Covers system administration tasks like maintaining, monitoring and customizing an initially installed system.
- About This Guide
- I Common Tasks
- II Booting a Linux System
- III System
- 15 32-Bit and 64-Bit Applications in a 64-Bit System Environment
- 16
journalctl
: Query thesystemd
Journal - 17 Basic Networking
- 17.1 IP Addresses and Routing
- 17.2 IPv6—The Next Generation Internet
- 17.3 Name Resolution
- 17.4 Configuring a Network Connection with YaST
- 17.5 NetworkManager
- 17.6 Configuring a Network Connection Manually
- 17.7 Basic Router Setup
- 17.8 Setting Up Bonding Devices
- 17.9 Setting Up Team Devices for Network Teaming
- 17.10 Software-Defined Networking with Open vSwitch
- 18 Printer Operation
- 19 The X Window System
- 20 Accessing File Systems with FUSE
- 21 Managing Kernel Modules
- 22 Dynamic Kernel Device Management with
udev
- 22.1 The
/dev
Directory - 22.2 Kernel
uevents
andudev
- 22.3 Drivers, Kernel Modules and Devices
- 22.4 Booting and Initial Device Setup
- 22.5 Monitoring the Running
udev
Daemon - 22.6 Influencing Kernel Device Event Handling with
udev
Rules - 22.7 Persistent Device Naming
- 22.8 Files used by
udev
- 22.9 For More Information
- 22.1 The
- 23 Live Patching the Linux Kernel Using kGraft
- 24 Special System Features
- 25 Persistent Memory
- IV Services
- 26 Time Synchronization with NTP
- 27 The Domain Name System
- 28 DHCP
- 29 Sharing File Systems with NFS
- 30 Samba
- 31 On-Demand Mounting with Autofs
- 32 SLP
- 33 The Apache HTTP Server
- 33.1 Quick Start
- 33.2 Configuring Apache
- 33.3 Starting and Stopping Apache
- 33.4 Installing, Activating, and Configuring Modules
- 33.5 Enabling CGI Scripts
- 33.6 Setting Up a Secure Web Server with SSL
- 33.7 Running Multiple Apache Instances on the Same Server
- 33.8 Avoiding Security Problems
- 33.9 Troubleshooting
- 33.10 For More Information
- 34 Setting Up an FTP Server with YaST
- 35 The Proxy Server Squid
- 35.1 Some Facts about Proxy Caches
- 35.2 System Requirements
- 35.3 Basic Usage of Squid
- 35.4 The YaST Squid Module
- 35.5 The Squid Configuration File
- 35.6 Configuring a Transparent Proxy
- 35.7 Using the Squid Cache Manager CGI Interface (
cachemgr.cgi
) - 35.8 squidGuard
- 35.9 Cache Report Generation with Calamaris
- 35.10 For More Information
- 36 Web Based Enterprise Management Using SFCB
- V Mobile Computers
- VI Troubleshooting
- A An Example Network
- B GNU licenses
- 3.1 YaST Online Update
- 5.1 Main Window of YaST in Text Mode
- 5.2 The Software Installation Module
- 7.1 Boot Loader: Snapshots
- 8.1 vncviewer
- 8.2 Remmina's Main Window
- 8.3 Remote Desktop Preference
- 8.4 Quick-starting
- 8.5 Remmina Viewing SLES 15 Remote Session
- 8.6 Reading Path to the Profile File
- 8.7 Remote Administration
- 8.8 VNC Session Settings
- 8.9 Joining a Persistent VNC Session
- 12.1 Secure Boot Support
- 12.2 UEFI: Secure Boot Process
- 13.1 GRUB 2 boot editor
- 13.2 Boot Code Options
- 13.3 Code Options
- 13.4 Boot loader Options
- 13.5 Kernel Parameters
- 14.1 Services Manager
- 16.1 YaST systemd Journal
- 17.1 Simplified Layer Model for TCP/IP
- 17.2 TCP/IP Ethernet Packet
- 17.3 Configuring Network Settings
- 17.4
wicked
architecture - 25.1 NVDIMM Region Layout
- 26.1 YaST: NTP Server
- 26.2 Advanced NTP Configuration: Security Settings
- 27.1 DNS Server Installation: Forwarder Settings
- 27.2 DNS Server Installation: DNS Zones
- 27.3 DNS Server Installation: Finish Wizard
- 27.4 DNS Server: Logging
- 27.5 DNS Server: Zone Editor (Basics)
- 27.6 DNS Server: Zone Editor (NS Records)
- 27.7 DNS Server: Zone Editor (MX Records)
- 27.8 DNS Server: Zone Editor (SOA)
- 27.9 Adding a Record for a Master Zone
- 27.10 Adding a Reverse Zone
- 27.11 Adding a Reverse Record
- 28.1 DHCP Server: Card Selection
- 28.2 DHCP Server: Global Settings
- 28.3 DHCP Server: Dynamic DHCP
- 28.4 DHCP Server: Start-Up
- 28.5 DHCP Server: Host Management
- 28.6 DHCP Server: Chroot Jail and Declarations
- 28.7 DHCP Server: Selecting a Declaration Type
- 28.8 DHCP Server: Configuring Subnets
- 28.9 DHCP Server: TSIG Configuration
- 28.10 DHCP Server: Interface Configuration for Dynamic DNS
- 28.11 DHCP Server: Network Interface and Firewall
- 29.1 NFS Server Configuration Tool
- 30.1 Determining Windows Domain Membership
- 30.2 Windows Explorer Dialog
- 30.3 Windows Explorer Directory Listing with Compressed Files
- 30.4 Adding a New Samba Share with Snapshotting Enabled
- 30.5 The tab in Windows Explorer
- 33.1 HTTP Server Wizard: Default Host
- 33.2 HTTP Server Wizard: Summary
- 33.3 HTTP Server Configuration: Listen Ports and Addresses
- 33.4 HTTP Server Configuration: Server Modules
- 34.1 FTP Server Configuration — Start-Up
- 36.1 Package Selection for Web-Based Enterprise Management Pattern
- 36.2 Package selection of additional CIM providers
- 37.1 Integrating a Mobile Computer in an Existing Environment
- 38.1 GNOME Network Connections Dialog
- 41.1 HTML Report Generated by SCA Tool
- 41.2 HTML Report Generated by SCA Appliance
- 42.1 Checking Media
- 42.2 US Keyboard Layout
- 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
- 2.1 Useful Flags and Options
- 6.1 The Most Important RPM Query Options
- 6.2 RPM Verify Options
- 14.1 Service Management Commands
- 14.2 Commands for enabling and disabling services
- 14.3 System V runlevels and
systemd
target units - 17.1 Private IP Address Domains
- 17.2 Parameters for /etc/host.conf
- 17.3 Databases Available via /etc/nsswitch.conf
- 17.4 Configuration Options for NSS “Databases”
- 17.5 Feature Comparison between Bonding and Team
- 19.1 Generating PFL from Fontconfig rules
- 19.2 Results from Generating PFL from Fontconfig Rules with Changed Order
- 19.3 Results from Generating PFL from Fontconfig Rules
- 24.1
ulimit
: Setting Resources for the User - 36.1 Commands for Managing sfcbd
- 37.1 Use Cases for NetworkManager
- 37.2 Overview of Various Wi-Fi Standards
- 40.1 Man Pages—Categories and Descriptions
- 42.1 Log files
- 42.2 System Information With the
/proc
File System - 42.3 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
- 13.1 Usage of grub2-mkconfig
- 13.2 Usage of grub2-mkrescue
- 13.3 Usage of grub2-script-check
- 13.4 Usage of grub2-once
- 14.1 List Active Services
- 14.2 List Failed Services
- 14.3 List all processes belonging to a service
- 17.1 Writing IP Addresses
- 17.2 Linking IP Addresses to the Netmask
- 17.3 Sample IPv6 Address
- 17.4 IPv6 Address Specifying the Prefix Length
- 17.5 Common Network Interfaces and Some Static Routes
- 17.6
/etc/resolv.conf
- 17.7
/etc/hosts
- 17.8
/etc/networks
- 17.9
/etc/host.conf
- 17.10
/etc/nsswitch.conf
- 17.11 Output of the Command ping
- 17.12 Configuration for Loadbalancing with Network Teaming
- 17.13 Configuration for DHCP Network Teaming Device
- 18.1 Error Message from
lpd
- 18.2 Broadcast from the CUPS Network Server
- 19.1 Specifying Rendering Algorithms
- 19.2 Aliases and Family Name Substitutions
- 19.3 Aliases and Family Name Substitutions
- 19.4 Aliases and Family Names Substitutions
- 22.1 Example
udev
Rules - 24.1 Entry in /etc/crontab
- 24.2 /etc/crontab: Remove Time Stamp Files
- 24.3 ulimit: Settings in ~/.bashrc
- 27.1 Forwarding Options in named.conf
- 27.2 A Basic /etc/named.conf
- 27.3 Entry to Disable Logging
- 27.4 Zone Entry for example.com
- 27.5 Zone Entry for example.net
- 27.6 The /var/lib/named/example.com.zone File
- 27.7 Reverse Lookup
- 28.1 The Configuration File /etc/dhcpd.conf
- 28.2 Additions to the Configuration File
- 30.1 A CD-ROM Share
- 30.2 [homes] Share
- 30.3 Global Section in smb.conf
- 30.4 Using
rpcclient
to Request a Windows Server 2012 Share Snapshot - 33.1 Basic Examples of Name-Based
VirtualHost
Entries - 33.2 Name-Based
VirtualHost
Directives - 33.3 IP-Based
VirtualHost
Directives - 33.4 Basic
VirtualHost
Configuration - 33.5 VirtualHost CGI Configuration
- 35.1 A Request With
squidclient
- 35.2 Defining ACL Rules
- 41.1 Output of
hostinfo
When Logging In asroot
Copyright © 2006–2025 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.
