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SUSE Linux Enterprise Server 15 SP3

Administration Guide

  

This guide covers system administration tasks like maintaining, monitoring and customizing an initially installed system.

Publication Date: November 28, 2024
List of Figures
List of Tables
List of Examples

Copyright © 2006–2024 SUSE LLC and contributors. All rights reserved.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled “GNU Free Documentation License”.

For SUSE trademarks, see https://www.suse.com/company/legal/. All third-party trademarks are the property of their respective owners. Trademark symbols (®, ™ etc.) denote trademarks of SUSE and its affiliates. Asterisks (*) denote third-party trademarks.

All information found in this book has been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. Neither SUSE LLC, its affiliates, the authors nor the translators shall be held liable for possible errors or the consequences thereof.

Preface

  

1 Available documentation

  
Online documentation

Our documentation is available online at https://documentation.suse.com. Browse or download the documentation in various formats.

Note
Note: Latest updates

The latest updates are usually available in the English-language version of this documentation.

SUSE Knowledgebase

If you have run into an issue, also check out the Technical Information Documents (TIDs) that are available online at https://www.suse.com/support/kb/. Search the SUSE Knowledgebase for known solutions driven by customer need.

Release notes

For release notes, see https://www.suse.com/releasenotes/.

In your system

For offline use, the release notes are also available under /usr/share/doc/release-notes on your system. The documentation for individual packages is available at /usr/share/doc/packages.

Many commands are also described in their manual pages. To view them, run man, followed by a specific command name. If the man command is not installed on your system, install it with sudo zypper install man.

2 Improving the documentation

  

Your feedback and contributions to this documentation are welcome. The following channels for giving feedback are available:

Service requests and support

For services and support options available for your product, see https://www.suse.com/support/.

To open a service request, you need a SUSE subscription registered at SUSE Customer Center. Go to https://scc.suse.com/support/requests, log in, and click Create New.

Bug reports

Report issues with the documentation at https://bugzilla.suse.com/.

To simplify this process, click the Report an issue icon next to a headline in the HTML version of this document. This preselects the right product and category in Bugzilla and adds a link to the current section. You can start typing your bug report right away.

A Bugzilla account is required.

Contributions

To contribute to this documentation, click the Edit source document icon next to a headline in the HTML version of this document. This will take you to the source code on GitHub, where you can open a pull request.

A GitHub account is required.

Note
Note: Edit source document only available for English

The Edit source document icons are only available for the English version of each document. For all other languages, use the Report an issue icons instead.

For more information about the documentation environment used for this documentation, see the repository's README.

Mail

You can also report errors and send feedback concerning the documentation to <>. Include the document title, the product version, and the publication date of the document. Additionally, include the relevant section number and title (or provide the URL) and provide a concise description of the problem.

3 Documentation conventions

  

The following notices and typographic conventions are used in this document:

  • /etc/passwd: Directory names and file names

  • PLACEHOLDER: Replace PLACEHOLDER with the actual value

  • PATH: An environment variable

  • ls, --help: Commands, options, and parameters

  • user: The name of a user or group

  • package_name: The name of a software package

  • Alt, Alt–F1: A key to press or a key combination. Keys are shown in uppercase as on a keyboard.

  • File, File › Save As: menu items, buttons

  • AMD/Intel This paragraph is only relevant for the AMD64/Intel 64 architectures. The arrows mark the beginning and the end of the text block.

    IBM Z, POWER This paragraph is only relevant for the architectures IBM Z and POWER. The arrows mark the beginning and the end of the text block.

  • Chapter 1, “Example chapter”: A cross-reference to another chapter in this guide.

  • Commands that must be run with root privileges. You can also prefix these commands with the sudo command to run them as a non-privileged user: 

    # command
> sudo command

  • Commands that can be run by non-privileged users: 

    > command

  • Commands can be split into two or multiple lines by a backslash character (\) at the end of a line. The backslash informs the shell that the command invocation will continue after the line's end: 

    > echo a b \
c d

  • A code block that shows both the command (preceded by a prompt) and the respective output returned by the shell: 

    > command
output

  • Notices

    Warning
    Warning: Warning notice

    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
    Important: Important notice

    Important information you should be aware of before proceeding.

    Note
    Note: Note notice

    Additional information, for example about differences in software versions.

    Tip
    Tip: Tip notice

    Helpful information, like a guideline or a piece of practical advice.

  • Compact Notices

    Note

    Additional information, for example about differences in software versions.

    Tip

    Helpful information, like a guideline or a piece of practical advice.

4 Support

  

Find the support statement for SUSE Linux Enterprise Server and general information about technology previews below. For details about the product lifecycle, see https://www.suse.com/lifecycle.

If you are entitled to support, find details on how to collect information for a support ticket at https://documentation.suse.com/sles-15/html/SLES-all/cha-adm-support.html.

4.1 Support statement for SUSE Linux Enterprise Server

  

To receive support, you need an appropriate subscription with SUSE. To view the specific support offers available to you, go to https://www.suse.com/support/ and select your product.

The support levels are defined as follows:

L1

Problem determination, which means technical support designed to provide compatibility information, usage support, ongoing maintenance, information gathering and basic troubleshooting using available documentation.

L2

Problem isolation, which means technical support designed to analyze data, reproduce customer problems, isolate a problem area and provide a resolution for problems not resolved by Level 1 or prepare for Level 3.

L3

Problem resolution, which means technical support designed to resolve problems by engaging engineering to resolve product defects which have been identified by Level 2 Support.

For contracted customers and partners, SUSE Linux Enterprise Server is delivered with L3 support for all packages, except for the following:

  • Technology previews.

  • Sound, graphics, fonts, and artwork.

  • Packages that require an additional customer contract.

  • Some packages shipped as part of the module Workstation Extension are L2-supported only.

  • Packages with names ending in -devel (containing header files and similar developer resources) will only be supported together with their main packages.

SUSE will only support the usage of original packages. That is, packages that are unchanged and not recompiled.

4.2 Technology previews

  

Technology previews are packages, stacks, or features delivered by SUSE to provide glimpses into upcoming innovations. Technology previews are included for your convenience to give you a chance to test new technologies within your environment. We would appreciate your feedback. If you test a technology preview, please contact your SUSE representative and let them know about your experience and use cases. Your input is helpful for future development.

Technology previews have the following limitations:

  • Technology previews are still in development. Therefore, they may be functionally incomplete, unstable, or otherwise not suitable for production use.

  • Technology previews are not supported.

  • Technology previews may only be available for specific hardware architectures.

  • Details and functionality of technology previews are subject to change. As a result, upgrading to subsequent releases of a technology preview may be impossible and require a fresh installation.

  • SUSE may discover that a preview does not meet customer or market needs, or does not comply with enterprise standards. Technology previews can be removed from a product at any time. SUSE does not commit to providing a supported version of such technologies in the future.

For an overview of technology previews shipped with your product, see the release notes at https://www.suse.com/releasenotes.

Part I Common tasks

  
  • 1 Bash and Bash scripts

    • Today, many people use computers with a graphical user interface (GUI) like GNOME. Although GUIs offer many features, they're limited when performing automated task execution. Shells complement GUIs well, and this chapter gives an overview of some aspects of shells, in this case the Bash shell.

  • 2 sudo basics

    • Running certain commands requires root privileges. However, for security reasons and to avoid mistakes, it is not recommended to log in as root. A safer approach is to log in as a regular user, and then use sudo to run commands with elevated privileges.

  • 3 Using YaST

    • YaST is a SUSE Linux Enterprise Server tool that provides a graphical interface for all essential installation and system configuration tasks. Whether you need to update packages, configure a printer, modify firewall settings, set up an FTP server, or partition a hard disk—you can do it using YaST. …

  • 4 YaST in text mode

    • The ncurses-based pseudo-graphical YaST interface is designed primarily to help system administrators to manage systems without an X server. The interface offers several advantages compared to the conventional GUI. You can navigate the ncurses interface using the keyboard, and there are keyboard sho…

  • 5 YaST online update

    • SUSE offers a continuous stream of software security updates for your product. By default, the update applet is used to keep your system up-to-date. Refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.5 “The GNOME package updater” for further information on the…

  • 6 Managing software with command line tools

    • This chapter describes Zypper and RPM, two command line tools for managing software. For a definition of the terminology used in this context (for example, repository, patch, or update) refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.1 “Definition of terms”.

  • 7 System recovery and snapshot management with Snapper

    • Snapper allows creating and managing file system snapshots. File system snapshots allow keeping a copy of the state of a file system at a certain point of time. The standard setup of Snapper is designed to allow rolling back system changes. However, you can also use it to create on-disk backups of user data. As the basis for this functionality, Snapper uses the Btrfs file system or thinly-provisioned LVM volumes with an XFS or Ext4 file system.

  • 8 Live kernel patching with KLP

    • This document describes the basic principles of the Kernel Live Patching (KLP) technology, and provides usage guidelines for the SLE Live Patching service.

  • 9 Transactional updates

    • Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root file system is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not affect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the admin must decide if a reboot is more expensive than disturbing running services. If reboots are too expensive then do not use transactional updates.

    Transactional updates are run daily by the transactional-update script. The script checks for available updates. If there are any updates, it creates a new snapshot of the root file system in the background, and then fetches updates from the release channels. After the new snapshot is completely updated, it is marked as active and will be the new default root file system after the next reboot of the system. 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.

  • 10 Remote graphical sessions with VNC

    • Virtual Network Computing (VNC) enables you to access a remote computer via a graphical desktop, and run remote graphical applications. VNC is platform-independent and accesses the remote machine from any operating system. This chapter describes how to connect to a VNC server with the desktop clients vncviewer and Remmina, and how to operate a VNC server.

    SUSE Linux Enterprise Server supports two different kinds of VNC sessions: One-time sessions that “live” as long as the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated.

    A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.

  • 11 File copying with RSync

    • Today, a typical user has several computers: home and workplace machines, a laptop, a smartphone or a tablet. This makes the task of keeping files and documents in synchronization across multiple devices all the more important.

