conceptual information model that describes system management. It is not bound to a particular implementation and enables the interchange of management information between management systems, networks, services and applications. There are two parts to CIM — the CIM Specification and the CIM Schema.
The CIM Specification describes the language, naming and meta schema. The meta schema is a formal definition of the model. It defines the terms used to express the model and their usage and semantics. The elements of the meta schema are classes, properties, and methods. The meta schema also supports indications and associations as types of classes, and references as types of properties.
The CIM Schema provides the actual model descriptions. It supplies a set of classes with properties and associations that provide a well understood conceptual framework within which it is possible to organize the available information about the managed environment.
The Common Information Model Object Manager (CIMOM) is a CIM object manager or, more specifically, an application that manages objects according to the CIM standard. CIMOM manages communication between CIMOM providers and a CIM client, where the administrator manages the system.
CIMOM providers are software performing specific tasks within the CIMOM that are requested by client applications. Each provider instruments one or more aspects of the CIMOM's schema. These providers interact directly with the hardware.
Standards Based Linux Instrumentation for Manageability (SBLIM) is a collection of tools designed to support Web-Based Enterprise Management (WBEM). SUSE® Linux Enterprise Server uses the open source CIMOM (or CIM server) from the SBLIM project called Small Footprint CIM Broker .
Small Footprint CIM Broker is a CIM server intended for use in resource-limited or embedded environments. It is designed to be modular and lightweight at the same time. Its based on open standards and it supports CMPI providers, CIM-XML encoding, and Managed Object Format (MOF). It is highly configurable and performs stability even if the provider crashes. It is also easily accessible as it supports various transport protocols, such as HTTP, HTTPS, Unix domain sockets, Service Location Protocol (SLP), and Java Database Connectivity (JDBC).
37.2 Setting up SFCB #
To set up the Small Footprint CIM Broker (SFCB) environment, make sure the SUSE Linux Enterprise Server installation. Alternatively, select it as a component to install on a server that is already running. Make sure the following packages are installed on your system:
pattern in YaST is selected during- cim-schema, Common Information Model (CIM) schema
Contains the Common Information Model (CIM). CIM is a model for describing overall management information in a network or enterprise environments. CIM consists of a specification and a schema. The specification defines the details for integration with other management models. The schema provides the actual model descriptions.
- python2-pywbem
Contains a Python module for making CIM operation calls through the WBEM protocol to query and update managed objects.
- cmpi-provider-register, CIMOM neutral provider registration utility
Contains a utility allowing CMPI provider packages to register with whatever CIMOM happens to be present on the system.
- sblim-sfcb, small footprint CIM broker
Contains Small Footprint CIM Broker. It is a CIM server conforming to the CIM Operations over HTTP protocol. It is robust, with low resource consumption and, therefore, specifically suited for embedded and resource constrained environments. SFCB supports providers written against the Common Manageability Programming Interface (CMPI).
- sblim-sfcc
Contains Small Footprint CIM Client library runtime libraries.
- sblim-wbemcli
Contains WBEM command line interface. It is a stand-alone command line WBEM client especially suited for basic systems management tasks.
37.2.1 Starting, stopping and checking status for SFCB #
CIM server sfcbd daemon is installed together with Web-Based Enterprise Management software and is started by default at system start-up. The following table explains how to start, stop and check status for sfcbd.
Task |
Linux Command |
---|---|
Start sfcbd |
Enter |
Stop sfcbd |
Enter |
Check sfcbd status |
Enter |
37.2.2 Ensuring secure access #
The default setup of SFCB is relatively secure. However, check that the access to SFCB components is as secure as required for your organization.
37.2.2.1 Certificates #
Secure Sockets Layers (SSL) transports require a certificate for secure communication to occur. When SFCB is installed, it has a self-signed certificate generated.
You can replace the path to the default certificate with a path to a
commercial or self-signed one by changing the
sslCertificateFilePath: PATH_FILENAME
setting in /etc/sfcb/sfcb.cfg
. The file
must be in PEM format.
By default, SFCB expects a server certificate in the following location:
/etc/sfcb/server.pem
To generate a new certificate, run the following command:
>
sudo
sh /usr/share/sfcb/genSslCert.sh Generating SSL certificates in . Generating a 2048 bit RSA private key ...................................................................+++ .+++ writing new private key to '/var/tmp/sfcb.0Bjt69/key.pem' -----
By default, the script generates certificates
client.pem
, file.pem
and
server.pem
in the current working directory. If you
want the script to generate the certificates in
/etc/sfcb
directory, you need to append the path to
the command. If these files already exist, a warning message is displayed,
and the old certificates are not overwritten.
>
sudo
sh /usr/share/sfcb/genSslCert.sh /etc/sfcb Generating SSL certificates in . WARNING: server.pem SSL Certificate file already exists. old file will be kept intact. WARNING: client.pem SSL Certificate trust store already exists. old file will be kept intact.
You must remove the old certificates from the file system and run the command again.
To change the way SFCB uses certificates, see Section 37.2.2.3, “Authentication”.
37.2.2.2 Ports #
By default, SFCB is configured to accept all communications through the secure port 5989. The following paragraphs explain the communication port setup and recommended configuration.
- Port 5989 (secure)
The secure port that SFCB communications use via HTTPS services. This is the default. With this setting, all communications between the CIMOM and client applications are encrypted when sent over the Internet between servers and workstations. Users must authenticate with the client application to reach SFCB server. We recommend that you keep this setting. For the SFCB CIMOM to communicate with the necessary applications, this port must be open on routers and firewalls if they are present between the client application and the nodes being monitored.
- Port 5988 (insecure)
The insecure port that SFCB communications use via HTTP services. This setting is disabled by default. With this setting, all communications between the CIMOM and client applications are open for review when sent over the Internet between servers and workstations by anyone, without any authentication. We recommend that you use this setting only when attempting to debug a problem with the CIMOM. When the problem is resolved, disable the non-secure port option back. For the SFCB CIMOM to communicate with the necessary applications that require non-secure access, this port must be open in routers and firewalls between the client application and the nodes being monitored.
To change the default port assignments, see Section 37.2.2.2, “Ports”.
37.2.2.3 Authentication #
SFCB supports HTTP basic authentication and authentication based on client
certificates (HTTP over SSL connections). Basic HTTP authentication is
enabled by specifying doBasicAuth=true
in the SFCB
configuration file ( /etc/sfcb/sfcb.cfg
by
default). SUSE® Linux Enterprise Server installation of SFCB supports Pluggable Authentication
Modules (PAM) approach; therefore the local root user can authenticate to
the SFCB CIMOM with local root user credentials.
If the sslClientCertificate
configuration property is
set to accept
or require
, the SFCB HTTP adapter will request a
certificate from clients when connecting via HTTP over SSL (HTTPS). If
require
is specified, the client
must provide a valid certificate
(according to the client trust store specified via
sslClientTrustStore
). If the client fails to do
so, the connection will be rejected by the CIM server.
The setting sslClientCertificate=accept
may not be
obvious. It is very useful if both basic and client certificate
authentication are allowed. If the client can provide a valid certificate,
HTTPS connection will be established and the basic authentication
procedure will not be executed. If this function cannot verify the
certificate, the HTTP basic authentication will take place instead.
37.3 SFCB CIMOM configuration #
SFCB is a lightweight implementation of the CIM server, but it is also highly configurable. Several options can control its behavior. You can control the SFCB server in three ways:
by setting appropriate environment variables
by using command line options
by changing its configuration file
37.3.1 Environment variables #
Several environment variables directly affect the behavior of SFCB. You
need to restart the SFCB daemon by systemctl restart
sfcb
for these changes to take effect.
PATH
Specifies the path to the
sfcbd
daemon and utilities.LD_LIBRARY_PATH
Specifies the path to the sfcb runtime libraries. Alternatively, you can add this path to the system-wide dynamic loader configuration file
/etc/ld.so.conf
.SFCB_PAUSE_PROVIDER
Specifies the provider name. The SFCB server pauses after the provider is loaded for the first time. You can then attach a runtime debugger to the provider's process for debugging purposes.
SFCB_PAUSE_CODEC
Specifies the name of the SFCB codec (currently supports only
http
. The SFCB server pauses after the codec is loaded for the first time. You can then attach a runtime debugger to the process.SFCB_TRACE
Specifies the level of debug messages for SFCB. Valid values are 0 (no debug messages), or 1 (key debug messages) to 4 (all debug messages). Default is 1.
SFCB_TRACE_FILE
By default, SFCB outputs its debug messages to standard error output (STDERR). Setting this variable causes the debug messages to be written to a specified file instead.
SBLIM_TRACE
Specifies the level of debug messages for SBLIM providers. Valid values are 0 (no debug messages), or 1 (key debug messages) to 4 (all debug messages).
SBLIM_TRACE_FILE
By default, SBLIM provider outputs its trace messages to STDERR. Setting this variable causes the trace messages to be written to a specified file instead.
37.3.2 Command line options #
sfcbd
, the SFCB daemon, has several command line
options that switch particular runtime features on or off. Enter these
options when SFCB daemon starts.
-c, --config-file
=FILEWhen SFCB daemon starts, it reads its configuration from
/etc/sfcb/sfcb.cfg
by default. With this option, you can specify an alternative configuration file.-d, --daemon
Forces sfcbd and its child processes to run in the background.
-s, --collect-stats
Turns on runtime statistics collecting. Various sfcbd runtime statistics will be written to the
sfcbStat
file in the current working directory. By default, no statistics are collected.-l, --syslog-level
=LOGLEVELSpecifies the level of verbosity for the system logging facility. LOGLEVEL can be one of LOG_INFO, LOG_DEBUG, or LOG_ERR, which is the default.
-k, --color-trace
=LOGLEVELPrints trace output in a different color per process for easier debugging.
-t, --trace-components
=NUMActivates component-level tracing messages, where NUM is an OR-ed bitmask integer that defines which component to trace. After you specify
-t ?
, it lists all the components and their associated integer bitmask:>
sfcbd -t ? --- Traceable Components: Int Hex --- providerMgr: 1 0x0000001 --- providerDrv: 2 0x0000002 --- cimxmlProc: 4 0x0000004 --- httpDaemon: 8 0x0000008 --- upCalls: 16 0x0000010 --- encCalls: 32 0x0000020 --- ProviderInstMgr: 64 0x0000040 --- providerAssocMgr: 128 0x0000080 --- providers: 256 0x0000100 --- indProvider: 512 0x0000200 --- internalProvider: 1024 0x0000400 --- objectImpl: 2048 0x0000800 --- xmlIn: 4096 0x0001000 --- xmlOut: 8192 0x0002000 --- sockets: 16384 0x0004000 --- memoryMgr: 32768 0x0008000 --- msgQueue: 65536 0x0010000 --- xmlParsing: 131072 0x0020000 --- responseTiming: 262144 0x0040000 --- dbpdaemon: 524288 0x0080000 --- slp: 1048576 0x0100000A useful value that reveals the internal functions of sfcbd but does not generate too many messages, is
-t
2019.
37.3.3 SFCB configuration file #
SFCB reads its runtime configuration from configuration file
/etc/sfcb/sfcb.cfg
after starting up. This behavior
can be overridden using -c
option at start-up.
The configuration file contains option
:
VALUE pairs, one per line. When making changes
to this file, you can use any text editor that saves the file in a format
that is native to the environment you are using.
Any setting that has the options commented out with a number sign (#) uses the default setting.
The following list of options may not be complete. See the content of
/etc/sfcb/sfcb.cfg
and
/usr/share/doc/packages/sblim-sfcb/README
for their
complete list.
37.3.3.1 httpPort #
Purpose#
Specifies the local port value that sfcbd should listen to receive HTTP
(insecure) requests from CIM clients. Default is 5988
.
Syntax#
httpPort:
PORT_NUMBER
37.3.3.2 enableHttp #
Purpose#
Specifies whether SFCB should accept HTTP client connections. Default is
false
.
Syntax#
enableHttp:
OPTION
Option |
Description |
---|---|
true |
Enables HTTP connections. |
false |
Disables HTTP connections. |
37.3.3.3 httpProcs #
Purpose#
Specifies the maximum number of simultaneous HTTP client connections
before new incoming HTTP requests are blocked. Default is
8
.
Syntax#
httpProcs:
MAX_NUMBER_OF_CONNECTIONS
37.3.3.4 httpUserSFCB, httpUser #
Purpose#
These options control what user the HTTP server will run under. If
httpUserSFCB
is true
, HTTP will run
under the same user as the SFCB main process. If it is
false
the user name specified for
httpUser
will be used. This setting is used for both HTTP
and HTTPS servers. httpUser
must be
specified if httpUserSFCB
is set to
false
. the default is true
.
Syntax#
httpUserSFCB: true
37.3.3.5 httpLocalOnly #
Purpose#
Specifies whether to limit HTTP requests to localhost only. Default is
false
.
Syntax#
httpLocalOnly: false
37.3.3.6 httpsPort #
Purpose#
Specifies the local port value where sfcbd listens for HTTPS requests from
CIM clients. Default is 5989
.
Syntax#
httpsPort: port_number
37.3.3.7 enableHttps #
Purpose#
Specifies if SFCB will accept HTTPS client connections. Default is
true
.
Syntax#
enableHttps: option
Option |
Description |
---|---|
true |
Enables HTTPS connections. |
false |
Disables HTTPS connections. |
37.3.3.8 httpsProcs #
Purpose#
Specifies the maximum number of simultaneous HTTPS client connections
before new incoming HTTPS requests are blocked. Default is
8
.
