journalctl
: Query the systemd
Journalupdate-alternatives
: Managing Multiple Versions of Commands and Filesudev
Covers system administration tasks like maintaining, monitoring and customizing an initially installed system.
klp
Tooljournalctl
: Query the systemd
Journalupdate-alternatives
: Managing Multiple Versions of Commands and Filesudev
/dev
Directoryuevents
and udev
udev
Daemonudev
Rulesudev
cachemgr.cgi
)wicked
architecturefirewalld
Zones in NetworkManagersystemd
Target Unitsulimit
: Setting Resources for the User/proc
File System/sys
File Systemrpm -q -i wget
java
Command/var/run/netconfig/resolv.conf
/etc/hosts
/etc/networks
/etc/host.conf
/etc/nsswitch.conf
lpd
udev
Rulesulimit
: Settings in ~/.bashrc
rpcclient
to Request a Windows Server 2012 Share SnapshotVirtualHost
EntriesVirtualHost
DirectivesVirtualHost
DirectivesVirtualHost
Configurationsquidclient
hostinfo
When Logging In as root
Copyright © 2006– 2021 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 other 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.
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:
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.
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.
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.
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.
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.
Documentation for our products is available at https://documentation.suse.com/, where you can also find the latest updates, and browse or download the documentation in various formats. The latest documentation updates are usually available in the English version of the documentation.
The following documentation is available for this product:
This Quick Start guides you step-by-step through the installation of SUSE® Linux Enterprise Server 15 SP1.
This guide details how to install single or multiple systems, and how to exploit the product-inherent capabilities for a deployment infrastructure. Choose from various approaches: local installation from physical installation media, customizing the standard installation images, network installation server, mass deployment using a remote-controlled, highly-customized, automated installation process, and initial system configuration.
Covers system administration tasks like maintaining, monitoring and customizing an initially installed system.
Describes virtualization technology in general, and introduces libvirt—the unified interface to virtualization—and detailed information on specific hypervisors.
Provides information about how to manage storage devices on a SUSE Linux Enterprise Server.
AutoYaST is a system for unattended mass deployment of SUSE Linux Enterprise Server systems using an AutoYaST profile containing installation and configuration data. The manual guides you through the basic steps of auto-installation: preparation, installation, and configuration.
Introduces basic concepts of system security, covering both local and network security aspects. Shows how to use the product inherent security software like AppArmor, SELinux, or the auditing system that reliably collects information about any security-relevant events. Supports the administrator with security-related choices and decisions in installing and setting up a secure SUSE Linux Enterprise Server and additional processes to further secure and harden that installation.
An administrator's guide for problem detection, resolution and optimization. Find how to inspect and optimize your system by means of monitoring tools and how to efficiently manage resources. Also contains an overview of common problems and solutions and of additional help and documentation resources.
An administrator's guide to Subscription Management Tool—a proxy system for SUSE Customer Center with repository and registration targets. Learn how to install and configure a local SMT server, mirror and manage repositories, manage client machines, and configure clients to use SMT.
Introduces the GNOME desktop of SUSE Linux Enterprise Server. It guides you through using and configuring the desktop and helps you perform key tasks. It is intended mainly for end users who want to make efficient use of GNOME as their default desktop.
The release notes for this product are available at https://www.suse.com/releasenotes/.
Your feedback and contribution to this documentation is welcome! Several channels are available:
For services and support options available for your product, refer to https://www.suse.com/support/.
To open a service request, you need a subscription at SUSE Customer Center. Go to https://scc.suse.com/support/requests, log in, and click .
Report issues with the documentation at https://bugzilla.suse.com/. To simplify this process, you can use the links next to headlines in the HTML version of this document. These preselect the right product and category in Bugzilla and add a link to the current section. You can start typing your bug report right away. A Bugzilla account is required.
To contribute to this documentation, use the
links next to headlines in the HTML version of this document. They take you to the source code on GitHub, where you can open a pull request. A GitHub account is required.For more information about the documentation environment used for this documentation, see the repository's README.
Alternatively, you can report errors and send feedback concerning the documentation to <doc-team@suse.com>. Make sure to include the document title, the product version and the publication date of the documentation. Refer to the relevant section number and title (or include the URL) and provide a concise description of the problem.
The following notices and typographical conventions are used in this documentation:
/etc/passwd
: directory names and file names
PLACEHOLDER: replace PLACEHOLDER with the actual value
PATH
: the environment variable PATH
ls
, --help
: commands, options, and
parameters
user
: users or groups
package name : name of a package
Alt, Alt–F1: a key to press or a key combination; keys are shown in uppercase as on a keyboard
, › : menu items, buttons
AMD/Intel This paragraph is only relevant for the AMD64/Intel 64 architecture. 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
and POWER
. The arrows
mark the beginning and the end of the text block.
Dancing Penguins (Chapter Penguins, ↑Another Manual): This is a reference to a chapter in another manual.
Commands that must be run with root
privileges. Often you can also
prefix these commands with the sudo
command to run them
as non-privileged user.
root #
command
tux >
sudo
command
Commands that can be run by non-privileged users.
tux >
command
Notices
Vital information you must be aware of before proceeding. Warns you about security issues, potential loss of data, damage to hardware, or physical hazards.
Important information you should be aware of before proceeding.
Additional information, for example about differences in software versions.
Helpful information, like a guideline or a piece of practical advice.
SUSE products are supported for up to 13 years. To check the life cycle dates for your product, see https://www.suse.com/lifecycle/.
For SUSE Linux Enterprise, the following life cycles and release cycles apply:
SUSE Linux Enterprise Server has a 13-year life cycle: 10 years of general support and three years of extended support.
SUSE Linux Enterprise Desktop has a 10-year life cycle: seven years of general support and three years of extended support.
Major releases are published every four years. Service packs are published every 12-14 months.
SUSE supports previous SUSE Linux Enterprise service packs for six months after the release of a new service pack.
For some products, Long Term Service Pack Support (LTSS) is available. Find information about our support policy and options at https://www.suse.com/support/policy.html and https://www.suse.com/support/programs/long-term-service-pack-support.html.
Modules have a different life cycle, update policy, and update timeline than their base products. Modules contain software packages and are fully supported parts of SUSE Linux Enterprise Server. For more information, see the Article “Modules and Extensions Quick Start”.
To receive support, you need an appropriate subscription with SUSE. To view the specific support offerings available to you, go to https://www.suse.com/support/ and select your product.
The support levels are defined as follows:
Problem determination, which means technical support designed to provide compatibility information, usage support, ongoing maintenance, information gathering and basic troubleshooting using available documentation.
Problem isolation, which means technical support designed to analyze data, reproduce customer problems, isolate problem area and provide a resolution for problems not resolved by Level 1 or prepare for Level 3.
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.
Technology previews are packages, stacks, or features delivered by SUSE to provide glimpses into upcoming innovations. The previews are included for your convenience to give you the 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.
However, technology previews come with the following limitations:
Technology previews are still in development. Therefore, they may be functionally incomplete, unstable, or in other ways 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.
Technology previews can be dropped at any time. For example, if SUSE discovers that a preview does not meet the customer or market needs, or does not prove to comply with enterprise standards. 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/.
Today, many people use computers with a graphical user interface (GUI) like GNOME. Although GUIs offer many features, they're limited when performing automated task execution. Shells complement GUIs well, and this chapter gives an overview of some aspects of shells, in this case the Bash shell.
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…
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 20 “Installing or Removing Software”, Section 20.5 “The GNOME Package Updater” for further information on the…
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…
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.
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 20 “Installing or Removing Software”, Section 20.1 “Definition of Terms”.
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.
This document describes the basic principles of the Kernel Live Patching (KLP) technology, and provides usage guidelines for the SLE Live Patching service.
Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root filesystem is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not affect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the admin must decide if a reboot is more expensive than disturbing running services. If reboots are too expensive then do not use transactional updates.
Transactional updates are run daily by the
transactional-update
script. The script checks for
available updates. If there are any updates, it creates a new snapshot of
the root file system in the background, and then fetches updates from the
release channels. After the new snapshot is completely updated, it is
marked as active and will be the new default root file system after the next
reboot of the system. When transactional-update
is set to run
automatically (which is the default behavior) it also reboots the system.
Both the time that the update runs and the reboot maintenance window are
configurable.
Only packages that are part of the snapshot of the root file system can be updated. If packages contain files that are not part of the snapshot, the update could fail or break the system.
RPMs that require a license to be accepted cannot be updated.
Virtual Network Computing (VNC) enables you to access a remote computer via a graphical desktop, and run remote graphical applications. VNC is platform-independent and accesses the remote machine from any operating system. This chapter describes how to connect to a VNC server with the desktop clients vncviewer and Remmina, and how to operate a VNC server.
SUSE Linux Enterprise Server supports two different kinds of VNC sessions: One-time sessions that “live” as long as the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated.
A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.
Today, a typical user has several computers: home and workplace machines, a laptop, a smartphone or a tablet. This makes the task of keeping files and documents in synchronization across multiple devices all the more important.
Today, many people use computers with a graphical user interface (GUI) like GNOME. Although GUIs offer many features, they're limited when performing automated task execution. Shells complement GUIs well, and this chapter gives an overview of some aspects of shells, in this case the Bash shell.
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. If you need further information about other shells, search for shell in YaST.
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.
“Ordinary” interactive shell. This is normally the case when starting xterm, konsole, gnome-terminal, or similar command-line interface (CLI) tools.
Non-interactive shell. This is invoked when invoking a shell script at the command line.
Depending on the type of shell you use, different configuration files will be read. The following tables show the login and non-login shell configuration files.
File |
Description |
---|---|
|
Do not modify this file, otherwise your modifications may be destroyed during your next update! |
|
Use this file if you extend |
|
Contains system-wide configuration files for specific programs |
|
Insert user specific configuration for login shells here |
Note that the login shell also sources the configuration files listed under Table 1.2, “Bash Configuration Files for Non-Login Shells”.
|
Do not modify this file, otherwise your modifications may be destroyed during your next update! |
|
Use this file to insert your system-wide modifications for Bash only |
|
Insert user specific configuration here |
Additionally, Bash uses some more files:
File |
Description |
---|---|
|
Contains a list of all commands you have typed |
|
Executed when logging out |
|
User defined aliases of frequently used commands. See
|
There are special shells that block users from logging into
the system: /bin/false
and
/sbin/nologin
. Both fail silently
when the user attempts to log into the system. This was intended
as a security measure for system users, though modern
Linux operating systems have more effective tools for controlling system
access, such as PAM and AppArmor.
The default on SUSE Linux Enterprise Server is to assign /bin/bash
to human users, and /bin/false
or
/sbin/nologin
to system users.
The nobody
user has /bin/bash
for historical reasons, as
it is a minimally-privileged user that used to be the default for system users.
However, whatever little bit of security gained by using
nobody
is lost when
multiple system users use it. It should be possible to change it to
/sbin/nologin
; the fastest way to test it is change
it and see if it breaks any services or applications.
Use the following command to list which shells are assigned to all users,
system and human users, in /etc/passwd
. The output
varies according to the services and users on your system:
tux >
sort -t: -k 7 /etc/passwd | awk -F: '{print $1"\t" $7}' | column -t
tux /bin/bash
nobody /bin/bash
root /bin/bash
avahi /bin/false
chrony /bin/false
dhcpd /bin/false
dnsmasq /bin/false
ftpsecure /bin/false
lightdm /bin/false
mysql /bin/false
postfix /bin/false
rtkit /bin/false
sshd /bin/false
tftp /bin/false
unbound /bin/false
bin /sbin/nologin
daemon /sbin/nologin
ftp /sbin/nologin
lp /sbin/nologin
mail /sbin/nologin
man /sbin/nologin
nscd /sbin/nologin
polkitd /sbin/nologin
pulse /sbin/nologin
qemu /sbin/nologin
radvd /sbin/nologin
rpc /sbin/nologin
statd /sbin/nologin
svn /sbin/nologin
systemd-coredump /sbin/nologin
systemd-network /sbin/nologin
systemd-timesync /sbin/nologin
usbmux /sbin/nologin
vnc /sbin/nologin
wwwrun /sbin/nologin
messagebus /usr/bin/false
scard /usr/sbin/nologin
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 include ls
,
mkdir
, cp
, mv
,
rm
and rmdir
.
/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
.
If 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 of root
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.
/tmp
at Boot Time
Data 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 the Filesystem 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 the howto
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 44.1, “Log Files”.
Shell scripts provide a convenient way to perform a wide range of tasks: collecting data, searching for a word or phrase in a text and other useful things. The following example shows a small shell script that prints a text:
#!/bin/sh 1 # Output the following line: 2 echo "Hello World" 3
The first line begins with the Shebang
characters ( | |
The second line is a comment beginning with the hash sign. We recommend that you comment difficult lines. With proper commenting, you can remember the purpose and function of the line. Also, other readers will hopefully understand your script. Commenting is considered good practice in the development community. | |
The third line uses the built-in command |
Before you can run this script, there are a few prerequisites:
Every script should contain a Shebang line (as in the example above). If the line is missing, you need to call the interpreter manually.
You can save the script wherever you want. However, it is a good idea to
save it in a directory where the shell can find it. The search path in a
shell is determined by the environment variable PATH
.
Usually a normal user does not have write access to
/usr/bin
. Therefore it is recommended to save your
scripts in the users' directory ~/bin/
. The above
example gets the name hello.sh
.
The script needs executable permissions. Set the permissions with the following command:
tux >
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 with
hello.sh
.
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 file listing.txt
:
tux >
ls > listing.txt
Command >> File
Appends the output of the command to a file. For example, the
ls
command appends its output to the file
listing.txt
:
tux >
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:
tux >
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 by
grep
to filter only those lines which contain
cpu
:
tux >
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
:
tux >
find / -name "foo*" 2>/dev/null
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
):
tux >
alias lt='ls -ltr'
To view all alias definitions, use alias
. Remove your
alias with unalias
and the corresponding alias name.
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:
tux >
printenv PATH
A variable, be it global or local, can also be viewed with
echo
:
tux >
echo $PATH
To set a local variable, use a variable name followed by the equal sign, followed by the value:
tux >
PROJECT="SLED"
Do not insert spaces around the equal sign, otherwise you get an error. To
set an environment variable, use export
:
tux >
export NAME="tux"
To remove a variable, use unset
:
tux >
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 |
For example, if you have the script foo.sh
you can
execute it like this:
tux >
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" "" ""
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:
tux >
file=/home/tux/book/book.tar.bz2tux >
echo ${file#*/} home/tux/book/book.tar.bz2
${VAR##pattern}
removes the longest possible match from the left:
tux >
file=/home/tux/book/book.tar.bz2tux >
echo ${file##*/} book.tar.bz2
${VAR%pattern}
removes the shortest possible match from the right:
tux >
file=/home/tux/book/book.tar.bz2tux >
echo ${file%.*} /home/tux/book/book.tar
${VAR%%pattern}
removes the longest possible match from the right:
tux >
file=/home/tux/book/book.tar.bz2tux >
echo ${file%%.*} /home/tux/book/book
${VAR/pattern_1/pattern_2}
substitutes the content of VAR from the PATTERN_1 with PATTERN_2:
tux >
file=/home/tux/book/book.tar.bz2tux >
echo ${file/tux/wilber} /home/wilber/book/book.tar.bz2
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 with
ls
regardless of their exit codes:
tux >
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):
tux >
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:
tux >
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:
tux >
hello() { echo "Hello $1"; }
You can call this function like this:
tux >
hello Tux
which prints:
Hello Tux
To control the flow of your script, a shell has while
,
if
, for
and case
constructs.
The if
command is used to check expressions. For
example, the following code tests whether the current user is Tux:
if test $USER = "tux"; then echo "Hello Tux." else echo "You are not Tux." fi
The test expression can be as complex or simple as possible. The following
expression checks if the file foo.txt
exists:
if test -e /tmp/foo.txt ; then echo "Found foo.txt" fi
The test expression can also be abbreviated in square brackets:
if [ -e /tmp/foo.txt ] ; then echo "Found foo.txt" fi
Find more useful expressions at https://bash.cyberciti.biz/guide/If..else..fi.
for
Command #Edit source
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
Important information about Bash is provided in the man pages man
bash
. More about this topic can be found in the following list:
http://tldp.org/LDP/Bash-Beginners-Guide/html/index.html—Bash Guide for Beginners
http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html—BASH Programming - Introduction HOW-TO
http://tldp.org/LDP/abs/html/index.html—Advanced Bash-Scripting Guide
http://www.grymoire.com/Unix/Sh.html—Sh - the Bourne Shell
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.
sudo
Usage #Edit source
sudo
is simple to use, yet very powerful.
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 | |
For a limited amount of time, you do not need to enter 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
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:~ >
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”.
sudo
#Edit source
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
.
The main policy configuration file for sudo
is
/etc/sudoers
. As it is possible to lock yourself out
of the system because of 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
.
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
.
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 for Host_List
.
NOPASSWD:|PASSWD:
The user will not be prompted for a password when running commands
matching CMDSPEC
after NOPASSWD:
.
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
.
Although the default configuration is often sufficient for simple setups and desktop environments, custom configurations can be very useful.
sudo
without root
Password #Edit source
In cases with special restrictions (“user X can only run command Y as
root
”) it is not possible. In other cases, it is still
favorable to have some kind of separation. By convention, members of the
group wheel
can run all commands
with sudo
as root.
Add yourself to the wheel
group
If your user account is not already member of the
wheel
group, add it by running
sudo usermod -a -G wheel
USERNAME
and logging out and in
again. Verify that the change was successful by running groups
USERNAME
.
Make authentication with the invoking user's password the default.
Create the file /etc/sudoers.d/userpw
with
visudo
(see Section 2.2.1, “Editing the Configuration Files”) and
add:
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'!
Do 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 of
wheel
.
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.
sudo
with X.Org Applications #Edit source
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
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
.
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 20 “Installing or Removing Software”, Section 20.5 “The GNOME Package Updater” for further information on the update applet. This chapter covers the alternative tool for updating software packages: YaST Online Update.
The current patches for SUSE® Linux Enterprise Server are available from an update software repository. If you have registered your product during the installation, an update repository is already configured. If you have not registered SUSE Linux Enterprise Server, you can do so by starting the in YaST. Alternatively, you can manually add an update repository from a source you trust. To add or remove repositories, start the Repository Manager with › in YaST. Learn more about the Repository Manager in Book “Deployment Guide”, Chapter 20 “Installing or Removing Software”, Section 20.4 “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:
Fix severe security hazards and should always be installed.
Fix issues that could compromise your computer.
Fix non-security relevant issues or provide enhancements.
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 :
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.The YaST Online Update dialog allows you to either install all available patches at once or manually select the desired patches. You may also revert patches that have been applied to the system.
By default, all new patches (except optional
ones) that
are currently available for your system are already marked for installation.
They will be applied automatically once you click
or .
If one or multiple patches require a system reboot, you will be notified
about this before the patch installation starts. You can then either decide
to continue with the installation of the selected patches, skip the
installation of all patches that need rebooting and install the rest, or go
back to the manual patch selection.
Start YaST and select
› .
To automatically apply all new patches (except optional
ones) that are currently available for your system, click
or .
First modify the selection of patches that you want to apply:
Use the respective filters and views that the interface provides. For details, refer to Section 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.
Do not deselect any security
-related patches without
a very good reason. These patches fix severe security hazards and
prevent your system from being exploited.
Most patches include updates for several packages. To change actions for single packages, right-click a package in the package view and choose an action.
To confirm your selection and apply the selected patches, proceed with
or .After the installation is complete, click
to leave the YaST . Your system is now up-to-date.
You may configure automatic updates with a daily, weekly, or
monthly schedule with YaST. Install the
yast2-online-update-configuration
package.
By default, updates are downloaded as delta RPMs. Since rebuilding RPM packages from delta RPMs is a memory- and processor-intensive task, certain setups or hardware configurations might require you to disable the use of delta RPMs for the sake of performance.