1 Bash and Bash scripts

  

Today, many people use computers with a graphical user interface (GUI) like GNOME. Although GUIs offer many features, they're limited when performing automated task execution. Shells complement GUIs well, and this chapter gives an overview of some aspects of shells, in this case the Bash shell.

1.1 What is “the shell”?

  

Traditionally, the Linux shell is Bash (Bourne again Shell). When this chapter speaks about “the shell” it means Bash. There are more shells available (ash, csh, ksh, zsh, …), each employing different features and characteristics.

1.1.1 Bash configuration files

  

A shell can be invoked as an:

  1. 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.

  2. Interactive non-login shell.  This is normally the case when starting xterm, konsole, gnome-terminal, or similar command-line interface (CLI) tools.

  3. Non-interactive non-login shell.  This is invoked when invoking a shell script at the command line.

Depending on the type of shell you use, different configuration files will be read. The following tables show the login and non-login shell configuration files.

Tip
Tip

Bash looks for its configuration files in a specific order depending on the type of shell where it is run. Find more details on the Bash man page (man 1 bash). Search for the headline INVOCATION.

Table 1.1: Bash configuration files for login shells
  

File

Description

/etc/profile

Do not modify this file, otherwise your modifications may be destroyed during your next update!

/etc/profile.local

Use this file if you extend /etc/profile

/etc/profile.d/

Contains system-wide configuration files for specific programs

~/.profile

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”.

Table 1.2: Bash configuration files for non-login shells
  

/etc/bash.bashrc

Do not modify this file, otherwise your modifications may be destroyed during your next update!

/etc/bash.bashrc.local

Use this file to insert your system-wide modifications for Bash only

~/.bashrc

Insert user specific configuration here

Additionally, Bash uses some more files:

Table 1.3: Special files for Bash
  

File

Description

~/.bash_history

Contains a list of all commands you have typed

~/.bash_logout

Executed when logging out

~/.alias

User defined aliases of frequently used commands. See man 1 alias for more details about defining aliases.

No-Login Shells

There are special shells that block users from logging into the system: /bin/false and /sbin/nologin. Both fail silently when the user attempts to log into the system. This was intended as a security measure for system users, though modern Linux operating systems have more effective tools for controlling system access, such as PAM and AppArmor.

The default on SUSE Linux Enterprise Server is to assign /bin/bash to human users, and /bin/false or /sbin/nologin to system users. The nobody user has /bin/bash for historical reasons, as it is a minimally-privileged user that used to be the default for system users. However, whatever little bit of security gained by using nobody is lost when multiple system users use it. It should be possible to change it to /sbin/nologin; the fastest way to test it is change it and see if it breaks any services or applications.

Use the following command to list which shells are assigned to all users, system and human users, in /etc/passwd. The output varies according to the services and users on your system: 

> sort -t: -k 7 /etc/passwd | awk -F: '{print $1"\t" $7}' | column -t
tux               /bin/bash
nobody            /bin/bash
root              /bin/bash
avahi             /bin/false
chrony            /bin/false
dhcpd             /bin/false
dnsmasq           /bin/false
ftpsecure         /bin/false
lightdm           /bin/false
mysql             /bin/false
postfix           /bin/false
rtkit             /bin/false
sshd              /bin/false
tftp              /bin/false
unbound           /bin/false
bin               /sbin/nologin
daemon            /sbin/nologin
ftp               /sbin/nologin
lp                /sbin/nologin
mail              /sbin/nologin
man               /sbin/nologin
nscd              /sbin/nologin
polkitd           /sbin/nologin
pulse             /sbin/nologin
qemu              /sbin/nologin
radvd             /sbin/nologin
rpc               /sbin/nologin
statd             /sbin/nologin
svn               /sbin/nologin
systemd-coredump  /sbin/nologin
systemd-network   /sbin/nologin
systemd-timesync  /sbin/nologin
usbmux            /sbin/nologin
vnc               /sbin/nologin
wwwrun            /sbin/nologin
messagebus        /usr/bin/false
scard             /usr/sbin/nologin

1.1.2 The directory structure

  

The following table provides a short overview of the most important higher-level directories that you find on a Linux system. Find more detailed information about the directories and important subdirectories in the following list.

Table 1.4: Overview of a standard directory tree
  

Directory

Contents

/

Root directory—the starting point of the directory tree.

/bin

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.

/boot

Static files of the boot loader.

/dev

Files needed to access host-specific devices.

/etc

Host-specific system configuration files.

/home

Holds the home directories of all users who have accounts on the system. However, root's home directory is not located in /home but in /root.

/lib

Essential shared libraries and kernel modules.

/media

Mount points for removable media.

/mnt

Mount point for temporarily mounting a file system.

/opt

Add-on application software packages.

/root

Home directory for the superuser root.

/sbin

Essential system binaries.

/srv

Data for services provided by the system.

/tmp

Temporary files.

/usr

Secondary hierarchy with read-only data.

/var

Variable data such as log files.

/windows

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.

Note
Note: Home directory in a network environment

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.

Important
Important: Cleaning up /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 40.1, “Log files”.

/windows

Only available if you have both Microsoft Windows and Linux installed on your system. Contains the Windows data available on the Windows partition of your system. Whether you can edit the data in this directory depends on the file system your Windows partition uses. If it is FAT32, you can open and edit the files in this directory. For NTFS, SUSE Linux Enterprise Server also includes write access support. However, the driver for the NTFS-3g file system has limited functionality.

1.2 Writing shell scripts

  

Shell scripts provide a convenient way to perform a wide range of tasks: collecting data, searching for a word or phrase in a text and other useful things. The following example shows a small shell script that prints a text:

Example 1.1: A shell script printing a text
  
#!/bin/sh 1
# Output the following line: 2
echo "Hello World" 3

1

The first line begins with the Shebang characters (#!) which indicate that this file is a script. The interpreter, specified after the Shebang, executes the script. In this case, the specified interpreter is /bin/sh.

2

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.

3

The third line uses the built-in command echo to print the corresponding text.

Before you can run this script, there are a few prerequisites:

  1. Every script should contain a Shebang line (as in the example above). If the line is missing, you need to call the interpreter manually.

  2. 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.

  3. The script needs executable permissions. Set the permissions with the following command: 

    > chmod +x ~/bin/hello.sh

If you have fulfilled all of the above prerequisites, you can execute the script in the following ways:

  1. As absolute path.  The script can be executed with an absolute path. In our case, it is ~/bin/hello.sh.

  2. Everywhere.  If the PATH environment variable contains the directory where the script is located, you can execute the script with hello.sh.

1.3 Redirecting command events

  

Each command can use three channels, either for input or output:

  • Standard output.  This is the default output channel. Whenever a command prints something, it uses the standard output channel.

  • Standard input.  If a command needs input from users or other commands, it uses this channel.

  • Standard error.  Commands use this channel for error reporting.

To redirect these channels, there are the following possibilities:

Command > File

Saves the output of the command into a file, an existing file will be deleted. For example, the ls command writes its output into the file listing.txt: 

> ls > listing.txt
Command >> File

Appends the output of the command to a file. For example, the ls command appends its output to the file listing.txt: 

> ls >> listing.txt
Command < File

Reads the file as input for the given command. For example, the read command reads in the content of the file into the variable: 

> read a < foo
Command1 | Command2

Redirects the output of the left command as input for the right command. For example, the cat command outputs the content of the /proc/cpuinfo file. This output is used by grep to filter only those lines which contain cpu: 

> cat /proc/cpuinfo | grep cpu

Every channel has a file descriptor: 0 (zero) for standard input, 1 for standard output and 2 for standard error. It is allowed to insert this file descriptor before a < or > character. For example, the following line searches for a file starting with foo, but suppresses its errors by redirecting it to /dev/null: 

> find / -name "foo*" 2>/dev/null

1.4 Using aliases

  

An alias is a shortcut definition of one or more commands. The syntax for an alias is: 

alias NAME=DEFINITION

For example, the following line defines an alias lt that outputs a long listing (option -l), sorts it by modification time (-t), and prints it in reverse sorted order (-r): 

> alias lt='ls -ltr'

To view all alias definitions, use alias. Remove your alias with unalias and the corresponding alias name.

1.5 Using variables in Bash

  

A shell variable can be global or local. Global variables, or environment variables, can be accessed in all shells. In contrast, local variables are visible in the current shell only.

To view all environment variables, use the printenv command. If you need to know the value of a variable, insert the name of your variable as an argument: 

> printenv PATH

A variable, be it global or local, can also be viewed with echo: 

> echo $PATH

To set a local variable, use a variable name followed by the equal sign, followed by the value: 

> PROJECT="SLED"

Do not insert spaces around the equal sign, otherwise you get an error. To set an environment variable, use export: 

> export NAME="tux"

To remove a variable, use unset: 

> unset NAME

The following table contains some common environment variables which can be used in you shell scripts:

Table 1.5: Useful environment variables
  

HOME

the home directory of the current user

HOST

the current host name

LANG

when a tool is localized, it uses the language from this environment variable. English can also be set to C

PATH

the search path of the shell, a list of directories separated by colon

PS1

specifies the normal prompt printed before each command

PS2

specifies the secondary prompt printed when you execute a multi-line command

PWD

current working directory

USER

the current user

1.5.1 Using argument variables

  

For example, if you have the script foo.sh you can execute it like this: 

> foo.sh "Tux Penguin" 2000

To access all the arguments which are passed to your script, you need positional parameters. These are $1 for the first argument, $2 for the second, and so on. You can have up to nine parameters. To get the script name, use $0.