Syntax#
httpsProcs:
MAX_NUMBER_OF_CONNECTIONS
37.3.3.9 enableInterOp #
Purpose#
Specifies if SFCB will provide the interop namespace
for indication support. Default is true
.
Syntax#
enableInterOp:
OPTION
Option |
Description |
---|---|
true |
Enables interop namespace. |
false |
Disables interop namespace. |
37.3.3.10 provProcs #
Purpose#
Specifies the maximum number of simultaneous provider processes. After
this point, if a new incoming request requires loading a new provider,
then one of the existing providers will first be automatically unloaded.
Default is 32
.
Syntax#
provProcs:
MAX_NUMBER_OF_PROCS
37.3.3.11 doBasicAuth #
Purpose#
Switches basic authentication on or off based on the client user
identifier before it accepts the request. Default value is
true
which means that basic client authentication is
performed.
Syntax#
doBasicAuth:
OPTION
Option |
Description |
---|---|
true |
Enables basic authentication. |
false |
Disables basic authentication. |
37.3.3.12 basicAuthLib #
Purpose#
Specifies the local library name. The SFCB server loads the library to
authenticate the client user identifier. Default is
sfcBasicPAMAuthentication
.
Syntax#
provProcs:
MAX_NUMBER_OF_PROCS
37.3.3.13 useChunking #
Purpose#
This option switches the use of HTTP/HTTPS “chunking” on or
off. If switched on, the server will return large volumes of response data
to the client in smaller “chunks”, rather than buffer the
data and send it back all in one chunk. Default is true
.
Syntax#
useChunking:
OPTION
Option |
Description |
---|---|
true |
Enables HTTP/HTTPS data chunking. |
false |
Disables HTTP/HTTPS data chunking. |
37.3.3.14 keepaliveTimeout #
Purpose#
Specifies the maximum time in seconds that SFCB HTTP process waits between
two requests on one connection before it terminates. Setting it to
0
disables HTTP keep-alive. Default is
0
.
Syntax#
keepaliveTimeout:
SECS
37.3.3.15 keepaliveMaxRequest #
Purpose#
Specifies the maximum number of consecutive requests on one connection.
Setting it to 0
disables HTTP keep-alive. Default value
is 10
.
Syntax#
keepaliveMaxRequest:
NUMBER_OF_CONNECTIONS
37.3.3.16 registrationDir #
Purpose#
Specifies the registration directory, which contains the provider
registration data, the staging area, and the static repository. Default is
/var/lib/sfcb/registration
.
Syntax#
registrationDir:
DIR
37.3.3.17 providerDirs #
Purpose#
Specifies a space-separated list of directories where SFCB is searching
for provider libraries. Default is /usr/lib64 /usr/lib64
/usr/lib64/cmpi
.
Syntax#
providerDirs:
DIR
37.3.3.18 providerSampleInterval #
Purpose#
Specifies the interval in seconds at which the provider manager is
checking for idle providers. Default is 30
.
Syntax#
providerSampleInterval:
SECS
37.3.3.19 providerTimeoutInterval #
Purpose#
Specifies the interval in seconds before an idle provider gets unloaded by
the provider manager. Default is 60
.
Syntax#
providerTimeoutInterval:
SECS
37.3.3.20 providerAutoGroup #
Purpose#
If the provider registration file does not specify any other group, and
the option is set to true
, all providers in the
same shared library are executed in the same process.
Syntax#
providerAutoGroup:
OPTION
Option |
Description |
---|---|
true |
Enables grouping of providers. |
false |
Disables grouping of providers. |
37.3.3.21 sslCertificateFilePath #
Purpose#
Specifies the name of the file that contains the server certificate. The
file must be in PEM (Privacy Enhanced Mail, RFC 1421 and RFC 1424) format.
This file is only required if enableHttps
is set to
true
. Default is
/etc/sfcb/server.pem
.
Syntax#
sslCertificateFilePath:
PATH
37.3.3.22 sslKeyFilePath #
Purpose#
Specifies the name of the file that contains the private key for the
server certificate. The file must be in PEM format and may not be
protected by passphrase. This file is only required if
enableHttps
is set to true
. Default
is /etc/sfcb/file.pem
.
Syntax#
sslKeyFilePath:
PATH
37.3.3.23 sslClientTrustStore #
Purpose#
Specifies the name of the file that contains either the CA or self-signed
certificates of the clients. This file must be in PEM format and is only
required if sslClientCertificate
is set to
accept
or require
. Default is
/etc/sfcb/client.pem
.
Syntax#
sslClientTrustStore:
PATH
37.3.3.24 sslClientCertificate #
Purpose#
Specifies the way SFCB handles client certificate based authentication. If
set to ignore
, it will not request a certificate from
the client. If set to accept
it will request a
certificate from the client but will not fail if the client does not
present one. If set to require
, it will refuse the
client connection if the client does not present a certificate. Default
value is ignore
.
Syntax#
sslClientCertificate:
OPTION
Option |
Description |
---|---|
ignore |
Disables requesting a client certificate. |
accept |
Disables requesting a client certificate. Will not fail if no certificate is present. |
require |
Refuses the client connection without a valid certificate. |
37.3.3.25 certificateAuthLib #
Purpose#
Specifies the name of the local library to request for the user
authentication based on client certificate. This is only requested if
sslClientCertificate
is not set to
ignore
. Default value is
sfcCertificateAuthentication
.
Syntax#
certificateAuthLib:
FILE
37.3.3.26 traceLevel #
Purpose#
Specifies the trace level for SFCB. You can override it by setting
environment variable SFCB_TRACE_LEVEL
. Default value is
0
.
Syntax#
traceLevel:
NUM_LEVEL
37.3.3.27 traceMask #
Purpose#
Specifies the trace mask for SFCB. you can override it by the command line
option --trace-components
. Default value is
0
.
Syntax#
traceMask:
MASK
37.3.3.28 traceFile #
Purpose#
Specifies the trace file for SFCB. You can override it by setting
environment variable SFCB_TRACE_FILE
. Default value is
stderr
(standard error output).
Syntax#
traceFile:
OUTPUT
37.4 Advanced SFCB tasks #
This chapter covers more advanced topics related to SFCB usage. To understand them, you need to have basic knowledge of the Linux file system and experience with the Linux command line. This chapter includes the following tasks:
Installing CMPI providers
Testing SFCB
Using
wbemcli
CIM client
37.4.1 Installing CMPI providers #
To install a CMPI provider, you need to make sure that its shared library
is copied into one of the directories specified by
providerDirs
configuration option, see
Section 37.3.3.17, “providerDirs”. The provider must also be
properly registered using sfcbstage
and
sfcbrepos
commands.
The provider package is usually prepared for SFCB, so that its installation takes care of the proper registration. Most SBLIM providers are prepared for SFCB.
37.4.1.1 Class repository #
Class repository is a place where SFCB stores
information about CIM classes. It usually consists of a directory tree
with namespace components. Typical CIM namespaces are
root/cimv2
or root/interop
, which
respectively translate to the class repository directory path on the file
system
/var/lib/sfcb/registration/repository/root/cimv2
and
/var/lib/sfcb/registration/repository/root/interop
Each namespace directory contains the file
classSchemas
. The file has a compiled binary
representation of all the CIM classes registered under that namespace. It
also contains necessary information about their CIM superclasses.
In addition, each namespace directory may contain a file
qualifiers
which contains all qualifiers for the
namespace. When sfcbd restarts, the class provider will scan the directory
/var/lib/sfcb/registration/repository/
and all its
subdirectories to determine the registered namespaces. Then
classSchemas
files are decoded and the class
hierarchy for each namespace is built.
37.4.1.2 Adding new classes #
SFCB cannot make live CIM class manipulations. You need to add, change or
remove classes offline and restart SFCB service with systemctl
restart sfcb
to register the changes.
To store providers class and registration information, SFCB uses a place
called staging area. On SUSE® Linux Enterprise Server systems, it is the
directory structure under /var/lib/sfcb/stage/
.
To add a new provider, you need to:
Copy the provider class definition files to the
./mofs
subdirectory of staging area directory (/var/lib/sfcb/stage/mofs
).Copy a registration file which contains the name of the class or classes and type of provider, and the name of the executable library file into the
./regs
subdirectory.
There are two default “mof” (class definition) files in the
staging directory: indication.mof
and
interop.mof
. MOF files under the root stage directory
/var/lib/sfcb/stage/mofs
will be copied into each
namespace after running sfcbrepos
command. The
interop.mof
will only be compiled into the
interop namespace.
The directory layout may look like the following example:
>
ls /var/lib/sfcb/stage
default.reg mofs regs
>
ls /var/lib/sfcb/stage/mofs
indication.mof root
>
ls /var/lib/sfcb/stage/mofs/root
cimv2 interop suse virt
>
ls -1 /var/lib/sfcb/stage/mofs/root/cimv2 | less
Linux_ABIParameter.mof
Linux_BaseIndication.mof
Linux_Base.mof
Linux_DHCPElementConformsToProfile.mof
Linux_DHCPEntity.mof
[..]
OMC_StorageSettingWithHints.mof
OMC_StorageVolumeDevice.mof
OMC_StorageVolume.mof
OMC_StorageVolumeStorageSynchronized.mof
OMC_SystemStorageCapabilities.mof
>
ls -1 /var/lib/sfcb/stage/mofs/root/interop
ComputerSystem.mof
ElementConformsToProfile.mof
HostSystem.mof
interop.mof
Linux_DHCPElementConformsToProfile.mof
[..]
OMC_SMIElementSoftwareIdentity.mof
OMC_SMISubProfileRequiresProfile.mof
OMC_SMIVolumeManagementSoftware.mof
ReferencedProfile.mof
RegisteredProfile.mof
>
ls -1 /var/lib/sfcb/stage/regs
AllocationCapabilities.reg
Linux_ABIParameter.reg
Linux_BaseIndication.reg
Linux_DHCPGlobal.reg
Linux_DHCPRegisteredProfile.reg
[..]
OMC_Base.sfcb.reg
OMC_CopyServices.sfcb.reg
OMC_PowerManagement.sfcb.reg
OMC_Server.sfcb.reg
RegisteredProfile.reg
>
cat /var/lib/sfcb/stage/regs/Linux_DHCPRegisteredProfile.reg
[Linux_DHCPRegisteredProfile]
provider: Linux_DHCPRegisteredProfileProvider
location: cmpiLinux_DHCPRegisteredProfile
type: instance
namespace: root/interop
#
[Linux_DHCPElementConformsToProfile]
provider: Linux_DHCPElementConformsToProfileProvider
location: cmpiLinux_DHCPElementConformsToProfile
type: instance association
namespace: root/cimv2
#
[Linux_DHCPElementConformsToProfile]
provider: Linux_DHCPElementConformsToProfileProvider
location: cmpiLinux_DHCPElementConformsToProfile
type: instance association
namespace: root/interop
SFCB uses a custom provider registration file for each provider.
All SBLIM providers on the SBLIM Web site already include a registration file that is used to generate the .reg file for SFCB.
The format of SFCB registration file is:
[<class-name>] provider: <provide-name> location: <library-name> type: [instance] [association] [method] [indication] group: <group-name> unload: never namespace: <namespace-for-class> ...
where:
<class-name>
The CIM class name (required)
<provider-name>
The CMPI provider name (required)
<location-name>
The name of the provider library (required)
type
The type of the provider (required). This can be any combination of:
instance
,association
,method
orindication
.<group-name>
Multiple providers can be grouped together and run under a single process to further minimize runtime resources. All providers registered under the same <group-name> will be executed under the same process. By default each provider will be run as a separate process.
unload
Specifies the unload policy for the provider. Currently the only supported option is
never
, which specifies that the provider will not be monitored for idle times and will never be unloaded. By default each provider will be unloaded when its idle times exceed the value specified in the configuration file.namespace
List of namespaces for which this provider can be executed. This is required, although for most providers this will be
root/cimv2
.
Once all the class definitions and provider registration files are stored
in the staging area, you need to rebuild the SFCB class repository with
the command sfcbrepos
-f
.
You can add, change or remove classes this way. After rebuilding the class
repository, restart SFCB with command systemctl restart
sfcb
.
Alternatively, the SFCB package contains a utility that will copy provider class mof files and registration files to the correct locations in the staging area.
sfcbstage
-r
[provider.reg]
[class1.mof] [class2.mof] ...
After running this command you still need to rebuild the class repository and restart SFCB service.
37.4.2 Testing SFCB #
The SFCB package includes two testing scripts: wbemcat
and xmltest
.
wbemcat
sends raw CIM-XML data via HTTP protocol to the
specified SFCB host (localhost by default) listening on port 5988. Then it
displays the returned results. The following file contains the CIM-XML
representation of a standard EnumerateClasses request:
<?xml version="1.0" encoding="utf-8"?> <CIM CIMVERSION="2.0" DTDVERSION="2.0"> <MESSAGE ID="4711" PROTOCOLVERSION="1.0"> <SIMPLEREQ> <IMETHODCALL NAME="EnumerateClasses"> <LOCALNAMESPACEPATH> <NAMESPACE NAME="root"/> <NAMESPACE NAME="cimv2"/> </LOCALNAMESPACEPATH> <IPARAMVALUE NAME="ClassName"> <CLASSNAME NAME=""/> </IPARAMVALUE> <IPARAMVALUE NAME="DeepInheritance"> <VALUE>TRUE</VALUE> </IPARAMVALUE> <IPARAMVALUE NAME="LocalOnly"> <VALUE>FALSE</VALUE> </IPARAMVALUE> <IPARAMVALUE NAME="IncludeQualifiers"> <VALUE>FALSE</VALUE> </IPARAMVALUE> <IPARAMVALUE NAME="IncludeClassOrigin"> <VALUE>TRUE</VALUE> </IPARAMVALUE> </IMETHODCALL> </SIMPLEREQ> </MESSAGE> </CIM>
Sending this request to SFCB CIMOM returns a list of all supported classes
for which there is a registered provider. Suppose you save the file as
cim_xml_test.xml
.