Some patches, such as kernel updates or packages requiring license agreements, require user interaction, which would cause the automatic update procedure to stop. You can configure skipping patches that require user interaction.
Use the
tab in the YaST module to review available and installed patches, including references to bug reports and CVE bulletins.After installation, start YaST and select yast2-online-update-configuration is not installed, you will be prompted to do that.
› . Choose › . If the
Alternatively, start the module with
yast2 online_update_configuration
from the command
line.
Choose the update interval:
, , or .Sometimes patches may require the attention of the administrator, for example when restarting critical services. For example, this might be an update for Docker Open Source Engine that requires all containers to be restarted. Before these patches are installed, the user is informed about the consequences and is asked to confirm the installation of the patch. Such patches are called “Interactive Patches”.
When installing patches automatically, it is assumed that you have accepted the installation of interactive patches. If you prefer to review these patches before they get installed, check
. In this case, interactive patches will be skipped during automated patching. Make sure to periodically run a manual online update, to check whether interactive patches are waiting to be installed.To automatically accept any license agreements, activate
.To automatically install all packages recommended by updated packages, activate
.To disable the use of delta RPMs (for performance reasons), un-check
.To filter the patches by category (such as security or recommended), check
and add the appropriate patch categories from the list. Only patches of the selected categories will be installed. It is a good practice to enable only automatic updates, and to manually review all others. Patching is usually reliable, but you may wish to test non-security patches, and roll them back if you encounter any problems.supply patches for package management and YaST features and modules.
patches provide crucial updates and bugfixes.
patches are optional bugfixes and enhancements.
are new packages.
is equivalent to miscellaneous.
is unused.
Confirm your configuration by clicking
.The automatic online update does not automatically restart the system afterward. If there are package updates that require a system reboot, you need to do this manually.
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.
YaST has a set of advanced key combinations.
Take and save a screenshot. May not be available when YaST is running under some desktop environments.
Enable/disable the color palette optimized for vision impaired users.
Enable/disable logging of debug messages.
Open a file dialog to save log files to a non-standard location.
Send a DebugEvent. YaST modules can react to this by executing special debugging actions. The result depends on the specific YaST module.
Start/stop macro recorder.
Replay macro.
Show style sheet editor.
Dump widget tree to the log file.
Open a terminal window (xterm). Useful for installation process via VNC.
Show widget tree browser.
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.
YaST in text mode has a set of advanced key combinations.
List advanced hotkeys.
Change color schema.
Quit the application.
Refresh screen.
List advanced hotkeys.
Dump dialog to the log file as a screenshot.
Open YDialogSpy to see the widget hierarchy.
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.
Alt shortcuts can be executed with Esc instead of Alt. For example, Esc–H replaces Alt–H. (First press Esc, then press H.)
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.
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.
Besides the text mode interface, YaST provides a pure command line interface. To get a list of YaST command line options, enter:
tux >
sudo
yast -h
If you know the 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:
tux >
sudo
yast -i package_name
or
tux >
sudo
yast --install -i package_name
package_name can be a single short package name (for example gvim) installed with dependency checking, or the full path to an RPM package which is installed without dependency checking.
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”.
To save time, you can start individual YaST modules directly. To start a module, enter:
tux >
sudo
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
.
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:
tux >
sudo
yast module_name help
If a module does not provide command line support, it is started in a text mode and the following message appears:
This YaST module does not support the command line interface.
The following sections describe all YaST modules with command line support, together with a brief explanation of all their commands and available options.
All YaST modules support the following commands:
Lists all the module's supported commands together with their description:
tux >
sudo
yast lan help
Same as help
, but adds a detailed list of each
command's options together with their description:
tux >
sudo
yast lan longhelp
Same as longhelp
, but the output is structured as
an XML document and redirected to a file:
tux >
sudo
yast lan xmlhelp xmlfile=/tmp/yast_lan.xml
If you need to spend more time querying a module's settings, run the
interactive mode. The YaST shell opens, where
you can enter all the module's commands without the sudo yast
...
prefix. To leave the interactive mode, enter
exit
.
Adds a new add-on product from the specified path:
tux >
sudo
yast add-on http://server.name/directory/Lang-AddOn-CD1/
You can use the following protocols to specify the source path: http:// ftp:// nfs:// disk:// cd:// or dvd://.
Displays and configures the Linux Audit Framework. Refer to the
Book “Security and Hardening Guide” for more details. yast
audit-laf
accepts the following commands:
Sets an option:
tux >
sudo
yast audit-laf set log_file=/tmp/audit.log
For a complete list of options, run yast audit-laf set
help
.
Displays settings of an option:
tux >
sudo
yast audit-laf show diskspace space_left: 75 space_left_action: SYSLOG admin_space_left: 50 admin_space_left_action: SUSPEND action_mail_acct: root disk_full_action: SUSPEND disk_error_action: SUSPEND
For a complete list of options, run yast audit-laf show
help
.
Manages the DHCP server and configures its settings. yast
dhcp-server
accepts the following commands:
Disables the DHCP server service.
Enables the DHCP server service.
Configures settings for individual hosts.
Specifies to which network interface to listen to:
tux >
sudo
yast dhcp-server interface current Selected Interfaces: eth0 Other Interfaces: bond0, pbu, eth1
For a complete list of options, run yast dhcp-server interface
help
.
Manages global DHCP options. For a complete list of options, run
yast dhcp-server options help
.
Prints the status of the DHCP service.
Manages the DHCP subnet options. For a complete list of options, run
yast dhcp-server subnet help
.
Manages the DNS server configuration. yast dns-server
accepts the following commands:
Displays access control list settings:
tux >
sudo
yast dns-server acls show ACLs: ----- Name Type Value ---------------------------- any Predefined localips Predefined localnets Predefined none Predefined
Configures zone resource records:
tux >
sudo
yast dnsrecord add zone=example.org query=office.example.org type=NS value=ns3
For a complete list of options, run yast dns-server dnsrecord
help
.
Configures DNS forwarders:
tux >
sudo
yast dns-server forwarders add ip=10.0.0.100tux >
sudo
yast dns-server forwarders show [...] Forwarder IP ------------ 10.0.0.100
For a complete list of options, run yast dns-server forwarders
help
.
Handles 'A' and its related 'PTR' record at once:
tux >
sudo
yast dns-server host show zone=example.org
For a complete list of options, run yast dns-server host
help
.
Configures logging settings:
tux >
sudo
yast dns-server logging set updates=no transfers=yes
For a complete list of options, run yast dns-server logging
help
.
Configures zone mail servers:
tux >
sudo
yast dns-server mailserver add zone=example.org mx=mx1 priority=100
For a complete list of options, run yast dns-server mailserver
help
.
Configures zone name servers:
tux >
sudo
yast dns-server nameserver add zone=example.com ns=ns1
For a complete list of options, run yast dns-server nameserver
help
.
Configures the start of authority (SOA) record:
tux >
sudo
yast dns-server soa set zone=example.org serial=2006081623 ttl=2D3H20S
For a complete list of options, run yast dns-server soa
help
.
Manages the DNS server service:
tux >
sudo
yast dns-server startup atboot
For a complete list of options, run yast dns-server startup
help
.
Configures zone transport rules. For a complete list of options, run
yast dns-server transport help
.
Manages DNS zones:
tux >
sudo
yast dns-server zones add name=example.org zonetype=master
For a complete list of options, run yast dns-server zones
help
.
Prints information about all disks or partitions. The only supported
command is list
followed by either of the following
options:
Lists all configured disks in the system:
tux >
sudo
yast disk list disks Device | Size | FS Type | Mount Point | Label | Model ---------+------------+---------+-------------+-------+------------- /dev/sda | 119.24 GiB | | | | SSD 840 /dev/sdb | 60.84 GiB | | | | WD1003FBYX-0
Lists all partitions in the system:
tux >
sudo
yast disk list partitions Device | Size | FS Type | Mount Point | Label | Model ---------------+------------+---------+-------------+-------+------ /dev/sda1 | 1.00 GiB | Ext2 | /boot | | /dev/sdb1 | 1.00 GiB | Swap | swap | | /dev/sdc1 | 698.64 GiB | XFS | /mnt/extra | | /dev/vg00/home | 580.50 GiB | Ext3 | /home | | /dev/vg00/root | 100.00 GiB | Ext3 | / | | [...]
Configures FTP server settings. yast ftp-server
accepts
the following options:
Controls secure connections via SSL and TLS. SSL
options are valid for the vsftpd
only.
tux >
sudo
yast ftp-server SSL enabletux >
sudo
yast ftp-server TLS disable
Configures access permissions:
tux >
sudo
yast ftp-server access authen_only
For a complete list of options, run yast ftp-server access
help
.
Configures access permissions for anonymous users:
tux >
sudo
yast ftp-server anon_access can_upload
For a complete list of options, run yast ftp-server
anon_access help
.
Specifies the directory for anonymous users. The directory must already exist on the server:
tux >
sudo
yast ftp-server anon_dir set_anon_dir=/srv/ftp
For a complete list of options, run yast ftp-server anon_dir
help
.
Controls change root environment (chroot):
tux >
sudo
yast ftp-server chroot enabletux >
sudo
yast ftp-server chroot disable
Sets the maximum idle time in minutes before FTP server terminates the current connection:
tux >
sudo
yast ftp-server idle-time set_idle_time=15
Controls whether to save the log messages into a log file:
tux >
sudo
yast ftp-server logging enabletux >
sudo
yast ftp-server logging disable
Specifies the maximum number of concurrently connected clients:
tux >
sudo
yast ftp-server max_clients set_max_clients=1500
Specifies the maximum number of concurrently connected clients via IP:
tux >
sudo
yast ftp-server max_clients_ip set_max_clients=20
Specifies the maximum data transfer rate permitted for anonymous clients (KB/s):
tux >
sudo
yast ftp-server max_rate_anon set_max_rate=10000
Specifies the maximum data transfer rate permitted for locally authenticated users (KB/s):
tux >
sudo
yast ftp-server max_rate_authen set_max_rate=10000
Specifies the port range for passive connection replies:
tux >
sudo
yast ftp-server port_range set_min_port=20000 set_max_port=30000
For a complete list of options, run yast ftp-server port_range help
.
Displays FTP server settings.
Controls the FTP start-up method:
tux >
sudo
yast ftp-server startup atboot
For a complete list of options, run yast ftp-server startup
help
.
Specifies the file umask for authenticated:anonymous
users:
tux >
sudo
yast ftp-server umask set_umask=177:077
Specifies the text to display when someone connects to the FTP server:
tux >
sudo
yast ftp-server welcome_message set_message="hello everybody"
Configures the HTTP server (Apache2). yast http-server
accepts the following commands:
Configures the HTTP server host settings:
tux >
sudo
yast http-server configure host=main servername=www.example.com \ serveradmin=admin@example.com
For a complete list of options, run yast http-server configure
help
.
Configures virtual hosts:
tux >
sudo
yast http-server hosts create servername=www.example.com \ serveradmin=admin@example.com documentroot=/var/www
For a complete list of options, run yast http-server hosts
help
.
Specifies the ports and network addresses where the HTTP server should listen:
tux >
sudo
yast http-server listen add=81tux >
sudo
yast http-server listen list Listen Statements: ================== :80 :81tux >
sudo
yast http-server delete=80
For a complete list of options, run yast http-server listen
help
.
Enables or disables the wizard mode:
tux >
sudo
yast http-server mode wizard=on
Controls the Apache2 server modules:
tux >
sudo
yast http-server modules enable=php5,rewritetux >
sudo
yast http-server modules disable=ssltux >
sudo
http-server modules list [...] Enabled rewrite Disabled ssl Enabled php5 [...]
Configures kdump
settings. For more information
on kdump
, refer to the
Book “System Analysis and Tuning Guide”, Chapter 17 “Kexec and Kdump”, Section 17.7 “Basic Kdump Configuration”. yast kdump
accepts the following commands:
Copies the kernel into the dump directory.
Specifies the kernel_string part of the name
of the custom kernel. The naming scheme is
/boot/vmlinu[zx]-kernel_string[.gz]
.
tux >
sudo
yast kdump customkernel kernel=kdump
For a complete list of options, run yast kdump customkernel
help
.
Specifies the (compression) format of the dump kernel image. Available formats are 'none', 'ELF', 'compressed', or 'lzo':
tux >
sudo
yast kdump dumpformat dump_format=ELF
Specifies the dump level number in the range from 0 to 31:
tux >
sudo
yast kdump dumplevel dump_level=24
Specifies the destination for saving dump images:
tux >
sudo
kdump dumptarget taget=ssh server=name_server port=22 \ dir=/var/log/dump user=user_name
For a complete list of options, run yast kdump dumptarget
help
.
Controls whether the system should reboot immediately after saving the core in the kdump kernel:
tux >
sudo
yast kdump immediatereboot enabletux >
sudo
yast kdump immediatereboot disable
Specifies how many old dump images are kept. Specify zero to keep them all:
tux >
sudo
yast kdump keepolddumps no=5
Specifies the command line that needs to be passed off to the kdump kernel:
tux >
sudo
yast kdump kernelcommandline command="ro root=LABEL=/"
Specifies the command line that you need to append to the default command line string:
tux >
sudo
yast kdump kernelcommandlineappend command="ro root=LABEL=/"
Specifies an e-mail address for sending copies of notification messages:
tux >
sudo
yast kdump notificationcc email="user1@example.com user2@example.com"
Specifies an e-mail address for sending notification messages:
tux >
sudo
yast kdump notificationto email="user1@example.com user2@example.com"
Displays kdump
settings:
tux >
sudo
yast kdump show Kdump is disabled Dump Level: 31 Dump Format: compressed Dump Target Settings target: file file directory: /var/crash Kdump immediate reboots: Enabled Numbers of old dumps: 5
Specifies the file with the plain text SMTP password used for sending notification messages:
tux >
sudo
yast kdump smtppass pass=/path/to/file
Specifies the SMTP server host name used for sending notification messages:
tux >
sudo
yast kdump smtpserver server=smtp.server.com
Specifies the SMTP user name used for sending notification messages:
tux >
sudo
yast kdump smtpuser user=smtp_user
Enables or disables start-up options:
tux >
sudo
yast kdump startup enable alloc_mem=128,256tux >
sudo
yast kdump startup disable
Configures the system keyboard for virtual consoles. It does not affect
the keyboard settings in graphical desktop environments, such as GNOME
or KDE. yast keyboard
accepts the following commands:
Lists all available keyboard layouts.
Activates new keyboard layout setting:
tux >
sudo
yast keyboard set layout=czech
Displays the current keyboard configuration.
Configures network cards. yast lan
accepts the
following commands:
Configures a new network card:
tux >
sudo
yast lan add name=vlan50 ethdevice=eth0 bootproto=dhcp
For a complete list of options, run yast lan add
help
.
Deletes an existing network card:
tux >
sudo
yast lan delete id=0
Changes the configuration of an existing network card:
tux >
sudo
yast lan edit id=0 bootproto=dhcp
Displays a summary of network card configuration:
tux >
sudo
yast lan list id name, bootproto 0 Ethernet Card 0, NONE 1 Network Bridge, DHCP
Configures system languages. yast language
accepts the
following commands:
Lists all available languages.
Specifies the main system languages and secondary languages as well:
tux >
sudo
yast language set lang=cs_CZ languages=en_US,es_ES no_packages
Displays the configuration of the mail system:
tux >
sudo
yast mail summary
Controls the NFS client. yast nfs
accepts the following
commands:
Adds a new NFS mount:
tux >
sudo
yast nfs add spec=remote_host:/path/to/nfs/share file=/local/mount/point
For a complete list of options, run yast nfs add
help
.
Deletes an existing NFS mount:
tux >
sudo
yast nfs delete spec=remote_host:/path/to/nfs/share file=/local/mount/point
For a complete list of options, run yast nfs delete
help
.
Changes an existing NFS mount:
tux >
sudo
yast nfs edit spec=remote_host:/path/to/nfs/share \ file=/local/mount/point type=nfs4
For a complete list of options, run yast nfs edit
help
.
Lists existing NFS mounts:
tux >
sudo
yast nfs list Server Remote File System Mount Point Options ---------------------------------------------------------------- nfs.example.com /mnt /nfs/mnt nfs nfs.example.com /home/tux/nfs_share /nfs/tux nfs
Configures the NFS server. yast nfs-server
accepts the
following commands:
Adds a directory to export:
tux >
sudo
yast nfs-server add mountpoint=/nfs/export hosts=*.allowed_hosts.com
For a complete list of options, run yast nfs-server add
help
.
Deletes a directory from the NFS export:
tux >
sudo
yast nfs-server delete mountpoint=/nfs/export
Specifies additional parameters for the NFS server:
tux >
sudo
yast nfs-server set enablev4=yes security=yes
For a complete list of options, run yast nfs-server set
help
.
Starts the NFS server service:
tux >
sudo
yast nfs-server start
Stops the NFS server service:
tux >
sudo
yast nfs-server stop
Displays a summary of the NFS server configuration:
tux >
sudo
yast nfs-server summary NFS server is enabled NFS Exports * /mnt * /home NFSv4 support is enabled. The NFSv4 domain for idmapping is localdomain. NFS Security using GSS is enabled.
Configures the NIS client. yast nis
accepts the
following commands:
Changes global settings of a NIS client:
tux >
sudo
yast nis configure server=nis.example.com broadcast=yes
For a complete list of options, run yast nis configure
help
.
Disables the NIS client:
tux >
sudo
yast nis disable
Enables your machine as NIS client:
tux >
sudo
yast nis enable server=nis.example.com broadcast=yes automounter=yes
For a complete list of options, run yast nis enable
help
.
Shows available NIS servers for a given domain:
tux >
sudo
yast nis find domain=nisdomain.com
Displays a configuration summary of a NIS client.
Configures a NIS server. yast nis-server
accepts the
following commands:
Configures a NIS master server:
tux >
sudo
yast nis-server master domain=nisdomain.com yppasswd=yes
For a complete list of options, run yast nis-server master
help
.
Configures a NIS slave server:
tux >
sudo
yast nis-server slave domain=nisdomain.com master_ip=10.100.51.65
For a complete list of options, run yast nis-server slave
help
.
Stops a NIS server:
tux >
sudo
yast nis-server stop
Displays a configuration summary of a NIS server:
tux >
sudo
yast nis-server summary
Configures proxy settings. yast proxy
accepts the
following commands:
Specifies the authentication options for proxy:
tux >
sudo
yast proxy authentication username=tux password=secret
For a complete list of options, run yast proxy authentication
help
.
Enables or disables proxy settings.
Changes the current proxy settings:
tux >
sudo
yast proxy set https=proxy.example.com
For a complete list of options, run yast proxy set
help
.
Displays proxy settings.
Controls remote desktop settings. yast rdp
accepts the
following commands:
Allows remote access to the server's desktop:
tux >
sudo
yast rdp allow set=yes
Displays the remote desktop configuration summary.
Configures the Samba client settings. yast samba-client
accepts the following commands:
Changes global settings of Samba:
tux >
sudo
yast samba-client configure workgroup=FAMILY
Verifies if the machine is a member of a domain:
tux >
sudo
yast samba-client isdomainmember domain=SMB_DOMAIN
Makes the machine a member of a domain:
tux >
sudo
yast samba-client joindomain domain=SMB_DOMAIN user=username password=pwd
Enables or disables Winbind services (the
winbindd
daemon):
tux >
sudo
yast samba-client winbind enabletux >
sudo
yast samba-client winbind disable
Configures Samba server settings. yast samba-server
accepts the following commands:
Specifies the back-end for storing user information:
tux >
sudo
yast samba-server backend smbpasswd
For a complete list of options, run yast samba-server backend
help
.
Configures global settings of the Samba server:
tux >
sudo
yast samba-server configure workgroup=FAMILY description='Home server'
For a complete list of options, run yast samba-server
configure help
.