The following script foo.sh prints all arguments from 1 to 4: 

#!/bin/sh
echo \"$1\" \"$2\" \"$3\" \"$4\"

If you execute this script with the above arguments, you get: 

"Tux Penguin" "2000" "" ""

1.5.2 Using variable substitution

  

Variable substitutions apply a pattern to the content of a variable either from the left or right side. The following list contains the possible syntax forms:

${VAR#pattern}

removes the shortest possible match from the left: 

> file=/home/tux/book/book.tar.bz2
> echo ${file#*/}
home/tux/book/book.tar.bz2
${VAR##pattern}

removes the longest possible match from the left: 

> file=/home/tux/book/book.tar.bz2
> echo ${file##*/}
book.tar.bz2
${VAR%pattern}

removes the shortest possible match from the right: 

> file=/home/tux/book/book.tar.bz2
> echo ${file%.*}
/home/tux/book/book.tar
${VAR%%pattern}

removes the longest possible match from the right: 

> file=/home/tux/book/book.tar.bz2
> echo ${file%%.*}
/home/tux/book/book
${VAR/pattern_1/pattern_2}

substitutes the content of VAR from the PATTERN_1 with PATTERN_2: 

> file=/home/tux/book/book.tar.bz2
> echo ${file/tux/wilber}
/home/wilber/book/book.tar.bz2

1.6 Grouping and combining commands

  

Shells allow you to concatenate and group commands for conditional execution. Each command returns an exit code which determines the success or failure of its operation. If it is 0 (zero) the command was successful, everything else marks an error which is specific to the command.

The following list shows, how commands can be grouped:

Command1 ; Command2

executes the commands in sequential order. The exit code is not checked. The following line displays the content of the file with cat and then prints its file properties with ls regardless of their exit codes: 

> cat filelist.txt ; ls -l filelist.txt
Command1 && Command2

runs the right command, if the left command was successful (logical AND). The following line displays the content of the file and prints its file properties only, when the previous command was successful (compare it with the previous entry in this list): 

> cat filelist.txt && ls -l filelist.txt
Command1 || Command2

runs the right command, when the left command has failed (logical OR). The following line creates only a directory in /home/wilber/bar when the creation of the directory in /home/tux/foo has failed: 

> mkdir /home/tux/foo || mkdir /home/wilber/bar
funcname(){ ... }

creates a shell function. You can use the positional parameters to access its arguments. The following line defines the function hello to print a short message: 

> hello() { echo "Hello $1"; }

You can call this function like this: 

> hello Tux

which prints: 

Hello Tux

1.7 Working with common flow constructs

  

To control the flow of your script, a shell has while, if, for and case constructs.

1.7.1 The if control command

  

The if command is used to check expressions. For example, the following code tests whether the current user is Tux: 

if test $USER = "tux"; then
  echo "Hello Tux."
else
  echo "You are not Tux."
fi

The test expression can be as complex or simple as possible. The following expression checks if the file foo.txt exists: 

if test -e /tmp/foo.txt ; then
  echo "Found foo.txt"
fi

The test expression can also be abbreviated in square brackets: 

if [ -e /tmp/foo.txt ] ; then
  echo "Found foo.txt"
fi

Find more useful expressions at https://bash.cyberciti.biz/guide/If..else..fi.

1.7.2 Creating loops with the for command

  

The for loop allows you to execute commands to a list of entries. For example, the following code prints some information about PNG files in the current directory: 

for i in *.png; do
 ls -l $i
done

1.8 More information

  

Important information about Bash is provided in the man pages man bash. More about this topic can be found in the following list:

2 sudo basics

  

Running certain commands requires root privileges. However, for security reasons and to avoid mistakes, it is not recommended to log in as root. A safer approach is to log in as a regular user, and then use sudo to run commands with elevated privileges.

On SUSE Linux Enterprise Server, sudo is configured to work similarly to su. However, sudo provides a flexible mechanism that allows users to run commands with privileges of any other user. This can be used to assign roles with specific privileges to certain users and groups. For example, it is possible to allow members of the group users to run a command with the privileges of user wilber. Access to the command can be further restricted by disallowing any command options. While su always requires the root password for authentication with PAM, sudo can be configured to authenticate with your own credentials. This means that the users do not have to share the root password, which improves security.

2.1 Basic sudo usage

  

The following chapter provides an introduction to basic usage of sudo.

2.1.1 Running a single command

  

As a regular user, you can run any command as root by adding sudo before it. This prompts you to provide the root password. If authenticated successfully, this runs the command as root: 

> id -un1
tux
> sudo id -un
root's password:2
root
> id -un
tux3
> sudo id -un
4
root

1

The id -un command prints the login name of the current user.

2

The password is not shown during input, neither as clear text nor as masking characters.

3

Only commands that start with sudo run with elevated privileges.

4

The elevated privileges persist for a certain period of time, so you do not need to provide the root password again.

Tip
Tip: I/O redirection

When using sudo, I/O redirection does not work: 

> sudo echo s > /proc/sysrq-trigger
bash: /proc/sysrq-trigger: Permission denied
> sudo cat < /proc/1/maps
bash: /proc/1/maps: Permission denied

In the example above, only the echo and cat commands run with elevated privileges. The redirection is done by the user's shell with user privileges. To perform redirection with elevated privileges, either start a shell as in Section 2.1.2, “Starting a shell” or use the dd utility: 

echo s | sudo dd of=/proc/sysrq-trigger
sudo dd if=/proc/1/maps | cat

2.1.2 Starting a shell

  

Using sudo every time to run a command with elevated privileges is not always practical. While you can use the sudo bash command, it is recommended to use one of the built-in mechanisms to start a shell:

sudo -s (<command>)

Starts a shell specified by the SHELL environment variable or the target user's default shell. If a command is specified, it is passed to the shell (with the -c option). Otherwise the shell runs in interactive mode. 

tux:~ > sudo -s
root's password:
root:/home/tux # exit
tux:~ >
sudo -i (<command>)

Similar to -s, but starts the shell as a login shell. This means that the shell's start-up files (.profile etc.) are processed, and the current working directory is set to the target user's home directory. 

tux:~ > sudo -i
root's password:
root:~ # exit
tux:~ >
Tip
Tip: Environment variables

By default, sudo does not propagate environment variables. This behavior can be changed using the env_reset option (see Useful flags and options).

2.2 Configuring sudo

  

sudo provides a wide range on configurable options.

Note
Note: Locked yourself out of sudo

If you accidentally locked yourself out of sudo, use su - and the root password to start a root shell. To fix the error, run visudo.

2.2.1 Editing the configuration files

  

The main policy configuration file for sudo is /etc/sudoers. As it is possible to lock yourself out of the system if the file is malformed, it is strongly recommended to use visudo for editing. It prevents editing conflicts and checks for syntax errors before saving the modifications.

You can use another editor instead of vi by setting the EDITOR environment variable, for example: 

sudo EDITOR=/usr/bin/nano visudo

Keep in mind that the /etc/sudoers file is supplied by the system packages, and modifications done directly in the file may break updates. Therefore, it is recommended to put custom configuration into files in the /etc/sudoers.d/ directory. Use the following command to create or edit a file: 

sudo visudo -f /etc/sudoers.d/NAME

The command bellow opens the file using a different editor (in this case, nano): 

sudo EDITOR=/usr/bin/nano visudo -f /etc/sudoers.d/NAME
Note
Note: Ignored files in /etc/sudoers.d

The #includedir directive in /etc/sudoers ignores files that end with the ~ (tilde) character or contain the . (dot) character.

For more information on the visudo command, run man 8 visudo.

2.2.2 Basic sudoers configuration syntax

  

The sudoers configuration files contain two types of options: strings and flags. While strings can contain any value, flags can be turned either ON or OFF. The most important syntax constructs for sudoers configuration files are as follows: 

# Everything on a line after # is ignored 1
Defaults !insults # Disable the insults flag 2
Defaults env_keep += "DISPLAY HOME" # Add DISPLAY and HOME to env_keep
tux ALL = NOPASSWD: /usr/bin/frobnicate, PASSWD: /usr/bin/journalctl 3

1

There are two exceptions: #include and #includedir are regular commands.

2

Remove the ! character to set the desired flag to ON.

3

See Section 2.2.3, “Basic sudoers rules”.

Useful flags and options
  
targetpw

This flag controls whether the invoking user is required to enter the password of the target user (ON) (for example root) or the invoking user (OFF). 

Defaults targetpw # Turn targetpw flag ON
rootpw

If set, sudo prompts for the root password. The default is OFF. 

Defaults !rootpw # Turn rootpw flag OFF
env_reset

If set, sudo constructs a minimal environment with TERM, PATH, HOME, MAIL, SHELL, LOGNAME, USER, USERNAME, and SUDO_*. Additionally, variables listed in env_keep are imported from the calling environment. The default is ON. 

Defaults env_reset # Turn env_reset flag ON
env_keep

List of environment variables to keep when the env_reset flag is ON. 

# Set env_keep to contain EDITOR and PROMPT
Defaults env_keep = "EDITOR PROMPT"
Defaults env_keep += "JRE_HOME" # Add JRE_HOME
Defaults env_keep -= "JRE_HOME" # Remove JRE_HOME
env_delete

List of environment variables to remove when the env_reset flag is OFF. 

# Set env_delete to contain EDITOR and PROMPT
Defaults env_delete = "EDITOR PROMPT"
Defaults env_delete += "JRE_HOME" # Add JRE_HOME
Defaults env_delete -= "JRE_HOME" # Remove JRE_HOME

The Defaults token can also be used to create aliases for a collection of users, hosts, and commands. Furthermore, it is possible to apply an option only to a specific set of users.

For detailed information about the /etc/sudoers configuration file, consult man 5 sudoers.

2.2.3 Basic sudoers rules

  

Each rule follows the following scheme ([] marks optional parts): 

#Who      Where         As whom      Tag                What
User_List Host_List = [(User_List)] [NOPASSWD:|PASSWD:] Cmnd_List
sudoers rule syntax
  
User_List

One or several (separated by comma) identifiers: either a user name, a group in the format %GROUPNAME, or a user ID in the format #UID. Negation can be specified with the ! prefix.

Host_List

One or several (separated by comma) identifiers: either a (fully qualified) host name or an IP address. Negation can be specified with the ! prefix. ALL is a common choice for Host_List.

NOPASSWD:|PASSWD:

The user is not prompted for a password when running commands matching Cmd_List after NOPASSWD:.