>
wbemcat cim_xml_test.xml | less
HTTP/1.1 200 OK
Content-Type: application/xml; charset="utf-8"
Content-Length: 337565
Cache-Control: no-cache
CIMOperation: MethodResponse
<?xml version="1.0" encoding="utf-8" ?>
<CIM CIMVERSION="2.0" DTDVERSION="2.0">
<MESSAGE ID="4711" PROTOCOLVERSION="1.0">
<SIMPLERSP>
<IMETHODRESPONSE NAME="EnumerateClasses">
[..]
<CLASS NAME="Linux_DHCPParamsForEntity" SUPERCLASS="CIM_Component">
<PROPERTY.REFERENCE NAME="GroupComponent" REFERENCECLASS="Linux_DHCPEntity">
</PROPERTY.REFERENCE>
<PROPERTY.REFERENCE NAME="PartComponent" REFERENCECLASS="Linux_DHCPParams">
</PROPERTY.REFERENCE>
</CLASS>
</IRETURNVALUE>
</IMETHODRESPONSE>
</SIMPLERSP>
</MESSAGE>
</CIM>
The classes listed will vary depending on what providers are installed on your system.
The second script xmltest
is also used to send a raw
CIM-XML test file to the SFCB CIMOM. It then compares the returned results
against a previously saved “OK” result file. If there does not
yet exist a corresponding “OK” file, it will be created for
later use:
>
xmltest cim_xml_test.xml Running test cim_xml_test.xml ... OK Saving response as cim_xml_test.OK#
xmltest cim_xml_test.xml Running test cim_xml_test.xml ... Passed
37.4.3 Command line CIM client: wbemcli #
In addition to wbemcat
and xmltest
,
the SBLIM project includes a more advanced command line CIM client
wbemcli
. The client is used to send CIM requests to SFCB
server and display returned results. It is independent of CIMOM library and
can be used with all WBEM compliant implementations.
For example, if you need to list all the classes implemented by SBLIM providers registered to your SFCB, send the “EnumerateClasses” (ec) request to SFCB:
>
wbemcli -dx ec http://localhost/root/cimv2
To server: <?xml version="1.0" encoding="utf-8" ?>
<CIM CIMVERSION="2.0" DTDVERSION="2.0">
<MESSAGE ID="4711" PROTOCOLVERSION="1.0"><SIMPLEREQ><IMETHODCALL \
NAME="EnumerateClasses"><LOCALNAMESPACEPATH><NAMESPACE NAME="root"> \
</NAMESPACE><NAMESPACE NAME="cimv2"></NAMESPACE> \
</LOCALNAMESPACEPATH>
<IPARAMVALUE NAME="DeepInheritance"><VALUE>TRUE</VALUE> \
</IPARAMVALUE>
<IPARAMVALUE NAME="LocalOnly"><VALUE>FALSE</VALUE></IPARAMVALUE>
<IPARAMVALUE NAME="IncludeQualifiers"><VALUE>FALSE</VALUE> \
</IPARAMVALUE>
<IPARAMVALUE NAME="IncludeClassOrigin"><VALUE>TRUE</VALUE> \
</IPARAMVALUE>
</IMETHODCALL></SIMPLEREQ>
</MESSAGE></CIM>
From server: Content-Type: application/xml; charset="utf-8"
From server: Content-Length: 337565
From server: Cache-Control: no-cache
From server: CIMOperation: MethodResponse
From server: <?xml version="1.0" encoding="utf-8" ?>
<CIM CIMVERSION="2.0" DTDVERSION="2.0">
<MESSAGE ID="4711" PROTOCOLVERSION="1.0">
<SIMPLERSP>
<IMETHODRESPONSE NAME="EnumerateClasses">
<IRETURNVALUE>
<CLASS NAME="CIM_ResourcePool" SUPERCLASS="CIM_LogicalElement">
<PROPERTY NAME="Generation" TYPE="uint64">
</PROPERTY>
<PROPERTY NAME="ElementName" TYPE="string">
</PROPERTY>
<PROPERTY NAME="Description" TYPE="string">
</PROPERTY>
<PROPERTY NAME="Caption" TYPE="string">
</PROPERTY>
<PROPERTY NAME="InstallDate" TYPE="datetime">
</PROPERTY>
[..]
<CLASS NAME="Linux_Ext4FileSystem" SUPERCLASS="CIM_UnixLocalFileSystem">
<PROPERTY NAME="FSReservedCapacity" TYPE="uint64">
</PROPERTY>
<PROPERTY NAME="TotalInodes" TYPE="uint64">
</PROPERTY>
<PROPERTY NAME="FreeInodes" TYPE="uint64">
</PROPERTY>
<PROPERTY NAME="ResizeIncrement" TYPE="uint64">
<VALUE>0</VALUE>
</PROPERTY>
<PROPERTY NAME="IsFixedSize" TYPE="uint16">
<VALUE>0</VALUE>
</PROPERTY>
[..]
The -dx
option shows you the actual XML sent to SFCB by
wbemcli
and the actual XML received. In the above
example, the first of many returned classes was
CIM_ResourcePool
followed by
Linux_Ext4FileSystem
. Similar entries will appear for
all of the other registered classes.
If you omit the -dx
option, wbemcli
will display only a compact representation of the returned data:
>
wbemcli ec http://localhost/root/cimv2
localhost:5988/root/cimv2:CIM_ResourcePool Generation=,ElementName=, \
Description=,Caption=,InstallDate=,Name=,OperationalStatus=, \
StatusDescriptions=,Status=,HealthState=,PrimaryStatus=, \
DetailedStatus=,OperatingStatus=,CommunicationStatus=,InstanceID=, \
PoolID=,Primordial=,Capacity=,Reserved=,ResourceType=, \
OtherResourceType=,ResourceSubType=, \AllocationUnits=
localhost:5988/root/cimv2:Linux_Ext4FileSystem FSReservedCapacity=, \
TotalInodes=,FreeInodes=,ResizeIncrement=,IsFixedSize=,NumberOfFiles=, \
OtherPersistenceType=,PersistenceType=,FileSystemType=,ClusterSize=, \
MaxFileNameLength=,CodeSet=,CasePreserved=,CaseSensitive=, \
CompressionMethod=,EncryptionMethod=,ReadOnly=,AvailableSpace=, \
FileSystemSize=,BlockSize=,Root=,Name=,CreationClassName=,CSName=, \
CSCreationClassName=,Generation=,ElementName=,Description=,Caption=, \
InstanceID=,InstallDate=,OperationalStatus=,StatusDescriptions=, \
Status=,HealthState=,PrimaryStatus=,DetailedStatus=,OperatingStatus= \
,CommunicationStatus=,EnabledState=,OtherEnabledState=,RequestedState= \
,EnabledDefault=,TimeOfLastStateChange=,AvailableRequestedStates=, \
TransitioningToState=,PercentageSpaceUse=
[..]
37.5 More information #
- https://www.dmtf.org
Distributed Management Task Force Web site
- https://www.dmtf.org/standards/wbem/
Web-Based Enterprise Management (WBEM) Web site
- https://www.dmtf.org/standards/cim/
Common Information Model (CIM) Web site
- http://sblim.sourceforge.net/wiki/index.php/Main_Page
Standards Based Linux Instrumentation (SBLIM) Web site
Part V Troubleshooting #
- 38 Help and documentation
SUSE® Linux Enterprise Server comes with several sources of information and documentation, available online or integrated into your installed system.
- 39 Gathering system information for support
For a quick overview of all relevant system information of a machine, SUSE Linux Enterprise Server offers the
hostinfo
package. It also helps system administrators to check for tainted kernels (that are not supported) or any third-party packages installed on a machine.In case of problems, a detailed system report may be created with either the
supportconfig
command line tool or the YaST module. Both will collect information about the system such as: current kernel version, hardware, installed packages, partition setup, and much more. The result is a TAR archive of files. After opening a Service Request (SR), you can upload the TAR archive to Global Technical Support. It will help to locate the issue you reported and to assist you in solving the problem.Additionally, you can analyze the
supportconfig
output for known issues to help resolve problems faster. For this purpose, SUSE Linux Enterprise Server provides both an appliance and a command line tool forSupportconfig Analysis
(SCA).- 40 Common problems and their solutions
This chapter describes a range of potential problems and their solutions. Even if your situation is not precisely listed, there may be one similar enough to offer hints to the solution of your problem.
38 Help and documentation #
SUSE® Linux Enterprise Server comes with several sources of information and documentation, available online or integrated into your installed system.
- Product Documentation
Extensive documentation for SUSE Linux Enterprise Server is available at https://documentation.suse.com/#sles. Topics covered range from deployment, upgrade and system administration to virtualization, system tuning and security, among others.
At https://documentation.suse.com/sbp-supported.html, you can find SUSE's best practice series of documents covering hands-on documentation on implementation scenarios. At https://documentation.suse.com/trd-supported.html, our technical reference documentation series provides guides on deploying solution components from SUSE and its partners.
- Documentation in
/usr/share/doc
This directory holds release notes for your system (in the subdirectory
release-notes
). It also contains information of installed packages in the subdirectorypackages
. Find more detailed information in Section 38.1, “Documentation directory”.- Man pages and info pages for shell commands
When working with the shell, you do not need to know the options of the commands by heart. Traditionally, the shell provides integrated help by means of man pages and info pages. Read more in Section 38.2, “Man pages” and Section 38.3, “Info pages”.
- Desktop help center
The help center of the GNOME desktop (Help) provides central access to the GNOME desktop documentation.
- Separate help packages for some applications
When installing new software with YaST, the software documentation is usually installed automatically and appears in the help center of your desktop. However, some applications, such as GIMP, may have different online help packages that can be installed separately with YaST and do not integrate into the help centers.
38.1 Documentation directory #
The traditional directory to find documentation on your installed Linux
system is /usr/share/doc
. The directory contains the
release notes and information about the packages installed on your system,
plus manuals and more.
In the Linux world, manuals and other kinds of documentation are
available in the form of packages, like software. How much and which
information you find in /usr/share/docs
also depends
on the (documentation) packages installed. If you cannot find the
subdirectories mentioned here, check if the respective packages are
installed on your system and add them with YaST, if needed.
38.1.1 Release notes #
We provide HTML, PDF, RTF and text versions of SUSE Linux Enterprise Server release
notes. They are available on your installed system under
/usr/share/doc/release-notes/
or online at your
product-specific Web page at https://www.suse.com/releasenotes//.
38.1.2 Package documentation #
Under packages
, find the documentation
that is included in the software packages installed on your system. For
every package, a subdirectory
/usr/share/doc/packages/PACKAGENAME
is created. It often contains README files for the package and sometimes
examples, configuration files, or additional scripts. The following list
introduces typical files to be found under
/usr/share/doc/packages
. None of these entries are
mandatory and many packages might only include a few of them.
AUTHORS
List of the main developers.
BUGS
Known bugs or malfunctions. May also contain a link to a Bugzilla Web page where you can search all bugs.
CHANGES
,ChangeLog
Summary of changes from version to version. Usually interesting for developers, because it is very detailed.
COPYING
,LICENSE
Licensing information.
FAQ
Question and answers collected from mailing lists or newsgroups.
INSTALL
How to install this package on your system. As the package is already installed by the time you get to read this file, you can safely ignore the contents of this file.
README
,README.*
General information on the software. For example, for what purpose and how to use it.
TODO
Features planned for the future.
MANIFEST
List of files with a brief summary.
NEWS
Description of what is new in this version.
38.2 Man pages #
Man pages are an essential part of any Linux system. They explain the usage
of a command and all available options and parameters. Man pages can be
accessed with man
followed by the name of the command,
for example, man ls
.
Man pages are displayed directly in the shell. To navigate them, move up and
down with Page ↑ and Page ↓.
Move between the beginning and the end of a document with
Home and End. End this viewing
mode by pressing Q. Learn more about the
man
command itself with man man
. Man
pages are sorted in categories as shown in
Table 38.1, “Man pages—categories and descriptions” (taken from the man page for man
itself).
Number |
Description |
---|---|
1 |
Executable programs or shell commands |
2 |
System calls (functions provided by the kernel) |
3 |
Library calls (functions within program libraries) |
4 |
Special files (usually found in |
5 |
File formats and conventions ( |
6 |
Games |
7 |
Miscellaneous (including macro packages and conventions), for example, man(7), groff(7) |
8 |
System administration commands (usually only for |
9 |
Kernel routines (nonstandard) |
Each man page consists of several parts labeled NAME, SYNOPSIS, DESCRIPTION, SEE ALSO, LICENSING, and AUTHOR. There may be additional sections available depending on the type of command.
38.3 Info pages #
Info pages are another important source of information on your system.
Usually, they are more detailed than man pages. They consist of more than
command line options and contain sometimes whole tutorials or reference
documentation. To view the info page for a certain command, enter
info
followed by the name of the command, for example,
info ls
. You can browse an info page with a viewer
directly in the shell and display the different sections, called
“nodes”. Use Space to move forward and
<— to move backward. Within a node, you can also
browse with Page ↑ and Page ↓
but only Space and <— will
take you also to the previous or subsequent node. Press Q
to end the viewing mode. Not every command comes with an info page and vice
versa.