About This Guide #
This guide is intended for use by professional network and system administrators during the operation of SUSE® Linux Enterprise. As such, it is solely concerned with ensuring that SUSE Linux Enterprise is properly configured and that the required services on the network are available to allow it to function properly as initially installed. This guide does not cover the process of ensuring that SUSE Linux Enterprise offers proper compatibility with your enterprise's application software or that its core functionality meets those requirements. It assumes that a full requirements audit has been done and the installation has been requested, or that a test installation for such an audit has been requested.
This guide contains the following:
- Support and Common Tasks
SUSE Linux Enterprise offers a wide range of tools to customize various aspects of the system. This part introduces a few of them. A breakdown of available device technologies, high availability configurations, and advanced administration possibilities introduces the system to the administrator.
- System
Learn more about the underlying operating system by studying this part. SUSE Linux Enterprise supports several hardware architectures and you can use this to adapt your own applications to run on SUSE Linux Enterprise. The boot loader and boot procedure information assists you in understanding how your Linux system works and how your own custom scripts and applications may blend in with it.
- Services
SUSE Linux Enterprise is designed to be a network operating system. It offers a wide range of network services, such as DNS, DHCP, Web, proxy, and authentication services. It also integrates well into heterogeneous environments, including MS Windows clients and servers.
- Mobile Computers
Laptops, and the communication between mobile devices like PDAs, or cellular phones and SUSE Linux Enterprise need some special attention. Take care for power conservation and for the integration of different devices into a changing network environment. Also get in touch with the background technologies that provide the needed functionality.
- Troubleshooting
Provides an overview of finding help and additional documentation when you need more information or want to perform specific tasks. There is also a list of the most frequent problems with explanations of how to fix them.
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:root #
command
tux >
sudo
command
Commands that can be run by non-privileged users:
tux >
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:tux >
echo
a b \ c dA code block that shows both the command (preceded by a prompt) and the respective output returned by the shell:
tux >
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 they offer lots of features, their use is limited when it comes to the execution of automated tasks. Shells are a good addition to GUIs and this chapter gives you an overview of some aspects of shells, in this case Bash.
- 2 sudo
Many commands and system utilities need to be run as root to modify files and/or perform tasks that only the super user is allowed to. For security reasons and to avoid accidentally running dangerous commands, it is generally advisable not to log in directly as root. Instead, it is recommended to wo…
- 3 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 14 “Installing or Removing Software”, Section 14.5 “Keeping the System Up-to-date” for further information on…
- 4 YaST
YaST is the installation and configuration tool for SUSE Linux Enterprise Server. It has a graphical interface and the capability to customize your system quickly during and after the installation. It can be used to set up hardware, configure the network, system services, and tune your security sett…
- 5 YaST in Text Mode
This section is intended for system administrators and experts who do not run an X server on their systems and depend on the text-based installation tool. It provides basic information about starting and operating YaST in text mode.
- 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 14 “Installing or Removing Software”, Section 14.1 “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 Remote Access with VNC
Virtual Network Computing (VNC) enables you to control a remote computer via a graphical desktop (as opposed to a remote shell access). VNC is platform-independent and lets you access the remote machine from any operating system.
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.
- 9 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 sync across multiple devices all more important.
- 10 GNOME Configuration for Administrators
This chapter introduces GNOME configuration options which administrators can use to adjust system-wide settings, such as customizing menus, installing themes, configuring fonts, changing preferred applications, and locking down capabilities.
1 Bash and Bash Scripts #
Today, many people use computers with a graphical user interface (GUI) like GNOME. Although they offer lots of features, their use is limited when it comes to the execution of automated tasks. Shells are a good addition to GUIs and this chapter gives you an overview of some aspects of shells, in this case Bash.
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 Knowing the 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 tools.
Non-interactive non-login shell. This is used when invoking a shell script at the command line.
Depending on which type of shell you use, different configuration files are being 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 can 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 can 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 been typing |
|
Executed when logging out |
|
User defined aliases of frequently used commands. See
|
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 42.1, “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. It is recommended to comment difficult lines to remember what they do. | |
The third line uses the built-in command |
Before you can run this script you need some 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.txt
Command >> File
Appends the output of the command to a file. For example, the
ls
command appends its output to the filelisting.txt
:ls >> listing.txt
Command < 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 < foo
Command1 | 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.txt
Command1 && 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.txt
Command1 || 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/bar
funcname(){ ... }
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 Tux
which 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 angled brackets:
if [ -e /tmp/foo.txt ] ; then echo "Found foo.txt" fi
Find more useful expressions at http://www.cyberciti.biz/nixcraft/linux/docs/uniqlinuxfeatures/lsst/ch03sec02.html.
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 For 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 #
Many commands and system utilities need to be run as root
to modify
files and/or perform tasks that only the super user is allowed to. For
security reasons and to avoid accidentally running dangerous commands, it is
generally advisable not to log in directly as root
. Instead, it is
recommended to work as a normal, unprivileged user and use the sudo
command to run commands with elevated privileges.
On SUSE Linux Enterprise Server, sudo
is configured by default to work similarly to su.
However, sudo
offers the possibility to allow users to run commands with
privileges of any other user in a highly configurable manner. This can be
used to assign roles with specific privileges to certain users and groups. It
is for example possible to allow members of the group users
to run a
command with the privileges of wilber
. Access to the command can be
further restricted by, for example, forbidding to specify 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 increases security by not having to share the root
password. For
example, you can allow members of the group users
to run a command
frobnicate
as wilber
, with the restriction that
no arguments are specified. This can be used to assign roles with specific
abilities to certain users and groups.
2.1 Basic sudo
Usage #
sudo
is simple to use, yet very powerful.
2.1.1 Running a Single Command #
Logged in as normal user, you can run any command as root
by
adding sudo
before it. It will prompt for the root password and, if
authenticated successfully, run the command as root
:
tux >
id -un
1 tuxtux >
sudo id -un
root's password:2 roottux >
id -un
tux3tux >
sudo id -un
4 root
The | |
The password is not shown during input, neither as clear text nor as bullets. | |
Only commands started with | |
The elevated privileges persist for a certain period of time, so you
do not need to provide the |
I/O redirection does not work as you would probably expect:
tux >
sudo echo s > /proc/sysrq-trigger bash: /proc/sysrq-trigger: Permission deniedtux >
sudo cat < /proc/1/maps bash: /proc/1/maps: Permission denied
Only the echo
/cat
binary is run with
elevated privileges, while the redirection is performed by the user's
shell with user privileges. You can either start a shell like in
Section 2.1.2, “Starting a Shell” or use the dd
utility
instead:
echo s | sudo dd of=/proc/sysrq-trigger sudo dd if=/proc/1/maps | cat
2.1.2 Starting a Shell #
Having to add sudo
before every command can be cumbersome. While you
could specify a shell as a command sudo bash
, it is
recommended to rather 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 given, it is passed to the shell (with the-c
option), else the shell is run in interactive mode.tux:~ >
sudo -i root's password:root:/home/tux #
exittux:~ >
sudo -i (<command>)
Like
-s
, but starts the shell as 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:~ >
2.1.3 Environment Variables #
By default, sudo
does not propagate environment variables:
tux >
ENVVAR=test env | grep ENVVAR ENVVAR=testtux >
ENVVAR=test sudo env | grep ENVVAR root's password: 1tux >
The empty output shows that the environment variable
|
This behavior can be changed by the env_reset
option,
see Table 2.1, “Useful Flags and Options”.