PASSWD is the default. It only needs to be specified when both PASSWD and NOPASSWD are on the same line: 

tux ALL = PASSWD: /usr/bin/foo, NOPASSWD: /usr/bin/bar
Cmnd_List

One or several (separated by comma) specifiers: A path to an executable, followed by an optional allowed argument. 

/usr/bin/foo     # Anything allowed
/usr/bin/foo bar # Only "/usr/bin/foo bar" allowed
/usr/bin/foo ""  # No arguments allowed

ALL can be used as User_List, Host_List, and Cmnd_List.

A rule that allows tux to run all commands as root without entering a password: 

tux ALL = NOPASSWD: ALL

A rule that allows tux to run systemctl restart apache2: 

tux ALL = /usr/bin/systemctl restart apache2

A rule that allows tux to run wall as admin with no arguments: 

tux ALL = (admin) /usr/bin/wall ""
Warning
Warning: Unsafe rules

Do not use rules like ALL ALL = ALL without Defaults targetpw. Otherwise anyone can run commands as root.

2.3 sudo use cases

  

While the default configuration works for standard usage scenarios, you can customize the default configuration to meet your specific needs.

2.3.1 Using sudo without root password

  

By design, members of the group wheel can run all commands with sudo as root. The following procedure explains how to add a user account to the wheel group.

  1. Verify that the wheel group exists: 

    > getent group wheel

    If the previous command returned no result, install the system-group-wheel package that creates the wheel group: 

    > sudo zypper install system-group-wheel

  2. Add your user account to the group wheel.

    If your user account is not already a member of the wheel group, add it using the sudo usermod -a -G wheel USERNAME command. Log out and log in again to enable the change. Verify that the change was successful by running the groups USERNAME command.

  3. Authenticate with the user account's normal password.

    Create the file /etc/sudoers.d/userpw using the visudo command (see Section 2.2.1, “Editing the configuration files”) and add the following: 

    Defaults !targetpw

  4. Select a new default rule.

    Depending on whether you want users to re-enter their passwords, uncomment the appropriate line in /etc/sudoers and comment out the default rule. 

    ## Uncomment to allow members of group wheel to execute any command
# %wheel ALL=(ALL) ALL

## Same thing without a password
# %wheel ALL=(ALL) NOPASSWD: ALL

  5. Make the default rule more restrictive.

    Comment out or remove the allow-everything rule in /etc/sudoers: 

    ALL     ALL=(ALL) ALL   # WARNING! Only use this together with 'Defaults targetpw'!
    Warning
    Warning: Dangerous rule in sudoers

    Do not skip this step. Otherwise any user can execute any command as root!

  6. Test the configuration.

    Run sudo as member and non-member of wheel. 

    tux:~ > groups
users wheel
tux:~ > sudo id -un
tux's password:
root
wilber:~ > groups
users
wilber:~ > sudo id -un
wilber is not in the sudoers file.  This incident will be reported.

2.3.2 Using sudo with X.Org applications

  

Starting graphical applications with sudo usually results in the following error: 

> sudo xterm
xterm: Xt error: Can't open display: %s
xterm: DISPLAY is not set

A simple workaround is to use xhost to temporarily allow the root user to access the local user's X session. This is done using the following command: 

xhost si:localuser:root

The command below removes the granted access: 

xhost -si:localuser:root
Warning
Warning: Potential security issue

Running graphical applications with root privileges has security implications. It is recommended to enable root access for a graphical application only as an exception. It is also recommended to revoke the granted root access as soon as the graphical application is closed.

2.4 More information

  

The sudo --help command offers a brief overview of the available command line options, while the man sudoers command provides detailed information about sudoers and its configuration.

3 Using YaST

  

YaST is a SUSE Linux Enterprise Server tool that provides a graphical interface for all essential installation and system configuration tasks. Whether you need to update packages, configure a printer, modify firewall settings, set up an FTP server, or partition a hard disk—you can do it using YaST. Written in Ruby, YaST features an extensible architecture that makes it possible to add new functionality via modules.

Additional information about YaST is available on the project's official Web site at https://yast.opensuse.org/.

3.1 YaST interface overview

  

YaST has two graphical interfaces: one for use with graphical desktop environments like KDE and GNOME, and an ncurses-based pseudo-graphical interface for use on systems without an X server (see Chapter 4, YaST in text mode).

In the graphical version of YaST, all modules in YaST are grouped by category, and the navigation sidebar allows you to quickly access modules in the desired category. The search field at the top makes it possible to find modules by their names. To find a specific module, enter its name into the search field, and you should see the modules that match the entered string as you type.

Important
Important: List of installed YaST modules

The list of installed modules for the ncurses-based and GUI version of YaST may differ. Before starting any YaST module, verify that it is installed for the version of YaST that you are using.

3.2 Useful key combinations

  

The graphical version of YaST supports keyboard shortcuts

Print Screen

Take and save a screenshot. It may not work on certain desktop environments.

Shift–F4

Enable and disable the color palette optimized for visually-impaired users.

Shift–F7

Enable/disable logging of debug messages.

Shift–F8

Open a file dialog to save log files to a user-defined location.

Ctrl–Shift–Alt–D

Send a DebugEvent. YaST modules can react to this by executing special debugging actions. The result depends on the specific YaST module.

Ctrl–Shift–Alt–M

Start and stop macro recorder.

Ctrl–Shift–Alt–P

Replay macro.

Ctrl–Shift–Alt–S

Show style sheet editor.

Ctrl–Shift–Alt–T

Dump widget tree to the log file.

Ctrl–Shift–Alt–X

Open a terminal window (xterm). Useful for installation process via VNC.

Ctrl–Shift–Alt–Y

Show widget tree browser.

4 YaST in text mode

  

The ncurses-based pseudo-graphical YaST interface is designed primarily to help system administrators to manage systems without an X server. The interface offers several advantages compared to the conventional GUI. You can navigate the ncurses interface using the keyboard, and there are keyboard shortcuts for practically all interface elements. The ncurses interface is light on resources, and runs fast even on modest hardware. You can run the ncurses-based version of YaST via an SSH connection, so you can administer remote systems. Keep in mind that the minimum supported size of the terminal emulator in which to run YaST is 80x25 characters.

Main window of YaST in text mode
Figure 4.1: Main window of YaST in text mode
  

To launch the ncurses-based version of YaST, open the terminal and run the sudo yast2 command. Use the Tab or arrow keys to navigate between interface elements like menu items, fields, and buttons. All menu items and buttons in YaST can be accessed using the appropriate function keys or keyboard shortcuts. For example, you can cancel the current operation by pressing F9, while the F10 key can be used to accept the changes. Each menu item and button in YaST's ncurses-based interface has a highlighted letter in its label. This letter is part of the keyboard shortcut assigned to the interface element. For example, the letter Q is highlighted in the Quit button. This means that you can activate the button by pressing Alt–Alt+Q.

Tip
Tip: Refreshing YaST dialogs

If a YaST dialog gets corrupted or distorted (for example, while resizing the window), press Ctrl–L to refresh and restore its contents.

4.1 Navigation in modules

  

The following description of the control elements in the YaST modules assumes that all function keys and Alt key combinations work and are not assigned to different global functions. Read Section 4.3, “Restriction of key combinations” for information about possible exceptions.

Moving between buttons and selection lists

Use →| to move between the buttons and frames containing selection lists. To navigate in the opposite direction, use Alt–→| or Shift–→| combinations.

Navigating in selection lists

Use the arrow keys (↑ and ↓) to move through the individual elements in an active frame containing a selection list. If individual entries are longer than the frame's width, use Shift–→ or Shift–← to scroll horizontally. If the arrow key causes the selection to move to another frame, use Ctrl–E or Ctrl–A instead.

Working with buttons, radio buttons, and check boxes

To select items with empty square brackets (check boxes) or empty parentheses (radio buttons), press Space or Enter. Alternatively, radio buttons and check boxes can be selected directly with Alt–highlighted_letter. In this case, you do not need to confirm with Enter. If you navigate to an item with →|, press Enter to execute the selected action or activate the respective menu item.

Function keys

The function keys (from F1 to F12) enable quick access to the various buttons. Available function key combinations (FX) are shown in the bottom line of the YaST screen. Which function keys are actually mapped to which buttons depend on the active YaST module, because the different modules offer different buttons (Details, Info, Add, Delete, etc.). Use F10 for Accept, OK, Next, and Finish. Press F1 to access the YaST help.

Using the navigation tree

Some YaST modules use a navigation tree in the left part of the window to select configuration dialogs. Use the arrow keys (↑ and ↓) to navigate in the tree. Use Space to open or close tree items. In the ncurses mode, Enter must be pressed after a selection in the navigation tree to show the selected dialog. This is an intentional behavior to save time-consuming redraws when browsing through the navigation tree.

Selecting software in the software installation module

Use the filters on the left side to list packages matching the specified string. Installed packages are marked with the letter i. To change the status of a package, press Space or Enter. Alternatively, use the Actions menu to select the needed status change (install, delete, update, taboo, or lock).

The software installation module
Figure 4.2: The software installation module
  

4.2 Advanced key combinations

  

The ncurses-based version of YaST offers several advanced key combinations.

Shift–F1

List advanced hotkeys.

Shift–F4

Change color schema.

Ctrl–Q

Quit the application.

Ctrl–L

Refresh screen.

Ctrl–DF1

List advanced hotkeys.

Ctrl–DShift–D

Dump dialog to the log file as a screenshot.

Ctrl–DShift–Y

Open YDialogSpy to see the widget hierarchy.

4.3 Restriction of key combinations

  

If your window manager uses global Alt combinations, the Alt combinations in YaST might not work. Keys like Alt or Shift can also be occupied by the settings of the terminal.

Using Alt instead of Esc

Alt shortcuts can be executed with Esc instead of Alt. For example, Esc–H replaces Alt–H. (Press Esc, then press H.)

Backward and forward navigation with Ctrl–F and Ctrl–B

If the Alt and Shift combinations are taken over by the window manager or the terminal, use the combinations Ctrl–F (forward) and Ctrl–B (backward) instead.