38.4 Online resources #
In addition to the online versions of the SUSE manuals installed under
/usr/share/doc
, you can also access the
product-specific manuals and documentation on the Web. For an overview of
all documentation available for SUSE Linux Enterprise Server check out your
product-specific documentation Web page at
https://documentation.suse.com/.
If you are searching for additional product-related information, you can also refer to the following Web sites:
- SUSE technical support
The SUSE Technical Support can be found at https://www.suse.com/support/ if you have questions or need solutions for technical problems.
- User community
There are several forums where you can dive in on discussions about SUSE products. See https://forums.suse.com/ for a list.
- SUSE blog
The SUSE blog offers articles, tips, Q and A: https://www.suse.com/c/blog/
- GNOME documentation
Documentation for GNOME users, administrators and developers is available at https://library.gnome.org/.
- The Linux documentation project
The Linux Documentation Project (TLDP) is run by a team of volunteers who write Linux-related documentation (see https://www.tldp.org). It is the most comprehensive documentation resource for Linux. The set of documents contains tutorials for beginners, but is mainly focused on experienced users and professional system administrators. TLDP publishes HOWTOs, FAQs, and guides (handbooks) under a free license. Parts of the documentation from TLDP are also available on SUSE Linux Enterprise Server.
39 Gathering system information for support #
For a quick overview of all relevant system information of a machine,
SUSE Linux Enterprise Server offers the
hostinfo
package. It also helps
system administrators to check for tainted kernels (that are not supported)
or any third-party packages installed on a machine.
In case of problems, a detailed system report may be created with either
the supportconfig
command line tool or the YaST
module. Both will collect information about the
system such as: current kernel version, hardware, installed packages,
partition setup, and much more. The result is a TAR archive of files. After
opening a Service Request (SR), you can upload the TAR archive to Global
Technical Support. It will help to locate the issue you reported and to
assist you in solving the problem.
Additionally, you can analyze the supportconfig
output
for known issues to help resolve problems faster. For this purpose,
SUSE Linux Enterprise Server provides both an appliance and a command line tool for
Supportconfig Analysis
(SCA).
39.1 Displaying current system information #
For a quick and easy overview of all relevant system information when
logging in to a server, use the package
hostinfo
. After it has been
installed on a machine, the console displays the following information to
any root
user that logs in to this machine:
hostinfo
when logging in as root
#Welcome to SUSE Linux Enterprise Server 15 SP2 Snapshot8 (x86_64) - Kernel \r (\l). Distribution: SUSE Linux Enterprise Server 15 SP2 Current As Of: Wed 25 Mar 2020 12:09:20 PM PDT Hostname: localhost Kernel Version: 5.3.18-8-default Architecture: x86_64 Installed: Thu 19 Mar 2020 11:25:13 AM PDT Status: Not Tainted Last Installed Package: Wed 25 Mar 2020 11:42:24 AM PDT Patches Needed: 0 Security: 0 3rd Party Packages: 219 Network Interfaces eth0: 192.168.2/24 2002:c0a8:20a::/64 Memory Total/Free/Avail: 7.4Gi/6.4Gi/6.8Gi (91% Avail) CPU Load Average: 7 (3%) with 2 CPUs
In case the output shows a tainted
kernel status, see
Section 39.6, “Support of kernel modules” for more details.
39.2 Collecting system information with supportconfig #
To create a TAR archive with detailed system information that you can hand over to Global Technical Support, use either:
the command
supportconfig
or,the YaST
module.
The command line tool is provided by the
package supportutils
which is installed by default.
The YaST module is also based on the command
line tool.
Depending on which packages are installed on your system, some of these
packages integrate Supportconfig plug-ins. When Supportconfig is executed,
all plug-ins are executed as well and create one or more result files for
the archive. That has the benefit that the only topics checked are those
that contain a specific plug-in for them. Supportconfig plug-ins are stored
in the directory /usr/lib/supportconfig/plugins/
.
39.2.1 Creating a service request number #
Supportconfig archives can be generated at any time. However, for handing over the Supportconfig data to Global Technical Support, you need to generate a service request number first. You will need it to upload the archive to support.
To create a service request, go to https://scc.suse.com/support/requests and follow the instructions on the screen. Write down the service request number.
SUSE treats system reports as confidential data. For details about our privacy commitment, see https://www.suse.com/company/policies/privacy/.
39.2.2 Upload targets #
After having created a service request number, you can upload your Supportconfig archives to Global Technical Support as described in Procedure 39.1, “Submitting information to support with YaST” or Procedure 39.2, “Submitting information to support from command line”. Use one of the following upload targets:
North America: FTP ftp://support-ftp.us.suse.com/incoming/, FTPS ftps://support-ftp.us.suse.com/incoming/
EMEA, Europe, the Middle East, and Africa: FTP ftp://support-ftp.emea.suse.com/incoming, FTPS ftps://support-ftp.emea.suse.com/incoming
Alternatively, you can manually attach the TAR archive to your service request using the service request URL: https://scc.suse.com/support/requests.
39.2.3 Creating a supportconfig archive with YaST #
To use YaST to gather your system information, proceed as follows:
Start YaST and open the
module.Click
.In the next window, select one of the Supportconfig options from the radio button list.
is preselected by default. If you want to test the report function first, use . For additional information on the other options, refer to thesupportconfig
man page.Press
.Enter your contact information. It is saved in the
basic-environment.txt
file and included in the created archive.To submit the archive to Global Technical Support, provide the required Section 39.2.2, “Upload targets” for details of which upload servers are available.
. YaST automatically suggests an upload server. To modify it, refer toTo submit the archive later, leave the
empty.Press
to start the information collection process.After the process is finished, press
.To review the collected data, select the desired file from
to view its contents in YaST. To remove a file from the TAR archive before submitting it to support, use . Press .Save the TAR archive. If you started the YaST module as
root
user, YaST prompts to save the archive to/var/log
(otherwise, to your home directory). The file name format isscc_HOST_DATE_TIME.tbz
.To upload the archive to support directly, make sure Step 5. To modify the upload target, check which upload servers are available in Section 39.2.2, “Upload targets”.
is activated. The shown here is the one that YaST suggests inTo skip the upload, deactivate
.Confirm the changes to close the YaST module.
39.2.4 Creating a supportconfig archive from command line #
The following procedure shows how to create a Supportconfig archive, but without submitting it to support directly. For uploading it, you need to run the command with certain options as described in Procedure 39.2, “Submitting information to support from command line”.
Open a shell and become
root
.Run
supportconfig
. Usually, it is enough to run this tool without any options. Some options are very common and are displayed in the following list:-E MAIL
,-N NAME
,-O COMPANY
,-P PHONE
Sets your contact data: e-mail address (
-E
), company name (-O
), your name (-N
), and your phone number (-P
).-i KEYWORDS
,-F
Limits the features to check. The placeholder KEYWORDS is a comma separated list of case-sensitive keywords. Get a list of all keywords with
supportconfig -F
.-r SRNUMBER
Defines your service request number when uploading the generated TAR archive.
Wait for the tool to complete the operation.
The default archive location is
/var/log
, with the file name format beingscc_HOST_DATE_TIME.tbz
39.2.5 Understanding the output of supportconfig
#
Whether you run supportconfig
through YaST or directly,
the script gives you a summary of what it did.
Support Utilities - Supportconfig Script Version: 3.0-98 Script Date: 2017 06 01 [...] Gathering system information Data Directory: /var/log/scc_d251_180201_1525 1 Basic Server Health Check... Done 2 RPM Database... Done 2 Basic Environment... Done 2 System Modules... Done 2 [...] File System List... Skipped 3 [...] Command History... Excluded 4 [...] Supportconfig Plugins: 1 5 Plugin: pstree... Done [...] Creating Tar Ball ==[ DONE ]=================================================================== Log file tar ball: /var/log/scc_d251_180201_1525.txz 6 Log file size: 732K Log file md5sum: bf23e0e15e9382c49f92cbce46000d8b =============================================================================
The temporary data directory to store the results. This directory is archived as tar file, see 6. | |
The feature was enabled (either by default or selected manually) and executed successfully. The result is stored in a file (see Table 39.1, “Comparison of features and file names in the TAR archive”). | |
The feature was skipped because some files of one or more RPM packages were changed. | |
The feature was excluded because it was deselected via the | |
The script found one plug-in and executes the plug-in
| |
The tar file name of the archive, by default compressed with |
39.2.6 Common supportconfig options #
The supportconfig
utility is usually called without any
options. Display a list of all options with
supportconfig
-h
or refer to the man
page. The following list gives a brief overview of some common use cases:
- Reducing the size of the information being gathered
Use the minimal option (
-m
):>
sudo
supportconfig -m- Limiting the information to a specific topic
If you have already localized a problem that relates to a specific area or feature set only, you should limit the collected information to the specific area for the next
supportconfig
run. For example, if you detected problems with LVM and want to test a recent change that you did to the LVM configuration. In that case it makes sense to gather the minimum Supportconfig information around LVM only:>
sudo
supportconfig -i LVMAdditional keywords can be separated through commas. For example, an additional disk test:
>
sudo
supportconfig -i LVM,DISKFor a complete list of feature keywords that you can use for limiting the collected information to a specific area, run:
>
sudo
supportconfig -F- Including additional contact information in the output:
>
sudo
supportconfig -E tux@example.org -N "Tux Penguin" -O "Penguin Inc." ...(all in one line)
- Collecting already rotated log files
>
sudo
supportconfig -lThis is especially useful in high logging environments or after a kernel crash when syslog rotates the log files after a reboot.
39.2.7 Overview of the archive content #
The TAR archive contains all the results from the features. Depending on
what you have selected (all or only a small set), the archive can contain
more or less files.
The set of features can be limited through the -i
option (see Section 39.2.6, “Common supportconfig options”).
To list the content of the archive, use the following tar
command:
#
tar
xf /var/log/scc_earth_180131_1545.tbz
The following file names are always available inside the TAR archive:
basic-environment.txt
Contains the date when this script was executed and system information like version of the distribution, hypervisor information, and more.
basic-health-check.txt
Contains some basic health checks like uptime, virtual memory statistics, free memory and hard disk, checks for zombie processes, and more.
hardware.txt
Contains basic hardware checks like information about the CPU architecture, list of all connected hardware, interrupts, I/O ports, kernel boot messages, and more.
messages.txt
Contains log messages from the system journal.
rpm.txt
Contains a list of all installed RPM packages, the name, where they are coming from, and their versions.
summary.xml
Contains some information in XML format like distribution, the version, and product specific fragments.
supportconfig.txt
Contains information about the
supportconfig
script itself.y2log.txt
Contains YaST specific information like specific packages, configuration files, and log files.
Table 39.1, “Comparison of features and file names in the TAR archive” lists all available features and their file names. Further service packs can extend the list, as can plug-ins.
Feature | File name |
---|---|
APPARMOR | security-apparmor.txt |
AUDIT | security-audit.txt |
AUTOFS | fs-autofs.txt |
BOOT | boot.txt |
BTRFS | fs-btrfs.txt |
DAEMONS | systemd.txt |
CIMOM | cimom.txt |
CRASH | crash.txt |
CRON | cron.txt |
DHCP | dhcp.txt |
DISK | fs-diskio.txt |
DNS | dns.txt |
DOCKER | docker.txt |
DRBD | drbd.txt |
ENV | env.txt |
ETC | etc.txt |
HA | ha.txt |
HAPROXY | haproxy.txt |
HISTORY | shell_history.txt |
IB | ib.txt |
IMAN | novell-iman.txt |
ISCSI | fs-iscsi.txt |
LDAP | ldap.txt |
LIVEPATCH | kernel-livepatch.txt |
LVM | lvm.txt |
MEM | memory.txt |
MOD | modules.txt |
MPIO | mpio.txt |
NET | network-*.txt |
NFS | nfs.txt |
NTP | ntp.txt |
NVME | nvme.txt |
OCFS2 | ocfs2.txt |
OFILES | open-files.txt |
print.txt | |
PROC | proc.txt |
SAR | sar.txt |
SLERT | slert.txt |
SLP | slp.txt |
SMT | smt.txt |
SMART | fs-smartmon.txt |
SMB | samba.txt |
SRAID | fs-softraid.txt |
SSH | ssh.txt |
SSSD | sssd.txt |
SYSCONFIG | sysconfig.txt |
SYSFS | sysfs.txt |
TRANSACTIONAL | transactional-update.txt |
TUNED | tuned.txt |
UDEV | udev.txt |
UFILES | fs-files-additional.txt |
UP | updates.txt |
WEB | web.txt |
X | x.txt |
39.3 Submitting information to Global Technical Support #
Use the YaST supportconfig
command line utility to submit system
information to the Global Technical Support. When you experience a server
issue and want the support's assistance, you will need to open a service
request first. For details, see
Section 39.2.1, “Creating a service request number”.
The following examples use 12345678901 as a placeholder for your service request number. Replace 12345678901 with the service request number you created in Section 39.2.1, “Creating a service request number”.
The following procedure assumes that you have already created a Supportconfig archive, but have not uploaded it yet. Make sure to have included your contact information in the archive as described in Section 39.2.3, “Creating a supportconfig archive with YaST”, Step 4. For instructions on how to generate and submit a Supportconfig archive in one go, see Section 39.2.3, “Creating a supportconfig archive with YaST”.
Start YaST and open the
module.Click
.In
specify the path to the existing Supportconfig archive or for it.YaST automatically proposes an upload server. If you want to modify it, refer to Section 39.2.2, “Upload targets” for details of which upload servers are available.
Proceed with
.Click
.