2.2 Configuring sudo
#
sudo
is a very flexible tool with extensive configuration.
If you accidentally locked yourself out of sudo
, use su
-
and the root
password to get 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 due to errors in this file, it is strongly
recommended to use visudo
for editing. It will prevent
simultaneous changes to the opened file and check for syntax errors before
saving the modifications.
Despite its name, you can also use editors other than vi by setting the
EDITOR
environment variable, for example:
sudo EDITOR=/usr/bin/nano visudo
However, the /etc/sudoers
file itself is supplied by
the system packages and modifications may break on updates. Therefore, it
is recommended to put custom configuration into files in the
/etc/sudoers.d/
directory. Any file in there is
automatically included. To create or edit a file in that subdirectory, run:
sudo visudo -f /etc/sudoers.d/NAME
Alternatively with a different editor (for example
nano
):
sudo EDITOR=/usr/bin/nano visudo -f /etc/sudoers.d/NAME
/etc/sudoers.d
The #includedir
command in
/etc/sudoers
, used for
/etc/sudoers.d
, ignores files that end in
~
(tilde) or contain a .
(dot).
For more information on the visudo
command, run
man 8 visudo
.
2.2.2 Basic sudoers Configuration Syntax #
In the sudoers configuration files, there are 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:
# Everything on a line after a # gets 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 | |
Option name |
Description |
Example |
---|---|---|
targetpw
|
This flag controls whether the invoking user is required to enter the
password of the target user (ON) (for example |
Defaults targetpw # Turn targetpw flag ON |
rootpw
|
If set, |
Defaults !rootpw # Turn rootpw flag OFF |
env_reset
|
If set, |
Defaults env_reset # Turn env_reset flag ON |
env_keep
|
List of environment variables to keep when the
|
# 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
|
# 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 Rules in sudoers #
Rules in the sudoers configuration can be very complex, so this section
will only cover the basics. Each rule follows the basic scheme
([]
marks optional parts):
#Who Where As whom Tag What User_List Host_List = [(User_List)] [NOPASSWD:|PASSWD:] Cmnd_List
User_List
One or more (separated by
,
) identifiers: Either a user name, a group in the format%GROUPNAME
or a user ID in the format#UID
. Negation can be performed with a!
prefix.Host_List
One or more (separated by
,
) identifiers: Either a (fully qualified) host name or an IP address. Negation can be performed with a!
prefix.ALL
is the usual choice forHost_List
.NOPASSWD:|PASSWD:
The user will not be prompted for a password when running commands matching
CMDSPEC
afterNOPASSWD:
.PASSWD
is the default, it only needs to be specified when both are on the same line:tux ALL = PASSWD: /usr/bin/foo, NOPASSWD: /usr/bin/bar
Cmnd_List
One or more (separated by
,
) specifiers: A path to an executable, followed by allowed arguments or nothing./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 ""
Constructs of the kind
ALL ALL = ALL
must not be used without Defaults
targetpw
, otherwise anyone can run commands as root
.
When specifying the group name in the sudoers
file, make sure that you use the the NetBIOS domain name instead of the realm, for example:
%DOMAIN\\GROUP_NAME ALL = (ALL) ALL
Keep in mind that when using winbindd, the format also depends on the winbind separator
option in the smb.conf
file. By default, it is \
. If it is changed, for example, to +
, then the account format in sudoers
file must be DOMAIN+GROUP_NAME
.
2.3 Common Use Cases #
Although the default configuration is often sufficient for simple setups and desktop environments, custom configurations can be very useful.
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:tux >
getent group wheel
If the previous command returned no result, install the system-group-wheel package that creates the
wheel
group:tux >
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 specific 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 forget this step, otherwise any user can execute any command as
root
!Test the configuration
Try to 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 #
When starting graphical applications with sudo
, you will encounter the
following error:
tux >
sudo xterm
xterm: Xt error: Can't open display: %s
xterm: DISPLAY is not set
YaST will pick the ncurses interface instead of the graphical one.
To use X.Org in applications started with sudo
, the environment
variables DISPLAY
and XAUTHORITY
need to be
propagated. To configure this, create the file
/etc/sudoers.d/xorg
, (see
Section 2.2.1, “Editing the Configuration Files”) and add the following line:
Defaults env_keep += "DISPLAY XAUTHORITY"
If not set already, set the XAUTHORITY
variable as follows:
export XAUTHORITY=~/.Xauthority
Now X.Org applications can be run as usual:
sudo yast2
2.4 More Information #
A quick overview about the available command line switches can be retrieved
by sudo --help
. An explanation and other important
information can be found in the man page: man 8 sudo
,
while the configuration is documented in man 5 sudoers
.
3 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 14 “Installing or Removing Software”, Section 14.5 “Keeping the System Up-to-date” 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 14 “Installing or Removing Software”, Section 14.4 “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//.
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.
3.1 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.3.2 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, press 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 3.1, “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. If you want 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.
3.3 Automatic Online Update #
YaST also offers the possibility to set up an automatic update with daily,
weekly or monthly schedule. To use the respective module, you need to
install the
yast2-online-update-configuration
package first.
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 to skip patches that require user interaction.
After installation, start YaST and select
› .Alternatively, start the module with
yast2 online_update_configuration
from the command line.Activate
.Choose the update interval:
, , or .To automatically accept any license agreements, activate
.Select if you want to
in case you want the update procedure to proceed fully automatically.Important: Skipping PatchesIf you select to skip any packages that require interaction, run a manual
occasionally to install those patches, too. Otherwise you might miss important patches.To automatically install all packages recommended by updated packages, activate
.To disable the use of delta RPMs (for performance reasons), deactivate
.To filter the patches by category (such as security or recommended), activate
and add the appropriate patch categories from the list. Only patches of the selected categories will be installed. Others will be skipped.Confirm your configuration with
.
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.
4 YaST #
YaST is the installation and configuration tool for SUSE Linux Enterprise Server. It has a graphical interface and the capability to customize your system quickly during and after the installation. It can be used to set up hardware, configure the network, system services, and tune your security settings.
4.1 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 5, 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.
4.2 Useful key combinations #
The graphical version of YaST supports keyboard shortcuts
- Print Screen
Take and save a screenshot. May not be available when YaST is running under some desktop environments.
- Shift–F4
Enable/disable the color palette optimized for vision impaired users.
- Shift–F7
Enable/disable logging of debug messages.
- Shift–F8
Open a file dialog to save log files to a non-standard 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/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.
5 YaST in Text Mode #
This section is intended for system administrators and experts who do not run an X server on their systems and depend on the text-based installation tool. It provides basic information about starting and operating YaST in text mode.
YaST in text mode uses the ncurses library to provide an easy pseudo-graphical user interface. The ncurses library is installed by default. The minimum supported size of the terminal emulator in which to run YaST is 80x25 characters.
When you start YaST in text mode, the YaST control center appears (see Figure 5.1). The main window consists of three areas. The left frame features the categories to which the various modules belong. This frame is active when YaST is started and therefore it is marked by a bold white border. The active category is selected. The right frame provides an overview of the modules available in the active category. The bottom frame contains the buttons for and .
When you start the YaST control center, the category ↓ and ↑ to change the category. To select a module from the category, activate the right frame with → and then use ↓ and ↑ to select the module. Keep the arrow keys pressed to scroll through the list of available modules. After selecting a module, press Enter to start it.
is selected automatically. UseVarious buttons or selection fields in the module contain a highlighted letter (yellow by default). Use Alt–highlighted_letter to select a button directly instead of navigating there with →|. Exit the YaST control center by pressing Alt–Q or by selecting and pressing Enter.
If a YaST dialog gets corrupted or distorted (for example, while resizing the window), press Ctrl–L to refresh and restore its contents.
5.2 Advanced Key Combinations #
YaST in text mode has a set of advanced key combinations.
- Shift–F1
Show a list of advanced hotkeys.
- Shift–F4
Change color schema.
- Ctrl–\
Quit the application.
- Ctrl–L
Refresh screen.
- Ctrl–D F1
Show a list of advanced hotkeys.
- Ctrl–D Shift–D
Dump dialog to the log file as a screenshot.
- Ctrl–D Shift–Y
Open YDialogSpy to see the widget hierarchy.
5.3 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.
- Replacing Alt with Esc
Alt shortcuts can be executed with Esc instead of Alt. For example, Esc–H replaces Alt–H. (First press Esc, then press H.)
- Backward and Forward Navigation with Ctrl–F and Ctrl–B
If the Alt and Shift combinations are occupied 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 occupied 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 pure text console.