Displays a list of available shares:
tux >
sudo
yast samba-server list Status Type Name ============================== Disabled Disk profiles Enabled Disk print$ Enabled Disk homes Disabled Disk groups Enabled Disk movies Enabled Printer printers
Specifies the role of the Samba server:
tux >
sudo
yast samba-server role standalone
For a complete list of options, run yast samba-server role
help
.
Enables or disables the Samba services (smb
and nmb
):
tux >
sudo
yast samba-server service enabletux >
sudo
yast samba-server service disable
Manipulates a single Samba share:
tux >
sudo
yast samba-server share name=movies browseable=yes guest_ok=yes
For a complete list of options, run yast samba-server share
help
.
Controls the security level of the host. yast security
accepts the following commands:
Specifies the security level of the host:
tux >
sudo
yast security level server
For a complete list of options, run yast security level
help
.
Sets the value of specific options:
tux >
sudo
yast security set passwd=sha512 crack=yes
For a complete list of options, run yast security set
help
.
Displays a summary of the current security configuration:
sudo
yast security summary
Configures sound card settings. yast sound
accepts the
following commands:
Configures a new sound card. Without any parameters, the command adds the first one detected.
tux >
sudo
yast sound add card=0 volume=75
For a complete list of options, run yast sound add
help
.
Lists available volume channels of a sound card:
tux >
sudo
yast sound channels card=0 Master 75 PCM 100
Lists all available sound kernel modules:
tux >
sudo
yast sound modules snd-atiixp ATI IXP AC97 controller (snd-atiixp) snd-atiixp-modem ATI IXP MC97 controller (snd-atiixp-modem) snd-virtuoso Asus Virtuoso driver (snd-virtuoso) [...]
Plays a test sound on a sound card:
tux >
sudo
yast sound playtest card=0
Removes a configured sound card:
tux >
sudo
yast sound remove card=0tux >
sudo
yast sound remove all
Specifies new values for a sound card:
tux >
sudo
yast sound set card=0 volume=80
Displays detailed information about a sound card:
tux >
sudo
yast sound show card=0 Parameters of card 'ThinkPad X240' (using module snd-hda-intel): align_buffer_size Force buffer and period sizes to be multiple of 128 bytes. bdl_pos_adj BDL position adjustment offset. beep_mode Select HDA Beep registration mode (0=off, 1=on) (default=1). Default Value: 0 enable_msi Enable Message Signaled Interrupt (MSI) [...]
Prints a configuration summary for all sound cards on the system:
tux >
sudo
yast sound summary
Specifies the volume level of a sound card:
sudo
yast sound volume card=0 play
Controls the variables in files under /etc/sysconfig
.
yast sysconfig
accepts the following commands:
Sets empty value to a variable:
tux >
sudo
yast sysconfig clear=POSTFIX_LISTEN
If the variable is available in several files, use the VARIABLE_NAME$FILE_NAME syntax:
tux >
sudo
yast sysconfig clear=CONFIG_TYPE$/etc/sysconfig/mail
Displays detailed information about a variable:
tux >
sudo
yast sysconfig details variable=POSTFIX_LISTEN Description: Value: File: /etc/sysconfig/postfix Possible Values: Any value Default Value: Configuration Script: postfix Description: Comma separated list of IP's NOTE: If not set, LISTEN on all interfaces
Displays summary of modified variables. Use all
to
list all variables and their values:
tux >
sudo
yast sysconfig list all AOU_AUTO_AGREE_WITH_LICENSES="false" AOU_ENABLE_CRONJOB="true" AOU_INCLUDE_RECOMMENDS="false" [...]
Sets a value to a variable:
tux >
sudo
yast sysconfig set DISPLAYMANAGER=gdm
If the variable is available in several files, use the VARIABLE_NAME$FILE_NAME syntax:
tux >
sudo
yast sysconfig set CONFIG_TYPE$/etc/sysconfig/mail=advanced
Configures a TFTP server. yast tftp-server
accepts the
following commands:
Specifies the directory of the TFTP server:
tux >
sudo
yast tftp-server directory path=/srv/tftptux >
sudo
yast tftp-server directory list Directory Path: /srv/tftp
Controls the status of the TFTP server service:
tux >
sudo
yast tftp-server status disabletux >
sudo
yast tftp-server status show Service Status: falsetux >
sudo
yast tftp-server status enable
Configures the time zone. yast timezone
accepts the
following commands:
Lists all available time zones grouped by region:
tux >
sudo
yast timezone list Region: Africa Africa/Abidjan (Abidjan) Africa/Accra (Accra) Africa/Addis_Ababa (Addis Ababa) [...]
Specifies new values for the time zone configuration:
tux >
sudo
yast timezone set timezone=Europe/Prague hwclock=local
Displays the time zone configuration summary:
tux >
sudo
yast timezone summary Current Time Zone: Europe/Prague Hardware Clock Set To: Local time Current Time and Date: Mon 12. March 2018, 11:36:21 CET
Manages user accounts. yast users
accepts the following
commands:
Adds a new user:
tux >
sudo
yast users add username=user1 password=secret home=/home/user1
For a complete list of options, run yast users add
help
.
Deletes an existing user account:
tux >
sudo
yast users delete username=user1 delete_home
For a complete list of options, run yast users delete
help
.
Changes an existing user account:
tux >
sudo
yast users edit username=user1 password=new_secret
For a complete list of options, run yast users edit
help
.
Lists existing users filtered by user type:
tux >
sudo
yast users list system
For a complete list of options, run yast users list
help
.
Displays details about a user:
tux >
sudo
yast users show username=wwwrun Full Name: WWW daemon apache List of Groups: www Default Group: wwwrun Home Directory: /var/lib/wwwrun Login Shell: /sbin/nologin Login Name: wwwrun UID: 456
For a complete list of options, run yast users show
help
.
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 20 “Installing or Removing Software”, Section 20.1 “Definition of Terms”.
Zypper is a command line package manager for installing, updating and removing packages. It also manages repositories. It is especially useful for accomplishing remote software management tasks or managing software from shell scripts.
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.
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
Additionally, you can choose from one or more global options by typing them immediately before the command:
tux >
sudo
zypper --non-interactive patch
In the above example, the option --non-interactive
means
that the command is run without asking anything (automatically applying
the default answers).
To use options that are specific to a particular command, type them immediately after the command:
tux >
sudo
zypper patch --auto-agree-with-licenses
In 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, license will be accepted automatically.
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 mplayer
Some 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 mc and vim packages from
the factory
repository while being verbose:
tux >
sudo
zypper -v install --from factory mc vim
The --from
option keeps all repositories
enabled (for solving any dependencies) while requesting the package from the
specified repository. --repo
is an alias for --from
, and you may use either one.
Most Zypper commands have a dry-run
option that does a
simulation of the given command. It can be used for test purposes.
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
Zypper subcommands are executables that are stored in the zypper_execdir,
/usr/lib/zypper/commands
. If a subcommand is not found
in the zypper_execdir, Zypper automatically searches the rest of your $PATH
for it. This enables writing your own local extensions and storing them in
userspace.
Executing subcommands in the Zypper shell, and using global Zypper options are not supported.
List your available subcommands:
tux >
zypper help subcommand
[...]
Available zypper subcommands in '/usr/lib/zypper/commands'
appstream-cache
lifecycle
migration
search-packages
Zypper subcommands available from elsewhere on your $PATH
<none>
View the help screen for a subcommand:
tux >
zypper help appstream-cache
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.
There are various ways to address packages with the commands
zypper install
and zypper remove
.
tux >
sudo
zypper install MozillaFirefox
tux >
sudo
zypper install MozillaFirefox-52.2
tux >
sudo
zypper install mozilla:MozillaFirefox
Where mozilla
is the alias of the repository from
which to install.
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*'
-debuginfo
Packages
When 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'
For example, to install a package without knowing its name, capabilities come in handy. The following command will install the package MozillaFirefox:
tux >
sudo
zypper install firefox
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'
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
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
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
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.
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 6.1.6, “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.
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.
Repositories from the SUSE Linux Enterprise Server installation media are still
configured but disabled after successful installation. You can use the
--plus-content
option to install packages from the
installation media instead of the online repositories. Before calling
zypper
, ensure the media is available, for example by
inserting the DVD into the computer's drive.
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.
There are three different ways to update software using Zypper: by
installing patches, by installing a new version of a package or by updating
the entire distribution. The latter is achieved with zypper
dist-upgrade
. Upgrading SUSE Linux Enterprise Server is discussed in
Book “Upgrade Guide”, Chapter 1 “Upgrade Paths and Methods”.
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.
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.
To find out whether patches are available, Zypper allows viewing the following information:
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.
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
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:
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
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
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
[...]
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 (while maintaining
system integrity), use:
tux >
sudo
zypper update
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.
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.
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 15, The systemd
Daemon.
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
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 http://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.
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.
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"
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
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.
The zypper search
command works on package names, or,
optionally, on package summaries and descriptions. Strings wrapped in
/
are interpreted as regular expressions. By default,
the search is not case-sensitive.
fire
tux >
zypper search "fire"
MozillaFirefox
tux >
zypper search --match-exact "MozillaFirefox"
tux >
zypper search -d fire
tux >
zypper search -u fire
fir
not followed be e
tux >
zypper se "/fir[^e]/"
To search for packages both within and outside of currently enabled SLE
modules, use the search-packages
subcommand. This
command contacts the SUSE Customer Center and searches all modules for matching packages,
for example:
tux >
zypper search-packages package1 package2
zypper search-packages
provides the following options:
Search for an exact match of your search string: -x
,
--match-exact
Group the results by module (default: group by package):
-g,
--group-by-module
Display more detailed information about packages: -d
,
--details
Output search results in XML: --xmlout
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.
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
SUSE products are generally supported for 10 years. Often, you can extend that standard lifecycle by using the extended support offerings of SUSE which add three years of support. Depending on your product, find the exact support lifecycle at https://www.suse.com/lifecycle.
To check the lifecycle of your product and the supported package, use the
zypper lifecycle
command as shown below:
root #
zypper lifecycle
Product end of support Codestream: SUSE Linux Enterprise Server 15 2028-07-31 SUSE Linux Enterprise Server 15 n/a* Module end of support Basesystem Module n/a* Server Applications Module n/a* Package end of support if different from product: SUSEConnect Now, installed 0.3.11-1.4, update available 0.3.11-3.3.1 ca-certificates-mozilla Now, installed 2.22-2.12, update available 2.24-4.3.1 curl Now, installed 7.60.0-1.1, update available 7.60.0-3.3.1 e2fsprogs Now, installed 1.43.8-2.44, update available 1.43.8-4.3.1 glibc Now, installed 2.26-11.8, update available 2.26-13.3.1
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.
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.
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.
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
http://en.opensuse.org/SDB:Zypper_usage. A list of
software changes for the latest SUSE Linux Enterprise Server version can be found at
http://en.opensuse.org/openSUSE:Zypper versions.
RPM (RPM Package Manager) is used for managing software packages. Its main
commands are rpm
and rpmbuild
. The
powerful RPM database can be queried by the users, system administrators and
package builders for detailed information about the installed software.
rpm
has five modes: installing, uninstalling
(or updating) software packages, rebuilding the RPM database, querying RPM
bases or individual RPM archives, integrity checking of packages and signing
packages. rpmbuild
can be used to build installable
packages from pristine sources.
Installable RPM archives are packed in a special binary format. These
archives consist of the program files to install and certain meta information
used during the installation by rpm
to configure the
software package or stored in the RPM database for documentation purposes.
RPM archives normally have the extension .rpm
.
For several packages, the components needed for software development
(libraries, headers, include files, etc.) have been put into separate
packages. These development packages are only needed if you want to compile
software yourself (for example, the most recent GNOME packages). They can
be identified by the name extension -devel
, such as the
packages alsa-devel
and
gimp-devel
.
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.
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 the noreplace
label was specified in the .spec
file.
Following an update, .rpmsave
and
.rpmnew
files should be removed after comparing them,
so they do not obstruct future updates. The .rpmorig
extension is assigned if the file has not previously been recognized by the
RPM database.
Otherwise, .rpmsave
is used. In other words,
.rpmorig
results from updating from a foreign format to
RPM. .rpmsave
results from updating from an older RPM
to a newer RPM. .rpmnew
does not disclose any
information to whether the system administrator has made any changes to the
configuration file. A list of these files is available in
/var/adm/rpmconfigcheck
. Some configuration files (like
/etc/httpd/httpd.conf
) are not overwritten to allow
continued operation.
The -U
switch is not only an
equivalent to uninstalling with the -e
option and
installing with the -i
option. Use -U
whenever possible.
To remove a package, enter rpm -e
PACKAGE. This command only deletes the package if
there are no unresolved dependencies. It is theoretically impossible to
delete Tcl/Tk, for example, as long as another application requires it. Even
in this case, RPM calls for assistance from the database. If such a deletion
is, for whatever reason, impossible (even if no
additional dependencies exist), it may be helpful to rebuild the RPM
database using the option --rebuilddb
.
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.
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
.
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 process
BUILD
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.
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.
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 20 “Installing or Removing Software”.
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.
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.
Although snapshots themselves do not differ in a technical sense, we distinguish between three types of snapshots, based on the events that trigger them:
A single snapshot is created every hour. Old snapshots are automatically deleted. By default, the first snapshot of the last ten days, months, and years are kept. Timeline snapshots are disabled by default.
Whenever one or more packages are installed with YaST or Zypper, a
pair of snapshots is created: one before the installation starts
(“Pre”) and another one after the installation has finished
(“Post”). In case an important system component such as the
kernel has been installed, the snapshot pair is marked as important
(important=yes
). Old snapshots are automatically
deleted. By default the last ten important snapshots and the last ten
“regular” (including administration snapshots) snapshots
are kept. Installation snapshots are enabled by default.
Whenever you administrate the system with YaST, a pair of snapshots is created: one when a YaST module is started (“Pre”) and another when the module is closed (“Post”). Old snapshots are automatically deleted. By default the last ten important snapshots and the last ten “regular” snapshots (including installation snapshots) are kept. Administration snapshots are enabled by default.
Some directories need to be excluded from snapshots for different reasons. The following list shows all directories that are excluded:
/boot/grub2/i386-pc
,
/boot/grub2/x86_64-efi
,
/boot/grub2/powerpc-ieee1275
,
/boot/grub2/s390x-emu
A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The first two directories are present on AMD64/Intel 64 machines, the latter two on IBM POWER and on IBM Z, respectively.
/home
If /home
does not reside on a separate partition, it
is excluded to avoid data loss on rollbacks.
/opt
Third-party products usually get installed to /opt
. It
is excluded to avoid uninstalling these applications on rollbacks.
/srv
Contains data for Web and FTP servers. It is excluded to avoid data loss on rollbacks.
/tmp
All directories containing temporary files and caches are excluded from snapshots.
/usr/local
This directory is used when manually installing software. It is excluded to avoid uninstalling these installations on rollbacks.
/var
This directory contains many variable files, including logs, temporary
caches, third party products in /var/opt
, and is the
default location for virtual machine images and databases. Therefore this
subvolume is created to exclude all of this variable data from snapshots
and has Copy-On-Write disabled.
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.
Each of the three snapshot types (timeline, installation, administration) can be enabled or disabled independently.
Enabling.
snapper -c root set-config "TIMELINE_CREATE=yes"
Disabling.
snapper -c root set-config "TIMELINE_CREATE=no"
Timeline snapshots are enabled by default, except for the root partition.
Enabling:
Install the package
snapper-zypp-plugin
Disabling:
Uninstall the package
snapper-zypp-plugin
Installation snapshots are enabled by default.
Enabling:
Set USE_SNAPPER
to yes
in
/etc/sysconfig/yast2
.
Disabling:
Set USE_SNAPPER
to no
in
/etc/sysconfig/yast2
.
Administration snapshots are enabled by default.
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>
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
.
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.
Apart from snapshots on Btrfs
file systems, Snapper
also supports taking snapshots on thinly-provisioned LVM volumes (snapshots
on regular LVM volumes are not supported) formatted
with XFS, Ext4 or Ext3. For more information and setup instructions on LVM
volumes, refer to Book “Deployment Guide”, Chapter 10 “Expert Partitioner”, Section 10.2 “LVM Configuration”.
To use Snapper on a thinly-provisioned LVM volume you need to create a
Snapper configuration for it. On LVM it is required to specify the file
system with
--fstype=lvm(FILESYSTEM)
.
ext3
, etx4
or xfs
are valid values for FILESYSTEM. Example:
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”.
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:
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.
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.
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 yast2 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 zypp(y2base)
in the
; Zypper snapshots are labeled
zypp(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
as yast MODULE_NAME
in the
; Zypper snapshots are labeled
zypp(zypper)
.
tux >
sudo
snapper list -t pre-post Pre # | Post # | Pre Date | Post Date | Description ------+--------+-------------------------------+-------------------------------+-------------- 311 | 312 | Tue 06 May 2018 14:05:46 CEST | Tue 06 May 2018 14:05:52 CEST | zypp(y2base) 340 | 341 | Wed 07 May 2018 16:15:10 CEST | Wed 07 May 2018 16:15:16 CEST | zypp(zypper) 342 | 343 | Wed 07 May 2018 16:20:38 CEST | Wed 07 May 2018 16:20:42 CEST | zypp(y2base) 344 | 345 | Wed 07 May 2018 16:21:23 CEST | Wed 07 May 2018 16:21:24 CEST | zypp(zypper) 346 | 347 | Wed 07 May 2018 16:41:06 CEST | Wed 07 May 2018 16:41:10 CEST | zypp(y2base) 348 | 349 | Wed 07 May 2018 16:44:50 CEST | Wed 07 May 2018 16:44:53 CEST | zypp(y2base) 350 | 351 | Wed 07 May 2018 16:46:27 CEST | Wed 07 May 2018 16:46:38 CEST | zypp(y2base)
Get a list of changed files for a snapshot pair with snapper
status
PRE..POST. Files
with content changes are marked with , files that
have been added are marked with and deleted files
are marked with .
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/Sigmd5
To 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.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 yast2 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 timeline
CONFIG 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..0
Replace 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 NAME
If 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 FILENAME2
If you do not specify file names, all changed files will be restored.
The GRUB 2 version included on SUSE Linux Enterprise Server can boot from Btrfs snapshots.
Together with Snapper's rollback feature, this allows to recover a
misconfigured system. Only snapshots created for the default Snapper
configuration (root
) are bootable.
As of SUSE Linux Enterprise Server 15 SP1 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:
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.
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, a single partition
and a single subvolume. Directories 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 partitions.
The system needs to be bootable via the installed boot loader.
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 rollback
and 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).
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.
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 | | | |
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 keysEach 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.
A complete system rollback, restoring the complete system to the identical state as it was in when a snapshot was taken, is not possible.
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.
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.
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.
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 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.
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.
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
.
You may enable snapshots for users' /home
directories, which supports a number of use cases:
Individual users may manage their own snapshots and rollbacks.
System users, for example database, system, and network admins who want to track copies of configuration files, documentation, and so on.
Samba shares with home directories and Btrfs backend.
Each user's directory is a Btrfs subvolume of /home
.
It is possible to set this up manually
(see Section 7.4.3, “Manually Enabling Snapshots in Home Directories”). However, a
more convenient way is to use pam_snapper
.
The pam_snapper
package installs the
pam_snapper.so
module and helper scripts, which
automate user creation and Snapper configuration.
pam_snapper
provides integration with the
useradd
command, pluggable
authentication modules (PAM), and Snapper. By default it creates snapshots
at user login and logout, and also creates time-based snapshots as some
users remain logged in for extended periods of time. You may change the
defaults using the normal Snapper commands and configuration files.
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.
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
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
The way Snapper behaves is defined in a configuration file that is specific
for each partition or Btrfs
subvolume. These
configuration files reside under /etc/snapper/configs/
.
In case the root file system is big enough (approximately 12 GB), snapshots
are automatically enabled for the root file system /
upon installation. The corresponding default configuration is named
root
. It creates and manages the YaST and Zypper
snapshot. See Section 7.5.1.1, “Configuration Data” for a list
of the default values.