The following procedure assumes that you have already created a Supportconfig archive, but have not uploaded it yet. For instructions on how to generate and submit a Supportconfig archive in one go, see Section 39.2.3, “Creating a supportconfig archive with YaST”.
Servers with Internet connectivity:
To use the default upload target, run:
>
sudo
supportconfig -ur 12345678901For the secure upload target, use the following:
>
sudo
supportconfig -ar 12345678901
Servers without Internet connectivity
Run the following:
>
sudo
supportconfig -r 12345678901Manually upload the
/var/log/scc_SR12345678901*tbz
archive to one of our FTP servers. Which one to use depends on your location in the world. For an overview, see Section 39.2.2, “Upload targets”.
After the TAR archive arrives in the incoming directory of our FTP server, it becomes automatically attached to your service request.
39.4 Analyzing system information #
System reports created with supportconfig
can be analyzed
for known issues to help resolve problems faster. For this purpose,
SUSE Linux Enterprise Server provides both an appliance and a command line tool for
Supportconfig Analysis
(SCA). The SCA appliance is a
server-side tool which is non-interactive. The SCA tool
(scatool
provided by the package
sca-server-report) runs on the client-side and is
executed from command line. Both tools analyze Supportconfig archives from
affected servers. The initial server analysis takes place on the SCA
appliance or the workstation on which scatool
is
running. No analysis cycles happen on the production server.
Both the appliance and the command line tool additionally need product-specific patterns that enable them to analyze the Supportconfig output for the associated products. Each pattern is a script that parses and evaluates a Supportconfig archive for one known issue. The patterns are available as RPM packages.
You can also develop your own patterns as briefly described in Section 39.4.3, “Developing custom analysis patterns”.
39.4.1 SCA command line tool #
The SCA command line tool lets you analyze a local machine using both
supportconfig
and the analysis patterns for the specific
product that is installed on the local machine. The tool creates an HTML
report showing its analysis results. For an example, see
Figure 39.1, “HTML report generated by SCA tool”.
The scatool
command is provided by the
sca-server-report package. It is
not installed by default. Additionally, you need the
sca-patterns-base package and any
of the product-specific
sca-patterns-* packages that
matches the product installed on the machine where you want to run the
scatool
command.
Execute the scatool
command either as root
user or
with sudo
. When calling the SCA tool, either
analyze an existing supportconfig
TAR archive or
let it generate and analyze a new archive in one go. The tool also provides
an interactive console with tab completion. It is possible to run
supportconfig
on an external machine and to execute the
subsequent analysis on the local machine.
Find some example commands below:
sudo scatool
-s
Calls
supportconfig
and generates a new Supportconfig archive on the local machine. Analyzes the archive for known issues by applying the SCA analysis patterns that match the installed product. Displays the path to the HTML report that is generated from the results of the analysis. It is usually written to the same directory where the Supportconfig archive can be found.sudo scatool
-s
-o
/opt/sca/reports/Same as
sudo scatool
-s
, only that the HTML report is written to the path specified with-o
.sudo scatool
-a
PATH_TO_TARBALL_OR_DIRAnalyzes the specified Supportconfig archive file (or the specified directory to where the Supportconfig archive has been extracted). The generated HTML report is saved in the same location as the Supportconfig archive or directory.
sudo scatool
-a
SLES_SERVER.COMPANY.COMEstablishes an SSH connection to an external server SLES_SERVER.COMPANY.COM and runs
supportconfig
on the server. The Supportconfig archive is then copied back to the local machine and is analyzed there. The generated HTML report is saved to the default/var/log
directory. (Only the Supportconfig archive is created on SLES_SERVER.COMPANY.COM).sudo scatool
-c
Starts the interactive console for
scatool
. Press →| twice to see the available commands.
For further options and information, run sudo scatool -h
or see the scatool
man page.
39.4.2 SCA appliance #
If you decide to use the SCA appliance for analyzing the Supportconfig archives, configure a dedicated server (or virtual machine) as the SCA appliance server. The SCA appliance server can then be used to analyze Supportconfig archives from all machines in your enterprise running SUSE Linux Enterprise Server or SUSE Linux Enterprise Desktop. You can simply upload Supportconfig archives to the appliance server for analysis. Interaction is not required. In a MariaDB database, the SCA appliance keeps track of all Supportconfig archives that have been analyzed . You can read the SCA reports directly from the appliance Web interface. Alternatively, you can have the appliance send the HTML report to any administrative user via e-mail. For details, see Section 39.4.2.5.4, “Sending SCA reports via e-mail”.
39.4.2.1 Installation quick start #
To install and set up the SCA appliance in a very fast way from the command line, follow the instructions here. The procedure is intended for experts and focuses on the bare installation and setup commands. For more information, refer to the more detailed description in Section 39.4.2.2, “Prerequisites” to Section 39.4.2.3, “Installation and basic setup”.
Web and LAMP Pattern
Web and Scripting Module (you must register the machine to be able to select this module).
root
privileges required
All commands in the following procedure must be run as root
.
After the appliance is set up and running, no more manual interaction is required. This way of setting up the appliance is therefore ideal for using cron jobs to create and upload Supportconfig archives.
On the machine on which to install the appliance, log in to a console and execute the following commands (make sure to accept the recommended packages):
>
sudo
zypper install sca-appliance-* sca-patterns-* \ vsftpd yast2 yast2-ftp-server>
sudo
systemctl enable apache2>
sudo
systemctl start apache2>
sudo
systemctl enable vsftpd>
sudo
systemctl start vsftpd>
sudo
yast ftp-serverIn YaST FTP Server, select
› › › › to .Execute the following commands:
>
sudo
systemctl enable mysql>
sudo
systemctl start mysql>
sudo
mysql_secure_installation>
sudo
setup-sca -fThe mysql_secure_installation will create a MariaDB
root
password.
This way of setting up the appliance requires manual interaction when typing the SSH password.
On the machine on which to install the appliance, log in to a console.
Execute the following commands:
>
sudo
zypper install sca-appliance-* sca-patterns-*>
sudo
systemctl enable apache2>
sudo
systemctl start apache2>
sudo
sudo systemctl enable mysql>
sudo
systemctl start mysql>
sudo
mysql_secure_installation>
sudo
setup-sca
39.4.2.2 Prerequisites #
To run an SCA appliance server, you need the following prerequisites:
All
sca-appliance-*
packages.The
sca-patterns-base
package. Additionally, any of the product-specificsca-patterns-*
for the type of Supportconfig archives that you want to analyze with the appliance.Apache
PHP
MariaDB
anonymous FTP server (optional)
39.4.2.3 Installation and basic setup #
As listed in Section 39.4.2.2, “Prerequisites”, the SCA appliance has several dependencies on other packages. Therefore you need do so some preparations before installing and setting up the SCA appliance server:
For Apache and MariaDB, install the
Web
andLAMP
installation patterns.Set up Apache, MariaDB, and optionally an anonymous FTP server. For more information, see Chapter 34, The Apache HTTP server and Chapter 35, Setting up an FTP server with YaST.
Configure Apache and MariaDB to start at boot time:
>
sudo
systemctl enable apache2 mysqlStart both services:
>
sudo
systemctl start apache2 mysql
Now you can install the SCA appliance and set it up as described in Procedure 39.5, “Installing and configuring the SCA appliance”.
After installing the packages, use the setup-sca
script for the basic configuration of the MariaDB administration and
report database that is used by the SCA appliance.
It can be used to configure the following options you have for uploading the Supportconfig archives from your machines to the SCA appliance:
scp
anonymous FTP server
Install the appliance and the SCA base-pattern library:
>
sudo
zypper install sca-appliance-* sca-patterns-baseAdditionally, install the pattern packages for the types of Supportconfig archives you want to analyze. For example, if you have SUSE Linux Enterprise Server 12 and SUSE Linux Enterprise Server 15 servers in your environment, install both the
sca-patterns-sle12
andsca-patterns-sle15
packages.To install all available patterns:
>
sudo
zypper install sca-patterns-*For basic setup of the SCA appliance, use the
setup-sca
script. How to call it depends on how you want to upload the Supportconfig archives to the SCA appliance server:If you have configured an anonymous FTP server that uses the
/srv/ftp/upload
directory, execute the setup script with the-f
option. Follow the instructions on the screen:>
sudo
setup-sca -fNote: FTP server using another directoryIf your FTP server uses another directory than
/srv/ftp/upload
, adjust the following configuration files first to make them point to the correct directory:/etc/sca/sdagent.conf
and/etc/sca/sdbroker.conf
.If you want to upload Supportconfig files to the
/tmp
directory of the SCA appliance server viascp
, call the setup script without any parameters. Follow the instructions on the screen:>
sudo
setup-sca
The setup script runs a few checks regarding its requirements and configures the needed components. It will prompt you for two passwords: the MySQL
root
password of the MariaDB that you have set up, and a Web user password with which to log in to the Web interface of the SCA appliance.Enter the existing MariaDB
root
password. It will allow the SCA appliance to connect to the MariaDB.Define a password for the Web user. It will be written to
/srv/www/htdocs/sca/web-config.php
and will be set as the password for the userscdiag
. Both user name and password can be changed at any time later, see Section 39.4.2.5.1, “Password for the Web interface”.
After successful installation and setup, the SCA appliance is ready for use, see Section 39.4.2.4, “Using the SCA appliance”. However, you should modify some options such as changing the password for the Web interface, changing the source for the SCA pattern updates, enabling archiving mode or configuring e-mail notifications. For details on that, see Section 39.4.2.5, “Customizing the SCA appliance”.
As the reports on the SCA appliance server contain security-relevant information, make sure to protect the data on the SCA appliance server against unauthorized access.
39.4.2.4 Using the SCA appliance #
You can upload existing Supportconfig archives to the SCA appliance manually or create new Supportconfig archives and upload them to the SCA appliance in one step. Uploading can be done via FTP or SCP. For both, you need to know the URL where the SCA appliance can be reached. For upload via FTP, an FTP server needs to be configured for the SCA appliance, see Procedure 39.5, “Installing and configuring the SCA appliance”.
39.4.2.4.1 Uploading supportconfig archives to the SCA appliance #
For creating a Supportconfig archive and uploading it via (anonymous) FTP:
>
sudo
supportconfig -U “ftp://SCA-APPLIANCE.COMPANY.COM/upload”For creating a Supportconfig archive and uploading it via SCP:
>
sudo
supportconfig -U “scp://SCA-APPLIANCE.COMPANY.COM/tmp”You will be prompted for the
root
user password of the server running the SCA appliance.If you want to manually upload one or multiple archives, copy the existing archive files (usually located at
/var/log/scc_*.tbz
) to the SCA appliance. As target, use either the appliance server's/tmp
directory or the/srv/ftp/upload
directory (if FTP is configured for the SCA appliance server).
39.4.2.4.2 Viewing SCA reports #
SCA reports can be viewed from any machine that has a browser installed and can access the report index page of the SCA appliance.
Start a Web browser and make sure that JavaScript and cookies are enabled.
As a URL, enter the report index page of the SCA appliance.
https://sca-appliance.company.com/sca
If in doubt, ask your system administrator.
You will be prompted for a user name and a password to log in.
Figure 39.2: HTML report generated by SCA appliance #After logging in, click the date of the report you want to read.
Click the
category first to expand it.In the
column, click an individual entry. This opens the corresponding article in the SUSE Knowledge base. Read the proposed solution and follow the instructions.If the
column of the shows any additional entries, click them. Read the proposed solution and follow the instructions.Check the SUSE Knowledge base (https://www.suse.com/support/kb/) for results that directly relate to the problem identified by SCA. Work at resolving them.
Check for results that can be addressed proactively to avoid future problems.
39.4.2.5 Customizing the SCA appliance #
The following sections show how to change the password for the Web interface, how to change the source for the SCA pattern updates, how to enable archiving mode, and how to configure e-mail notifications.
39.4.2.5.1 Password for the Web interface #
The SCA Appliance Web interface requires a user name and password for
logging in. The default user name is scdiag
and the
default password is linux
(if not specified otherwise,
see Procedure 39.5, “Installing and configuring the SCA appliance”). Change the default password
to a secure password at the earliest possibility. You can also modify the
user name.
Log in as
root
user at the system console of the SCA appliance server.Open
/srv/www/htdocs/sca/web-config.php
in an editor.Change the values of
$username
and$password
as desired.Save the file and exit.
39.4.2.5.2 Updates of SCA patterns #
By default, all sca-patterns-*
packages are updated regularly by a root
cron job that executes the
sdagent-patterns
script nightly, which in turn runs
zypper update sca-patterns-*
. A regular system update
will update all SCA appliance and pattern packages. To update the SCA
appliance and patterns manually, run:
>
sudo
zypper update sca-*
The updates are installed from the SUSE Linux Enterprise 15 SP3 update
repository by default. You can change the source for the updates to an
RMT server, if desired. When sdagent-patterns
runs
zypper update sca-patterns-*
, it gets the updates from
the currently configured update channel. If that channel is located on an
RMT server, the packages will be pulled from there.
Log in as
root
user at the system console of the SCA appliance server.Open
/etc/sca/sdagent-patterns.conf
in an editor.Change the entry
UPDATE_FROM_PATTERN_REPO=1
to
UPDATE_FROM_PATTERN_REPO=0
Save the file and exit. The machine does not require any restart to apply the change.
39.4.2.5.3 Archiving mode #
All Supportconfig archives are deleted from the SCA appliance after they have been analyzed and their results have been stored in the MariaDB database. However, for troubleshooting purposes it can be useful to keep copies of Supportconfig archives from a machine. By default, archiving mode is disabled.