5.4 YaST Command Line Options #
Besides the text mode interface, YaST provides a pure command line interface. To get a list of YaST command line options, enter:
yast -h
5.4.1 Starting the Individual Modules #
To save time, the individual YaST modules can be started directly. To start a module, enter:
yast <module_name>
View a list of all module names available on your system with yast
-l
or yast --list
. Start the network module,
for example, with yast lan
.
5.4.2 Installing Packages from the Command Line #
If you know a package name and the package is provided by any of your
active installation repositories, you can use the command line option
-i
to install the package:
yast -i <package_name>
or
yast --install <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.
If you need a command line based software management utility with functionality beyond what YaST provides, consider using Zypper. This utility uses the same software management library that is also the foundation for the YaST package manager. The basic usage of Zypper is covered in Section 6.1, “Using Zypper”.
5.4.3 Command Line Parameters of the YaST Modules #
To use YaST functionality in scripts, YaST provides command line support for individual modules. Not all modules have command line support. To display the available options of a module, enter:
yast <module_name> help
If a module does not provide command line support, the module is started in text mode and the following message appears:
This YaST module does not support the command line interface.
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 14 “Installing or Removing Software”, Section 14.1 “Definition of Terms”.
6.1 Using Zypper #
Zypper is a command line package manager for installing, updating and removing packages a well as for managing 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:
tux >
sudo zypper patch- Global Options
Additionally, you can choose from one or more global options by typing them immediately before the command:
tux >
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:
tux >
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:tux >
sudo zypper install mplayerSome options also require a single argument. The following command will list all known patterns:
tux >
zypper search -t pattern
You can combine all of the above. For example, the following command will
install the
aspell-de
and
aspell-fr
packages from the factory
repository while being verbose:
tux >
sudo zypper -v install --from factory aspell-de aspell-fr
The --from
option makes sure to keep all repositories
enabled (for solving any dependencies) while requesting the package from the
specified repository.
Most Zypper commands have a dry-run
option that does a
simulation of the given command. It can be used for test purposes.
tux >
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.
tux >
sudo zypper --userdata STRING patch
6.1.2 Installing and Removing Software with Zypper #
To install or remove packages, use the following commands:
tux >
sudo
zypper install PACKAGE_NAMEtux >
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.
6.1.2.1 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
tux >
sudo zypper install MozillaFirefox- By Exact Package Name and Version Number
tux >
sudo zypper install MozillaFirefox-52.2- By Repository Alias and Package Name
tux >
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”:
tux >
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:tux >
sudo zypper remove '*-debuginfo'- By Capability
For example, if you want to install a Perl module without knowing the name of the package, capabilities come in handy:
tux >
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:tux >
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).tux >
sudo zypper install 'firefox>=52.2'You can also combine a hardware architecture and version requirement:
tux >
sudo zypper install 'firefox.x86_64>=52.2'
- By Path to the RPM file
You can also specify a local or remote path to a package:
tux >
sudo zypper install /tmp/install/MozillaFirefox.rpmtux >
sudo zypper install http://download.example.com/MozillaFirefox.rpm
6.1.2.2 Combining Installation and Removal of Packages #
To install and remove packages simultaneously, use the
+/-
modifiers. To install
emacs
and simultaneously remove
vim
, use:
tux >
sudo zypper install emacs -vim
To remove emacs and simultaneously install vim , use:
tux >
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 --
:
tux >
sudo zypper install -emacs +vim # Wrongtux >
sudo zypper install vim -emacs # Correcttux >
sudo zypper install -- -emacs +vim # Correcttux >
sudo zypper remove emacs +vim # Correct
6.1.2.3 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:
tux >
sudo
zypper rm --clean-deps PACKAGE_NAME
6.1.2.4 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:
tux >
sudo zypper--non-interactive
install PACKAGE_NAME
This option allows the use of Zypper in scripts and cron jobs.
6.1.2.5 Installing or Downloading Source Packages #
To install the corresponding source package of a package, use:
tux >
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
:
tux >
sudo zypper source-install -D PACKAGE_NAME
To install only the build dependencies use -d
.
tux >
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 6.1.5, “Managing Repositories with Zypper” for details on repository management.
A list of all source packages available in your repositories can be obtained with:
tux >
zypper search -t srcpackage
You can also download source packages for all installed packages to a local directory. To download source packages, use:
tux >
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.
6.1.2.6 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:
tux >
sudo zypper --plus-content debug \
install "debuginfo(build-id)=eb844a5c20c70a59fc693cd1061f851fb7d046f4"
The build-id
string is reported by
gdb
for missing debuginfo packages.
6.1.2.7 Utilities #
To verify whether all dependencies are still fulfilled and to repair missing dependencies, use:
tux >
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:
tux >
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.
6.1.3 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 “Deployment Guide”, Chapter 20 “Upgrading SUSE Linux Enterprise”.
6.1.3.1 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:
tux >
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:
tux >
sudo
zypper patch --with-update
To install also optional patches, use:
tux >
sudo zypper patch --with-optional
To install all patches relating to a specific Bugzilla issue, use:
tux >
sudo zypper patch --bugzilla=NUMBER
To install all patches relating to a specific CVE database entry, use:
tux >
sudo zypper patch --cve=NUMBER
For example, to install a security patch with the CVE number
CVE-2010-2713
, execute:
tux >
sudo zypper patch --cve=CVE-2010-2713
To install only patches which affect Zypper and the package management itself, use:
tux >
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.
6.1.3.2 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
:tux >
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
list-patches
:tux >
zypper list-patches Loading repository data... Reading installed packages... Repository | Name | Version | Category | Status | Summary ---------------+-------------+---------+----------+---------+--------- SLES12-Updates | SUSE-2014-8 | 1 | security | needed | openssl: Update for OpenSSL- 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:tux >
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:tux >
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
:tux >
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:
tux >
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:
tux >
zypper list-patches --all --cve
Issue | No. | Patch | Category | Severity | Status
------+---------------+-------------------+-------------+-----------+----------
cve | CVE-2015-0287 | SUSE-SLE-Module.. | recommended | moderate | needed
cve | CVE-2014-3566 | SUSE-SLE-SERVER.. | recommended | moderate | not needed
[...]
6.1.3.3 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:
tux >
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:
tux >
sudo
zypper update PACKAGE_NAMEtux >
sudo
zypper install PACKAGE_NAME
A list of all new installable packages can be obtained with the command:
tux >
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:
tux >
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.
6.1.3.4 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:
tux >
sudo zypper packages --orphaned
With this list, you can decide if a package is still needed or can be removed safely.
6.1.4 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:
tux >
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.
tux >
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 14, The systemd
daemon.
6.1.5 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:
tux >
zypper repos
The result will look similar to the following output:
tux >
zypper repos
# | Alias | Name | Enabled | Refresh
--+--------------+---------------+---------+--------
1 | SLEHA-12-GEO | SLEHA-12-GEO | Yes | No
2 | SLEHA-12 | SLEHA-12 | Yes | No
3 | SLES12 | SLES12 | 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:
tux >
zypper repos -d
6.1.5.1 Adding Repositories #
To add a repository, run
tux >
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.
6.1.5.2 Refreshing Repositories #
zypper
enables you to fetch changes in packages from
configured repositories. To fetch the changes, run:
tux >
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:
tux >
sudo zypper --plus-content refresh
This option fetches changes in repositories, but keeps the disabled repositories in the same state—disabled.
6.1.5.3 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:
tux >
sudo zypper removerepo 1tux >
sudo zypper removerepo "SLEHA-12-GEO"
6.1.5.4 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:
tux >
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
:
tux >
sudo zypper renamerepo 'Mozilla Firefox' firefox
6.1.6 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:
tux >
zypper productstux >
zypper patternstux >
zypper packagestux >
zypper patches
To query all repositories for certain packages, use
search
. To get information regarding particular packages,
use the info
command.
6.1.6.1 zypper search
Usage #
The zypper search
command works on package names, or,
optionally, on package summaries and descriptions. String wrapped in
/
are interpreted as regular expressions. By default,
the search is not case-sensitive.
- Simple search for a package name containing
fire
tux >
zypper search "fire"- Simple search for the exact package
MozillaFirefox
tux >
zypper search --match-exact "MozillaFirefox"- Also search in package descriptions and summaries
tux >
zypper search -d fire- Only display packages not already installed
tux >
zypper search -u fire- Display packages containing the string
fir
not followed bee
tux >
zypper se "/fir[^e]/"
6.1.6.2 zypper what-provides
Usage #
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:
tux >
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.
6.1.6.3 zypper info
Usage #
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
:
tux >
zypper info --requires MozillaFirefox
6.1.7 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.
6.1.8 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:
tux >
sudo zypper refresh
If that does not help, try
tux >
sudo zypper refresh -fdb
This forces a complete refresh and rebuild of the database, including a forced download of raw metadata.