As explained in Section 7.1, “Default Setup”, enabling snapshots requires additional free space in the root file system. The amount depends on the amount of packages installed and the amount of changes made to the volume that is included in snapshots. The snapshot frequency and the number of snapshots that get archived also matter.
There is a minimum root file system size that is required to automatically
enable snapshots during the installation. Currently this size is
approximately 12 GB. This value may change in the future, depending on
architecture and the size of the base system. It depends on the values for
the following tags in the file /control.xml
from the
installation media:
<root_base_size> <btrfs_increase_percentage>
It is calculated with the following formula: ROOT_BASE_SIZE * (1 + BTRFS_INCREASE_PERCENTAGE/100)
Keep in mind that this value is a minimum size. Consider using more space for the root file system. As a rule of thumb, double the size you would use when not having enabled snapshots.
You may create your own configurations for other partitions formatted with
Btrfs
or existing subvolumes on a
Btrfs
partition. In the following example we will set up
a Snapper configuration for backing up the Web server data residing on a
separate, Btrfs
-formatted partition mounted at
/srv/www
.
After a configuration has been created, you can either use
snapper
itself or the YaST
module to restore files from these snapshots. In YaST you need to select
your , while you need to specify
your configuration for snapper
with the global switch
-c
(for example, snapper -c myconfig
list
).
To create a new Snapper configuration, run snapper
create-config
:
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
The snapper
command offers several subcommands for managing
existing configurations. You can list, show, delete and modify them:
Use the subcommand snapper list-configs
to get all
existing configurations:
tux >
sudo
snapper list-configs Config | Subvolume -------+---------- root | / usr | /usr local | /local
Use the subcommand snapper -c
CONFIG get-config
to display the
specified configuration. Replace CONFIG with
one of the configuration names shown by
snapper 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
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 by snapper list-configs
.
Possible values for OPTION and
VALUE are listed in Section 7.5.1.1, “Configuration Data”.
Use the subcommand snapper -c
CONFIG delete-config
to delete a
configuration. Replace CONFIG with one of the
configuration names shown by snapper list-configs
.
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 to yes
, 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.
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/www
The 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/or
ALLOW_GROUPS
to grant permissions to users and/or groups,
respectively. Multiple entries need to be separated by
Space. To grant permissions to the user
www_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
Snapper is not restricted to creating and managing snapshots automatically by configuration; you can also create snapshot pairs (“before and after”) or single snapshots manually using either the command-line tool or the YaST module.
All Snapper operations are carried out for an existing configuration (see
Section 7.5, “Creating and Modifying Snapper Configurations” for details). You can only take
snapshots of partitions or volumes for which a configuration exists. By
default the system configuration (root
) is used.
To create or manage snapshots for your own configuration you need to
explicitly choose it. Use the
drop-down box in YaST or specify the -c
on the command
line (snapper -c MYCONFIG
COMMAND
).
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), use snapper -c
root list
or snapper 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.
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 a
post
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 a
pre
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.
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).
Deletes old snapshots when a certain snapshot count is reached.
Deletes old snapshots having passed a certain age, but keeps several hourly, daily, monthly, and yearly snapshots.
Deletes pre/post snapshot pairs with empty diffs.
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 the
pre
snapshot number 30
. 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.
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"
10
Modifies the metadata of snapshot 10 for the default
(root
) configuration. The cleanup algorithm is set to
timeline
.
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.
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.
Snapshots occupy disk space and over time the amount of disk space occupied by the snapshots may become large. To prevent disks from running out of space, Snapper offers algorithms to automatically delete old snapshots. These algorithms differentiate between timeline snapshots and numbered snapshots (administration plus installation snapshot pairs). You can specify the number of snapshots to keep for each type.
In addition to that, you can optionally specify a disk space quota, defining the maximum amount of disk space the snapshots may occupy. It is also possible to automatically delete pre and post snapshots pairs that do not differ.
A clean-up algorithm is always bound to a single Snapper configuration, so you need to configure algorithms for each configuration. To prevent certain snapshots from being automatically deleted, refer to Can a snapshot be protected from deletion? .
The default setup (root
) is configured to do clean-up
for numbered snapshots and empty pre and post snapshot pairs. Quota support
is enabled—snapshots may not occupy more than 50% of the available
disk space of the root partition. Timeline snapshots are disabled by
default, therefore the timeline clean-up algorithm is also disabled.
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/or
NUMBER_LIMIT_IMPORTANT
and an
age specified with NUMBER_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"
for
NUMBER_LIMIT
and "4-10"
for
NUMBER_LIMIT_IMPORTANT
.
Example command to change or set:
tux >
sudo
snapper -c CONFIG set-config "NUMBER_LIMIT=10"
In 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 example 10
, 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
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 with
TIMELINE_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 for
TIMELINE_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.
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"
.
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
.
In addition to the number and/or timeline clean-up algorithms described above, Snapper supports quotas. You can define what percentage of the available space snapshots are allowed to occupy. This percentage value always applies to the Btrfs subvolume defined in the respective Snapper configuration.
Btrfs quotas are applied to subvolumes, not to users. You may apply
disk space quotas to users and groups (for example, with the
quota
command) in addition to using Btrfs quotas.
If Snapper was enabled during the installation, quota support is
automatically enabled. In case you manually enable Snapper at a later point
in time, you can enable quota support by running snapper
setup-quota
. This requires a valid configuration (see
Section 7.5, “Creating and Modifying Snapper Configurations” for more information).
Quota support is controlled by the following parameters of a Snapper configuration.
QGROUP
The Btrfs quota group used by Snapper. If not set, run snapper
setup-quota
. If already set, only change if you are familiar
with man 8 btrfs-qgroup
. This value is set with
snapper 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*
and
TIMELINE_LIMIT*
values, even if the quota will be
exceeded. It is therefore recommended to specify ranged values
(MIN-MAX
)
for NUMBER_LIMIT*
and
TIMELINE_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.
Snapshots share data, for efficient use of storage space, so using ordinary
commands like du
and df
won't measure
used disk space accurately. When you want to free up disk space on Btrfs
with quotas enabled, you need to know how much exclusive disk space is
used by each snapshot, rather than shared space. Snapper 0.6 and up reports
the used disk space for each snapshot in the
Used Space
column:
root #
snapper--iso list
# | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata
----+--------+-------+---------------------+------+------------+---------+-----------------------+--------------
0 | single | | | root | | | current |
1* | single | | 2019-07-22 13:08:38 | root | 16.00 KiB | | first root filesystem |
2 | single | | 2019-07-22 14:21:05 | root | 14.23 MiB | number | after installation | important=yes
3 | pre | | 2019-07-22 14:26:03 | root | 144.00 KiB | number | zypp(zypper) | important=no
4 | post | 3 | 2019-07-22 14:26:04 | root | 112.00 KiB | number | | important=no
5 | pre | | 2019-07-23 08:19:36 | root | 128.00 KiB | number | zypp(zypper) | important=no
6 | post | 5 | 2019-07-23 08:19:43 | root | 80.00 KiB | number | | important=no
7 | pre | | 2019-07-23 08:20:50 | root | 256.00 KiB | number | yast sw_single |
8 | pre | | 2019-07-23 08:23:22 | root | 112.00 KiB | number | zypp(ruby.ruby2.5) | important=no
9 | post | 8 | 2019-07-23 08:23:35 | root | 64.00 KiB | number | | important=no
10 | post | 7 | 2019-07-23 08:24:05 | root | 16.00 KiB | number | |
The btrfs
command provides another view of space used by
snapshots:
root #
btrfs qgroup show -p /
qgroupid rfer excl parent
-------- ---- ---- ------
0/5 16.00KiB 16.00KiB ---
[...]
0/272 3.09GiB 14.23MiB 1/0
0/273 3.11GiB 144.00KiB 1/0
0/274 3.11GiB 112.00KiB 1/0
0/275 3.11GiB 128.00KiB 1/0
0/276 3.11GiB 80.00KiB 1/0
0/277 3.11GiB 256.00KiB 1/0
0/278 3.11GiB 112.00KiB 1/0
0/279 3.12GiB 64.00KiB 1/0
0/280 3.12GiB 16.00KiB 1/0
1/0 3.33GiB 222.95MiB ---
The qgroupid
column displays the identification number for
each subvolume, assigning a qgroup level/ID combination.
The rfer
column displays the total amount of data
referred to in the subvolume.
The excl
column displays the exclusive data in each
subvolume.
The parent
column shows the parent qgroup of the subvolumes.
The final item, 1/0
, shows the totals for the parent
qgroup. In the above example, 222.95 MiB will be freed if all subvolumes
are removed. Run the following command to see which snapshots are associated
with each subvolume:
root #
btrfs subvolume list -st /
ID gen top level path
-- --- --------- ----
267 298 266 @/.snapshots/1/snapshot
272 159 266 @/.snapshots/2/snapshot
273 170 266 @/.snapshots/3/snapshot
274 171 266 @/.snapshots/4/snapshot
275 287 266 @/.snapshots/5/snapshot
276 288 266 @/.snapshots/6/snapshot
277 292 266 @/.snapshots/7/snapshot
278 296 266 @/.snapshots/8/snapshot
279 297 266 @/.snapshots/9/snapshot
280 298 266 @/.snapshots/10/snapshot
Doing an upgrade from one service pack to another results in snapshots occupying a lot of disk space on the system subvolumes. Manually deleting these snapshots after they are no longer needed is recommended. See Section 7.6.4, “Deleting Snapshots” for details.
/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.
Yes—refer to Section 7.3, “System Rollback by Booting from Snapshots” for details.
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 the number
or
timeline
algorithm assigned. To remove such an
assignment from one or more snapshots, proceed as follows:
List all available snapshots:
tux >
sudo
snapper list -a
Memorize 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 #n
Check the result by running snapper list -a
again.
The entry in the column Cleanup
should now be empty
for the snapshots you modified.
See the Snapper home page at http://snapper.io/.
This document describes the basic principles of the Kernel Live Patching (KLP) technology, and provides usage guidelines for the SLE Live Patching service.
klp
ToolKLP 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 enabling dynamic patching of the kernel, the technology also encourages users to install critical security updates without deferring them to a scheduled downtime.
Enabling KLP requires no special steps other than enabling the Live Patching service, and then applying the patches as they become available. The service is part of the normal software management system, and patches are installed (or removed) with the usual package management tools. There is no need to install or manually select special kernels.
A KLP patch is a kernel module, intended for replacing whole functions in the kernel. Kernel Live Patching primarily offers in-kernel infrastructure for integration of the patched code with the base kernel code at runtime.
The information provided in this document relates to the AMD64/Intel 64 and POWER architectures. KLP is supported on the Xen hypervisor.
Kernel Live Patching using KLP is for quick emergency response, when serious vulnerabilities or system stability issues are known and should be fixed as quickly as possible. It is not used for scheduled updates where time is not critical.
Typical use cases for Kernel Live Patching include systems like memory databases with huge amounts of RAM, where boot-up times of 15 minutes or more are not uncommon, large simulations that need weeks or months without a restart, or infrastructure building blocks providing continuous service to many customers.
The main advantage of Kernel Live Patching is that it never requires stopping the kernel, not even for a short time period.
A KLP patch is a .ko
kernel module in an RPM package.
It is inserted into the kernel using the insmod
command
when the package is installed or updated. Kernel Live Patching replaces whole functions in
the kernel, even if they are being executed. An updated KLP module can
replace an existing patch if necessary.
Kernel Live Patching is also lean—it contains only a small amount of code, because it leverages other standard Linux technologies.
Kernel Live Patching uses the ftrace infrastructure to perform patching. The following describes the implementation on the AMD64/Intel 64 architecture.
To patch a kernel function, Kernel Live Patching needs some space at the start of the function to insert a jump to a new function. This space is allocated during kernel compilation by GCC with function profiling turned on. In particular, a 5-byte call instruction is injected to the start of kernel functions. When such instrumented kernel is booting, profiling calls are replaced by 5-byte NOP (no operation) instructions.
After patching starts, the first byte is replaced by the INT3 (breakpoint) instruction. This ensures atomicity of the 5-byte instruction replacement. The other four bytes are replaced by the address to the new function. Finally, the first byte is replaced by the JMP (long jump) opcode.
Inter-processor non-maskable interrupts (IPI NMI) are used throughout the process to flush speculative decoding queues of other CPUs in the system. This allows switching to the new function without ever stopping the kernel, not even for a very short moment. The interruptions by IPI NMIs can be measured in microseconds and are not considered service interruptions as they happen while the kernel is running in any case.
Callers are never patched. Instead, the callee's NOPs are replaced by a JMP to the new function. JMP instructions remain forever. This takes care of function pointers, including in structures, and does not require saving any old data for the possibility of un-patching.
However, these steps alone would not be good enough: since the functions would be replaced non-atomically, a new fixed function in one part of the kernel could still be calling an old function elsewhere or vice versa. If the semantics of the function interfaces changed in the patch, chaos would ensue.
Thus, until all functions are replaced, Kernel Live Patching uses an approach based on trampolines and similar to RCU (read-copy-update), to ensure a consistent view of the world to each user space thread, kernel thread and kernel interrupt. A per-thread flag is set on each kernel entry and exit. This way, an old function would always call another old function and a new function always a new one. Once all processes have the "new universe" flag set, patching is complete, trampolines can be removed and the code can operate at full speed without performance impact other than an extra-long jump for each patched function.
To activate SLE Live Patching on your system, follow these steps:
Your SLES system must be registered. Register your system either during
system installation, or after installation with the YaST
yast2
registration
). If your SLES system is already registered,
but SLE Live Patching is not yet activated, run the
yast2 registration
command and
click .
Select
in the list of available extensions and click .Confirm the license terms and click
.Enter your SLE Live Patching registration code and click
.
Check the Live
Patching
and
SLE Live Patching Lifecycle Data
should be
automatically selected for installation, and there may be additional
packages to satisfy dependencies.
Click
to complete the installation. This will install the base Kernel Live Patching components on your system, the initial live patch, and any dependencies.This section describes how to find, install, and remove KLP patches.
Before installing new patches, run the klp status
command to query current status,
which must be ready
and not in_progress
.
You cannot apply new patches until previous patch installations are completed. Invocations of the old kernel functions are not completely eliminated until all sleeping processes wake up and get out of the way. This can take a considerable amount of time. Sleeping processes that use the old kernel functions are not considered a security issue. (See Section 8.6, “Stuck Kernel Execution Threads” for
information on managing prolonged in_progress
states.)
Use the normal package management system, zypper
or
YaST, to view and install available patches. The following example
searches for available patches, and then installs the most recent
patch. It is not necessary to install all patches in order; when there
are multiple patches available install the most recent.
tux >
sudo
zypper se kernel-livepatch | kernel-livepatch-4_12_14-25_16-default | Kernel live patch module | package | kernel-livepatch-4_12_14-25_19-default | Kernel live patch module | package | kernel-livepatch-4_12_14-25_22-default | Kernel live patch module | packagetux >
sudo
zypper in kernel-livepatch-4_12_14-25_22-default
If you need to remove a KLP patch, use zypper
just
as you would for any other package. List your installed live patch
packages by using zypper
to search for
kernel-livepatch
:
tux >
sudo
zypper se kernel-livepatch | kernel-livepatch-4_12_14-25_16-default | Kernel live patch module | package | kernel-livepatch-4_12_14-25_19-default | Kernel live patch module | package i | kernel-livepatch-4_12_14-25_22-default | Kernel live patch module | package
Remove the patch using zypper
:
tux >
sudo
zypper rm kernel-livepatch-4_12_14-25_22-default
Wait for initrd
to automatically rebuild, then reboot the
machine.
klp
Tool #Edit source
Several Kernel Live Patching management tasks can be simplified with the
klp
tool. The available commands are:
klp status
Displays the overall status of Kernel Live Patching (ready
or
in_progress
).
klp patches
Displays the list of loaded KLP patches.
klp blocking
Lists processes that are preventing Kernel Live Patching from finishing. By
default only the PIDs are listed. Specifying -v
prints
command lines if available. -vv
displays stack traces.
For detailed information, see man klp
.
Kernel threads must be prepared to handle Kernel Live Patching. Third-party software may
not support Kernel Live Patching, and may spawn kernel execution threads. These threads will block the patching process indefinitely. As an emergency measure, you may
force the completion of the patching process without waiting for all execution threads to cross the safety checkpoint by writing 0
into
/sys/kernel/livepatch/*/transition/
(replacing the
asterisk wildcard with your file name). Consult SUSE support before
performing this procedure.
Expiration dates of live patches can be accessed with zypper
lifecycle
. (Make sure that the package
lifecycle-data-sle-module-live-patching is installed.)
When the expiration date of a patch is reached, no further live patches for this kernel version will be supplied. Plan an update of your kernel before the end of the live patch lifecycle period.
For details about zypper lifecycle
, see the
Showing Life Cycle Information in the Admin
Guide.
Kernel Live Patching is based on replacing functions. Data structure alteration can be accomplished only indirectly with Kernel Live Patching. As a result, changes to kernel data structure require special care and, if the change is too large, rebooting might be required. Kernel Live Patching also might not be able to handle situations where one compiler is used to compile the old kernel and another compiler is used for compiling the patch.
Because of the way Kernel Live Patching works, support for third-party modules that are spawning kernel threads is limited.
Fixes for SUSE Common Vulnerability Scoring System (CVSS; SUSE CVSS is based on the CVSS v3.0 system) level 7+ vulnerabilities and bug fixes related to system stability or data corruption will be shipped in the scope of SLE Live Patching. It might not be possible to produce a live patch for all kinds of fixes fulfilling the above criteria. SUSE reserves the right to skip fixes where production of a kernel live patch is unviable because of technical reasons. For more information on CVSS, which is the base for the SUSE CVSS rating, see https://www.first.org/cvss/.
While resolving a technical difficulty with SUSE support, you may receive a Program Temporary Fix (PTF). PTFs may be issued for various packages including those forming the base of SLE Live Patching.
Kernel Live Patching PTFs complying with the conditions described in the previous section can be installed as usual and SUSE will ensure that the system in question does not need to be rebooted and that future live updates are applied cleanly.
PTFs issued for the base kernel disrupt the live patching process. First, installing the PTF kernel means a reboot as the kernel cannot be replaced as a whole at runtime. Second, another reboot is needed to replace the PTF with any regular maintenance updates for which the live patches are issued.
PTFs for other packages in SLE Live Patching can be treated like regular PTFs with the usual guarantees.
Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root filesystem is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not affect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the admin must decide if a reboot is more expensive than disturbing running services. If reboots are too expensive then do not use transactional updates.
Transactional updates are run daily by the
transactional-update
script. The script checks for
available updates. If there are any updates, it creates a new snapshot of
the root file system in the background, and then fetches updates from the
release channels. After the new snapshot is completely updated, it is
marked as active and will be the new default root file system after the next
reboot of the system. When transactional-update
is set to run
automatically (which is the default behavior) it also reboots the system.
Both the time that the update runs and the reboot maintenance window are
configurable.
Only packages that are part of the snapshot of the root file system can be updated. If packages contain files that are not part of the snapshot, the update could fail or break the system.
RPMs that require a license to be accepted cannot be updated.
As a technical preview, there are certain limitations in functionality. The
following packages will not work with transactional-update
:
The nginx default index.html page may not be available
tomcat-webapps and tomcat-admin-webapps
phpMyAdmin
sca-appliance-*
mpi-selector
emacs works except for Emacs games
bind and bind-chrootenv
docbook*
sblim-sfcb*
texlive*
iso_ent
openjade
opensp
pcp
plymouth
postgresql-server-10
pulseaudio-gdm-hooks
smartmontools
The updater component of the system installer does not work with a read-only filesystem as it has no support for transactional updates.
Further considerations:
In general it is a good idea to minimize the time between updating the system and rebooting the machine.
Only one update can be applied at a time. Be sure to reboot after an update, and before the next update is applied.
update-alternatives
should not be run after a
transactional update until the machine has been rebooted.