Log in as
root
user at the system console of the SCA appliance server.Open
/etc/sca/sdagent.conf
in an editor.Change the entry
ARCHIVE_MODE=0
to
ARCHIVE_MODE=1
Save the file and exit. The machine does not require any restart to apply the change.
After having enabled archive mode, the SCA appliance will save the
Supportconfig files to the /var/log/archives/saved
directory, instead of deleting them.
39.4.2.5.4 Sending SCA reports via e-mail #
The SCA appliance can e-mail a report HTML file for each Supportconfig
analyzed. This feature is disabled by default. When enabling it, you can
define a list of e-mail addresses to which the reports should be sent.
Define a level of status messages that trigger the sending of reports
(STATUS_NOTIFY_LEVEL
).
STATUS_NOTIFY_LEVEL
#- $STATUS_OFF
Deactivate sending of HTML reports.
- $STATUS_CRITICAL
Send only SCA reports that include a CRITICAL.
- $STATUS_WARNING
Send only SCA reports that include a WARNING or CRITICAL.
- $STATUS_RECOMMEND
Send only SCA reports that include a RECOMMEND, WARNING or CRITICAL.
- $STATUS_SUCCESS
Send SCA reports that include a SUCCESS, RECOMMEND, WARNING or CRITICAL.
Log in as
root
user at the system console of the SCA appliance server.Open
/etc/sca/sdagent.conf
in an editor.Search for the entry
STATUS_NOTIFY_LEVEL
. By default, it is set to$STATUS_OFF
(e-mail notifications are disabled).To enable e-mail notifications, change
$STATUS_OFF
to the level of status messages that you want to have e-mail reports for, for example:STATUS_NOTIFY_LEVEL=$STATUS_SUCCESS
For details, see Possible values for
STATUS_NOTIFY_LEVEL
.To define the list of recipients to which the reports should be sent:
Search for the entry
EMAIL_REPORT='root'
.Replace
root
with a list of e-mail addresses to which SCA reports should be sent. The e-mail addresses must be separated by spaces. For example:EMAIL_REPORT='tux@my.company.com wilber@your.company.com'
Save the file and exit. The machine does not require any restart to apply the changes. All future SCA reports will be e-mailed to the specified addresses.
39.4.2.6 Backing up and restoring the database #
To back up and restore the MariaDB database that stores the SCA reports,
use the scadb
command as described
below. scadb
is provided by the package
sca-appliance-broker.
Log in as
root
user at the system console of the server running the SCA appliance.Put the appliance into maintenance mode by executing:
#
scadb maintStart the backup with:
#
scadb backupThe data is saved to a TAR archive:
sca-backup-*sql.gz
.If you are using the pattern creation database to develop your own patterns (see Section 39.4.3, “Developing custom analysis patterns”), back up this data, too:
#
sdpdb backupThe data is saved to a TAR archive:
sdp-backup-*sql.gz
.Copy the following data to another machine or an external storage medium:
sca-backup-*sql.gz
sdp-backup-*sql.gz
/usr/lib/sca/patterns/local
(only needed if you have created custom patterns)
Reactivate the SCA appliance with:
#
scadb reset agents
To restore the database from your backup, proceed as follows:
Log in as
root
user at the system console of the server running the SCA appliance.Copy the newest
sca-backup-*sql.gz
andsdp-backup-*sql.gz
TAR archives to the SCA appliance server.To decompress the files, run:
#
gzip -d *-backup-*sql.gzTo import the data into the database, execute:
#
scadb import sca-backup-*sqlIf you are using the pattern creation database to create your own patterns, also import the following data with:
#
sdpdb import sdp-backup-*sqlIf you are using custom patterns, also restore
/usr/lib/sca/patterns/local
from your backup data.Reactivate the SCA appliance with:
#
scadb reset agentsUpdate the pattern modules in the database with:
#
sdagent-patterns -u
39.4.3 Developing custom analysis patterns #
The SCA appliance comes with a complete pattern development environment
(the SCA Pattern Database) that enables you to develop your own, custom
patterns. Patterns can be written in any programming language. To make them
available for the Supportconfig analysis process, they need to be saved to
/usr/lib/sca/patterns/local
and to be made executable.
Both the SCA appliance and the SCA tool will then run the custom patterns
against new Supportconfig archives as part of the analysis report. For
detailed instructions on how to create (and test) your own patterns, see
https://www.suse.com/c/blog/sca-pattern-development/.
39.5 Gathering information during the installation #
During the installation, supportconfig
is not available.
However, you can collect log files from YaST by using
save_y2logs
. This command will create a
.tar.xz
archive in the directory
/tmp
.
If issues appear very early during installation, you may be able to gather
information from the log file created by
linuxrc
. linuxrc
is a small command
that runs before YaST starts. This log file is available at
/var/log/linuxrc.log
.
The log files available during the installation are not available in the installed system anymore. Properly save the installation log files while the installer is still running.
39.6 Support of kernel modules #
An important requirement for every enterprise operating system is the level
of support you receive for your environment. Kernel modules are the most
relevant connector between hardware (“controllers”) and the
operating system. Every kernel module in SUSE Linux Enterprise has a
supported
flag that can take three possible values:
“yes”, thus
supported
“external”, thus
supported
“(empty, not set)”, thus
unsupported
The following rules apply:
All modules of a self-recompiled kernel are by default marked as unsupported.
Kernel modules supported by SUSE partners and delivered using
SUSE SolidDriver Program
are marked “external”.If the
supported
flag is not set, loading this module will taint the kernel. Tainted kernels are not supported. Unsupported Kernel modules are included in an extra RPM package (kernel-FLAVOR-extra
). That package is only available for SUSE Linux Enterprise Desktop and the SUSE Linux Enterprise Workstation Extension. Those kernels will not be loaded by default (FLAVOR=default
|xen
|...). In addition, these unsupported modules are not available in the installer, and thekernel-FLAVOR-extra
package is not part of the SUSE Linux Enterprise media.Kernel modules not provided under a license compatible to the license of the Linux kernel also taint the kernel. For details, see the state of
/proc/sys/kernel/tainted
.
39.6.1 Technical background #
Linux kernel: The value of
/proc/sys/kernel/unsupported
defaults to2
on SUSE Linux Enterprise 15 SP3 (do not warn in syslog when loading unsupported modules
). This default is used in the installer and in the installed system.modprobe
: Themodprobe
utility for checking module dependencies and loading modules appropriately checks for the value of thesupported
flag. If the value is “yes” or “external” the module will be loaded, otherwise it will not. For information on how to override this behavior, see Section 39.6.2, “Working with unsupported modules”.Note: SupportSUSE does not generally support the removal of storage modules via
modprobe -r
.
39.6.2 Working with unsupported modules #
While general supportability is important, situations can occur where loading an unsupported module is required. For example, for testing or debugging purposes, or if your hardware vendor provides a hotfix.
To override the default, edit
/etc/modprobe.d/10-unsupported-modules.conf
and change the value of the variableallow_unsupported_modules
to1
. If an unsupported module is needed in the initrd, do not forget to rundracut
-f
to update the initrd.If you only want to try loading a module once, you can use the
--allow-unsupported-modules
option withmodprobe
. For more information, see themodprobe
man page.During installation, unsupported modules may be added through driver update disks, and they will be loaded. To enforce loading of unsupported modules during boot and afterward, use the kernel command line option
oem-modules
. While installing and initializing thesuse-module-tools
package, the kernel flagTAINT_NO_SUPPORT
(/proc/sys/kernel/tainted
) will be evaluated. If the kernel is already tainted,allow_unsupported_modules
will be enabled. This will prevent unsupported modules from failing in the system being installed. If no unsupported modules are present during installation and the other special kernel command line option (oem-modules=1
) is not used, the default still is to disallow unsupported modules.
Remember that loading and running unsupported modules will make the kernel and the whole system unsupported by SUSE.
39.7 More information #
man supportconfig
—Thesupportconfig
man page.man supportconfig.conf
—The man page of the Supportconfig configuration file.man scatool
—Thescatool
man page.man scadb
—Thescadb
man page.man setup-sca
—Thesetup-sca
man page.https://mariadb.com/kb/en/—The MariaDB documentation.
http://httpd.apache.org/docs/ and Chapter 34, The Apache HTTP server—Documentation about the Apache Web server.
Chapter 35, Setting up an FTP server with YaST—Documentation of how to set up an FTP server.
https://www.suse.com/c/blog/sca-pattern-development/—Instructions on how to create (and test) your own SCA patterns.
https://www.suse.com/c/blog/basic-server-health-check-supportconfig/—A Basic Server Health Check with Supportconfig.
https://community.microfocus.com/img/gw/groupwise/w/groupwise/34308/create-your-own-supportconfig-plugin—Create Your Own Supportconfig Plugin.
https://www.suse.com/c/blog/creating-a-central-supportconfig-repository/—Creating a Central Supportconfig Repository.
40 Common problems and their solutions #
This chapter describes a range of potential problems and their solutions. Even if your situation is not precisely listed, there may be one similar enough to offer hints to the solution of your problem.
40.1 Finding and gathering information #
Linux reports things in a very detailed way. There are several places to look when you encounter problems with your system, most of which are standard to Linux systems in general, and some are relevant to SUSE Linux Enterprise Server systems. Most log files can be viewed with YaST ( › ).
YaST offers the possibility to collect all system information needed by the support team. Use
› and select the problem category. When all information is gathered, attach it to your support request.
A list of the most frequently checked log files follows with the description
of their typical purpose. Paths containing ~
refer to
the current user's home directory.
Log File |
Description |
---|---|
|
Messages from the desktop applications currently running. |
|
Log files from AppArmor, see Book “Security and Hardening Guide” for detailed information. |
|
Log file from Audit to track any access to files, directories, or resources of your system, and trace system calls. See Book “Security and Hardening Guide” for detailed information. |
|
Messages from the mail system. |
|
Log file from NetworkManager to collect problems with network connectivity |
|
Directory containing Samba server and client log messages. |
|
All messages from the kernel and system log daemon with the “warning” level or higher. |
|
Binary file containing user login records for the current
machine session. View it with |
|
Start-up and runtime log files from the X Window System. It is useful for debugging failed X start-ups. |
|
Directory containing YaST's actions and their results. |
|
Log file of Zypper. |
Apart from log files, your machine also supplies you with information about
the running system. See
Table 40.2: System information with the /proc
file system
/proc
file system #
File |
Description |
---|---|
|
Contains processor information, including its type, make, model, and performance. |
|
Shows which DMA channels are currently being used. |
|
Shows which interrupts are in use, and how many of each have been in use. |
|
Displays the status of I/O (input/output) memory. |
|
Shows which I/O ports are in use at the moment. |
|
Displays memory status. |
|
Displays the individual modules. |
|
Displays devices currently mounted. |
|
Shows the partitioning of all hard disks. |
|
Displays the current version of Linux. |
Apart from the /proc
file system, the Linux kernel
exports information with the sysfs
module, an in-memory
file system. This module represents kernel objects, their attributes and
relationships. For more information about sysfs
, see the
context of udev in Chapter 24, Dynamic kernel device management with udev
.
Table 40.3 contains
an overview of the most common directories under /sys
.
/sys
file system #
File |
Description |
---|---|
|
Contains subdirectories for each block device discovered in the system. Generally, these are mostly disk type devices. |
|
Contains subdirectories for each physical bus type. |
|
Contains subdirectories grouped together as a functional types of devices (like graphics, net, printer, etc.) |
|
Contains the global device hierarchy. |
Linux comes with several tools for system analysis and monitoring. See Book “System Analysis and Tuning Guide”, Chapter 2 “System monitoring utilities” for a selection of the most important ones used in system diagnostics.
Each of the following scenarios begins with a header describing the problem followed by a paragraph or two offering suggested solutions, available references for more detailed solutions, and cross-references to other scenarios that are related.
40.2 Boot problems #
Boot problems are situations when your system does not boot properly (does not boot to the expected target and login screen).
40.2.1 The GRUB 2 boot loader fails to load #
If the hardware is functioning properly, it is possible that the boot loader is corrupted and Linux cannot start on the machine. In this case, it is necessary to repair the boot loader. To do so, you need to start the Rescue System as described in Section 40.5.2, “Using the rescue system” and follow the instructions in Section 40.5.2.4, “Modifying and re-installing the boot loader”.
Alternatively, you can use the Rescue System to fix the boot loader as follows. Boot your machine from the installation media. In the boot screen, choose
› . Select the disk containing the installed system and kernel with the default kernel options.When the system is booted, start YaST and switch to
› . Make sure that the option is enabled, and click . This fixes the corrupted boot loader by overwriting it, or installs the boot loader if it is missing.Other reasons for the machine not booting may be BIOS-related:
- BIOS settings
Check your BIOS for references to your hard disk. GRUB 2 may simply not be started if the hard disk itself cannot be found with the current BIOS settings.
- BIOS boot order
Check whether your system's boot order includes the hard disk. If the hard disk option was not enabled, your system may install properly, but fails to boot when access to the hard disk is required.
40.2.2 No graphical login #
If the machine starts, but does not boot into the graphical login
manager, anticipate problems either with the choice of the default systemd
target or the configuration of the X Window System. To check the current
systemd default target run the command sudo systemctl
get-default
. If the value returned is not
graphical.target
, run the command sudo
systemctl isolate graphical.target
. If the graphical login screen
starts, log in and start › ›
and set the to . From now on the system should boot into the graphical
login screen.
If the graphical login screen does not start even if having booted or
switched to the graphical target, your desktop or X Window software is
probably misconfigured or corrupted. Examine the log files at
/var/log/Xorg.*.log
for detailed messages from the X
server as it attempted to start. If the desktop fails during start, it may
log error messages to the system journal that can be queried with the
command journalctl
(see Chapter 17, journalctl
: Query the systemd
journal
for more information). If these error messages hint at a configuration
problem in the X server, try to fix these issues. If the graphical system
still does not come up, consider reinstalling the graphical desktop.