Restriction of function keys

The function keys (F1 ... F12) are also used for functions. Certain function keys might be taken over by the terminal and may not be available for YaST. However, the Alt key combinations and function keys should always be fully available on a text-only console.

4.4 YaST command line options

  

Besides the text mode interface, YaST provides a command line interface. To get a list of YaST command line options, use the following command: 

> sudo yast -h

4.4.1 Installing packages from the command line

  

If you know the package name, and the package is provided by an active installation repository, you can use the command line option -i to install the package: 

> sudo yast -i package_name

or 

> sudo yast --install -i package_name

package_name can be a single short package name (for example gvim) installed with dependency checking, or the full path to an RPM package, which is installed without dependency checking.

While YaST offers basic functionality for managing software from the command line, consider using Zypper for more advanced package management tasks. Find more information on using Zypper in Section 6.1, “Using Zypper”.

4.4.2 Working with individual modules

  

To save time, you can start individual YaST modules using the following command: 

> sudo yast module_name

View a list of all modules available on your system with yast -l or yast --list.

4.4.3 Command line parameters of YaST modules

  

To use YaST functionality in scripts, YaST provides command line support for individual modules. However, not all modules have command line support. To display the available options of a module, use the following command: 

> sudo yast module_name help

If a module does not provide command line support, it is started in a text mode with the following message: 

This YaST module does not support the command line interface.

The following sections describe all YaST modules with command line support, along with a brief explanation of all their commands and available options.

4.4.3.1 Common YaST module commands

  

All YaST modules support the following commands:

help

Lists all the module's supported commands with their description: 

> sudo yast lan help
longhelp

Same as help, but adds a detailed list of all command's options and their descriptions: 

> sudo yast lan longhelp
xmlhelp

Same as longhelp, but the output is structured as an XML document and redirected to a file: 

> sudo yast lan xmlhelp xmlfile=/tmp/yast_lan.xml
interactive

Enters the interactive mode. This lets you run the module's commands without prefixing them with sudo yast. Use exit to leave the interactive mode.

4.4.3.2 yast add-on

  

Adds a new add-on product from the specified path: 

 > sudo yast add-on http://server.name/directory/Lang-AddOn-CD1/

You can use the following protocols to specify the source path: http:// ftp:// nfs:// disk:// cd:// or dvd://.

4.4.3.3 yast audit-laf

  

Displays and configures the Linux Audit Framework. Refer to the Book “Security and Hardening Guide” for more details. yast audit-laf accepts the following commands:

set

Sets an option: 

> sudo yast audit-laf set log_file=/tmp/audit.log

For a complete list of options, run yast audit-laf set help.

show

Displays settings of an option: 

> sudo yast audit-laf show diskspace
space_left: 75
space_left_action: SYSLOG
admin_space_left: 50
admin_space_left_action: SUSPEND
action_mail_acct: root
disk_full_action: SUSPEND
disk_error_action: SUSPEND

For a complete list of options, run yast audit-laf show help.

4.4.3.4 yast dhcp-server

  

Manages the DHCP server and configures its settings. yast dhcp-server accepts the following commands:

disable

Disables the DHCP server service.

enable

Enables the DHCP server service.

host

Configures settings for individual hosts.

interface

Specifies to which network interface to listen to: 

> sudo yast dhcp-server interface current
Selected Interfaces: eth0
Other Interfaces: bond0, pbu, eth1

For a complete list of options, run yast dhcp-server interface help.

options

Manages global DHCP options. For a complete list of options, run yast dhcp-server options help.

status

Prints the status of the DHCP service.

subnet

Manages the DHCP subnet options. For a complete list of options, run yast dhcp-server subnet help.

4.4.3.5 yast dns-server

  

Manages the DNS server configuration. yast dns-server accepts the following commands:

acls

Displays access control list settings: 

 > sudo yast dns-server acls show
 ACLs:
 -----
  Name       Type        Value
  ----------------------------
  any        Predefined
  localips   Predefined
  localnets  Predefined
  none       Predefined
dnsrecord

Configures zone resource records: 

> sudo yast dnsrecord add zone=example.org query=office.example.org type=NS value=ns3

For a complete list of options, run yast dns-server dnsrecord help.

forwarders

Configures DNS forwarders: 

> sudo yast dns-server forwarders add ip=10.0.0.100
> sudo yast dns-server forwarders show
[...]
Forwarder IP
------------
10.0.0.100

For a complete list of options, run yast dns-server forwarders help.

host

Handles 'A' and its related 'PTR' record at once: 

> sudo yast dns-server host show zone=example.org

For a complete list of options, run yast dns-server host help.

logging

Configures logging settings: 

> sudo yast dns-server logging set updates=no transfers=yes

For a complete list of options, run yast dns-server logging help.

mailserver

Configures zone mail servers: 

> sudo yast dns-server mailserver add zone=example.org mx=mx1 priority=100

For a complete list of options, run yast dns-server mailserver help.

nameserver

Configures zone name servers: 

> sudo yast dns-server nameserver add zone=example.com ns=ns1

For a complete list of options, run yast dns-server nameserver help.

soa

Configures the start of authority (SOA) record: 

> sudo yast dns-server soa set zone=example.org serial=2006081623 ttl=2D3H20S

For a complete list of options, run yast dns-server soa help.

startup

Manages the DNS server service: 

> sudo yast dns-server startup atboot

For a complete list of options, run yast dns-server startup help.

transport

Configures zone transport rules. For a complete list of options, run yast dns-server transport help.

zones

Manages DNS zones: 

> sudo yast dns-server zones add name=example.org zonetype=master

For a complete list of options, run yast dns-server zones help.

4.4.3.6 yast disk

  

Prints information about all disks or partitions. The only supported command is list followed by either of the following options:

disks

Lists all configured disks in the system: 

> sudo yast disk list disks
Device   | Size       | FS Type | Mount Point | Label | Model
---------+------------+---------+-------------+-------+-------------
/dev/sda | 119.24 GiB |         |             |       | SSD 840
/dev/sdb |  60.84 GiB |         |             |       | WD1003FBYX-0
partitions

Lists all partitions in the system: 

> sudo yast disk list partitions
Device         | Size       | FS Type | Mount Point | Label | Model
---------------+------------+---------+-------------+-------+------
/dev/sda1      |   1.00 GiB | Ext2    | /boot       |       |
/dev/sdb1      |   1.00 GiB | Swap    | swap        |       |
/dev/sdc1      | 698.64 GiB | XFS     | /mnt/extra  |       |
/dev/vg00/home | 580.50 GiB | Ext3    | /home       |       |
/dev/vg00/root | 100.00 GiB | Ext3    | /           |       |
[...]

4.4.3.7 yast ftp-server

  

Configures FTP server settings. yast ftp-server accepts the following options:

SSL, TLS

Controls secure connections via SSL and TLS. SSL options are valid for the vsftpd only. 

> sudo yast ftp-server SSL enable
> sudo yast ftp-server TLS disable
access

Configures access permissions: 

> sudo yast ftp-server access authen_only

For a complete list of options, run yast ftp-server access help.

anon_access

Configures access permissions for anonymous users: 

> sudo yast ftp-server anon_access can_upload

For a complete list of options, run yast ftp-server anon_access help.

anon_dir

Specifies the directory for anonymous users. The directory must already exist on the server: 

> sudo yast ftp-server anon_dir set_anon_dir=/srv/ftp

For a complete list of options, run yast ftp-server anon_dir help.

chroot

Controls change root environment (chroot): 

> sudo yast ftp-server chroot enable
> sudo yast ftp-server chroot disable
idle-time

Sets the maximum idle time in minutes before FTP server terminates the current connection: 

> sudo yast ftp-server idle-time set_idle_time=15
logging

Determines whether to save the log messages into a log file: 

> sudo yast ftp-server logging enable
> sudo yast ftp-server logging disable
max_clients

Specifies the maximum number of concurrently connected clients: 

> sudo yast ftp-server max_clients set_max_clients=1500
max_clients_ip

Specifies the maximum number of concurrently connected clients via IP: 

> sudo yast ftp-server max_clients_ip set_max_clients=20
max_rate_anon

Specifies the maximum data transfer rate permitted for anonymous clients (KB/s): 

> sudo yast ftp-server max_rate_anon set_max_rate=10000
max_rate_authen

Specifies the maximum data transfer rate permitted for locally authenticated users (KB/s): 

> sudo yast ftp-server max_rate_authen set_max_rate=10000
port_range

Specifies the port range for passive connection replies: 

> sudo yast ftp-server port_range set_min_port=20000 set_max_port=30000

For a complete list of options, run yast ftp-server port_range help.

show

Displays FTP server settings.

startup

Controls the FTP start-up method: 

> sudo yast ftp-server startup atboot

For a complete list of options, run yast ftp-server startup help.

umask

Specifies the file umask for authenticated:anonymous users: 

> sudo yast ftp-server umask set_umask=177:077
welcome_message

Specifies the text to display when someone connects to the FTP server: 

> sudo yast ftp-server welcome_message set_message="hello everybody"

4.4.3.8 yast http-server

  

Configures the HTTP server (Apache2). yast http-server accepts the following commands:

configure

Configures the HTTP server host settings: 

> sudo yast http-server configure host=main servername=www.example.com \
 serveradmin=admin@example.com

For a complete list of options, run yast http-server configure help.

hosts

Configures virtual hosts: 

> sudo yast http-server hosts create servername=www.example.com \
 serveradmin=admin@example.com documentroot=/var/www

For a complete list of options, run yast http-server hosts help.

listen

Specifies the ports and network addresses where the HTTP server should listen: 

> sudo yast http-server listen add=81
> sudo yast http-server listen list
Listen Statements:
==================
:80
:81
> sudo yast http-server delete=80

For a complete list of options, run yast http-server listen help.

mode

Enables or disables the wizard mode: 

> sudo yast http-server mode wizard=on
modules

Controls the Apache2 server modules: 

> sudo yast http-server modules enable=php5,rewrite
> sudo yast http-server modules disable=ssl
> sudo http-server modules list
[...]
Enabled rewrite
Disabled ssl
Enabled php5
[...]