6.1.9 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.
6.1.10 For 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.
Essentially, 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:
tux >
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 just 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:
tux >
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:
tux >
sudo applydeltarpm new.delta.rpm new.rpm
To derive it from the old RPM without accessing the file system, use the
-r
option:
tux >
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, “The Most Important 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 12
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:
tux >
rpm -q -f /bin/rpm /usr/bin/wget
rpm-4.11.2-15.1.x86_64
wget-1.14-17.1.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):
tux >
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-1.11.4.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, the BuildRoot
directive in the spec file is
deprecated since SUSE Linux Enterprise Server 12. If you still need this feature, use the
--buildroot
option as a workaround. For more detailed background information, see the support
database at https://www.suse.com/support/kb/doc?id=7017104.
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
:
root #
cd /usr/src/packages/SOURCES/root #
mv ../SPECS/wget.spec .root #
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 14 “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:
tux >
sudo snapper -c root create-config /
Afterward enable the different snapshot types as described in Section 7.1.3.1, “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 7.1.3.4, “Controlling Snapshot Archiving” for details.
7.1.1 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.
7.1.2 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 IBM Z, respectively.
/home
If
/home
does not reside on a separate partition, it is excluded to avoid data loss on rollbacks./opt
,/var/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
,/var/tmp
,/var/cache
,/var/crash
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/lib/libvirt/images
The default location for virtual machine images managed with libvirt. Excluded to ensure virtual machine images are not replaced with older versions during a rollback. By default, this subvolume is created with the option
no copy on write
./var/lib/mailman
,/var/spool
Directories containing mails or mail queues are excluded to avoid a loss of mails after a rollback.
/var/lib/named
Contains zone data for the DNS server. Excluded from snapshots to ensure a name server can operate after a rollback.
/var/lib/mariadb
,/var/lib/mysql
,/var/lib/pgqsl
These directories contain database data. By default, these subvolumes are created with the option
no copy on write
./var/log
Log file location. Excluded from snapshots to allow log file analysis after the rollback of a broken system. By default,
/var/log
has the NoCOW attribute set, disabling copy-on-write, which improves performance and reduces the number of duplicate blocks. Verify withlsattr
:tux >
lsattr -l /var/ /var/log No_COW
7.1.3 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.
7.1.3.1 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.
7.1.3.2 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>
7.1.3.3 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
.
tux >
sudo mount /dev/sda2 -o subvol=@ /mnttux >
sudo btrfs subvolume create /mnt/usr/importanttux >
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
.
7.1.3.4 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.
7.1.3.5 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 13 “Advanced Disk Setup”, Section 13.2 “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:
tux >
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 7.1.3.1, “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)
.tux >
sudo snapper list -t pre-post Pre # | Post # | Pre Date | Post Date | Description ------+--------+-------------------------------+-------------------------------+-------------- 311 | 312 | Tue 06 May 2014 14:05:46 CEST | Tue 06 May 2014 14:05:52 CEST | zypp(y2base) 340 | 341 | Wed 07 May 2014 16:15:10 CEST | Wed 07 May 2014 16:15:16 CEST | zypp(zypper) 342 | 343 | Wed 07 May 2014 16:20:38 CEST | Wed 07 May 2014 16:20:42 CEST | zypp(y2base) 344 | 345 | Wed 07 May 2014 16:21:23 CEST | Wed 07 May 2014 16:21:24 CEST | zypp(zypper) 346 | 347 | Wed 07 May 2014 16:41:06 CEST | Wed 07 May 2014 16:41:10 CEST | zypp(y2base) 348 | 349 | Wed 07 May 2014 16:44:50 CEST | Wed 07 May 2014 16:44:53 CEST | zypp(y2base) 350 | 351 | Wed 07 May 2014 16:46:27 CEST | Wed 07 May 2014 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 .tux >
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.tux >
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.tux >
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:
tux >
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:
tux >
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
tux >
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
tux >
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 12 SP5 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 7.1.2, “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
tux >
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:
root #
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.
root #
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:
tux >
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 7.1.2, “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 can enable snapshots for users' /home
directories, which supports a number of use cases:
Individual users can manage their own snapshots and rollbacks.
System users, for example database, system, and network admins, can 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 can 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
:
root #
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:
root #
/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:
root #
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.
root #
/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.
root #
btrfs subvol create /home/usernameroot #
snapper -c home_username create-config /home/usernameroot #
sed -i -e "s/ALLOW_USERS=\"\"/ALLOW_USERS=\"username\"/g" \ /etc/snapper/configs/home_usernameroot #
yast users add username=username home=/home/username password=passwordroot #
chown username.group /home/usernameroot #
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 in order to
automatically enable snapshots during the installation. 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
:
tux >
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:
tux >
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:tux >
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:
tux >
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:
tux >
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:tux >
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. If you
want 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 --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 #
Over time, snapshots grow in size, occupying an ever increasing amount of disk space. 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. In the default
setup, quota support is enabled, and snapshots must leave at least
20% of the available disk space on the root partition free. Timeline snapshots
are disabled by default, therefore the timeline clean-up algorithm is also
disabled.
Previous implementations of the clean-up algorithm only ensured that snapshots do not use more than the specified amount of disk space (default is 50%). In certain cases, this didn't prevent the system from running of disk space. Starting with SUSE Linux Enterprise Server 12 SP1, Snapper features an improved clean-up algorithm that keeps 20% of the available disk space free at all times.
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:
tux >
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. Only the youngest snapshots will be kept. Ignored if
NUMBER_CLEANUP
is set to"no"
.The default value is
"2-10"
forNUMBER_LIMIT
and"4-10"
forNUMBER_LIMIT_IMPORTANT
.Example command to change or set:
tux >
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:
tux >
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:
tux >
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 7.1.1, “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.
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).
On SUSE Linux Enterprise Server 12 SP5, using Btrfs quota groups can degrade file system performance.
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 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 7.1.2, “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: How much disk space is used by snapshots? How can I free disk space?
Displaying the amount of disk space a snapshot allocates is currently not supported by the
Btrfs
tools. However, if you have quota enabled, it is possible to determine how much space would be freed if all snapshots would be deleted:Get the quota group ID (
1/0
in the following example):tux >
sudo snapper -c root get-config | grep QGROUP QGROUP | 1/0Rescan the subvolume quotas:
tux >
sudo btrfs quota rescan -w /Show the data of the quota group (
1/0
in the following example):tux >
sudo btrfs qgroup show / | grep "1/0" 1/0 4.80GiB 108.82MiBThe third column shows the amount of space that would be freed when deleting all snapshots (
108.82MiB
).
To free space on a
Btrfs
partition containing snapshots you need to delete unneeded snapshots rather than files. Older snapshots occupy more space than recent ones. See Section 7.1.3.4, “Controlling Snapshot Archiving” for details.Doing an upgrade from one service pack to another results in snapshots occupying a lot of disk space on the system subvolumes, because a lot of data gets changed (package updates). Manually deleting these snapshots after they are no longer needed is recommended. See Section 7.6.4, “Deleting Snapshots” for details.
- 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:
tux >
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:
tux >
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 Remote Access with VNC #
Virtual Network Computing (VNC) enables you to control a remote computer via a graphical desktop (as opposed to a remote shell access). VNC is platform-independent and lets you access the remote machine from any operating system.
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 machine can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.
8.1 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.
8.1.1 Connecting Using the vncviewer CLI #
To start your VNC viewer and initiate a session with the server, use the command:
tux >
vncviewer jupiter.example.com:1
Instead of the VNC display number you can also specify the port number with two colons:
tux >
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 8.4, “Persistent VNC Sessions” for further info.
8.1.2 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 8.1.1, “Connecting Using the vncviewer CLI”
and click .
8.1.3 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.
8.2 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, or Spice.
8.2.1 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:
root #
zypper in remmina remmina-plugin-vnc
8.2.2 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.
8.2.3 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.8.2.4 Starting Remote Sessions #
You can either start a previously saved session, or quick-start a remote session without saving the connection details.
8.2.4.1 Quick-starting Remote Sessions #
To start a remote session quickly without adding and saving connection details, use the drop-down box and text field at the top of the main window.
Select the communication protocol from the drop-down box, for example 'VNC', then enter the VNC server's DNS or IP address followed by a colon and a display number, and confirm with Enter.
8.2.4.2 Opening Saved Remote Sessions #
To open a specific remote session, double-click it from the list of sessions.
8.2.4.3 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; for example 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.
8.2.5 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 8.2.3, “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.
8.2.6 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:
tux >
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 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.
8.3 One-time VNC Sessions #
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.
8.3.1 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 8.3.3, “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.