Do not create new system users or system groups after a transactional update until after reboot. It is acceptable to create normal users and groups (UID > 1000, GID > 1000).
YaST is not yet aware of transactional updates. If a YaST module needs
to install additional packages, this will not work. Normal system
operations only modifying configuration files in /etc
will work.
For php7-fastcgi, you must manually create a symlink,
/srv/www/cgi-bin/php
, that points to
/usr/bin/php-cgi
.
ntpis part of the Legacy Module for migration from older SLES versions. It is not supported on a new SUSE Linux Enterprise Server installation, and has been replaced by chrony. If you continue to use ntp, a fresh installation is required to work correctly with transactional updates.
sblim-sfcb: The whole sblim ecosystem is incompatible with transactional update.
btrfs-defrag
from the
btrfsmaintenance package does not work with a read-only
root filesystem.
For btrfs-balance
, the variable
BTRFS_BALANCE_MOUNTPOINTS
in
/etc/sysconfig/btrfsmaintenance
must be changed from
/
to /.snapshots
.
For btrfs-scrub
, the variable
BTRFS_SCRUB_MOUNTPOINTS
in
/etc/sysconfig/btrfsmaintenance
must be changed from
/
to /.snapshots
.
You must enable the Transactional Server Module during system installation, and then select the Transactional Server System Role. Installing any package from the Transactional Server Module later in a running system is NOT supported and may break the system.
Note that changing the subvolume layout of the root partition, or putting
sub-directories or subvolumes of the root partition on their own partitions
(except /home
, /var
,
/srv
, and /opt
) is not supported,
and will most likely break the system.
Automatic updates are controlled by a systemd.timer
that runs once per day. This applies all updates, and informs
rebootmgrd
that the machine should be rebooted. You may
adjust the time when the update runs, see systemd.timer(5). To adjust the
maintenance window, which is when rebootmgrd
reboots the
system, see rebootmgrd(8).
You can disable automatic transactional updates with this command:
root #
systemctl --now disable transactional-update.timer
transactional-update
Command #Edit source
The transactional-update
command enables you to install
or remove updates of your system in an atomic way. Updates are applied only
if all of them can be successfully installed.
transactional-update
creates a snapshot of your system
before the update is applied, and you can restore this snapshot.
All changes become active only after reboot.
cleanup
If the current root filesystem is identical to the active root
filesystem (after a reboot, before transactional-update
creates a new snapshot with updates), all old snapshots without a
cleanup algorithm get a cleanup algorithm set. This ensures that old
snapshots will be deleted by Snapper. (See the section about cleanup
algorithms in snapper(8).) This also removes all unreferenced (and thus
unused) /etc
overlay directories in
/var/lib/overlay
:
root #
transactional-update cleanup
pkg in/install
Installs individual packages from the available channels using the
zypper install
command. This command can also be used
to install Program Temporary Fix (PTF) RPM files.
root #
transactional-update pkg install package_name
or
root #
transactional-update pkg install rpm1 rpm2
pkg rm/remove
Removes individual packages from the active snapshot using the
zypper remove
command. This command can also be used
to remove PTF RPM files.
root #
transactional-update pkg remove package_name
pkg up/update
Updates individual packages from the active snapshot using the
zypper update
command. Only packages that are part of
the snapshot of the base file system can be updated.
root #
transactional-update pkg remove package_name
up/update
If there are new updates available, a new snapshot is created and
zypper up/update
updates the snapshot.
root #
transactional-update up
dup
If there are new updates available, a new snapshot is created and
zypper dup –no-allow-vendor-change
updates the
snapshot. The snapshot is activated afterwards and becomes the new root
file system after reboot.
root #
transactional-update dup
patch
If there are new updates available, a new snapshot is created and
zypper patch
updates the snapshot.
root #
transactional-update patch
rollback
This sets the default subvolume. On systems with a read-write file system
snapper rollback
is called. On a read-only file system
and without any argument, the current system is set to a new default root
file system. If you specify a number, that snapshot is used as the
default root file system. On a read-only file system, it does not create
any additional snapshots.
root #
transactional-update rollback snapshot_number
grub.cfg
This creates a new GRUB2 configuration. Sometimes it is necessary to
adjust the boot configuration, for example adding additional kernel
parameters. Edit /etc/default/grub, run
transactional-update grub.cfg
, and then reboot to
activate the change. You must immediately reboot, or the new GRUB2
configuration will be overwritten with the default by the next
transactional-update.
root #
transactional-update grub.cfg
reboot
This parameter triggers a reboot after the action is completed.
root #
transactional-update dup reboot
--help
This prints a help screen with options and subcommands.
root #
transactional-update --help
If the upgrade fails, run supportconfig
to collect log
data. Provide the resulting files, including
/var/log/transactional-update.log
to SUSE Support.
Virtual Network Computing (VNC) enables you to access a remote computer via a graphical desktop, and run remote graphical applications. VNC is platform-independent and accesses the remote machine from any operating system. This chapter describes how to connect to a VNC server with the desktop clients vncviewer and Remmina, and how to operate a VNC server.
SUSE Linux Enterprise Server supports two different kinds of VNC sessions: One-time sessions that “live” as long as the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated.
A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.
vncviewer
Client #Edit source
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.
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 10.4, “Configuring Persistent VNC Server Sessions” for further info.
By running vncviewer
without specifying
--listen
or a host to connect to, it will show a window
to ask for connection details. Enter the host into the field like in Section 10.1.1, “Connecting Using the vncviewer CLI”
and click .
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.
Remmina is a modern and feature rich remote desktop client. It supports several access methods, for example VNC, SSH, RDP, and Spice.
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
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.
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 of the profile. It will be listed in the main window.
The protocol to use when connecting to the remote session, for example VNC.
The IP or DNS address and display number of the remote server.
Credentials to use for remote authentication. Leave empty for no authentication.
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.You can either start a previously saved session, or quick-start a remote session without saving the connection details.
To start a remote session quickly without adding and saving connection details, use the drop-down box and text box at the top of the main window.
Select the communication protocol from the drop-down box, for example 'VNC', then enter the VNC server DNS or IP address followed by a colon and a display number, and confirm with Enter.
To open a specific remote session, double-click it from the list of sessions.
Remote sessions are opened in tabs of a separate window. Each tab hosts one session. The toolbar on the left of the window helps you manage the windows/sessions, such as toggle fullscreen mode, resize the window to match the display size of the session, send specific keystrokes to the session, take screenshots of the session, or set the image quality.
To edit a saved remote session, right-click its name in Remmina's main window and select . Refer to Section 10.2.3, “Adding Remote Sessions” for the description of the relevant fields.
To copy a saved remote session, right-click its name in Remmina's main window and select . In the window, change the name of the profile, optionally adjust relevant options, and confirm with .
To Delete a saved remote session, right-click its name in Remmina's main window and select . Confirm with in the next dialog.
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 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.
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.
YaST 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.
The default configuration on SUSE Linux Enterprise Server serves sessions with a
resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are
available on ports 5901
for
“regular” VNC viewers (equivalent to VNC display
1
) and on port
5801
for Web browsers.
Other configurations can be made available on different ports, see Section 10.3.3, “Configuring One-time VNC Sessions”.
VNC display numbers and X display numbers are independent in one-time sessions. A VNC display number is manually assigned to every configuration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the configurations, it automatically gets a free X display number.
By default, both the VNC client and server try to communicate securely via a self-signed SSL certificate, which is generated after installation. You can either use the default one, or replace it with your own. When using the self-signed certificate, you need to confirm its signature before the first connection—both in the VNC viewer and the Web browser.
To connect to a one-time VNC session, a VNC viewer must be installed, see
also Section 10.1, “The vncviewer
Client”. Alternatively use a
JavaScript-capable Web browser to view the VNC session by entering the
following URL: http://jupiter.example.com:5801
You can skip this section, if you do not need or want to modify the default configuration.
One-time VNC sessions are started via the systemd
socket
xvnc.socket
. By default it offers six
configuration blocks: three for VNC viewers (vnc1
to
vnc3
), and three serving a JavaScript client
(vnchttpd1
to vnchttpd3
). By default
only vnc1
and vnchttpd1
are active.
To activate the VNC server socket at boot time, run the following command:
tux >
sudo
systemctl enable xvnc.socket
To start the socket immediately, run:
tux >
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 10.1, “Enabling One-time VNC Sessions”, the ports
5801
and
5901
are opened in the firewall.
If the network interface serving the VNC sessions is protected by a
firewall, you need to manually open the respective ports when activating
additional ports for VNC sessions. See
Book “Security and Hardening Guide”, Chapter 24 “Masquerading and Firewalls” for instructions.
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 10.1, “The vncviewer
Client” for more details. Alternatively
use a JavaScript-capable Web browser to view the VNC session by entering the
following URL: http://jupiter.example.com:5801
There are two types of persistent VNC sessions:
vncserver
#Edit sourceThis 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 24 “Masquerading and Firewalls” for details on how to configure the firewall.
vncserver
uses the ports
5901
for display
:1
, 5902
for
display :2
, and so on. For persistent sessions, the
VNC display and the X display usually have the same number.
To start a session with a resolution of 1024x768 pixel and with a color depth of 16-bit, enter the following command:
vncserver -alwaysshared -geometry 1024x768 -depth 16
The vncserver
command picks an unused display number
when none is given and prints its choice. See man 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
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.
vncmanager
#Edit sourceStart
› › .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.
YaST 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.
After you enable the VNC session management as described in Procedure 10.3, “Enabling Persistent VNC Sessions”, you can normally connect to
the remote session with your favorite VNC viewer, such as
vncviewer
or Remmina. You will be presented with the
login screen. After you log in, the 'VNC' icon will appear in the system
tray of your desktop environment. Click the icon to open the window. If it does not appear or if your desktop
environment does not support icons in the system tray, run
vncmanager-controller
manually.
There are several settings that influence the VNC session's behavior:
This is equivalent to a one-time session. It is not visible to others and will be terminated after you disconnect from it. Refer to Section 10.3, “Configuring One-time Sessions on the VNC Server” for more information.
The session is visible to other users and keeps running even after you disconnect from it.
Here you can specify the name of the persistent session so that it is easily identified when reconnecting.
The session will be freely accessible without having to log in under user credentials.
You need to log in with a valid user name and password to access the session. Lists the valid user names in the
text box.Prevents multiple users from joining the session at the same time.
Allows multiple users to join the persistent session at the same time. Useful for remote presentations or trainings.
Confirm with
.After you set up a persistent VNC session as described in Section 10.4.2.1, “Configuring Persistent VNC Sessions”, you can join it with your VNC viewer. After your VNC client connects to the server, you will be prompted to choose whether you want to create a new session, or join the existing one:
After you click the name of the existing session, you may be asked for login credentials, depending on the persistent session settings.
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:
No authentication.
Authentication using custom password.
Authentication using PAM to verify user's password.
No encryption.
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.
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).
With 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).
Today, a typical user has several computers: home and workplace machines, a laptop, a smartphone or a tablet. This makes the task of keeping files and documents in synchronization across multiple devices all the more important.
Before you start using a synchronization tool, you should familiarize yourself with its features and functionality. Make sure to back up your important files.
For synchronizing a large amount of data over a slow network connection, Rsync offers a reliable method of transmitting only changes within files. This applies not only to text files but also binary files. To detect the differences between files, Rsync subdivides the files into blocks and computes check sums over them.
Detecting changes requires some computing power. So make sure that machines on both ends have enough resources, including RAM.
Rsync can be particularly useful when large amounts of data containing only minor changes need to be transmitted regularly. This is often the case when working with backups. Rsync can also be useful for mirroring staging servers that store complete directory trees of Web servers to a Web server in a DMZ.
Despite its name, Rsync is not a synchronization tool. Rsync is a tool that copies data only in one direction at a time. It does not and cannot do the reverse. If you need a bidirectional tool which can synchronize both source and destination, use Csync.
Rsync is a command-line tool that has the following basic syntax:
rsync [OPTION] SOURCE [SOURCE]... DEST
You can use Rsync on any local or remote machine, provided you have access and write permissions. It is possible to have multiple SOURCE entries. The SOURCE and DEST placeholders can be paths, URLs, or both.
Below are the most common Rsync options:
-v
Outputs more verbose text
-a
Archive mode; copies files recursively and preserves time stamps, user/group ownership, file permissions, and symbolic links
-z
Compresses the transmitted data
When working with Rsync, you should pay particular attention to trailing slashes. A trailing slash after the directory denotes the content of the directory. No trailing slash denotes the directory itself.
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/
.
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
.
Rsync can run as a daemon
(rsyncd
) listing 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/backup
Specify ownership. In this case, the directory is owned by user
tux
in group
users
:
root #
chown
tux.users /var/backup
Configure 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 | |
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 | |
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 rsyncd
Test 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:
tux >
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:
tux >
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.
Bidirectional file synchronizer, see https://www.csync.org/.
Creates incremental backups, see http://rsnapshot.org.
A file synchronizer similar to CSync but with a graphical interface, see http://www.seas.upenn.edu/~bcpierce/unison/.
A disaster recovery framework, see the Administration Guide of the SUSE Linux Enterprise High Availability Extension https://documentation.suse.com/sle-ha/.
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.
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.
This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 12, Introduction to the Boot Process. For details on Secure Boot support for UEFI machines, see Chapter 13, UEFI (Unified Extensible Firmware Interface).
systemd
DaemonThe program systemd is the process with process ID 1. It is responsible for initializing the system in the required way. systemd is started directly by the kernel and resists signal 9, which normally terminates processes. All other programs are either started directly by systemd or by one of its chi…
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.
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 system
The 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 the initramfs
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 two
systemd
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 an initramfs
. However, since the
initramfs
is stored as
/boot/initrd
, it is often called
“initrd”. In this chapter we exclusively use the name
initramfs
.
The Linux boot process consists of several stages, each represented by a different component:
During the initialization phase the machine's hardware is set up and the devices are prepared. This process differs significantly between hardware architectures.
SUSE Linux Enterprise Server uses the boot loader GRUB 2 on all architectures. Depending on the architecture and firmware, starting the GRUB 2 boot loader can be a multi-step process. The purpose of the boot loader is to load the kernel and the initial, RAM-based file system (initramfs). For more information about GRUB 2, refer to Chapter 14, The Boot Loader GRUB 2.
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.
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 ext2-formatted partition
/boot/zipl
. 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 parameter initgrub
, 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.
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
.
initramfs
file #Edit source
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
.
Because the initramfs
contains drivers, it needs
to be updated whenever a new version of one of its drivers is
available. This is done automatically when installing the package
containing the driver update. YaST or zypper will inform you about
this by showing the output of the command that generates the
initramfs
. However, there are some occasions
when you need to regenerate an initramfs
manually:
If you need to change hardware (for example, hard disks), and this
hardware requires different drivers to be in the kernel at boot time,
you must update the initramfs
file.
Open or create
/etc/dracut.conf.d/10-DRIVER.conf
and add the following line (mind the leading whitespace):
force_drivers+=" DRIVER1"
Replace DRIVER1 with the module name of the driver. If you need to add more than one driver, list them space-separated:
force_drivers+=" DRIVER1 DRIVER2"
Proceed with Procedure 12.1, “Generate an initramfs”.
Whenever you move swap files, or system directories like
/usr
in a running system to a RAID or logical
volume, you need to create an initramfs
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
with mount -a
and/or swapon -a
).
Proceed with Procedure 12.1, “Generate an initramfs”.
Whenever you add (or remove) a disk to a logical volume group
or a Btrfs RAID containing the root file system, you need to create an
initramfs
that contains support for the
enlarged volume. Follow the instructions at Procedure 12.1, “Generate an initramfs”.
Proceed with Procedure 12.1, “Generate an initramfs”.
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 with sysctl
--system
at runtime, the changes are not saved into the
initramfs
file. You need to update it by
proceeding as outlined in Procedure 12.1, “Generate an initramfs”.
Note that all commands in the following procedure need to be executed as
user root
.
Generate a new initramfs
file by running
dracut MY_INITRAMFS
Replace MY_INITRAMFS with a file name of
your choice. The new initramfs
will be created
as /boot/MY_INITRAMFS
.
Alternatively, run dracut -f
. This will overwrite
the currently used, existing file.
(Skip this step if you ran dracut -f
in the previous
step.) Create a link to the initramfs
file you
created in the previous step:
(cd /boot && ln -sf MY_INITRAMFS initrd)
On the IBM IBM Z architecture, additionally run
grub2-install
.
The temporary root file system mounted by the kernel from the
initramfs
contains the executable systemd
(which
is called init
on
initramfs
in the following, also see Section 12.1, “Terminology”. This program performs all actions needed
to mount the proper root file system. It provides kernel functionality for
the needed file system and device drivers for mass storage controllers with
udev
.
The main purpose of init
on
initramfs
is to prepare the mounting of and access
to the real root file system. Depending on your system configuration,
init
on initramfs
is
responsible for the following tasks.
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.
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.
If you configured your system to hold the root file system under RAID or
LVM, init
on initramfs
sets up LVM or RAID to enable access to the root file system later.
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
on initramfs
.
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.
When init
on initramfs
is called during the initial boot as part of the installation process, its
tasks differ from those mentioned above. Note that the installation system
also does not start systemd
from
initramfs
—these tasks are performed by
linuxrc
.
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.
As mentioned in Section 12.2.2.1, “The initramfs
file”, the boot process
starts with a minimum set of drivers that can be used with most
hardware configurations. On AArch64, POWER, and AMD64/Intel 64 machines,
linuxrc
starts an initial hardware scanning process
that determines the set of drivers suitable for your hardware
configuration. On IBM 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 with systemd
; for more information, see Section 15.6.4, “Loading Kernel Modules”.
When the hardware is properly recognized, the appropriate drivers are
loaded. The udev
program
creates the special device files and linuxrc
starts the installation system with the YaST installer.
Finally, linuxrc
starts YaST, which starts
the package installation and the system configuration.
After the “real” root file system has been found, it is
checked for errors and mounted. If this is successful, the
initramfs
is cleaned and the systemd
daemon on
the root file system is executed. systemd
is Linux's system and service
manager. It is the parent process that is started as PID 1 and acts as an
init system which brings up and maintains user space services. See Chapter 15, The systemd
Daemon for details.
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.
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.
Microsoft’s Key Exchange Key (KEK) is installed by default.
The Secure Boot feature is enabled by default on UEFI/x86_64 installations. You can find the
option in the tab of the dialog. It supports booting when the secure boot is activated in the firmware, while making it possible to boot when it is deactivated.The Secure Boot feature requires that a GUID Partitioning Table (GPT) replaces the old partitioning with a Master Boot Record (MBR). If YaST detects EFI mode during the installation, it will try to create a GPT partition. UEFI expects to find the EFI programs on a FAT-formatted EFI System Partition (ESP).
Supporting UEFI Secure Boot requires having a boot loader with a digital signature that the firmware recognizes as a trusted key. That key is trusted by the firmware a priori, without requiring any manual intervention.
There are two ways of getting there. One is to work with hardware vendors to have them endorse a SUSE key, which SUSE then signs the boot loader with. The other way is to go through Microsoft’s Windows Logo Certification program to have the boot loader certified and have Microsoft recognize the SUSE signing key (that is, have it signed with their KEK). By now, SUSE got the loader signed by UEFI Signing Service (that is Microsoft in this case).
At the implementation layer, SUSE uses the shim
loader which is installed by default. It is a smart solution that avoids
legal issues, and simplifies the certification and signing step
considerably. The shim
loader’s job is to load a
boot loader such as GRUB 2 and verify it; this boot loader in
turn will load kernels signed by a SUSE key only. SUSE provides this
functionality since SLE11 SP3 on fresh installations with UEFI Secure Boot
enabled.
There are two types of trusted users:
First, those who hold the keys. The Platform Key (PK) allows almost everything. The Key Exchange Key (KEK) allows all a PK can except changing the PK.
Second, anyone with physical access to the machine. A user with physical access can reboot the machine, and configure UEFI.