4.4.3.9 yast kdump

  

Configures kdump settings. For more information on kdump, refer to the Book “System Analysis and Tuning Guide”, Chapter 20 “Kexec and Kdump”, Section 20.7 “Basic Kdump configuration”. yast kdump accepts the following commands:

copykernel

Copies the kernel into the dump directory.

customkernel

Specifies the kernel_string part of the name of the custom kernel. The naming scheme is /boot/vmlinu[zx]-kernel_string[.gz]. 

> sudo yast kdump customkernel kernel=kdump

For a complete list of options, run yast kdump customkernel help.

dumpformat

Specifies the (compression) format of the dump kernel image. Available formats are 'none', 'ELF', 'compressed', or 'lzo': 

> sudo yast kdump dumpformat dump_format=ELF
dumplevel

Specifies the dump level number in the range from 0 to 31: 

> sudo yast kdump dumplevel dump_level=24
dumptarget

Specifies the destination for saving dump images: 

> sudo kdump dumptarget taget=ssh server=name_server port=22 \
 dir=/var/log/dump user=user_name

For a complete list of options, run yast kdump dumptarget help.

immediatereboot

Controls whether the system should reboot immediately after saving the core in the kdump kernel: 

> sudo yast kdump immediatereboot enable
> sudo yast kdump immediatereboot disable
keepolddumps

Specifies how many old dump images are kept. Specify zero to keep them all: 

> sudo yast kdump keepolddumps no=5
kernelcommandline

Specifies the command line that needs to be passed off to the kdump kernel: 

> sudo yast kdump kernelcommandline command="ro root=LABEL=/"
kernelcommandlineappend

Specifies the command line that you need to append to the default command line string: 

> sudo yast kdump kernelcommandlineappend command="ro root=LABEL=/"
notificationcc

Specifies an e-mail address for sending copies of notification messages: 

> sudo yast kdump notificationcc email="user1@example.com user2@example.com"
notificationto

Specifies an e-mail address for sending notification messages: 

> sudo yast kdump notificationto email="user1@example.com user2@example.com"
show

Displays kdump settings: 

> sudo yast kdump show
Kdump is disabled
Dump Level: 31
Dump Format: compressed
Dump Target Settings
target: file
file directory: /var/crash
Kdump immediate reboots: Enabled
Numbers of old dumps: 5
smtppass

Specifies the file with the plain text SMTP password used for sending notification messages: 

> sudo yast kdump smtppass pass=/path/to/file
smtpserver

Specifies the SMTP server host name used for sending notification messages: 

> sudo yast kdump smtpserver server=smtp.server.com
smtpuser

Specifies the SMTP user name used for sending notification messages: 

> sudo yast kdump smtpuser user=smtp_user
startup

Enables or disables start-up options: 

> sudo yast kdump startup enable alloc_mem=128,256
> sudo yast kdump startup disable

4.4.3.10 yast keyboard

  

Configures the system keyboard for virtual consoles. It does not affect the keyboard settings in graphical desktop environments, such as GNOME or KDE. yast keyboard accepts the following commands:

list

Lists all available keyboard layouts.

set

Activates new keyboard layout setting: 

> sudo yast keyboard set layout=czech
summary

Displays the current keyboard configuration.

4.4.3.11 yast lan

  

Configures network cards. yast lan accepts the following commands:

add

Configures a new network card: 

> sudo yast lan add name=vlan50 ethdevice=eth0 bootproto=dhcp

For a complete list of options, run yast lan add help.

delete

Deletes an existing network card: 

> sudo yast lan delete id=0
edit

Changes the configuration of an existing network card: 

> sudo yast lan edit id=0 bootproto=dhcp
list

Displays a summary of network card configuration: 

> sudo yast lan list
id name,           bootproto
0 Ethernet Card 0, NONE
1 Network Bridge,  DHCP

4.4.3.12 yast language

  

Configures system languages. yast language accepts the following commands:

list

Lists all available languages.

set

Specifies the main system languages and secondary languages: 

> sudo yast language set lang=cs_CZ languages=en_US,es_ES no_packages

4.4.3.13 yast mail

  

Displays the configuration of the mail system: 

> sudo yast mail summary

4.4.3.14 yast nfs

  

Controls the NFS client. yast nfs accepts the following commands:

add

Adds a new NFS mount: 

> sudo yast nfs add spec=remote_host:/path/to/nfs/share file=/local/mount/point

For a complete list of options, run yast nfs add help.

delete

Deletes an existing NFS mount: 

> sudo yast nfs delete spec=remote_host:/path/to/nfs/share file=/local/mount/point

For a complete list of options, run yast nfs delete help.

edit

Changes an existing NFS mount: 

> sudo yast nfs edit spec=remote_host:/path/to/nfs/share \
 file=/local/mount/point type=nfs4

For a complete list of options, run yast nfs edit help.

list

Lists existing NFS mounts: 

> sudo yast nfs list
Server            Remote File System    Mount Point    Options
----------------------------------------------------------------
nfs.example.com   /mnt                  /nfs/mnt       nfs
nfs.example.com   /home/tux/nfs_share   /nfs/tux       nfs

4.4.3.15 yast nfs-server

  

Configures the NFS server. yast nfs-server accepts the following commands:

add

Adds a directory to export: 

> sudo yast nfs-server add mountpoint=/nfs/export hosts=*.allowed_hosts.com

For a complete list of options, run yast nfs-server add help.

delete

Deletes a directory from the NFS export: 

 > sudo yast nfs-server delete mountpoint=/nfs/export
set

Specifies additional parameters for the NFS server: 

> sudo yast nfs-server set enablev4=yes security=yes

For a complete list of options, run yast nfs-server set help.

start

Starts the NFS server service: 

> sudo yast nfs-server start
stop

Stops the NFS server service: 

> sudo yast nfs-server stop
summary

Displays a summary of the NFS server configuration: 

> sudo yast nfs-server summary
NFS server is enabled
NFS Exports
* /mnt
* /home

NFSv4 support is enabled.
The NFSv4 domain for idmapping is localdomain.
NFS Security using GSS is enabled.

4.4.3.16 yast nis

  

Configures the NIS client. yast nis accepts the following commands:

configure

Changes global settings of a NIS client: 

> sudo yast nis configure server=nis.example.com broadcast=yes

For a complete list of options, run yast nis configure help.

disable

Disables the NIS client: 

> sudo yast nis disable
enable

Enables your machine as NIS client: 

> sudo yast nis enable server=nis.example.com broadcast=yes automounter=yes

For a complete list of options, run yast nis enable help.

find

Shows available NIS servers for a given domain: 

> sudo yast nis find domain=nisdomain.com
summary

Displays a configuration summary of a NIS client.

4.4.3.17 yast nis-server

  

Configures a NIS server. yast nis-server accepts the following commands:

master

Configures a NIS master server: 

> sudo yast nis-server master domain=nisdomain.com yppasswd=yes

For a complete list of options, run yast nis-server master help.

slave

Configures a NIS slave server: 

> sudo yast nis-server slave domain=nisdomain.com master_ip=10.100.51.65

For a complete list of options, run yast nis-server slave help.

stop

Stops a NIS server: 

> sudo yast nis-server stop
summary

Displays a configuration summary of a NIS server: 

> sudo yast nis-server summary

4.4.3.18 yast proxy

  

Configures proxy settings. yast proxy accepts the following commands:

authentication

Specifies the authentication options for proxy: 

> sudo yast proxy authentication username=tux password=secret

For a complete list of options, run yast proxy authentication help.

enable, disable

Enables or disables proxy settings.

set

Changes the current proxy settings: 

> sudo yast proxy set https=proxy.example.com

For a complete list of options, run yast proxy set help.

summary

Displays proxy settings.

4.4.3.19 yast rdp

  

Controls remote desktop settings. yast rdp accepts the following commands:

allow

Allows remote access to the server's desktop: 

> sudo yast rdp allow set=yes
list

Displays the remote desktop configuration summary.

4.4.3.20 yast samba-client

  

Configures the Samba client settings. yast samba-client accepts the following commands:

configure

Changes global settings of Samba: 

> sudo yast samba-client configure workgroup=FAMILY
isdomainmember

Checks whether the machine is a member of a domain: 

> sudo yast samba-client isdomainmember domain=SMB_DOMAIN
joindomain

Makes the machine a member of a domain: 

> sudo yast samba-client joindomain domain=SMB_DOMAIN user=username password=pwd
winbind

Enables or disables Winbind services (the winbindd daemon): 

> sudo yast samba-client winbind enable
> sudo yast samba-client winbind disable

4.4.3.21 yast samba-server

  

Configures Samba server settings. yast samba-server accepts the following commands:

backend

Specifies the back-end for storing user information: 

> sudo yast samba-server backend smbpasswd

For a complete list of options, run yast samba-server backend help.

configure

Configures global settings of the Samba server: 

> sudo yast samba-server configure workgroup=FAMILY description='Home server'

For a complete list of options, run yast samba-server configure help.

list

Displays a list of available shares: 

> sudo yast samba-server list
Status     Type Name
==============================
Disabled   Disk profiles
Enabled    Disk print$
Enabled    Disk homes
Disabled   Disk groups
Enabled    Disk movies
Enabled    Printer printers
role

Specifies the role of the Samba server: 

> sudo yast samba-server role standalone

For a complete list of options, run yast samba-server role help.

service

Enables or disables the Samba services (smb and nmb): 

> sudo yast samba-server service enable
> sudo yast samba-server service disable
share

Manipulates a single Samba share: 

> sudo yast samba-server share name=movies browseable=yes guest_ok=yes

For a complete list of options, run yast samba-server share help.

4.4.3.22 yast security

  

Controls the security level of the host. yast security accepts the following commands:

level

Specifies the security level of the host: 

> sudo yast security level server

For a complete list of options, run yast security level help.

set

Sets the value of a specific option: 

> sudo yast security set passwd=sha512 crack=yes

For a complete list of options, run yast security set help.

summary

Displays a summary of the current security configuration: 

sudoyast security summary

4.4.3.23 yast sound

  

Configures sound card settings. yast sound accepts the following commands:

add

Configures a new sound card. Without any parameters, the command adds the first detected card. 