40.2.3 Root Btrfs partition cannot be mounted #
If a btrfs
root partition
becomes corrupted, try the following options:
Mount the partition with the
-o recovery
option.If that fails, run
btrfs-zero-log
on your root partition.
40.2.4 Force checking root partitions #
If the root partition becomes corrupted, use the parameter
forcefsck on the boot prompt. This passes the option
-f
(force) to the fsck
command.
40.2.5 Disable swap to enable booting #
When a swap device is not available and the system cannot enable it during boot, booting may fail. Try disabling all swap devices by appending the following options to the kernel command line:
systemd.device_wants_unit=off systemd.mask=swap.target
You may also try disabling specific swap devices:
systemd.mask=dev-sda1.swap
40.2.6 GRUB 2 fails during reboot on a dual-boot system #
If GRUB 2 fails during reboot, disable the
Fast Boot
setting in the BIOS.
40.3 Login problems #
Login problems occur when your system refuses to accept the user name and password, or accepts them but then fails to start the graphic desktop, produces errors, or drops to a command line, for example.
40.3.1 Valid user name and password combinations fail #
This often occurs when the system is configured to use network
authentication or directory services and cannot retrieve results from
its configured servers. The root
user is the only local user that
can still log in to these machines. The following
are common reasons a machine appears functional but cannot process
logins correctly:
The network is not working. For further directions on this, turn to Section 40.4, “Network problems”.
DNS is not working at the moment (which prevents GNOME from working and the system from making validated requests to secure servers). One indication that this is the case is that the machine takes a long time to respond to any action. Find more information about this topic in Section 40.4, “Network problems”.
If the system is configured to use Kerberos, the system's local time may have drifted past the accepted variance with the Kerberos server time (this is typically 300 seconds). If NTP (network time protocol) is not working properly or local NTP servers are not working, Kerberos authentication ceases to function because it depends on common clock synchronization across the network.
The system's authentication configuration is misconfigured. Check the PAM configuration files involved for any typographical errors or misordering of directives. For additional background information about PAM and the syntax of the configuration files involved, refer to Book “Security and Hardening Guide”, Chapter 2 “Authentication with PAM”.
The home partition is encrypted. Find more information about this topic in Section 40.3.3, “Login to encrypted home partition fails”.
In cases that do not involve external network problems, the solution is
to log in as root
and repair the configuration. If you cannot log
in to the running system, reboot it into the rescue mode as outlined in
Procedure 14.3, “Entering rescue mode”.
40.3.2 Valid user name and password not accepted #
This is by far the most common problem users encounter, because there are many reasons this can occur. Depending on whether you use local user management and authentication or network authentication, login failures occur for different reasons.
Local user management can fail for the following reasons:
The user may have entered the wrong password.
The user's home directory containing the desktop configuration files is corrupted or write protected.
There may be problems with the X Window System authenticating this particular user, especially if the user's home directory has been used with another Linux distribution before installing the current one.
To locate the reason for a local login failure, proceed as follows:
Check whether the user remembered their password correctly before you start debugging the whole authentication mechanism. If the user may have not have remembered their password correctly, use the YaST User Management module to change the user's password. Pay attention to the Caps Lock key and unlock it, if necessary.
Log in as
root
and check the system journal withjournalctl -e
for error messages of the login process and of PAM.Try to log in from a console (using Ctrl–Alt–F1). If this is successful, the blame cannot be put on PAM, because it is possible to authenticate this user on this machine. Try to locate any problems with the X Window System or the GNOME desktop. For more information, refer to Section 40.3.4, “GNOME desktop has issues”.
If the user's home directory has been used with another Linux distribution, remove the
Xauthority
file in the user's home. Use a console login via Ctrl–Alt–F1 and runrm .Xauthority
as this user. This should eliminate X authentication problems for this user. Try graphical login again.If the desktop could not start because of corrupt configuration files, proceed with Section 40.3.4, “GNOME desktop has issues”.
In the following, common reasons a network authentication for a particular user may fail on a specific machine are listed:
The user may have entered the wrong password.
The user name exists in the machine's local authentication files and is also provided by a network authentication system, causing conflicts.
The home directory exists but is corrupt or unavailable. Perhaps it is write protected or is on a server that is inaccessible at the moment.
The user does not have permission to log in to that particular host in the authentication system.
The machine has changed host names, for whatever reason, and the user does not have permission to log in to that host.
The machine cannot reach the authentication server or directory server that contains that user's information.
There may be problems with the X Window System authenticating this particular user, especially if the user's home has been used with another Linux distribution before installing the current one.
To locate the cause of the login failures with network authentication, proceed as follows:
Check whether the user remembered their password correctly before you start debugging the whole authentication mechanism.
Determine the directory server which the machine relies on for authentication and make sure that it is up and running and properly communicating with the other machines.
Determine that the user's user name and password work on other machines to make sure that their authentication data exists and is properly distributed.
See if another user can log in to the misbehaving machine. If another user can log in without difficulty or if
root
can log in, log in and examine the system journal with thejournalctl -e
> file. Locate the time stamps that correspond to the login attempts and determine if PAM has produced any error messages.Try to log in from a console (using Ctrl–Alt–F1). If this is successful, the problem is not with PAM or the directory server on which the user's home is hosted, because it is possible to authenticate this user on this machine. Try to locate any problems with the X Window System or the GNOME desktop. For more information, refer to Section 40.3.4, “GNOME desktop has issues”.
If the user's home directory has been used with another Linux distribution, remove the
Xauthority
file in the user's home. Use a console login via Ctrl–Alt–F1 and runrm .Xauthority
as this user. This should eliminate X authentication problems for this user. Try graphical login again.If the desktop could not start because of corrupt configuration files, proceed with Section 40.3.4, “GNOME desktop has issues”.
40.3.3 Login to encrypted home partition fails #
It is recommended to use an encrypted home partition for laptops. If you cannot log in to your laptop, the reason might be that your partition could not be unlocked.
During the boot time, you need to enter the passphrase to unlock your encrypted partition. If you do not enter it, the boot process continues, leaving the partition locked.
To unlock your encrypted partition, proceed as follows:
Switch to the text console with Ctrl–Alt–F1.
Become
root
.Restart the unlocking process again with:
#
systemctl restart home.mountEnter your passphrase to unlock your encrypted partition.
Exit the text console and switch back to the login screen with Alt–F7.
Log in as usual.
40.3.4 GNOME desktop has issues #
If you are experiencing issues with the GNOME desktop, there are several ways to troubleshoot the misbehaving graphical desktop environment. The recommended procedure described below offers the safest option to fix a broken GNOME desktop.
Launch YaST and switch to
.Open the
dialog and click .Fill out the required fields and click
to create a new user.Log out and log in as the new user. This gives you a fresh GNOME environment.
Copy individual subdirectories from the
~/.local/
and~/.config/
directories of the old user account to the respective directories of the new user account.Log out and log in again as the new user after every copy operation to check whether GNOME still works correctly.
Repeat the previous step until you find the configuration file that breaks GNOME.
Log in as the old user, and move the offending configuration file to a different location. Log out and log in again as the old user.
Delete the previously created user.
40.4 Network problems #
Many problems of your system may be network-related, even though they do not seem to be at first. For example, the reason for a system not allowing users to log in may be a network problem of some kind. This section introduces a simple checklist you can apply to identify the cause of any network problem encountered.
When checking the network connection of your machine, proceed as follows:
If you use an Ethernet connection, check the hardware first. Make sure that your network cable is properly plugged into your computer and router (or hub, etc.). The control lights next to your Ethernet connector are normally both be active.
If the connection fails, check whether your network cable works with another machine. If it does, your network card causes the failure. If hubs or switches are included in your network setup, they may be faulty, as well.
If using a wireless connection, check whether the wireless link can be established by other machines. If not, contact the wireless network's administrator.
When you have checked your basic network connectivity, try to find out which service is not responding. Gather the address information of all network servers needed in your setup. Either look them up in the appropriate YaST module or ask your system administrator. The following list gives some typical network servers involved in a setup together with the symptoms of an outage.
- DNS (name service)
A broken or malfunctioning name service affects the network's functionality in many ways. If the local machine relies on any network servers for authentication and these servers cannot be found because of name resolution issues, users would not even be able to log in. Machines in the network managed by a broken name server would not be able to “see” each other and communicate.
- NTP (time service)
A malfunctioning or completely broken NTP service could affect Kerberos authentication and X server functionality.
- NFS (file service)
If any application needs data stored in an NFS mounted directory, it cannot start or function properly if this service was down or misconfigured. In the worst case scenario, a user's personal desktop configuration would not come up if their home directory containing the
.gconf
subdirectory could not be found because of a faulty NFS server.- Samba (file service)
If any application needs data stored in a directory on a faulty Samba server, it cannot start or function properly.
- NIS (user management)
If your SUSE Linux Enterprise Server system relies on a faulty NIS server to provide the user data, users cannot log in to this machine.
- LDAP (user management)
If your SUSE Linux Enterprise Server system relies on a faulty LDAP server to provide the user data, users cannot log in to this machine.
- Kerberos (authentication)
Authentication will not work and login to any machine fails.
- CUPS (network printing)
Users cannot print.
Check whether the network servers are running and whether your network setup allows you to establish a connection:
Important: LimitationsThe debugging procedure described below only applies to a simple network server/client setup that does not involve any internal routing. It assumes both server and client are members of the same subnet without the need for additional routing.
Use
ping
IP_ADDRESS/HOSTNAME (replace with the host name or IP address of the server) to check whether each one of them is up and responding to the network. If this command is successful, it tells you that the host you were looking for is up and running and that the name service for your network is configured correctly.If ping fails with
destination host unreachable
, either your system or the desired server is not properly configured or down. Check whether your system is reachable by runningping
IP address or YOUR_HOSTNAME from another machine. If you can reach your machine from another machine, it is the server that is not running or not configured correctly.If ping fails with
unknown host
, the name service is not configured correctly or the host name used was incorrect. For further checks on this matter, refer to Step 4.b. If ping still fails, either your network card is not configured correctly or your network hardware is faulty.Use
host
HOSTNAME to check whether the host name of the server you are trying to connect to is properly translated into an IP address and vice versa. If this command returns the IP address of this host, the name service is up and running. If thehost
command fails, check all network configuration files relating to name and address resolution on your host:/var/run/netconfig/resolv.conf
This file is used to keep track of the name server and domain you are currently using. It is a symbolic link to
/run/netconfig/resolv.conf
and is usually automatically adjusted by YaST or DHCP. Make sure that this file has the following structure and all network addresses and domain names are correct:search FULLY_QUALIFIED_DOMAIN_NAME nameserver IPADDRESS_OF_NAMESERVER
This file can contain more than one name server address, but at least one of them must be correct to provide name resolution to your host. If needed, adjust this file using the YaST Network Settings module (Hostname/DNS tab).
If your network connection is handled via DHCP, enable DHCP to change host name and name service information by selecting
(can be set globally for any interface or per interface) and in the YaST Network Settings module (Hostname/DNS tab)./etc/nsswitch.conf
This file tells Linux where to look for name service information. It should look like this:
... hosts: files dns networks: files dns ...
The
dns
entry is vital. It tells Linux to use an external name server. Normally, these entries are automatically managed by YaST, but it would be prudent to check.If all the relevant entries on the host are correct, let your system administrator check the DNS server configuration for the correct zone information. For detailed information about DNS, refer to Chapter 31, The domain name system. If you have made sure that the DNS configuration of your host and the DNS server are correct, proceed with checking the configuration of your network and network device.
If your system cannot establish a connection to a network server and you have excluded name service problems from the list of possible culprits, check the configuration of your network card.
Use the command
ip addr show
NETWORK_DEVICE to check whether this device was properly configured. Make sure that theinet address
with the netmask (/MASK
) is configured correctly. An error in the IP address or a missing bit in your network mask would render your network configuration unusable. If necessary, perform this check on the server as well.If the name service and network hardware are properly configured and running, but certain external network connections still get long timeouts or fail entirely, use
traceroute
FULLY_QUALIFIED_DOMAIN_NAME (executed asroot
) to track the network route these requests are taking. This command lists any gateway (hop) that a request from your machine passes on its way to its destination. It lists the response time of each hop and whether this hop is reachable. Use a combination of traceroute and ping to track down the culprit and let the administrators know.
When you have identified the cause of your network trouble, you can resolve it yourself (if the problem is located on your machine) or let the system administrators of your network know about your findings so they can reconfigure the services or repair the necessary systems.
40.4.1 NetworkManager problems #
If you have a problem with network connectivity, narrow it down as described in Procedure 40.2, “How to identify network problems”. If NetworkManager seems to be the culprit, proceed as follows to get logs providing hints on why NetworkManager fails:
Open a shell and log in as
root
.Restart the NetworkManager:
>
sudo
systemctl restart NetworkManagerOpen a Web page, for example, http://www.opensuse.org as normal user to see, if you can connect.
Collect any information about the state of NetworkManager in
/var/log/NetworkManager
.
For more information about NetworkManager, refer to Chapter 26, Using NetworkManager.
40.5 Data problems #
Data problems are when the machine may or may not boot properly but, in either case, it is clear that there is data corruption on the system and that the system needs to be recovered. These situations call for a backup of your critical data, enabling you to recover the system state from before your system failed.