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.
8.3.2 Initiating a One-time VNC Session #
To connect to a one-time VNC session, a VNC viewer must be installed, see
also Section 8.1, “The vncviewer
Client”.
8.3.3 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 Java applet
(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:
tux >
sudo
systemctl reload xvnc.socket
When activating Remote Administration as described in
Procedure 8.1, “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 16 “Masquerading and Firewalls” for instructions.
8.4 Persistent VNC 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 trainings 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 8.1, “The vncviewer
Client” for more details.
There are two types of persistent VNC sessions:
8.4.1 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 16 “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 1024x769 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
8.4.1.1 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.
8.4.2 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.
8.4.2.1 Configuring Persistent VNC Sessions #
After you enable the VNC session management as described in
Procedure 8.3, “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 8.3, “One-time VNC Sessions” 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. List 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. Good for remote presentations or trainings.
Confirm with
.8.4.2.2 Joining Persistent VNC Sessions #
After you set up a persistent VNC session as described in Section 8.4.2.1, “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.
8.5 Encrypted VNC Communication #
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).
Tip: Path to Certificate and KeySome 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).
8.6 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.
9 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 sync across multiple devices all 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.
9.1 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 is able to synchronize both source and destination, use Csync.
9.2 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 timestamps, 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.
9.3 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:
tux >
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/
:
tux >
rsync
-avz tux /var/backup/
Find the copy in the absolute path
/var/backup/tux/
.
9.4 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:
tux >
rsync
-avz file.tar.xz tux@192.168.1.1:
Depending on what you prefer, these commands are also possible and equivalent:
tux >
rsync
-avz file.tar.xz 192.168.1.1:~tux >
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:
tux >
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
.
9.5 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:
9.6 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
jupiter
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
:root #
mkdir
/var/backupSpecify ownership. In this case, the directory is owned by user
tux
in groupusers
:root #
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/
:root #
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
:root #
chmod
0600 /etc/rsyncd.secrets
Start and enable the rsyncd daemon with:
root #
systemctl
enable rsyncdroot #
systemctl
start rsyncdTest the access to your Rsync server:
tux >
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.
9.7 For More Information #
- CSync
Bidirectional file synchronizer, see https://www.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 https://documentation.suse.com/sle-ha/.
10 GNOME Configuration for Administrators #
This chapter introduces GNOME configuration options which administrators can use to adjust system-wide settings, such as customizing menus, installing themes, configuring fonts, changing preferred applications, and locking down capabilities.
These configuration options are stored in the Dconf system. Access the
Dconf system with tools such as the dconf
command
line interface or the dconf-editor
GUI tool.
10.1 Starting Applications Automatically #
To automatically start applications in GNOME, use one of the following methods:
To run applications for each user: Put
.desktop
files in/usr/share/gnome/autostart
.To run applications for an individual user: Put
.desktop
files in~/.config/autostart
.
To disable an application that starts automatically, add
X-Autostart-enabled=false
to the
.desktop
file.
10.2 Automounting and Managing Media Devices #
GNOME Files (nautilus
) monitors volume-related events and
responds with a user-specified policy. You can use GNOME Files to
automatically mount hotplugged drives and inserted removable media,
automatically run programs, and play audio CDs or video DVDs. GNOME Files
can also automatically import photos from a digital camera.
System administrators can set system-wide defaults. For more information, see Section 10.3, “Changing Preferred Applications”.
10.3 Changing Preferred Applications #
To change users' preferred applications, edit
/etc/gnome_defaults.conf
. Find further hints within
this file.
For more information about MIME types, see http://www.freedesktop.org/Standards/shared-mime-info-spec.
10.4 Adding Document Templates #
To add document templates for users, fill in the
Templates
directory in a user's home directory. You
can do this manually for each user by copying the files into
~/Templates
, or system-wide by adding a
Templates
directory with documents to
/etc/skel
before the user is created.
A user creates a new document from a template by right-clicking the desktop and selecting
.10.5 For More Information #
For more information, see http://help.gnome.org/admin/.
Part II Booting a Linux System #
- 11 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 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.
- 13 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 11, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 12, UEFI (Unified Extensible Firmware Interface).
- 14 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…
11 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.
11.1 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
.
11.2 The Linux Boot Process #
The Linux boot process consists of several stages, each represented by a different component:
11.2.1 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 13, The Boot Loader GRUB 2.
11.2.1.1 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.
11.2.1.2 Initialization and Boot Loader Phase on IBM IBM Z #
On IBM 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
that 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.
11.2.2 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
.
11.2.2.1 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
.
11.2.2.1.1 Regenerating the initramfs #
Since 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 11.1, “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 11.1, “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 11.1, “Generate an initramfs”.Proceed with Procedure 11.1, “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 11.1, “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 11.1, “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 13.2.1, “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:root #
cd /bootGenerate a new
initramfs
file withdracut
, replacing MY_INITRAMFS with a file name of your choice:root #
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
:root #
ln -sf MY_INITRAMFSinitrd
On the IBM IBM Z architecture, additionally run
grub2-install
.
11.2.3 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 11.1, “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 14 “Mass Storage over IP Networks: iSCSI”, Section 14.3.1 “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.
11.2.3.1 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
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 11.2.2.1, “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 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 14.6.4, “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.
11.2.4 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 14, The systemd
daemon for details.
12 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.
12.1 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.
12.1.1 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 essentially 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.
12.1.2 MOK (Machine Owner Key) #
If the user (“machine owner”) wants to replace any components
of the boot process, Machine Owner Keys (MOKs) are to be used. The
mokutils
tool will help with signing components
and managing MOKs.
The enrollment process begins with rebooting the machine and interrupting
the boot process (for example, pressing a key) when
shim
loads. shim
will
then go into enrollment mode, allowing the user to replace the default SUSE
key with keys from a file on the boot partition. If the user chooses to do
so, shim
will then calculate a hash of that file
and put the result in a “Boot Services Only” variable. This
allows shim
to detect any change of the file made
outside of Boot Services and thus avoid tampering with the list of
user-approved MOKs.
All of this happens during boot time—only verified code is executing now. Therefore, only a user present at the console can use the machine owner's set of keys. It cannot be malware or a hacker with remote access to the OS because hackers or malware can only change the file, but not the hash stored in the “Boot Services Only” variable.
The boot loader, after having been loaded and verified by
shim
, will call back to
shim
when it wants to verify the kernel—to
avoid duplication of the verification code. Shim
will use the same list of MOKs for this and tell the boot loader whether it
can load the kernel.
This way, you can install your own kernel or boot loader. It is only
necessary to install a new set of keys and authorize them by being
physically present during the first reboot. Because MOKs are a list rather
than single MOK, you can make shim
trust keys
from several vendors, allowing dual- and multi-boot from the boot loader.
12.1.3 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.p12
Generate an NSS database for use with
pesign
:certutil -d . -N
Import 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 -s
List the signatures on the kernel image:
pesign -n . -S -i vmlinuz.signed
At 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.der
Copy 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.der
The
--root-pw
option enables usage of theroot
user directly.Check the list of certificates that are prepared to be enrolled:
mokutil --list-new
Reboot 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.
12.1.4 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.
12.1.5 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 video mode support, the kernel can retrieve video mode from UEFI to configure KMS mode with the same parameters.
UEFI booting from USB devices is supported.
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.
Kexec and Kdump are disabled.
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.
12.2 For 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.
13 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 11, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 12, UEFI (Unified Extensible Firmware Interface).
13.1 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.
13.2 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.
13.2.1 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 13.3, “Configuring the Boot Loader with YaST”.
13.2.2 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:
tux >
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.
13.2.3 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.
13.2.4 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
13.2.6 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:
tux >
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:
tux >
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.
13.3 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.13.3.1 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 your changes.
The
tab includes the following additional options:Activates the partition that contains the
/boot
directorythe 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.
13.3.2 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 13.2.4, “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.
13.3.3 Configuring Advanced Options #
Advanced boot options can be configured via the
tab.13.3.3.1 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 more information, see Section 13.2.6, “Setting a Boot Password”.
13.3.3.2 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 these may result in performance loss. Choose one of the following options to strike a balance between security and performance, depending on your situation:
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 can be then set from the
list, and graphical theme definition file can be specified with the file-chooser.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
13.4 Differences in Terminal Usage on IBM 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.
13.4.1 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 13.4.2, “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.
13.4.2 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 |
13.5 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 13.1: 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 Shim and regenerate the UEFI boot table. To do so, use:
root #
shim-install --config-file=/boot/grub2/grub.cfggrub2-mkrescue
Creates a bootable rescue image of your installed GRUB 2 configuration.