> sudo yast sound add card=0 volume=75

For a complete list of options, run yast sound add help.

channels

Lists available volume channels of a sound card: 

> sudo yast sound channels card=0
Master 75
PCM 100
modules

Lists all available sound kernel modules: 

> sudo yast sound modules
snd-atiixp ATI IXP AC97 controller (snd-atiixp)
snd-atiixp-modem ATI IXP MC97 controller (snd-atiixp-modem)
snd-virtuoso Asus Virtuoso driver (snd-virtuoso)
[...]
playtest

Plays a test sound on a sound card: 

> sudo yast sound playtest card=0
remove

Removes a configured sound card: 

> sudo yast sound remove card=0
> sudo yast sound remove all
set

Specifies new values for a sound card: 

> sudo yast sound set card=0 volume=80
show

Displays detailed information about a sound card: 

> sudo yast sound show card=0
Parameters of card 'ThinkPad X240' (using module snd-hda-intel):

align_buffer_size
 Force buffer and period sizes to be multiple of 128 bytes.
bdl_pos_adj
 BDL position adjustment offset.
beep_mode
 Select HDA Beep registration mode (0=off, 1=on) (default=1).
 Default Value: 0
enable_msi
 Enable Message Signaled Interrupt (MSI)
[...]
summary

Prints a configuration summary for all sound cards on the system: 

> sudo yast sound summary
volume

Specifies the volume level of a sound card: 

sudoyast sound volume card=0 play

4.4.3.24 yast sysconfig

  

Controls the variables in files under /etc/sysconfig. yast sysconfig accepts the following commands:

clear

Sets empty value to a variable: 

> sudo yast sysconfig clear=POSTFIX_LISTEN
Tip
Tip: Variable in multiple files

If the variable is available in several files, use the VARIABLE_NAME$FILE_NAME syntax: 

> sudo yast sysconfig clear=CONFIG_TYPE$/etc/sysconfig/mail
details

Displays detailed information about a variable: 

> sudo yast sysconfig details variable=POSTFIX_LISTEN
Description:
Value:
File: /etc/sysconfig/postfix
Possible Values: Any value
Default Value:
Configuration Script: postfix
Description:
 Comma separated list of IP's
 NOTE: If not set, LISTEN on all interfaces
list

Displays summary of modified variables. Use all to list all variables and their values: 

> sudo yast sysconfig list all
AOU_AUTO_AGREE_WITH_LICENSES="false"
AOU_ENABLE_CRONJOB="true"
AOU_INCLUDE_RECOMMENDS="false"
[...]
set

Sets a value for a variable: 

> sudo yast sysconfig set DISPLAYMANAGER=gdm
Tip
Tip: Variable in multiple files

If the variable is available in several files, use the VARIABLE_NAME$FILE_NAME syntax: 

> sudo yast sysconfig set CONFIG_TYPE$/etc/sysconfig/mail=advanced

4.4.3.25 yast tftp-server

  

Configures a TFTP server. yast tftp-server accepts the following commands:

directory

Specifies the directory of the TFTP server: 

> sudo yast tftp-server directory path=/srv/tftp
> sudo yast tftp-server directory list
Directory Path: /srv/tftp
status

Controls the status of the TFTP server service: 

> sudo yast tftp-server status disable
> sudo yast tftp-server status show
Service Status: false
> sudo yast tftp-server status enable

4.4.3.26 yast timezone

  

Configures the time zone. yast timezone accepts the following commands:

list

Lists all available time zones grouped by region: 

> sudo yast timezone list
Region: Africa
Africa/Abidjan (Abidjan)
Africa/Accra (Accra)
Africa/Addis_Ababa (Addis Ababa)
[...]
set

Specifies new values for the time zone configuration: 

> sudo yast timezone set timezone=Europe/Prague hwclock=local
summary

Displays the time zone configuration summary: 

> sudo yast timezone summary
Current Time Zone: Europe/Prague
Hardware Clock Set To: Local time
Current Time and Date: Mon 12. March 2018, 11:36:21 CET

4.4.3.27 yast users

  

Manages user accounts. yast users accepts the following commands:

add

Adds a new user: 

> sudo yast users add username=user1 password=secret home=/home/user1

For a complete list of options, run yast users add help.

delete

Deletes an existing user account: 

> sudo yast users delete username=user1 delete_home

For a complete list of options, run yast users delete help.

edit

Changes an existing user account: 

> sudo yast users edit username=user1 password=new_secret

For a complete list of options, run yast users edit help.

list

Lists existing users filtered by user type: 

> sudo yast users list system

For a complete list of options, run yast users list help.

show

Displays details about a user: 

> sudo yast users show username=wwwrun
Full Name: WWW daemon apache
List of Groups: www
Default Group: wwwrun
Home Directory: /var/lib/wwwrun
Login Shell: /sbin/nologin
Login Name: wwwrun
UID: 456

For a complete list of options, run yast users show help.

5 YaST online update

  

SUSE offers a continuous stream of software security updates for your product. By default, the update applet is used to keep your system up-to-date. Refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.5 “The GNOME package updater” for further information on the update applet. This chapter covers the alternative tool for updating software packages: YaST Online Update.

The current patches for SUSE® Linux Enterprise Server are available from an update software repository. If you have registered your product during the installation, an update repository is already configured. If you have not registered SUSE Linux Enterprise Server, you can do so by starting the Product Registration 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 Software › Software Repositories in YaST. Learn more about the Repository Manager in Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.4 “Managing software repositories and services”.

Note
Note: Error on accessing the update catalog

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//.

Note
Note: Firewall settings for receiving updates

By default, the firewall on SUSE Linux Enterprise Server only blocks incoming connections. If your system is behind another firewall that blocks outgoing traffic, make sure to allow connections to https://scc.suse.com/ and https://updates.suse.com on ports 80 and 443 in order to receive updates.

SUSE provides updates with different relevance levels:

Security updates

Fix severe security hazards and should always be installed.

Recommended updates

Fix issues that could compromise your computer.

Optional updates

Fix non-security relevant issues or provide enhancements.

5.1 The online update dialog

  

To open the YaST Online Update dialog, start YaST and select Software  › Online Update. Alternatively, start it from the command line with yast2 online_update.

The Online Update window consists of four sections.

YaST online update
Figure 5.1: YaST online update
  

The Summary section on the left lists the available patches for SUSE Linux Enterprise Server. The patches are sorted by security relevance: security, recommended, and optional. You can change the view of the Summary section by selecting one of the following options from Show Patch Category:

Needed patches (default view)

Non-installed patches that apply to packages installed on your system.

Unneeded patches

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

All patches available for SUSE Linux Enterprise Server.

Each list entry in the Summary section consists of a symbol and the patch name. For an overview of the possible symbols and their meaning, press Shift–F1. Actions required by Security and Recommended patches are automatically preset. These actions are Autoinstall, Autoupdate and Autodelete.

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 Summary section to view a short Patch Description at the bottom left corner of the dialog. The upper right section lists the packages included in the selected patch (a patch can consist of several packages). Click an entry in the upper right section to view details about the respective package that is included in the patch.

5.2 Installing patches

  

The YaST Online Update dialog allows you to either install all available patches at once or manually select the desired patches. You may also revert patches that have been applied to the system.

By default, all new patches (except optional ones) that are currently available for your system are already marked for installation. They will be applied automatically once you click Accept or Apply. 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.

Procedure 5.1: Applying patches with YaST online update
  

  1. Start YaST and select Software › Online Update.

  2. To automatically apply all new patches (except optional ones) that are currently available for your system, click Apply or Accept.

  3. First modify the selection of patches that you want to apply:

    1. Use the respective filters and views that the interface provides. For details, refer to Section 5.1, “The online update dialog”.

    2. Select or deselect patches according to your needs and wishes by right-clicking the patch and choosing the respective action from the context menu.

      Important
      Important: Always apply security updates

      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.

    3. 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.

    4. To confirm your selection and apply the selected patches, proceed with Apply or Accept.

  4. After the installation is complete, click Finish to leave the YaST Online Update. Your system is now up-to-date.

5.3 Viewing retracted patches

  

Maintenance updates are carefully tested, to minimize the risk of introducing a bug. If a patch proves to contain a bug, it is automatically retracted. A new update (with a higher version number) is issued to revert the buggy patch, and is blocked from being installed again. You can see retracted patches, and their history, on the Package Classification tab.

Viewing retracted patches and history
Figure 5.2: Viewing retracted patches and history
  

5.4 Automatic online update

  

You may configure automatic updates with a daily, weekly, or monthly schedule with YaST. Install the yast2-online-update-configuration package.

By default, updates are downloaded as delta RPMs. Since rebuilding RPM packages from delta RPMs is a memory- and processor-intensive task, certain setups or hardware configurations might require you to disable the use of delta RPMs for the sake of performance.

Some patches, such as kernel updates or packages requiring license agreements, require user interaction, which would cause the automatic update procedure to stop. You can configure skipping patches that require user interaction.

Use the Patches tab in the YaST Software module to review available and installed patches, including references to bug reports and CVE bulletins.

Procedure 5.2: Configuring the automatic online update
  

  1. After installation, start YaST and select Software › Online Update. Choose Configuration › Online Update. If the yast2-online-update-configuration is not installed, you will be prompted to do that.

    YaST online update configuration
    Figure 5.3: YaST online update configuration
      

    Alternatively, start the module with yast2 online_update_configuration from the command line.

  2. Choose the update interval: Daily, Weekly, or Monthly.

  3. 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 Skip Interactive Patches. 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.

  4. To automatically accept any license agreements, activate Agree with Licenses.

  5. To automatically install all packages recommended by updated packages, activate Include Recommended Packages.

  6. To disable the use of delta RPMs (for performance reasons), un-check Use Delta RPMs.

  7. To filter the patches by category (such as security or recommended), check Filter by Category 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 Security 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.