UEFI offers two types of variables to fulfill the needs of those users:
The first is the so-called “Authenticated Variables”, which can be updated from both within the boot process (the so-called Boot Services Environment) and the running OS. This can be done only when the new value of the variable is signed with the same key that the old value of the variable was signed with. And they can only be appended to or changed to a value with a higher serial number.
The second is the so-called “Boot Services Only Variables”.
These variables are accessible to any code that runs during the boot
process. After the boot process ends and before the OS starts, the boot
loader must call the ExitBootServices
call. After
that, these variables are no longer accessible, and the OS cannot touch
them.
The various UEFI key lists are of the first type, as this allows online updating, adding, and blacklisting of keys, drivers, and firmware fingerprints. It is the second type of variable, the “Boot Services Only Variable”, that helps to implement Secure Boot in a secure and open source-friendly manner, and thus compatible with GPLv3.
SUSE starts with shim
—a small and simple EFI
boot loader signed by SUSE and Microsoft.
This allows shim
to load and execute.
shim
then goes on to verify that the boot loader
it wants to load is trusted.
In a default situation shim
will use an
independent SUSE certificate embedded in its body. In addition,
shim
will allow to “enroll”
additional keys, overriding the default SUSE key. In the following, we call
them “Machine Owner Keys” or MOKs for short.
Next the boot loader will verify and then boot the kernel, and the kernel will do the same on the modules.
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 a single MOK, you can make shim
trust keys
from several vendors, allowing dual- and multi-boot from the boot loader.
The following is based on http://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 http://en.opensuse.org/openSUSE:UEFI_Image_File_Sign_Tools#Create_Your_Own_Certificate.
Package the key and the certificate as a PKCS#12 structure:
tux >
openssl pkcs12 -export -inkey key.asc -in cert.pem \
-name kernel_cert -out cert.p12
Generate an NSS database for use with pesign
:
tux >
certutil -d . -N
Import the key and the certificate contained in PKCS#12 into the NSS database:
tux >
pk12util -d . -i cert.p12
“Bless” the kernel with the new signature using
pesign
:
tux >
pesign -n . -c kernel_cert -i arch/x86/boot/bzImage \
-o vmlinuz.signed -s
List the signatures on the kernel image:
tux >
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:
tux >
openssl x509 -in cert.pem -outform der -out cert.der
Copy the certificate to the ESP for easier access:
tux >
sudo
cp cert.der /boot/efi/
Use mokutil
to launch the MOK list automatically.
Import the certificate to MOK:
tux >
mokutil --root-pw --import cert.der
The --root-pw
option enables usage of the root
user directly.
Check the list of certificates that are prepared to be enrolled:
tux >
mokutil --list-new
Reboot the system; shim
should launch
MokManager. You need to enter the root
password to confirm the
import of the certificate to the MOK list.
Check if the newly imported key was enrolled:
tux >
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.
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.
When booting in Secure Boot mode, the following features apply:
Installation to UEFI default boot loader location, a mechanism to keep or restore the EFI boot entry.
Reboot via UEFI.
Xen hypervisor will boot with UEFI when there is no legacy BIOS to fall back to.
UEFI IPv6 PXE boot support.
UEFI videomode support, the kernel can retrieve video mode from UEFI to configure KMS mode with the same parameters.
UEFI booting from USB devices is supported.
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.
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.
This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 12, Introduction to the Boot Process. For details on Secure Boot support for UEFI machines, see Chapter 13, UEFI (Unified Extensible Firmware Interface).
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.
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 command grub2-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 these entries will also
be parsed when using grub-once
.
/etc/default/grub
This file controls the user settings of GRUB 2 and usually includes additional environmental settings such as backgrounds and themes.
/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 some 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 will
automatically run this command.
/boot/grub2/grub.cfg
#Edit source
The graphical splash screen with the boot menu is based on the GRUB 2
configuration file /boot/grub2/grub.cfg
, which
contains information about all partitions or operating systems that can be
booted by the menu.
Every time the system is booted, GRUB 2 loads the menu file directly from
the file system. For this reason, GRUB 2 does not need to be re-installed
after changes to the configuration file. grub.cfg
is
automatically rebuilt with kernel installations or removals.
grub.cfg
is compiled from the file
/etc/default/grub
and scripts found in the
/etc/grub.d/
directory when running the command
grub2-mkconfig -o /boot/grub2/grub.cfg
. Therefore you should never
edit the file manually. Instead, edit the related source files or use the
YaST module to modify the configuration as
described in Section 14.3, “Configuring the Boot Loader with YaST”.
/etc/default/grub
#Edit sourceMore general options of GRUB 2 belong here, 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_
In addition to already defined variables, the user may introduce their own
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 set in this file are general options that affect all boot entries. Specific options for Xen kernels or the Xen hypervisor can be set via the GRUB_*_XEN_* configuration options. See below for details.
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 the
grub2-once
or grub2-set-default
commands. While grub2-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 the GRUB_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
will cause 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 mode. 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 will completely replace 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 will
only replace parameters ofGRUB_CMDLINE_LINUX_DEFAULT
.
GRUB_CMDLINE_XEN
This entry specifies the kernel parameters for the Xen guest kernel
only—the operation principle is the same as for
GRUB_CMDLINE_LINUX
.
GRUB_CMDLINE_XEN_DEFAULT
Same as GRUB_CMDLINE_XEN
—the operation
principle is the same as for
GRUB_CMDLINE_LINUX_DEFAULT
.
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 default
gfxterm
(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. Note that 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 typing videoinfo
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 will be 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.
/etc/grub.d
#Edit source
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.
If you want 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 will be 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 the
exec 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 will be automatically included into
/boot/grub2/grub.cfg
just after 40_custom at
boot time.
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 usually
sufficient, particularly in the case of 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. Note that
GRUB 2 partition numbers start with 1
and not with
0
as in GRUB Legacy.
(hd1) /dev/disk-by-id/DISK3 ID (hd2) /dev/disk-by-id/DISK1 ID (hd3) /dev/disk-by-id/DISK2 ID
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 the set
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, you will be prompted 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 will boot the selected boot entry.
For more information, see https://www.gnu.org/software/grub/manual/grub.html#Security.
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.
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
directory. For POWER systems it
activates the PReP partition. Use this option on systems with
old BIOS and/or legacy operating systems because they may fail
to boot from a non-active partition. It is safe to leave this
option active.
If MBR contains a custom 'non-GRUB' code, this option replaces it with a generic, operating system independent code. If you deactivate this option, the system may become unbootable.
Starts TrustedGRUB2, which supports trusted computing functionality (Trusted Platform Module (TPM)). For more information refer to https://github.com/Sirrix-AG/TrustedGRUB2.
The
section includes the following options:This is appropriate for traditional legacy BIOS booting.
This is appropriate for UEFI booting.
This is usually the best choice if you have an already working system.
In most cases YaST defaults to the appropriate choice.
If your computer has more than one hard disk, you can specify the boot sequence of the disks. The first disk in the list is where GRUB 2 will be installed in the case of booting from MBR. It is the disk where SUSE Linux Enterprise Server is installed by default. The rest of the list is a hint for GRUB 2's device mapper (see Section 14.2.4, “Mapping between BIOS Drives and Linux Devices”).
The default value is usually valid for almost all deployments. If you change the boot order of disks wrongly, the system may become unbootable on the next reboot. For example, if the first disk in the list is not part of the BIOS boot order, and the other disks in the list have empty MBRs.
Open the
tab.Click
.If more than one disk is listed, select a disk and click
or to reorder the displayed disks.Click
two times to save the changes.Advanced boot parameters can be configured via the
tab.Change the value of
by typing in a new value and clicking the appropriate arrow key with your mouse.When selected, the boot loader searches for other systems like Windows or other Linux installations.
Hides the boot menu and boots the default entry.
Select the desired entry from the “Default Boot Section” list. Note that the “>” sign in the boot entry name delimits the boot section and its subsection.
Protects the boot loader and the system with an additional password. For
details on manual configuration, see Section 14.2.6, “Setting a Boot Password”.
If this option is activated, the boot password is required on every boot,
which means the system does not boot automatically. However, if you prefer
the behavior of GRUB 1, additionally enable . With this setting, anybody is allowed to select
a boot entry and boot the system, whereas the password for the GRUB 2 root
user is only required for modifying boot entries.
Specify optional kernel parameters here to enable/disable system features, add drivers, etc.
SUSE has released one or more kernel boot command line parameters for all software mitigations that have been deployed to prevent CPU side-channel attacks. Some of those may result in performance loss. Choose one the following options to strike a balance between security and performance, depending on your setting:
Enables all mitigations required for your CPU model, but does not protect against cross-CPU thread attacks. This setting may impact performance to some degree, depending on the workload. .
Provides the full set of available security mitigations. Enables all mitigations required for your CPU model. In addition, it disables Simultaneous Multithreading (SMT) to avoid side-channel attacks across multiple CPU threads. This setting may further impact performance, depending on the workload. .
Disables all mitigations. Side-channel attacks against your CPU are possible, depending on the CPU model. This setting has no impact on performance. .
Does not set any mitigation level. Specify your CPU mitigations manually by using the kernel command line options. .
When checked, the boot menu appears on a graphical splash screen rather than in a text mode. The resolution of the boot screen is set automatically by default, but you can manually set it via
. The graphical theme definition file can be specified with the file-chooser. Only change this if you want to apply your own, custom-made theme.
If your machine is controlled via a serial console, activate this option
and specify which COM port to use at which speed. See info
grub
or
http://www.gnu.org/software/grub/manual/grub.html#Serial-terminal
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.
Interactivity is strongly limited. Typing often does not result in visual feedback. To see where the cursor is, type an underscore (_).
The 3270 terminal is much better at displaying and refreshing screens than the 3215 terminal.
“Traditional” cursor movement is not possible. Alt, Meta, Ctrl and the cursor keys do not work. To move the cursor, use the key combinations listed in Section 14.4.2, “Key Combinations”.
The caret (^) is used as a control character. To type a literal ^ followed by a letter, type ^, ^, LETTER.
The Enter key does not work, use ^–J instead.
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 |
grub2-mkconfig
Generates a new /boot/grub2/grub.cfg
based on
/etc/default/grub
and the scripts from
/etc/grub.d/
.
grub2-mkconfig -o /boot/grub2/grub.cfg
Running grub2-mkconfig
without any parameters prints
the configuration to STDOUT where it can be reviewed. Use
grub2-script-check
after
/boot/grub2/grub.cfg
has been written to check its
syntax.
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.cfg
grub2-mkrescue
Creates a bootable rescue image of your installed GRUB 2 configuration.
grub2-mkrescue -o save_path/name.iso iso
grub2-script-check
Checks the given file for syntax errors.
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.
grub2-once number_of_the_boot_entry
grub2-once
HelpCall the program without any option to get a full list of all possible options.
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.
systemd
Daemon #Edit source
The program systemd
is the process with process ID 1. It is responsible for
initializing the system in the required way. systemd
is started directly by
the kernel and resists signal 9, which normally terminates processes.
All other programs are either started directly by systemd or by one of its
child processes.
Systemd is a replacement for the System V init daemon. systemd
is fully
compatible with System V init (by supporting init scripts). One of the main
advantages of systemd is that it considerably speeds up boot time by
aggressively paralleling service starts. Furthermore, systemd only starts a
service when it is really needed. Daemons are not started unconditionally at
boot time, but rather when being required for the first time. systemd also
supports Kernel Control Groups (cgroups), snapshotting and restoring the
system state and more. See http://www.freedesktop.org/wiki/Software/systemd/ for details.
This section will go into detail about the concept behind 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
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 .socket
Path. 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. Usually 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 see http://www.freedesktop.org/software/systemd/man/systemd.unit.html
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, since there is only one
command to memorize for the majority of service-handling 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
.
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:
systemctl reload|restart|start|status|stop|... MY_SERVICE(S)
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:
tux >
sudo
systemctl start MY_1ST_SERVICE MY_2ND_SERVICE
To list all services available on the system:
tux >
sudo
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 will be 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 will be 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 |
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.
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 completely 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 |
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.
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
.
default.target
The target that is booted by default. Not a “real” target,
but rather a symbolic link to another target like
graphic.target
. Can be permanently changed via
YaST (see Section 15.4, “Managing Services with YaST”). To change it for
a session, use the kernel parameter
systemd.unit=MY_TARGET.target
at the boot prompt.
emergency.target
Starts an emergency shell on the console. Only use it at the boot prompt
as systemd.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 system without network.
To remain compatible with the System V init runlevel system, systemd
provides special targets named
runlevelX.target
mapping the
corresponding runlevels numbered X.
If you want to know 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 |
/etc/inittab
The runlevels in a System V init system are configured in
/etc/inittab
. systemd does not
use this configuration. Refer to
Section 15.5.3, “Creating Custom Targets” for instructions on how
to create your own bootable target.
Use the following commands to operate with target units:
Task |
systemd Command |
System V init Command |
---|---|---|
Change the current target/runlevel |
|
|
Change to the default target/runlevel |
|
n/a |
Get the current target/runlevel |
With systemd there is usually more than one active target. The command lists all currently active targets. |
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 |
systemd offers the means to analyze the system start-up process. You can
review the list of all services and their status (rather than having to
parse /var/log/
). systemd also allows you to scan the
start-up procedure to find out how much time each service start-up
consumes.
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
chronyd.service loaded active running NTP Server Daemon
polkit.service loaded active running Authorization Manager
postfix.service loaded active running Postfix Mail Transport Ag+
rc-local.service loaded active exited /etc/init.d/boot.local Co+
rsyslog.service loaded active running System Logging Service
[...]
LOAD = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB = The low-level unit activation state, values depend on unit type.
161 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.
To restrict the output to services that failed to start, use the
--failed
option:
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
[...]
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.
root #
systemd-analyze
Startup finished in 2666ms (kernel) + 21961ms (userspace) = 24628ms
root #
systemd-analyze blame
15.000s backup-rpmdb.service
14.879s mandb.service
7.646s backup-sysconfig.service
4.940s postfix.service
4.921s logrotate.service
4.640s libvirtd.service
4.519s display-manager.service
3.921s btrfsmaintenance-refresh.service
3.466s lvm2-monitor.service
2.774s plymouth-quit-wait.service
2.591s firewalld.service
2.137s initrd-switch-root.service
1.954s ModemManager.service
1.528s rsyslog.service
1.378s apparmor.service
[...]
root #
systemd-analyze plot > jupiter.example.com-startup.svg
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
:
tux >
dmesg -T | less
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
.
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
› › .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).Select a service from the table. The
column shows whether it is currently running ( ) or not ( ). Toggle its status by choosing .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.
Select a service from the table. The
column shows whether it is currently or . Toggle its status by choosing .By enabling or disabling a service you configure whether it is started during booting (
) or not ( ). This setting will not affect the current session. To change its status in the current session, you need to start or stop it.
To view the status message of a service, select it from the list and
choose systemctl
-l
status
MY_SERVICE.
Faulty runlevel settings may make your system unusable. Before applying your changes, make absolutely sure that you know their consequences.
systemd
#Edit source
The following sections contain some examples for
systemd
customization.
Always do systemd customization in /etc/systemd/
,
never in /usr/lib/systemd/
.
Otherwise your changes will be overwritten by the next update of systemd.
The systemd unit files are located in
/usr/lib/systemd/system
. If you want to customize
them, proceed as follows:
Copy the files you want to modify from
/usr/lib/systemd/system
to
/etc/systemd/system
. Keep the file names identical
to the original ones.
Modify the copies in /etc/systemd/system
according
to your needs.
For an overview of your configuration changes, use the
systemd-delta
command. It can compare and identify
configuration files that override other configuration files. For details,
refer to the systemd-delta
man page.
The modified files in /etc/systemd
will take
precedence over the original files in
/usr/lib/systemd/system
, provided that their file name
is the same.
xinetd
Services to systemd
#Edit source
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
).
If you only want to add a few lines to a configuration file or modify a small part of it, you can use so-called “drop-in” files. Drop-in files let you extend the configuration of unit files without having to edit or override the unit files themselves.
For example, to change one value for the FOOBAR
service located in
/usr/lib/systemd/system/FOOBAR.SERVICE
,
proceed as follows:
Create a directory called
/etc/systemd/system/FOOBAR.service.d/
.
Note the .d
suffix. The directory must otherwise be
named like the service that you want to patch with the drop-in file.
In that directory, create a file
WHATEVERMODIFICATION.conf
.
Make sure it only contains the line with the value that you want to modify.
Save your changes to the file. It will be used as an extension of the original file.
On System V init SUSE systems, runlevel 4 is unused to allow
administrators to create their own runlevel configuration. systemd allows
you to create any number of custom targets. It is suggested to start by
adapting an existing target such as
graphical.target
.
Copy the configuration file
/usr/lib/systemd/system/graphical.target
to
/etc/systemd/system/MY_TARGET.target
and adjust it according to your needs.
The configuration file copied in the previous step already covers the
required (“hard”) dependencies for the target. To also cover
the wanted (“soft”) dependencies, create a directory
/etc/systemd/system/MY_TARGET.target.wants
.
For each wanted service, create a symbolic link from
/usr/lib/systemd/system
into
/etc/systemd/system/MY_TARGET.target.wants
.
When you have finished setting up the target, reload the systemd configuration to make the new target available:
tux >
sudo
systemctl daemon-reload
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.
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:
tux >
sudo
systemctl status systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.timer - Daily Cleanup of Temporary Directories Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-clean.timer; static) Active: active (waiting) since Tue 2018-04-09 15:30:36 CEST; 1 weeks 6 days ago Docs: man:tmpfiles.d(5) man:systemd-tmpfiles(8) Apr 09 15:30:36 jupiter systemd[1]: Starting Daily Cleanup of Temporary Directories. Apr 09 15:30:36 jupiter systemd[1]: Started Daily Cleanup of Temporary Directories.
For more information on temporary files handling, see man 5
tmpfiles.d
.
Section 15.6.9, “Debugging Services” explains how
to view log messages for a given service. However, displaying log messages
is not restricted to service logs. You can also access and query the
complete log messages written by systemd
—the so-called
“Journal”. Use the command
journalctl
to display the complete log messages
starting with the oldest entries. Refer to man 1
journalctl
for options such as applying filters or
changing the output format.
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
.
tux >
sudo
systemctl snapshot MY_SNAPSHOT.snapshot
tux >
sudo
systemctl delete MY_SNAPSHOT.snapshot
tux >
sudo
systemctl show MY_SNAPSHOT.snapshot
tux >
sudo
systemctl isolate MY_SNAPSHOT.snapshot
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.
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:
Create a drop-in file in /etc/modules-load.d
directory (see man modules-load.d
for the syntax)
Create a drop-in file in /etc/tmpfiles.d
(see
man tmpfiles.d
for the syntax)
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
):
tux >
sudo
systemctl daemon-reloadtux >
sudo
systemctl enable before
Every time you modify the service file, you need to run:
tux >
sudo
systemctl daemon-reload
On a traditional System V init system it is not always possible to clearly assign 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 terminate correctly, leaving some 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
. The result will look like the following
(shortened) 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
├─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.
As explained in Section 15.6.6, “Kernel Control Groups (cgroups)”, it is not always possible to assign a process to its parent service process in a System V init system. This makes it difficult to terminate a service and all of its children. Child processes that have not been terminated will remain as zombie processes.
systemd's concept of confining each service into a cgroup makes it possible
to clearly identify all child processes of a service and therefore allows
you to send a signal to each of these processes. Use systemctl
kill
to send signals to services. For a list of available signals
refer to man 7 signals
.
SIGTERM
to a Service
SIGTERM
is the default signal that is sent.
tux >
sudo
systemctl kill MY_SERVICE
Use the -s
option to specify the signal that should be
sent.
tux >
sudo
systemctl kill -s SIGNAL MY_SERVICE
By default the kill
command sends the signal to
all
processes of the specified cgroup. You can restrict
it to the control
or the main
process.