Example 13.2: Usage of grub2-mkrescue #grub2-mkrescue -o save_path/name.iso iso
grub2-script-check
Checks the given file for syntax errors.
Example 13.3: 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 13.4: 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.
13.6 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.
13.7 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.
14 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/.
14.1 The systemd
concept #
This section will go into detail about the concept behind systemd.
14.1.1 What Is systemd #
systemd is a system and session manager for Linux, compatible with System V and LSB init scripts. The main features are:
provides aggressive parallelization capabilities
uses socket and D-Bus activation for starting services
offers on-demand starting of daemons
keeps track of processes using Linux cgroups
supports snapshotting and restoring of the system state
maintains mount and automount points
implements an elaborate transactional dependency-based service control logic
14.1.2 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
14.2 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 →| to
automatically complete it. This feature is only available in the
bash
shell and requires the installation of the
package bash-completion
.
14.2.1 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:
systemctl start MY_1ST_SERVICE MY_2ND_SERVICE
To list all services available on the system:
systemctl list-unit-files --type=service
The following table lists the most important service management commands for systemd and System V init:
Task |
systemd Command |
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 |
14.2.2 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.
14.2.2.1 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 |
14.3 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.
14.3.1 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 14.4, “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 14.5.5, “Creating Custom Targets” for instructions on
how to create your own bootable target.
14.3.1.1 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 |
14.3.2 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 /varlog/
). systemd also allows you to
scan the start-up procedure to find out how much time each service start-up
consumes.
14.3.2.1 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
.
root #
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
ntpd.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:
root #
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
[...]
14.3.2.2 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
root #
systemd-analyze Startup finished in 2666ms (kernel) + 21961ms (userspace) = 24628ms- Listing the Services Start-Up Time
root #
systemd-analyze blame 6472ms systemd-modules-load.service 5833ms remount-rootfs.service 4597ms network.service 4254ms systemd-vconsole-setup.service 4096ms postfix.service 2998ms xdm.service 2483ms localnet.service 2470ms SuSEfirewall2_init.service 2189ms avahi-daemon.service 2120ms systemd-logind.service 1210ms xinetd.service 1080ms ntp.service [...] 75ms fbset.service 72ms purge-kernels.service 47ms dev-vda1.swap 38ms bluez-coldplug.service 35ms splash_early.service- Services Start-Up Time Graphics
root #
systemd-analyze plot > jupiter.example.com-startup.svg
14.3.2.3 Review the Complete Start-Up Process #
The above-mentioned commands let you review the services that started and
the time it took to start them. If you need to know more details, you can
tell systemd
to verbosely log the complete start-up procedure by
entering the following parameters at the boot prompt:
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
14.3.3 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
.
14.4 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.
14.5 Customizing systemd
#
The following sections describe how to customize systemd
unit files.
14.5.1 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
.
14.5.2 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.
14.5.3 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
.tux >
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:tux >
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.tux >
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:tux >
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:tux >
systemd-analyze cat-config systemd/journald.conf
14.5.4 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:
root #
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:
root #
cat /usr/lib/systemd/system/example.socket
[Socket]
ListenStream=0.0.0.0:10085
Accept=false
[Install]
WantedBy=sockets.target
root #
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
).
14.5.5 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
.Once you have finished setting up the target, reload the systemd configuration to make the new target available:
systemctl daemon-reload
14.6 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.
14.6.1 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:
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 2014-09-09 15:30:36 CEST; 1 weeks 6 days ago Docs: man:tmpfiles.d(5) man:systemd-tmpfiles(8) Sep 09 15:30:36 jupiter systemd[1]: Starting Daily Cleanup of Temporary Directories. Sep 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
.
14.6.2 System Log #
Section 14.6.9, “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.
14.6.3 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
systemctl snapshot MY_SNAPSHOT.snapshot
- Delete a Snapshot
systemctl delete MY_SNAPSHOT.snapshot
- View a Snapshot
systemctl show MY_SNAPSHOT.snapshot
- Activate a Snapshot
systemctl isolate MY_SNAPSHOT.snapshot
14.6.4 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.
14.6.5 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
):systemctl daemon-reload systemctl enable before
Every time you modify the service file, you need to run:
systemctl daemon-reload
14.6.6 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:
root #
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
├─ntpd.service
│ └─1328 /usr/sbin/ntpd -p /var/run/ntp/ntpd.pid -g -u ntp:ntp -c /etc/ntp.conf
├─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 9 “Kernel Control Groups” for more information about cgroups.
14.6.7 Terminating services (sending signals) #
As explained in Section 14.6.6, “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 stop a service and its children. Child processes that have not been terminated remain as zombie processes.
systemd
's concept of confining each service into a cgroup makes it
possible to 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.tux >
sudo
systemctl kill MY_SERVICE- Sending SIGNAL to a service
Use the
-s
option to specify the signal that should be sent.tux >
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
:tux >
sudo
systemctl kill -s SIGHUP --kill-who=main MY_SERVICE
14.6.8 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.
14.6.9 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:root #
systemctl start apache2 Job failed. See system journal and 'systemctl status' for details.root #
systemctl status apache2 Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: failed (Result: exit-code) since Mon, 04 Jun 2012 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 Jun 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:tux >
sudo
systemctl status chronydtux >
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
:tux >
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.
14.7 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.
14.7.1 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.
14.7.2 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.
14.7.3 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:
tux >
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
.
14.7.4 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. Additionally, 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
.
14.8 More information #
For more information on systemd refer to the following online resources:
- Homepage
- systemd for Administrators
Lennart 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 #
- 15 32-Bit and 64-Bit Applications in a 64-Bit System Environment
SUSE® Linux Enterprise Server is available for several 64-bit platforms. This does not necessarily mean that all the applications included have already been ported to 64-bit platforms. SUSE Linux Enterprise Server supports the use of 32-bit applications in a 64-bit system environment. This chapter o…
- 16
journalctl
: Query thesystemd
Journal When
systemd
replaced traditional init scripts in SUSE Linux Enterprise 12 (see Chapter 14, Thesystemd
daemon), it introduced its own logging system called journal. There is no need to run asyslog
based service anymore, as all system events are written in the journal.- 17 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.
- 18 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 12 “Setting Up Hardware Components with YaST”, Section 12.3 “Set…
- 19 The X Window System
The X Window System (X11) is the de facto standard for graphical user interfaces in Unix. 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). This chapter provides basic information on the X configuration…
- 20 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.- 21 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…
- 22 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 …
- 23 Live Patching the Linux Kernel Using kGraft
This document describes the basic principles of the kGraft live patching technology and provides usage guidelines for the SLE Live Patching service.
kGraft is a live patching technology for runtime patching of the Linux kernel, without stopping the kernel. This maximizes system uptime, and thus system availability, which is important for mission-critical systems. By allowing dynamic patching of the kernel, the technology also encourages users to install critical security updates without deferring them to a scheduled downtime.
A kGraft patch is a kernel module, intended for replacing whole functions in the kernel. kGraft primarily offers in-kernel infrastructure for integration of the patched code with base kernel code at runtime.
SLE Live Patching is a service provided on top of regular SUSE Linux Enterprise Server maintenance. kGraft patches distributed through SLE Live Patching supplement regular SLES maintenance updates. Common update stack and procedures can be used for SLE Live Patching deployment.
The information provided in this document relates to the AMD64/Intel 64 and POWER architectures. In case you use a different architecture, the procedures may differ.
- 24 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).- 25 Persistent Memory
This chapter contains additional information about using SUSE Linux Enterprise Server with non-volatile main memory, also known as Persistent Memory, comprising one or more NVDIMMs.
15 32-Bit and 64-Bit Applications in a 64-Bit System Environment #
SUSE® Linux Enterprise Server is available for several 64-bit platforms. This does not necessarily mean that all the applications included have already been ported to 64-bit platforms. SUSE Linux Enterprise Server supports the use of 32-bit applications in a 64-bit system environment. This chapter offers a brief overview of how this support is implemented on 64-bit SUSE Linux Enterprise Server platforms.
SUSE Linux Enterprise Server for the 64-bit platforms IBM POWER, IBM 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 ppc 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 compiling 32-bit applications, it only offers runtime support for 32-bit binaries.
15.1 Runtime Support #
If an application is available both for 32-bit and 64-bit environments, parallel installation of both versions is bound to lead to problems. In such cases, decide on one of the two versions and install and use this.
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. On a 64-bit operating system that also runs 32-bit applications it is necessary to always install both versions of a PAM module.
To be executed correctly, every application requires a range of libraries. Unfortunately, the names for the 32-bit and 64-bit versions of these libraries are identical. They must be differentiated from each other in another way.