40.5.1 Managing partition images #
Sometimes you need to perform a backup from an entire partition or even
hard disk. Linux comes with the dd
tool which can create
an exact copy of your disk. Combined with gzip
you save
some space.
Start a Shell as user
root
.Select your source device. Typically this is something like
/dev/sda
(labeled as SOURCE).Decide where you want to store your image (labeled as BACKUP_PATH). It must be different from your source device. In other words: if you make a backup from
/dev/sda
, your image file must not to be stored under/dev/sda
.Run the commands to create a compressed image file:
#
dd if=/dev/SOURCE | gzip > /BACKUP_PATH/image.gzRestore the hard disk with the following commands:
#
gzip -dc /BACKUP_PATH/image.gz | dd of=/dev/SOURCE
If you only need to back up a partition, replace the SOURCE placeholder with your respective partition. In this case, your image file can lie on the same hard disk, but on a different partition.
40.5.2 Using the rescue system #
There are several reasons a system could fail to come up and run properly. A corrupted file system following a system crash, corrupted configuration files, or a corrupted boot loader configuration are the most common ones.
To help you to resolve these situations, SUSE Linux Enterprise Server contains a rescue system that you can boot. The rescue system is a small Linux system that can be loaded into a RAM disk and mounted as root file system, allowing you to access your Linux partitions from the outside. Using the rescue system, you can recover or modify any important aspect of your system.
Manipulate any type of configuration file.
Check the file system for defects and start automatic repair processes.
Access the installed system in a “change root” environment.
Check, modify, and re-install the boot loader configuration.
Recover from a badly installed device driver or unusable kernel.
Resize partitions using the parted command. Find more information about this tool at the GNU Parted Web site http://www.gnu.org/software/parted/parted.html.
The rescue system can be loaded from various sources and locations. The simplest option is to boot the rescue system from the original installation medium.
On IBM Z the installation system can be used for rescue purposes. To start the rescue system follow the instructions in Section 40.6, “IBM Z: using initrd as a rescue system”.
Insert the installation medium into your DVD drive.
Reboot the system.
At the boot screen, press F4 and choose . Then choose from the main menu.
Enter
root
at theRescue:
prompt. A password is not required.
If your hardware setup does not include a DVD drive, you can boot the rescue
system from a network source. The following example applies to a remote boot
scenario—if using another boot medium, such as a DVD, modify the
info
file accordingly and boot as you would for a
normal installation.
Enter the configuration of your PXE boot setup and add the lines
install=PROTOCOL://INSTSOURCE
andrescue=1
. If you need to start the repair system, userepair=1
instead. As with a normal installation, PROTOCOL stands for any of the supported network protocols (NFS, HTTP, FTP, etc.) and INSTSOURCE for the path to your network installation source.Boot the system using “Wake on LAN”, as described in Book “Deployment Guide”, Chapter 17 “Preparing network boot environment”, Section 17.5 “Using wake-on-LAN for remote wakeups”.
Enter
root
at theRescue:
prompt. A password is not required.
When you have entered the rescue system, you can use the virtual consoles that can be reached with Alt–F1 to Alt–F6.
A shell and other useful utilities, such as the mount program, are
available in the /bin
directory. The
/sbin
directory contains important file and network
utilities for reviewing and repairing the file system. This directory also
contains the most important binaries for system maintenance, such as
fdisk
, mkfs
, mkswap
,
mount
, and shutdown
,
ip
and ss
for maintaining the network.
The directory /usr/bin
contains the vi editor, find,
less, and SSH.
To see the system messages, either use the command dmesg
or view the system log with journalctl
.
40.5.2.1 Checking and manipulating configuration files #
As an example for a configuration that might be fixed using the rescue system, imagine you have a broken configuration file that prevents the system from booting properly. You can fix this using the rescue system.
To manipulate a configuration file, proceed as follows:
Start the rescue system using one of the methods described above.
To mount a root file system located under
/dev/sda6
to the rescue system, use the following command:>
sudo
mount /dev/sda6 /mntAll directories of the system are now located under
/mnt
Change the directory to the mounted root file system:
>
sudo
cd /mntOpen the problematic configuration file in the vi editor. Adjust and save the configuration.
Unmount the root file system from the rescue system:
>
sudo
umount /mntReboot the machine.
40.5.2.2 Repairing and checking file systems #
Generally, file systems cannot be repaired on a running system. If you
encounter serious problems, you may not even be able to mount your root
file system and the system boot may end with a “kernel panic”.
In this case, the only way is to repair the system from the outside. The
system contains the fsck
utility to check and repair
multiple file system types, such as ext2
,
ext3
, ext4
, msdos
,
and vfat
. Use the -t
option to specify
which file system to check.
The following command checks all ext4
file systems found
in the /etc/fstab
specification:
>
sudo
fsck -t ext4 -A
For Btrfs, you can use the btrfs check
command found in
the btrfsprogs package.
Find topics about the Btrfs file system in the following places:
The Storage Administration Guide includes https://documentation.suse.com/sles/html/SLES-all/cha-filesystems.html#sec-filesystems-major-btrfs and https://documentation.suse.com/sles/15-SP5/html/SLES-all/cha-resize-fs.html#sec-resize-fs-btrfs sections.
The following article https://www.suse.com/support/kb/doc/?id=000018769 describes how to recover from Btrfs errors.
The following article includes links to multiple Btrfs related topics https://www.suse.com/support/kb/doc/?id=000018779.
The
man 8 btrfs-check
man page details all options of thebtrfs check
command.
40.5.2.3 Accessing the installed system #
If you need to access the installed system from the rescue system, you need to do this in a change root environment. For example, to modify the boot loader configuration, or to execute a hardware configuration utility.
To set up a change root environment based on the installed system, proceed as follows:
- Tip: Import LVM volume groups
If you are using an LVM setup (refer to Book “Storage Administration Guide” for more general details), import all existing volume groups to be able to find and mount the device(s):
root
vgimport -aRun
lsblk
to check which node corresponds to the root partition. It is/dev/sda2
in our example:>
lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 149,1G 0 disk ├─sda1 8:1 0 2G 0 part [SWAP] ├─sda2 8:2 0 20G 0 part / └─sda3 8:3 0 127G 0 part └─cr_home 254:0 0 127G 0 crypt /home Mount the root partition from the installed system:
>
sudo
mount /dev/sda2 /mntMount
/proc
,/dev
, and/sys
partitions:>
sudo
mount -t proc none /mnt/proc>
sudo
mount --rbind /dev /mnt/dev>
sudo
mount --rbind /sys /mnt/sysNow you can “change root” into the new environment, keeping the
bash
shell:>
chroot /mnt /bin/bashFinally, mount the remaining partitions from the installed system:
>
mount -aNow you have access to the installed system. Before rebooting the system, unmount the partitions with
umount
-a
and leave the “change root” environment withexit
.
Although you have full access to the files and applications of the
installed system, there are some limitations. The kernel that is running is
the one that was booted with the rescue system, not with the change root
environment. It only supports essential hardware and it is not possible to
add kernel modules from the installed system unless the kernel versions are
identical. Always check the version of the currently running (rescue)
kernel with uname -r
and then find out if a matching
subdirectory exists in the /lib/modules
directory in
the change root environment. If yes, you can use the installed modules,
otherwise you need to supply their correct versions on other media, such as
a flash disk. Most often the rescue kernel version differs from the
installed one — then you cannot simply access a sound card, for
example. It is also not possible to start a graphical user interface.
Also note that you leave the “change root” environment when you switch the console with Alt–F1 to Alt–F6.
40.5.2.4 Modifying and re-installing the boot loader #
Sometimes a system cannot boot because the boot loader configuration is corrupted. The start-up routines cannot, for example, translate physical drives to the actual locations in the Linux file system without a working boot loader.
To check the boot loader configuration and re-install the boot loader, proceed as follows:
Perform the necessary steps to access the installed system as described in Section 40.5.2.3, “Accessing the installed system”.
Check that the GRUB 2 boot loader is installed on the system. If not, install the package
grub2
and run>
sudo
grub2-install /dev/sdaCheck whether the following files are correctly configured according to the GRUB 2 configuration principles outlined in Chapter 14, The boot loader GRUB 2 and apply fixes if necessary.
/etc/default/grub
/boot/grub2/device.map
/boot/grub2/grub.cfg
(this file is generated, do not edit)/etc/sysconfig/bootloader
Re-install the boot loader using the following command sequence:
>
sudo
grub2-mkconfig -o /boot/grub2/grub.cfgUnmount the partitions, log out from the “change root” environment, and reboot the system:
>
umount -a exit reboot
40.5.2.5 Fixing kernel installation #
A kernel update may introduce a new bug which can impact the operation of your system. For example a driver for a piece of hardware in your system may be faulty, which prevents you from accessing and using it. In this case, revert to the last working kernel (if available on the system) or install the original kernel from the installation media.
To prevent failures to boot after a faulty kernel update, use the kernel
multiversion feature and tell libzypp
which
kernels you want to keep after the update.
For example to always keep the last two kernels and the currently running one, add
multiversion.kernels = latest,latest-1,running
to the /etc/zypp/zypp.conf
file. See
Book “Deployment Guide”, Chapter 23 “Installing multiple kernel versions” for more information.
A similar case is when you need to re-install or update a broken driver for a device not supported by SUSE Linux Enterprise Server. For example when a hardware vendor uses a specific device, such as a hardware RAID controller, which needs a binary driver to be recognized by the operating system. The vendor typically releases a Driver Update Disk (DUD) with the fixed or updated version of the required driver.
In both cases you need to access the installed system in the rescue mode and fix the kernel related problem, otherwise the system may fail to boot correctly:
Boot from the SUSE Linux Enterprise Server installation media.
If you are recovering after a faulty kernel update, skip this step. If you need to use a driver update disk (DUD), press F6 to load the driver update after the boot menu appears, and choose the path or URL to the driver update and confirm with .
Choose Enter. If you chose to use DUD, you will be asked to specify where the driver update is stored.
from the boot menu and pressEnter
root
at theRescue:
prompt. A password is not required.Manually mount the target system and “change root” into the new environment. For more information, see Section 40.5.2.3, “Accessing the installed system”.
If using DUD, install/re-install/update the faulty device driver package. Always make sure the installed kernel version exactly matches the version of the driver you are installing.
If fixing faulty kernel update installation, you can install the original kernel from the installation media with the following procedure.
Identify your DVD device with
hwinfo --cdrom
and mount it withmount /dev/sr0 /mnt
.Navigate to the directory where your kernel files are stored on the DVD, for example
cd /mnt/suse/x86_64/
.Install required
kernel-*
,kernel-*-base
, andkernel-*-extra
packages of your flavor with therpm -i
command.
Update configuration files and reinitialize the boot loader if needed. For more information, see Section 40.5.2.4, “Modifying and re-installing the boot loader”.
Remove any bootable media from the system drive and reboot.
40.6 IBM Z: using initrd as a rescue system #
If the kernel of the SUSE® Linux Enterprise Server for IBM Z is upgraded or modified, it is possible to reboot the system accidentally in an inconsistent state, so standard procedures of IPLing the installed system fail. In such a case, you may use the installation system for rescue purposes.
IPL the SUSE Linux Enterprise Server for IBM Z installation system as described in
Book “Deployment Guide”, Chapter 5 “Installation on IBM Z and LinuxONE”, Section 5.3 “Preparing for installation”. Choose and enter all required parameters. After the
installation system has loaded and you are asked which display type to use to
control the installation, select SSH
. Now you can log in
to the system with SSH as root
without a password.
In this state, no disks are configured. You need to configure them before you can proceed.
Configure DASDs with the following command:
dasd_configure 0.0.0150 1 0
0.0.0150 is the channel to which the DASD is connected. The
1
means activate the disk (a0
at this place would deactivate the disk). The0
stands for “no DIAG mode” for the disk (a1
here would enable DAIG access to the disk).Now the DASD is online (check with
cat /proc/partitions
) and can used for subsequent commands.
To configure a zFCP disk, it is necessary to first configure the zFCP adapter. Do this with the following command:
zfcp_host_configure 0.0.4000 1
0.0.4000
is the channel to which the adapter is attached and1
stands for activate (a0
here would deactivate the adapter).After the adapter is activated, a disk can be configured. Do this with the following command:
zfcp_disk_configure 0.0.4000 1234567887654321 8765432100000000 1
0.0.4000
is the previously-used channel ID,1234567887654321
is the WWPN (World wide Port Number), and8765432100000000
is the LUN (logical unit number). The1
stands for activating the disk (a0
here would deactivate the disk).Now the zFCP disk is online (check with
cat /proc/partitions
) and can used for subsequent commands.
Now the rescue system is fully set up and you can start repairing the installed system. See Section 40.5.2, “Using the rescue system” for instructions on how to repair the most common issues.
A An example network #
This example network is used across all network-related chapters of the SUSE® Linux Enterprise Server documentation.
B GNU licenses #
This appendix contains the GNU Free Documentation License version 1.2.
GNU Free Documentation License #
Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
0. PREAMBLE #
The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or non-commercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
1. APPLICABILITY AND DEFINITIONS #
This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.
The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.
A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.
2. VERBATIM COPYING #
You may copy and distribute the Document in any medium, either commercially or non-commercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.
3. COPYING IN QUANTITY #
If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.
4. MODIFICATIONS #
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
State on the Title page the name of the publisher of the Modified Version, as the publisher.
Preserve all the copyright notices of the Document.
Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
Include an unaltered copy of this License.
Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.
Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.
Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.
You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS #
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".
6. COLLECTIONS OF DOCUMENTS #
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS #
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
8. TRANSLATION #
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
9. TERMINATION #
You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE #
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents #
Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.