The latter is for example useful to force a service to reload its
configuration by sending SIGHUP
:
tux >
sudo
systemctl kill -s SIGHUP --kill-who=main MY_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.
Terminating dbus
or restarting it
in the running system is similar to an attempt to terminate or restart pid
1. It will break systemd client/server communication and make 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.
By default, systemd is not overly verbose. If a service was started
successfully, no output will be produced. In case of a failure, a short
error message will be displayed. However, systemctl
status
provides means to debug 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.
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 Apr 2018 16:52:26 +0200; 29s ago Process: 3088 ExecStart=/usr/sbin/start_apache2 -D SYSTEMD -k start (code=exited, status=1/FAILURE) CGroup: name=systemd:/system/apache2.service Apr 04 16:52:26 g144 start_apache2[3088]: httpd2-prefork: Syntax error on line 205 of /etc/apache2/httpd.conf: Syntax error on li...alHost>
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
To display a “live stream” of service messages, use the
--follow
option, which works like
tail
-f
:
tux >
sudo
systemctl --follow status chronyd
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.
For more information on systemd refer to the following online resources:
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.
SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. But SUSE Linux Enterprise Server supports 32-bit application use in 64-bit system environments. This chapter offers a brief overview of 32-bit support im…
journalctl
: Query the systemd
Journal
When systemd
replaced traditional init scripts in SUSE Linux Enterprise 12
(see Chapter 15, 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.
update-alternatives
: Managing Multiple Versions of Commands and FilesOften, there are several versions of the same tool installed on a system. To give administrators a choice and to make it possible to install and use different versions side by side, the alternatives system allows managing such versions consistently.
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.
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 19 “Setting Up Hardware Components with YaST”, Section 19.3 “Set…
SUSE Linux Enterprise Server includes the X.org server and the GNOME desktop. This chapter describes the configuration of the graphical user interface for all users.
FUSE is the acronym for file system in user space.
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.
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…
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 …
This chapter starts with information about various software packages, the
virtual consoles and the keyboard layout. We talk about software components
like bash
,
cron
and
logrotate
, because they were
changed or enhanced during the last release cycles. Even if they are small
or considered of minor importance, users should change their default
behavior, because these components are often closely coupled with the
system. The chapter concludes with a section about language and
country-specific settings (I18N and L10N).
NetworkManager is the ideal solution for laptops and other portable computers. It supports state-of-the-art encryption types and standards for network connections, including connections to 802.1X protected networks. 802.1X is the “IEEE Standard for Local and Metropolitan Area Networks—Port-Based Net…
The features and hardware described in this chapter do not exist on IBM Z, making this chapter irrelevant for these platforms.
This chapter contains additional information on when SUSE Linux Enterprise Server is used in a virtual machine.
This chapter contains additional information about using SUSE Linux Enterprise with non-volatile main memory, also known as Persistent Memory, comprising one or more NVDIMMs.
SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. But SUSE Linux Enterprise Server supports 32-bit application use in 64-bit system environments. This chapter offers a brief overview of 32-bit support implementation on 64-bit SUSE Linux Enterprise Server platforms.
SUSE Linux Enterprise Server for the 64-bit platforms POWER, IBM Z and AMD64/Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment “out-of-the-box.” The corresponding 32-bit platforms are 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 compilation of 32-bit applications. It only offers runtime support for 32-bit binaries.
If an application is available for both 32-bit and 64-bit environments, installing both versions may cause problems. In such cases, decide on one version to install to avoid potential runtime errors.
An exception to this rule is PAM (pluggable authentication modules). SUSE Linux Enterprise Server uses PAM in the authentication process as a layer that mediates between user and application. Always install both PAM versions on 64-bit operating systems that also run 32-bit applications.
For correct execution, every application requires a range of libraries. Unfortunately, the names are identical for the 32-bit and 64-bit versions of these libraries. They must be differentiated from each other in another way.
To retain compatibility with 32-bit versions, 64-bit and
32-bit libraries are stored in the same location. The 32-bit
version of libc.so.6
is located under
/lib/libc.so.6
in both 32-bit and 64-bit
environments.
All 64-bit libraries and object files are located in directories called
lib64
. The 64-bit object files normally
found under /lib
and
/usr/lib
are now found under
/lib64
and /usr/lib64
. This means
that space is available for 32-bit libraries under /lib
and /usr/lib
, so the file name for both versions can
remain unchanged.
If the data content of 32-bit subdirectories under /lib
does not
depend on word size, they are not moved. This scheme conforms to LSB (Linux Standards Base)
and FHS (File System Hierarchy Standard).
The 64-bit kernels for AMD64/Intel 64, POWER and IBM Z offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical to the ABI for the corresponding 32-bit kernel. This means that communication between both 32-bit and 64-bit applications with 64-bit kernels are identical.
The 32-bit system call emulation for 64-bit kernels does not support
all the APIs used by system programs. This depends on the platform. For this
reason, few applications, like lspci
, must be
compiled on non-POWER platforms as 64-bit programs to
function properly. On IBM Z, not all ioctls are available in the
32-bit kernel ABI.
A 64-bit kernel can only load 64-bit kernel modules. You must compile 64-bit modules specifically for 64-bit kernels. It is not possible to use 32-bit kernel modules with 64-bit kernels.
Some applications require separate kernel-loadable modules. If you intend to use a 32-bit application in a 64-bit system environment, contact the provider of the application and SUSE. Make sure that the 64-bit version of the kernel-loadable module and the 32-bit compiled version of the kernel API are available for this module.
journalctl
: Query the systemd
Journal #Edit source
When systemd
replaced traditional init scripts in SUSE Linux Enterprise 12
(see Chapter 15, 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:
tux >
sudo
systemctl status systemd-journald systemd-journald.service - Journal Service Loaded: loaded (/usr/lib/systemd/system/systemd-journald.service; static) Active: active (running) since Mon 2014-05-26 08:36:59 EDT; 3 days ago Docs: man:systemd-journald.service(8) man:journald.conf(5) Main PID: 413 (systemd-journal) Status: "Processing requests..." CGroup: /system.slice/systemd-journald.service └─413 /usr/lib/systemd/systemd-journald [...]
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/
must exist with correct
ownership and permissions so 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.
root #
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:
root #
systemctl restart systemd-journald
journalctl
Useful Switches #Edit source
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:
tux >
sudo
journalctl /usr/lib/systemd/systemd
Shows only the most recent journal messages, and prints new log entries as they are added to the journal.
Prints the messages and jumps to the end of the journal, so that the latest entries are visible within the pager.
Prints the messages of the journal in reverse order, so that the latest entries are listed first.
Shows only kernel messages. This is equivalent to the field match
_TRANSPORT=kernel
(see
Section 17.3.3, “Filtering Based on Fields”).
Shows only messages for the specified systemd
unit. This is equivalent
to the field match
_SYSTEMD_UNIT=UNIT
(see
Section 17.3.3, “Filtering Based on Fields”).
tux >
sudo
journalctl -u apache2 [...] Jun 03 10:07:11 pinkiepie systemd[1]: Starting The Apache Webserver... Jun 03 10:07:12 pinkiepie systemd[1]: Started The Apache Webserver.
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.
journalctl
can filter messages based on a specific
system boot. To list all available boots, run
tux >
sudo
journalctl --list-boots -1 097ed2cd99124a2391d2cffab1b566f0 Mon 2014-05-26 08:36:56 EDT—Fri 2014-05-30 05:33:44 EDT 0 156019a44a774a0bb0148a92df4af81b Fri 2014-05-30 05:34:09 EDT—Fri 2014-05-30 06:15:01 EDT
The first column lists the boot offset: 0
for the
current boot, -1
for the previous one,
-2
for the one prior to that, etc. The second column
contains the boot ID followed by the limiting time stamps of the specific
boot.
Show all messages from the current boot:
tux >
sudo
journalctl -b
If you need to see journal messages from the previous boot, add an offset parameter. The following example outputs the previous boot messages:
tux >
sudo
journalctl -b -1
Another way is to list boot messages based on the boot ID. For this purpose, use the _BOOT_ID field:
tux >
sudo
journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b
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:
tux >
sudo
journalctl --since "now" -f
Show all messages since last midnight till 3:20am:
tux >
sudo
journalctl --since "today" --until "3:20"
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:
tux >
sudo
journalctl _PID=1039
Show messages belonging to a specific user ID:
# journalctl _UID=1000
Show messages from the kernel ring buffer (the same as
dmesg
produces):
tux >
sudo
journalctl _TRANSPORT=kernel
Show messages from the service's standard or error output:
tux >
sudo
journalctl _TRANSPORT=stdout
Show messages produced by a specified service only:
tux >
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service
If two different fields are specified, only entries that match both expressions at the same time are shown:
tux >
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1488
If two matches refer to the same field, all entries matching either expression are shown:
tux >
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service _SYSTEMD_UNIT=dbus.service
You can use the '+' separator to combine two expressions in a logical 'OR'. The following example shows all messages from the Avahi service process with the process ID 1480 together with all messages from the D-Bus service:
tux >
sudo
journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service
systemd
Errors #Edit source
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:
tux >
sudo
systemctl status apache2 apache2.service - The Apache Webserver Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: failed (Result: exit-code) since Tue 2014-06-03 11:08:13 CEST; 7min ago Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND \ -k graceful-stop (code=exited, status=1/FAILURE)
The ID of the process causing the failure is 11026.
Show the verbose version of messages related to process ID 11026:
tux >
sudo
journalctl -o verbose _PID=11026 [...] MESSAGE=AH00526: Syntax error on line 6 of /etc/apache2/default-server.conf: [...] MESSAGE=Invalid command 'DocumenttRoot', perhaps misspelled or defined by a module [...]
Fix the typo inside /etc/apache2/default-server.conf
,
start the apache2 service, and print its status:
tux >
sudo
systemctl start apache2 && systemctl status apache2 apache2.service - The Apache Webserver Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: active (running) since Tue 2014-06-03 11:26:24 CEST; 4ms ago Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND -k graceful-stop (code=exited, status=1/FAILURE) Main PID: 11263 (httpd2-prefork) Status: "Processing requests..." CGroup: /system.slice/apache2.service ├─11263 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11280 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11281 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11282 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11283 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] └─11285 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
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
tux >
sudo
systemctl restart systemd-journald
If the journal log data is saved to a persistent location (see
Section 17.1, “Making the Journal Persistent”), it uses up to 10% of the file
system the /var/log/journal
resides on. For example,
if /var/log/journal
is located on a 30 GB
/var
partition, the journal may use up to 3 GB of the
disk space. To change this limit, change (and uncomment) the
SystemMaxUse
option:
SystemMaxUse=50M
/dev/ttyX
#Edit source
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
Journald is backward compatible with traditional syslog implementations
such as rsyslog
. Make sure the following is valid:
rsyslog is installed.
tux >
sudo
rpm -q rsyslog rsyslog-7.4.8-2.16.x86_64
rsyslog service is enabled.
tux >
sudo
systemctl is-enabled rsyslog enabled
Forwarding to syslog is enabled in
/etc/systemd/journald.conf
.
ForwardToSyslog=yes
systemd
Journal #Edit source
For an easy way of filtering the systemd journal (without dealing
with the journalctl syntax), you can use the YaST journal module. After
installing it with sudo zypper in yast2-journal
, start it
from YaST by selecting › . Alternatively, start it
from command line by entering sudo yast2 journal
.
The module displays the log entries in a table. The search box on top allows
you to search for entries that contain certain characters, similar to using
grep
. To filter the entries by date and time, unit, file,
or priority, click and set the respective
options.
You can view the journal with GNOME Logs.
Start it from the application menu. To view system log messages, it
needs to be run as root, for example with xdg-su
gnome-logs
. This command can be executed when pressing
Alt–F2.
update-alternatives
: Managing Multiple Versions of Commands and Files #Edit sourceOften, there are several versions of the same tool installed on a system. To give administrators a choice and to make it possible to install and use different versions side by side, the alternatives system allows managing such versions consistently.
On SUSE Linux Enterprise Server, some programs perform the same or similar tasks. For example,
if Java 1.7 and Java 1.8 are both installed on the system, the alternatives system script
(update-alternatives
) is called from inside the RPM package.
By default, the alternatives system will refer to version 1.8: Higher versions also have a
higher priority. However, the administrator can change the default and
can point the generic name to version 1.7.
The following terminology is used in this chapter:
The default /var/lib/rpm/alternatives
directory contains information
about the current state of alternatives.
The name of a specific file in the file system, which can be made accessible via a generic name using the alternatives system.
The default /etc/alternatives
directory containing symbolic links.
A name (for example, /usr/bin/edit
) that refers to
one file out of several available using the alternatives system.
A set of related symbolic links that can be updated as a group.
The link in a link group that determines how the other links in the group are configured.
A link in a link group controlled by the master link.
A file that is a reference to another file in the same file system. The alternatives system uses symbolic links in the alternatives directory to switch between versions of a file.
Symbolic links in the alternatives directory can be modified by the
administrator through the update-alternatives
command.
The alternatives system provides the update-alternatives
command to
create, remove, maintain, and show information about symbolic links.
While these symbolic links usually point to commands, they can also point
to JAR archives, man pages, and other files.
Examples in this chapter use commands and man pages, but they are also
applicable to other file types.
The alternatives system uses the alternatives directory to collect links to possible alternatives. When a new package with an alternative is installed, the new alternative is added to the system. Whether the new package's alternative is selected as the default depends on its priority and on the mode that is set. Usually, packages with a higher version also have a higher priority. The alternatives system can operate in two modes:
Automatic Mode. In this mode, the alternatives system ensures that the links in the group point to the highest priority alternatives appropriate for the group.
Manual Mode. In this mode, the alternatives system does not make any changes to the system administrator's settings.
For example, the java
command has the following link
hierarchy in the alternatives system:
By default, the update-alternatives
script is called
from inside an RPM package. When a package is installed or removed, the
script takes care of all its symbolic links.
But you can run it manually from the command line for:
displaying the current alternatives for a generic name.
changing the defaults of an alternative.
creating a set of related files for an alternative.
To retrieve the names of all configured alternatives, use:
tux >
ls /var/lib/alternatives
To get an overview of all configured alternatives and their values, use
tux >
sudo
update-alternatives --get-selections
asadmin auto /usr/bin/asadmin-2.7 awk auto /usr/bin/gawk chardetect auto /usr/bin/chardetect-3.6 dbus-launch auto /usr/bin/dbus-launch.x11 default-displaymanager auto /usr/lib/X11/displaymanagers/gdm [...]
The easiest way to check the alternatives is to follow the symbolic links of
your command.
For example, if you want to know what the java
command is referring to, use the following command:
tux >
readlink --canonicalize /usr/bin/java
/usr/lib64/jvm/jre-10-openjdk/bin/java
If you see the same path (in our example, it is
/usr/bin/java
),
there are no alternatives available for this command.
To see the full alternatives (including slaves), use the
--display
option:
tux >
sudo
update-alternatives --display java
java - auto mode link best version is /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java link currently points to /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java link java is /usr/bin/java slave java.1.gz is /usr/share/man/man1/java.1.gz slave jre is /usr/lib64/jvm/jre slave jre_exports is /usr/lib64/jvm-exports/jre slave keytool is /usr/bin/keytool slave keytool.1.gz is /usr/share/man/man1/keytool.1.gz slave orbd is /usr/bin/orbd slave orbd.1.gz is /usr/share/man/man1/orbd.1.gz [...]
By default, commands in /usr/bin
refer to the
alternatives directory with the highest priority. For example,
by default, the command java
shows the following
version number:
tux >
java -version
openjdk version "10.0.1" 2018-04-17 OpenJDK Runtime Environment (build 10.0.1+10-suse-lp150.1.11-x8664) OpenJDK 64-Bit Server VM (build 10.0.1+10-suse-lp150.1.11-x8664, mixed mode)
To change the default java
command to refer
to a previous version, run:
tux >
sudo
update-alternatives --config java
root's password: There are 2 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/lib64/jvm/jre-10-openjdk/bin/java 2005 auto mode 1 /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java 1805 manual mode 2 /usr/lib64/jvm/jre-10-openjdk/bin/java 2005 manual mode 3 /usr/lib64/jvm/jre-11-openjdk/bin/java 0 manual mode Press <enter> to keep the current choice[*], or type selection number:
Depending on your system and installed versions, the exact Java version
number will be different.
After you have selected 1
, java
shows the following version number:
tux >
java -version
java version "1.8.0_171" OpenJDK Runtime Environment (IcedTea 3.8.0) (build 1.8.0_171-b11 suse-lp150.2.3.1-x86_64) OpenJDK 64-Bit Server VM (build 25.171-b11, mixed mode)
Also, keep in mind the following points:
When working in manual mode and installing another Java version, the alternatives system neither touches the links nor changes the generic name.
When working in automatic mode and installing another Java version, the alternatives system changes the Java master link and all slave links (as you can see in Section 18.4, “Viewing Details on Specific Alternatives”). To check the master-slave relationships, use:
tux >
sudo
update-alternatives --display java
This section describes how to set up custom alternatives on a system. The example makes the following assumptions:
There are two scripts, foo-2
and foo-3
,
with similar functionality.
The scripts are stored in the /usr/local/bin
directory to avoid any conflicts with the system tools in
/usr/bin
.
There is a master link foo
that points to either
foo-2
or foo-3
.
To provide alternatives on your system, follow these steps:
Copy your scripts into the /usr/local/bin
directory.
Make the scripts executable:
tux >
sudo
chmod +x /usr/local/bin/foo-{2,3}
Run update-alternatives
for both scripts:
tux >
sudo
update-alternatives --install \ /usr/local/bin/foo 1\ foo 2\ /usr/local/bin/foo-2 3\ 200 4tux >
sudo
update-alternatives --install \ /usr/local/bin/foo 1\ foo 2\ /usr/local/bin/foo-3 3\ 300 4
The options after --install
have the following meanings:
The generic name. To avoid confusion, this is usually the script name without any version numbers. | |
The name of the master link. Must be the same. | |
The path to the original script(s) located in
| |
The priority.
We give |
Check the master link:
tux >
sudo
update-alternatives --display foo
foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo /usr/local/bin/foo-2 - priority 200 /usr/local/bin/foo-3 - priority 300
After you completed the described steps, you can use the master link
/usr/local/bin/foo
.
If needed, you can install additional alternatives. To remove an alternative, use the following command:
tux >
sudo
update-alternatives --remove foo /usr/local/bin/foo-2
After this script has been removed, the alternatives system for the foo group looks like this:
tux >
sudo
update-alternatives --display foo
foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo /usr/local/bin/foo-3 - priority 300
If you have alternatives, the script itself is not enough. Most commands are not completely stand-alone: They usually ship with additional files, such as extensions, configurations, or man pages. To create alternatives which are dependent on a master link, use slave alternatives.
Let us assume we want to extend our example in Section 18.6, “Installing Custom Alternatives” and provide man pages and configuration files:
Two man pages, foo-2.1.gz
and foo-3.1.gz
stored in the /usr/local/man/man1
directory.
Two configuration files, foo-2.conf
and
foo-3.conf
, stored in /etc
.
Follow these steps to add the additional files to your alternatives:
Copy the configuration files into /etc
:
tux >
sudo
cp foo-{2,3}.conf /etc
Copy the man pages into the /usr/local/man/man1
directory:
tux >
sudo
cp foo-{2,3}.1.gz /usr/local/man/man1/
Add the slave links to the main scripts with the --slave
option:
tux >
sudo
update-alternatives --install \ /usr/local/bin/foo foo /usr/local/bin/foo-2 200 \ --slave /usr/local/man/man1/foo.1.gz \ foo.1.gz \ /usr/local/man/man1/foo-2.1.gz \ --slave /etc/foo.conf \ foo.conf \ /etc/foo-2.conf
tux >
sudo
update-alternatives --install \ /usr/local/bin/foo foo /usr/local/bin/foo-3 300 \ --slave /usr/local/man/man1/foo.1.gz \ foo.1.gz \ /usr/local/man/man1/foo-3.1.gz \ --slave /etc/foo.conf \ foo.conf \ /etc/foo-3.conf
Check the master link:
foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo slave foo.1.gz is /usr/local/man/man1/foo.1.gz slave foo.conf is /etc/foo.conf /usr/local/bin/foo-2 - priority 200 slave foo.1.gz: /usr/local/man/man1/foo-2.1.gz slave foo.conf: /etc/foo-2.conf /usr/local/bin/foo-3 - priority 300 slave foo.1.gz: /usr/local/man/man1/foo-3.1.gz slave foo.conf: /etc/foo-3.conf
If you change the links with update-alternatives --config foo
to foo-2
, then all slave links will change as well.
Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.
Linux and other Unix operating systems use the TCP/IP protocol. It is not a single network protocol, but a family of network protocols that offer various services. The protocols listed in Several Protocols in the TCP/IP Protocol Family, are provided for exchanging data between two machines via TCP/IP. Networks combined by TCP/IP, comprising a worldwide network, are also called “the Internet.”
RFC stands for Request for Comments. RFCs are documents that describe various Internet protocols and implementation procedures for the operating system and its applications. The RFC documents describe the setup of Internet protocols. For more information about RFCs, see http://www.ietf.org/rfc.html.
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.
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.
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.
Internet Group Management Protocol: This protocol controls machine behavior when implementing IP multicast.
As shown in Figure 19.1, “Simplified Layer Model for TCP/IP”, data exchange takes place in different layers. The actual network layer is the insecure data transfer via IP (Internet protocol). On top of IP, TCP (transmission control protocol) guarantees, to a certain extent, security of the data transfer. The IP layer is supported by the underlying hardware-dependent protocol, such as Ethernet.
The diagram provides one or two examples for each layer. The layers are ordered according to abstraction levels. The lowest layer is very close to the hardware. The uppermost layer, however, is almost a complete abstraction from the hardware. Every layer has its own special function. The special functions of each layer are mostly implicit in their description. The data link and physical layers represent the physical network used, such as Ethernet.
Almost all hardware protocols work on a packet-oriented basis. The data to transmit is collected into packets (it cannot be sent all at once). The maximum size of a TCP/IP packet is approximately 64 KB. Packets are normally quite smaller, as the network hardware can be a limiting factor. The maximum size of a data packet on an Ethernet is about fifteen hundred bytes. The size of a TCP/IP packet is limited to this amount when the data is sent over an Ethernet. If more data is transferred, more data packets need to be sent by the operating system.
For the layers to serve their designated functions, additional information regarding each layer must be saved in the data packet. This takes place in the header of the packet. Every layer attaches a small block of data, called the protocol header, to the front of each emerging packet. A sample TCP/IP data packet traveling over an Ethernet cable is illustrated in Figure 19.2, “TCP/IP Ethernet Packet”. The proof sum is located at the end of the packet, not at the beginning. This simplifies things for the network hardware.
When an application sends data over the network, the data passes through each layer, all implemented in the Linux kernel except the physical layer. Each layer is responsible for preparing the data so it can be passed to the next layer. The lowest layer is ultimately responsible for sending the data. The entire procedure is reversed when data is received. Like the layers of an onion, in each layer the protocol headers are removed from the transported data. Finally, the transport layer is responsible for making the data available for use by the applications at the destination. In this manner, one layer only communicates with the layer directly above or below it. For applications, it is irrelevant whether data is transmitted via a 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.
The discussion in this section is limited to IPv4 networks. For information about IPv6 protocol, the successor to IPv4, refer to Section 19.2, “IPv6—The Next Generation Internet”.
Every computer on the Internet has a unique 32-bit address. These 32 bits (or 4 bytes) are normally written as illustrated in the second row in Example 19.1, “Writing IP Addresses”.
IP Address (binary): 11000000 10101000 00000000 00010100 IP Address (decimal): 192. 168. 0. 20
In decimal form, the four bytes are written in the decimal number system, separated by periods. The IP address is assigned to a host or a network interface. It can be used only once throughout the world. There are exceptions to this rule, but these are not relevant to the following passages.
The points in IP addresses indicate the hierarchical system. Until the 1990s, IP addresses were strictly categorized in classes. However, this system proved too inflexible and was discontinued. Now, classless routing (CIDR, classless interdomain routing) is used.
Netmasks are used to define the address range of a subnet. If two hosts are in the same subnet, they can reach each other directly. If they are not in the same subnet, they need the address of a gateway that handles all the traffic for the subnet. To check if two IP addresses are in the same subnet, simply “AND” both addresses with the netmask. If the result is identical, both IP addresses are in the same local network. If there are differences, the remote IP address, and thus the remote interface, can only be reached over a gateway.
To understand how the netmask works, look at
Example 19.2, “Linking IP Addresses to the Netmask”. The netmask consists of 32 bits
that identify how much of an IP address belongs to the network. All those
bits that are 1
mark the corresponding bit in the IP
address as belonging to the network. All bits that are 0
mark bits inside the subnet. This means that the more bits are
1
, the smaller the subnet is. Because the netmask always
consists of several successive 1
bits, it is also
possible to count the number of bits in the netmask. In
Example 19.2, “Linking IP Addresses to the Netmask” the first net with 24 bits could
also be written as 192.168.0.0/24
.
IP address (192.168.0.20): 11000000 10101000 00000000 00010100 Netmask (255.255.255.0): 11111111 11111111 11111111 00000000 --------------------------------------------------------------- Result of the link: 11000000 10101000 00000000 00000000 In the decimal system: 192. 168. 0. 0 IP address (213.95.15.200): 11010101 10111111 00001111 11001000 Netmask (255.255.255.0): 11111111 11111111 11111111 00000000 --------------------------------------------------------------- Result of the link: 11010101 10111111 00001111 00000000 In the decimal system: 213. 95. 15. 0
To give another example: all machines connected with the same Ethernet cable are usually located in the same subnet and are directly accessible. Even when the subnet is physically divided by switches or bridges, these hosts can still be reached directly.
IP addresses outside the local subnet can only be reached if a gateway is configured for the target network. In the most common case, there is only one gateway that handles all traffic that is external. However, it is also possible to configure several gateways for different subnets.
If a gateway has been configured, all external IP packets are sent to the appropriate gateway. This gateway then attempts to forward the packets in the same manner—from host to host—until it reaches the destination host or the packet's TTL (time to live) expires.
This is the netmask AND any address in the network, as shown in
Example 19.2, “Linking IP Addresses to the Netmask” under Result
.
This address cannot be assigned to any hosts.
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.
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 complete
127.0.0.0/8
loopback network
as defined with IPv4. With IPv6 there is only one loopback address
(::1
).
Because IP addresses must be unique all over the world, you cannot select random addresses. There are three address domains to use if you want to set up a private IP-based network. These cannot get any connection from the rest of the Internet, because they cannot be transmitted over the Internet. These address domains are specified in RFC 1597 and listed in Table 19.1, “Private IP Address Domains”.
Network/Netmask |
Domain |
---|---|
|
|
|
|
|
|
IPv6 is not supported by the CTC and IUCV network connections of the IBM Z hardware.
Because of the emergence of the World Wide Web (WWW), the Internet has experienced explosive growth, with an increasing number of computers communicating via TCP/IP in the past fifteen years. Since Tim Berners-Lee at CERN (http://public.web.cern.ch) invented the WWW in 1990, the number of Internet hosts has grown from a few thousand to about a hundred million.
As mentioned, an IPv4 address consists of only 32 bits. Also, quite a few IP addresses are lost—they cannot be used because of the way in which networks are organized. The number of addresses available in your subnet is two to the power of the number of bits, minus two. A subnet has, for example, 2, 6, or 14 addresses available. To connect 128 hosts to the Internet, for example, you need a subnet with 256 IP addresses, from which only 254 are usable, because two IP addresses are needed for the structure of the subnet itself: the broadcast and the base network address.
Under the current IPv4 protocol, DHCP or NAT (network address translation) are the typical mechanisms used to circumvent the potential address shortage. Combined with the convention to keep private and public address spaces separate, these methods can certainly mitigate the shortage. The problem with them lies in their configuration, which is a chore to set up and a burden to maintain. To set up a host in an IPv4 network, you need several address items, such as the host's own IP address, the subnetmask, the gateway address and maybe a name server address. All these items need to be known and cannot be derived from somewhere else.
With IPv6, both the address shortage and the complicated configuration should be a thing of the past. The following sections tell more about the improvements and benefits brought by IPv6 and about the transition from the old protocol to the new one.
The most important and most visible improvement brought by the new protocol is the enormous expansion of the available address space. An IPv6 address is made up of 128 bit values instead of the traditional 32 bits. This provides for as many as several quadrillion IP addresses.
However, IPv6 addresses are not only different from their predecessors with regard to their length. They also have a different internal structure that may contain more specific information about the systems and the networks to which they belong. More details about this are found in Section 19.2.2, “Address Types and Structure”.
The following is a list of other advantages of the new protocol:
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.
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.
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.
Realistically, it would be impossible to switch the entire Internet from IPv4 to IPv6 at one time. Therefore, it is crucial that both protocols can coexist not only on the Internet, but also on one system. This is ensured by compatible addresses (IPv4 addresses can easily be translated into IPv6 addresses) and by using several tunnels. See Section 19.2.3, “Coexistence of IPv4 and IPv6”. Also, systems can rely on a dual stack IP technique to support both protocols at the same time, meaning that they have two network stacks that are completely separate, such that there is no interference between the two protocol versions.
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).
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:
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.
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.
Addresses of this type are related to a group of interfaces. Packets with such an address are delivered to the member of the group that is closest to the sender, according to the principles of the underlying routing protocol. Anycast addresses are used to make it easier for hosts to find out about servers offering certain services in the given network area. All servers of the same type have the same anycast address. Whenever a host requests a service, it receives a reply from the server with the closest location, as determined by the routing protocol. If this server should fail for some reason, the protocol automatically selects the second closest server, then the third one, and so forth.
An IPv6 address is made up of eight four-digit fields, each representing 16
bits, written in hexadecimal notation. They are separated by colons
(:
). Any leading zero bytes within a given field may be
dropped, but zeros within the field or at its end may not. Another
convention is that more than four consecutive zero bytes may be collapsed
into a double colon. However, only one such ::
is
allowed per address. This kind of shorthand notation is shown in
Example 19.3, “Sample IPv6 Address”, where all three lines represent the
same address.
fe80 : 0000 : 0000 : 0000 : 0000 : 10 : 1000 : 1a4 fe80 : 0 : 0 : 0 : 0 : 10 : 1000 : 1a4 fe80 : : 10 : 1000 : 1a4
Each part of an IPv6 address has a defined function. The first bytes form
the prefix and specify the type of address. The center part is the network
portion of the address, but it may be unused. The end of the address forms
the host part. With IPv6, the netmask is defined by indicating the length
of the prefix after a slash at the end of the address. An address, as shown
in Example 19.4, “IPv6 Address Specifying the Prefix Length”, contains the information that
the first 64 bits form the network part of the address and the last 64 form
its host part. In other words, the 64
means that the
netmask is filled with 64 1-bit values from the left. As with IPv4, the IP
address is combined with AND with the values from the netmask to determine
whether the host is located in the same subnet or in another one.
fe80::10:1000:1a4/64
IPv6 knows about several predefined types of prefixes. Some are shown in Various IPv6 Prefixes.
00
IPv4 addresses and IPv4 over IPv6 compatibility addresses. These are used to maintain compatibility with IPv4. Their use still requires a router able to translate IPv6 packets into IPv4 packets. Several special addresses, such as the one for the loopback device, have this prefix as well.
2
or
3
as the
first digit
Aggregatable 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) and 2002::/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:
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.
The second part contains routing information about the subnet to which to deliver the packet.
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 an
EUI-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.
The IPv6 address is formed by the IPv4 address and a prefix consisting of 96 zero bits. This type of compatibility address is used for tunneling (see Section 19.2.3, “Coexistence of IPv4 and IPv6”) to allow IPv4 and IPv6 hosts to communicate with others operating in a pure IPv4 environment.
This type of address specifies a pure IPv4 address in IPv6 notation.
There are two address types for local use:
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.
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.
The migration of all hosts connected to the Internet from IPv4 to IPv6 is a gradual process. Both protocols will coexist for some time to come. The coexistence on one system is guaranteed where there is a dual stack implementation of both protocols. That still leaves the question of how an IPv6 enabled host should communicate with an IPv4 host and how IPv6 packets should be transported by the current networks, which are predominantly IPv4-based. The best solutions offer tunneling and compatibility addresses (see Section 19.2.2, “Address Types and Structure”).
IPv6 hosts that are more or less isolated in the (worldwide) IPv4 network can communicate through tunnels: IPv6 packets are encapsulated as IPv4 packets to move them across an IPv4 network. Such a connection between two IPv4 hosts is called a tunnel. To achieve this, packets must include the IPv6 destination address (or the corresponding prefix) and the IPv4 address of the remote host at the receiving end of the tunnel. A basic tunnel can be configured manually according to an agreement between the hosts' administrators. This is also called static tunneling.
However, the configuration and maintenance of static tunnels is often too labor-intensive to use them for daily communication needs. Therefore, IPv6 provides for three different methods of dynamic tunneling:
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.
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.
This method relies on special servers that provide dedicated tunnels for IPv6 hosts. It is described in RFC 3053.
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
).
The above overview does not cover the topic of IPv6 comprehensively. For a more in-depth look at the new protocol, refer to the following online documentation and books:
The starting point for everything about IPv6.
All information needed to start your own IPv6 network.
The list of IPv6-enabled products.
Here, find the Linux IPv6-HOWTO and many links related to the topic.
The fundamental RFC about IPv6.
A book describing all the important aspects of the topic is IPv6 Essentials by Silvia Hagen (ISBN 0-596-00125-8).
DNS assists in assigning an IP address to one or more names and assigning a name to an IP address. In Linux, this conversion is usually carried out by a special type of software known as bind. The machine that takes care of this conversion is called a name server. The names make up a hierarchical system in which each name component is separated by a period. The name hierarchy is, however, independent of the IP address hierarchy described above.
Consider a complete name, such as
jupiter.example.com
, written in the
format hostname.domain
. A full
name, called a fully qualified domain name (FQDN),
consists of a host name and a domain name
(example.com
). The latter
also includes the top level domain or TLD
(com
).
TLD assignment has become quite confusing for historical reasons.
Traditionally, three-letter domain names are used in the USA. In the rest of
the world, the two-letter ISO national codes are the standard. In addition
to that, longer TLDs were introduced in 2000 that represent certain spheres
of activity (for example, .info
,
.name
,
.museum
).
In the early days of the Internet (before 1990), the file
/etc/hosts
was used to store the names of all the
machines represented over the Internet. This quickly proved to be
impractical in the face of the rapidly growing number of computers connected
to the Internet. For this reason, a decentralized database was developed to
store the host names in a widely distributed manner. This database, similar
to the name server, does not have the data pertaining to all hosts in the
Internet readily available, but can dispatch requests to other name servers.
The top of the hierarchy is occupied by root name servers. These root name servers manage the top level domains and are run by the Network Information Center (NIC). Each root name server knows about the name servers responsible for a given top level domain. Information about top level domain NICs is available at http://www.internic.net.
DNS can do more than resolve host names. The name server also knows which host is receiving e-mails for an entire domain—the mail exchanger (MX).
For your machine to resolve an IP address, it must know about at least one name server and its IP address. Easily specify such a name server using YaST. The configuration of name server access with SUSE® Linux Enterprise Server is described in Section 19.4.1.4, “Configuring Host Name and DNS”. Setting up your own name server is described in Chapter 32, The Domain Name System.
The protocol whois
is closely related to DNS. With this
program, quickly find out who is responsible for a given domain.
The .local
top level domain is treated as link-local
domain by the resolver. DNS requests are send as multicast DNS requests
instead of normal DNS requests. If you already use the
.local
domain in your name server configuration, you
must switch this option off in /etc/host.conf
. For
more information, see the host.conf
manual page.
To switch off MDNS during installation, use
nomdns=1
as a boot parameter.
For more information on multicast DNS, see http://www.multicastdns.org.
There are many supported networking types on Linux. Most of them use different device names and the configuration files are spread over several locations in the file system. For a detailed overview of the aspects of manual network configuration, see Section 19.5, “Configuring a Network Connection Manually”.
All network interfaces with link up (with a network cable connected) are automatically configured. Additional hardware can be configured any time on the installed system. The following sections describe the network configuration for all types of network connections supported by SUSE Linux Enterprise Server.
On IBM Z platforms, hotpluggable network cards are supported, but not their automatic network integration via DHCP (as is the case on the PC). After they have been detected, you need to manually configure the interface.
To configure your Ethernet or Wi-Fi/Bluetooth card in YaST, select
› . After starting the module, YaST displays the dialog with four tabs: , , and .The Section 19.4.1.1, “Configuring Global Networking Options”.
tab allows you to set general networking options such as the network setup method, IPv6, and general DHCP options. For more information, seeThe Section 19.4.1.3, “Configuring an Undetected Network Card”. To change the configuration of an already configured card, see Section 19.4.1.2, “Changing the Configuration of a Network Card”.
tab contains information about installed network interfaces and configurations. Any properly detected network card is listed with its name. You can manually configure new cards, remove or change their configuration in this dialog. To manually configure a card that was not automatically detected, seeThe Section 19.4.1.4, “Configuring Host Name and DNS”.
tab allows to set the host name of the machine and name the servers to be used. For more information, seeThe Section 19.4.1.5, “Configuring Routing” for more information.
tab is used for the configuration of routing. SeeThe
tab of the YaST module allows you to set important global networking options, such as the use of NetworkManager, IPv6 and DHCP client options. These settings are applicable for all network interfaces.NetworkManager is now provided by the SUSE Linux Enterprise Workstation Extension. To install NetworkManager, activate the Workstation Extension repository, and select the NetworkManager packages.
In the nm-applet
should be used to configure
network options and the ,
and tabs of the
module are disabled.
For more information
on NetworkManager, see the SUSE Linux Enterprise Desktop documentation.
In the
choose whether to use the IPv6 protocol. It is possible to use IPv6 together with IPv4. By default, IPv6 is enabled. However, in networks not using IPv6 protocol, response times can be faster with IPv6 protocol disabled. To disable IPv6, deactivate . If IPv6 is disabled, the kernel no longer loads the IPv6 module automatically. This setting will be applied after reboot.In the
configure options for the DHCP client. The must be different for each DHCP client on a single network. If left empty, it defaults to the hardware address of the network interface. However, if you are running several virtual machines using the same network interface and, therefore, the same hardware address, specify a unique free-form identifier here.
The AUTO
to
send the current host name (that is the one defined in
/etc/HOSTNAME
). Make the option field empty for not
sending any host name.
If you do not want to change the default route according to the information from DHCP, deactivate
.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.You can set the IP address of the network card or the way its IP address is determined in the
tab of the dialog. Both IPv4 and IPv6 addresses are supported. The network card can have (which is useful for bonding devices), a (IPv4 or IPv6) or a assigned via or or both.If using
, select whether to use (for IPv4), (for IPv6) or .If possible, the first network card with link that is available during the installation is automatically configured to use automatic address setup via DHCP.
On IBM Z platforms, DHCP-based address configuration is only supported with network cards that have a MAC address. This is only the case with OSA and OSA Express cards.
DHCP should also be used if you are using a DSL line but with no static IP assigned by the ISP (Internet Service Provider). If you decide to use DHCP, configure the details in
in the tab of the dialog of the YaST network card configuration module. If you have a virtual host setup where different hosts communicate through the same interface, an is necessary to distinguish them.DHCP is a good choice for client configuration but it is not ideal for server configuration. To set a static IP address, proceed as follows:
Select a card from the list of detected cards in the
tab of the YaST network card configuration module and click .In the
tab, choose .
Enter the /64
.
Optionally, you can enter a fully qualified /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_R