To retain compatibility with the 32-bit version, the libraries are stored at
the same place in the system as in the 32-bit environment. The 32-bit
version of libc.so.6
is located under
/lib/libc.so.6
in both the 32-bit and 64-bit
environments.
All 64-bit libraries and object files are located in directories called
lib64
. The 64-bit object files that you would normally
expect to find under /lib
and
/usr/lib
are now found under
/lib64
and /usr/lib64
. This means
that there is space for the 32-bit libraries under /lib
and /usr/lib
, so the file name for both versions can
remain unchanged.
Subdirectories of 32-bit /lib
directories which contain
data content that does not depend on the word size are not moved. This
scheme conforms to LSB (Linux Standards Base) and FHS (File System Hierarchy
Standard).
15.2 Kernel Specifications #
The 64-bit kernels for AMD64/Intel 64, IBM POWER and IBM IBM Z offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical with the ABI for the corresponding 32-bit kernel. This means that the 32-bit application can communicate with the 64-bit kernel in the same way as with the 32-bit kernel.
The 32-bit emulation of system calls for a 64-bit kernel 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 IBM Z, not all ioctls are available in the
32-bit kernel ABI.
A 64-bit kernel can only load 64-bit kernel modules that have been specially compiled for this kernel. It is not possible to use 32-bit kernel modules.
Some applications require separate kernel-loadable modules. If you intend to use such a 32-bit application in a 64-bit system environment, contact the provider of this application and SUSE to 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.
16 journalctl
: Query the systemd
Journal #
When systemd
replaced traditional init scripts in SUSE Linux Enterprise 12
(see Chapter 14, The systemd
daemon), it introduced its own logging system
called journal. There is no need to run a
syslog
based service anymore, as all system events
are written in 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:
# 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 [...]
16.1 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, the
directory /var/log/journal/
with correct ownership and
permissions must exist, where the systemd-journald service can store its
data. systemd
will create the directory for you—and switch to
persistent logging—if you do the following:
As
root
, open/etc/systemd/journald.conf
for editing.# vi /etc/systemd/journald.conf
Uncomment the line containing
Storage=
and change it to[...] [Journal] Storage=persistent #Compress=yes [...]
Save the file and restart systemd-journald:
systemctl restart systemd-journald
16.2 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:
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.
- -e
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 16.3.3, “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 16.3.3, “Filtering Based on Fields”).# 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.
16.3 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.
16.3.1 Filtering Based on a Boot Number #
journalctl
can filter messages based on a specific
system boot. To list all available boots, run
# 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:
# 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:
# journalctl -b -1
Another way is to list boot messages based on the boot ID. For this purpose, use the _BOOT_ID field:
# journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b
16.3.2 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:
# journalctl --since "now" -f
Show all messages since last midnight till 3:20am:
# journalctl --since "today" --until "3:20"
16.3.3 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:
# 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):
# journalctl _TRANSPORT=kernel
Show messages from the service's standard or error output:
# journalctl _TRANSPORT=stdout
Show messages produced by a specified service only:
# journalctl _SYSTEMD_UNIT=avahi-daemon.service
If two different fields are specified, only entries that match both expressions at the same time are shown:
# journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1488
If two matches refer to the same field, all entries matching either expression are shown:
# 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:
# journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service
16.4 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:
# 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:
# 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:# 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 [...]
16.5 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
# systemctl restart systemd-journald
16.5.1 Changing the Journal Size Limit #
If the journal log data is saved to a persistent location (see
Section 16.1, “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
16.5.2 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
16.5.3 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.
# rpm -q rsyslog rsyslog-7.4.8-2.16.x86_64
rsyslog service is enabled.
# systemctl is-enabled rsyslog enabled
Forwarding to syslog is enabled in
/etc/systemd/journald.conf
.ForwardToSyslog=yes
16.6 Using YaST to Filter the systemd
Journal #
For an easy way of filtering the systemd journal (without having to deal
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 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 https://datatracker.ietf.org/.
- 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 17.1, “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 17.2, “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 100 Mbit/s FDDI network or via a 56-Kbit/s modem line. Likewise, it is irrelevant for the data line which kind of data is transmitted, as long as packets are in the correct format.
17.1 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 17.2, “IPv6—The Next Generation Internet”.
17.1.1 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 17.1, “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.
17.1.2 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 17.2, “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 17.2, “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 17.2, “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 17.1, “Private IP Address Domains”.
Network/Netmask |
Domain |
---|---|
|
|
|
|
|
|
17.2 IPv6—The Next Generation Internet #
IPv6 is not supported by the CTC and IUCV network connections of the IBM IBM Z hardware.
Due to 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.
17.2.1 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 17.2.2, “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 17.2.3, “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).
17.2.2 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 17.3, “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 17.4, “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 17.2.3, “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.
17.2.3 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 17.2.2, “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.
17.2.4 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
).
17.2.5 For 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).
17.3 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 17.4.1.4, “Configuring Host Name and DNS”. Setting up your own name server is described in Chapter 27, 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.
If you want to switch off MDNS during installation, use
nomdns=1
as a boot parameter.
For more information on multicast DNS, see http://www.multicastdns.org.
17.4 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 17.6, “Configuring a Network Connection Manually”.
All network interfaces with link up (with a network cable connected) are automatically configured.
With the Workstation Extension, SUSE Linux Enterprise Server can be set up to use NetworkManager. Under active NetworkManager, all network cards are configured. If NetworkManager is not active, only the first interface with link up (with a network cable connected) is 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 IBM Z platforms, hotpluggable network cards are supported, but not their automatic network integration via DHCP (as is the case on the PC). After detection, manually configure the interface.
17.4.1 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 17.4.1.1, “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 17.4.1.3, “Configuring an Undetected Network Card”. If you want to change the configuration of an already configured card, see Section 17.4.1.2, “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 17.4.1.4, “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 17.4.1.5, “Configuring Routing” for more information.
tab is used for the configuration of routing. See17.4.1.1 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 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
Chapter 38, Using NetworkManager.
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
.17.4.1.2 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.17.4.1.2.1 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 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 17.6.2.5, “/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 17.4.1.4, “Configuring Host Name and DNS”. To configure a gateway, proceed as described in Section 17.4.1.5, “Configuring Routing”.
17.4.1.2.2 Configuring Multiple Addresses #
One network device can have multiple IP addresses.
These so-called aliases or labels, respectively, work with IPv4 only.
With IPv6 they will be ignored. Using iproute2
network
interfaces can have one or more addresses.
Using YaST to set additional addresses for your network card, 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 . Do not include the interface name in the alias name.To activate the configuration, confirm the settings.
17.4.1.2.3 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 later 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.
17.4.1.2.4 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.
17.4.1.2.5 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 17.4.1.2.5, “Activating the Network Device” and choose in the pane.
17.4.1.2.6 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.
17.4.1.2.7 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 15 “Fibre Channel Storage over Ethernet Networks: FCoE”, Section 15.3 “Managing FCoE Services with YaST”.
17.4.1.2.8 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
.
17.4.1.2.9 Configuring the Firewall #
Without having to enter the detailed firewall setup as described in Book “Security and Hardening Guide”, Chapter 16 “Masquerading and Firewalls”, Section 16.4.1 “Configuring the Firewall with YaST”, 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.
17.4.1.3 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 PCMCIA or 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 17.4.1.2, “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.
17.4.1.4 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
and, if needed, the . The domain is especially important if the machine is a mail server. Note that the host name is global and applies to all set 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. 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
.127.0.0.2
(loopback) IP address in/etc/hosts
. This is a useful option if you want to have the host name resolvable at all times, even without active network.In
, select the way the DNS configuration (name servers, search list, the content of the/etc/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/etc/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
17.4.1.5 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.
17.4.2 IBM IBM Z: Configuring Network Devices #
SUSE Linux Enterprise Server for IBM IBM Z supports several types of network interfaces. YaST can be used to configure all of them.
17.4.2.1 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 .
17.4.2.2 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 (see the Linux for IBM
IBM Z: Device Drivers, Features, and Commands manual for
reference,
http://www.ibm.com/developerworks/linux/linux390/documentation_suse.html),
your IP address, and an appropriate netmask. Leave the network configuration
with and .
17.4.2.3 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.
17.4.2.4 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 (see the Linux for IBM IBM Z: Device Drivers,
Features, and Commands manual for reference,
http://www.ibm.com/developerworks/linux/linux390/documentation_suse.html),
your IP address and an appropriate netmask. Leave the network configuration
with and .
17.4.2.5 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.
17.5 NetworkManager #
With the Workstation Extension for SUSE Linux Enterprise Server, you can use NetworkManager instead of
wicked
.
NetworkManager is the ideal solution for laptops and other portable computers. With NetworkManager, you do not need to