    • Packagemanager and YaST supply patches for package management and YaST features and modules.

    • Security patches provide crucial updates and bugfixes.

    • Recommended patches are optional bugfixes and enhancements.

    • Optional are new packages.

    • Other is equivalent to miscellaneous.

    • Document is unused.

  8. Confirm your configuration by clicking OK.

The automatic online update does not automatically restart the system afterward. If there are package updates that require a system reboot, you need to do this manually.

6 Managing software with command line tools

  

This chapter describes Zypper and RPM, two command line tools for managing software. For a definition of the terminology used in this context (for example, repository, patch, or update) refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.1 “Definition of terms”.

6.1 Using Zypper

  

Zypper is a command line package manager for installing, updating and removing packages. It also manages repositories. It is especially useful for accomplishing remote software management tasks or managing software from shell scripts.

6.1.1 General usage

  

The general syntax of Zypper is: 

zypper [--global-options] COMMAND  [--command-options] [arguments]

The components enclosed in brackets are not required. See zypper help for a list of general options and all commands. To get help for a specific command, type zypper help COMMAND.

Zypper commands

The simplest way to execute Zypper is to type its name, followed by a command. For example, to apply all needed patches to the system, use: 

> sudo zypper patch
Global options

Additionally, you can choose from one or more global options by typing them immediately before the command: 

> sudo zypper --non-interactive patch

In the above example, the option --non-interactive means that the command is run without asking anything (automatically applying the default answers).

Command-specific options

To use options that are specific to a particular command, type them immediately after the command: 

> sudo zypper patch --auto-agree-with-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, licenses will be accepted automatically.

Arguments

Some commands require one or more arguments. For example, when using the command install, you need to specify which package or which packages you want to install: 

> sudo zypper install mplayer

Some options also require a single argument. The following command will list all known patterns: 

> zypper search -t pattern

You can combine all of the above. For example, the following command will install the mc and vim packages from the factory repository while being verbose: 

> sudo zypper -v install --from factory mc vim

The --from option keeps all repositories enabled (for solving any dependencies) while requesting the package from the specified repository. --repo is an alias for --from, and you may use either one.

Most Zypper commands have a dry-run option that does a simulation of the given command. It can be used for test purposes. 

> sudo zypper remove --dry-run MozillaFirefox

Zypper supports the global --userdata STRING option. You can specify a string with this option, which gets written to Zypper's log files and plug-ins (such as the Btrfs plug-in). It can be used to mark and identify transactions in log files. 

> sudo zypper --userdata STRING patch

6.1.2 Using Zypper subcommands

  

Zypper subcommands are executables that are stored in the zypper_execdir, /usr/lib/zypper/commands. If a subcommand is not found in the zypper_execdir, Zypper automatically searches the rest of your $PATH for it. This enables writing your own local extensions and storing them in userspace.

Executing subcommands in the Zypper shell, and using global Zypper options are not supported.

List your available subcommands: 

> zypper help subcommand
[...]
Available zypper subcommands in '/usr/lib/zypper/commands'

  appstream-cache
  lifecycle
  migration
  search-packages

Zypper subcommands available from elsewhere on your $PATH

  <none>

View the help screen for a subcommand: 

> zypper help appstream-cache

6.1.3 Installing and removing software with Zypper

  

To install or remove packages, use the following commands: 

> sudo zypper install PACKAGE_NAME
> sudo zypper remove PACKAGE_NAME
Warning
Warning: Do not remove mandatory system packages

Do not remove mandatory system packages like glibc , zypper , kernel . If they are removed, the system can become unstable or stop working altogether.

6.1.3.1 Selecting which packages to install or remove

  

There are various ways to address packages with the commands zypper install and zypper remove.

By exact package name
> sudo zypper install MozillaFirefox
By exact package name and version number
> sudo zypper install MozillaFirefox-52.2
By repository alias and package name
> sudo zypper install mozilla:MozillaFirefox

Where mozilla is the alias of the repository from which to install.

By package name using wild cards

You can select all packages that have names starting or ending with a certain string. Use wild cards with care, especially when removing packages. The following command will install all packages starting with “Moz”: 

> sudo zypper install 'Moz*'
Tip
Tip: Removing all -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: 

> sudo zypper remove '*-debuginfo'
By capability

For example, to install a package without knowing its name, capabilities come in handy. The following command will install the package MozillaFirefox: 

> sudo zypper install firefox
By capability, hardware architecture, or version

Together with a capability, you can specify a hardware architecture and a version:

  • The name of the desired hardware architecture is appended to the capability after a full stop. For example, to specify the AMD64/Intel 64 architectures (which in Zypper is named x86_64), use: 

    > sudo zypper install 'firefox.x86_64'

  • Versions must be appended to the end of the string and must be preceded by an operator: < (lesser than), <= (lesser than or equal), = (equal), >= (greater than or equal), > (greater than). 

    > sudo zypper install 'firefox>=74.2'

  • You can also combine a hardware architecture and version requirement: 

    > sudo zypper install 'firefox.x86_64>=74.2'
By path to the RPM file

You can also specify a local or remote path to a package: 

> sudo zypper install /tmp/install/MozillaFirefox.rpm
> sudo zypper install http://download.example.com/MozillaFirefox.rpm

6.1.3.2 Combining installation and removal of packages

  

To install and remove packages simultaneously, use the +/- modifiers. To install emacs and simultaneously remove vim , use: 

> sudo zypper install emacs -vim

To remove emacs and simultaneously install vim , use: 

> sudo zypper remove emacs +vim

To prevent the package name starting with the - being interpreted as a command option, always use it as the second argument. If this is not possible, precede it with --: 

> sudo zypper install -emacs +vim       # Wrong
> sudo zypper install vim -emacs        # Correct
> sudo zypper install -- -emacs +vim    # Correct
> sudo zypper remove emacs +vim         # Correct

6.1.3.3 Cleaning up dependencies of removed packages

  

If (together with a certain package), you automatically want to remove any packages that become unneeded after removing the specified package, use the --clean-deps option: 

> sudo zypper rm --clean-deps PACKAGE_NAME

6.1.3.4 Using Zypper in scripts

  

By default, Zypper asks for a confirmation before installing or removing a selected package, or when a problem occurs. You can override this behavior using the --non-interactive option. This option must be given before the actual command (install, remove, and patch), as can be seen in the following: 

> sudo zypper --non-interactive install PACKAGE_NAME

This option allows the use of Zypper in scripts and cron jobs.

6.1.3.5 Installing or downloading source packages

  

To install the corresponding source package of a package, use: 

> zypper source-install PACKAGE_NAME

When executed as root, the default location to install source packages is /usr/src/packages/ and ~/rpmbuild when run as user. These values can be changed in your local rpm configuration.

This command will also install the build dependencies of the specified package. If you do not want this, add the switch -D: 

> sudo zypper source-install -D PACKAGE_NAME

To install only the build dependencies use -d. 

> sudo zypper source-install -d PACKAGE_NAME

Of course, this will only work if you have the repository with the source packages enabled in your repository list (it is added by default, but not enabled). See Section 6.1.6, “Managing repositories with Zypper” for details on repository management.

A list of all source packages available in your repositories can be obtained with: 

> zypper search -t srcpackage

You can also download source packages for all installed packages to a local directory. To download source packages, use: 

> zypper source-download

The default download directory is /var/cache/zypper/source-download. You can change it using the --directory option. To only show missing or extraneous packages without downloading or deleting anything, use the --status option. To delete extraneous source packages, use the --delete option. To disable deleting, use the --no-delete option.

6.1.3.6 Installing packages from disabled repositories

  

Normally you can only install or refresh packages from enabled repositories. The --plus-content TAG option helps you specify repositories to be refreshed, temporarily enabled during the current Zypper session, and disabled after it completes.

For example, to enable repositories that may provide additional -debuginfo or -debugsource packages, use --plus-content debug. You can specify this option multiple times.

To temporarily enable such 'debug' repositories to install a specific -debuginfo package, use the option as follows: 

> sudo zypper --plus-content debug \
   install "debuginfo(build-id)=eb844a5c20c70a59fc693cd1061f851fb7d046f4"

The build-id string is reported by gdb for missing debuginfo packages.

Note
Note: Disabled installation media

Repositories from the SUSE Linux Enterprise Server installation media are still configured but disabled after successful installation. You can use the --plus-content option to install packages from the installation media instead of the online repositories. Before calling zypper, ensure the media is available, for example by inserting the DVD into the computer's drive.

6.1.3.7 Utilities

  

To verify whether all dependencies are still fulfilled and to repair missing dependencies, use: 

> zypper verify

In addition to dependencies that must be fulfilled, some packages “recommend” other packages. These recommended packages are only installed if actually available and installable. In case recommended packages were made available after the recommending package has been installed (by adding additional packages or hardware), use the following command: 

> sudo zypper install-new-recommends

This command is very useful after plugging in a Web cam or Wi-Fi device. It will install drivers for the device and related software, if available. Drivers and related software are only installable if certain hardware dependencies are fulfilled.

6.1.4 Updating software with Zypper

  

There are three different ways to update software using Zypper: by installing patches, by installing a new version of a package or by updating the entire distribution. The latter is achieved with zypper dist-upgrade. Upgrading SUSE Linux Enterprise Server is discussed in Book “Upgrade Guide”, Chapter 1 “Upgrade paths and methods”.

6.1.4.1 Installing all needed patches

  

Patching SUSE Linux Enterprise is the most reliable way to install new versions of installed packages. It guaranties that all required packages with correct versions are installed and ensures that package versions considered as conflicting are omitted.

To install all officially released patches that apply to your system, run: 

> sudo zypper patch

All patches available from repositories configured on your computer are checked for their relevance to your installation. If they are relevant (and not classified as optional or feature), they are installed immediately. If zypper patch succeeds, it is guaranteed that no vulnerable version package is installed unless you confirmed the exception. Note that the official update repository is only available after registering your SUSE Linux Enterprise Server installation.

If a patch that is about to be installed includes changes that require a system reboot, you will be warned before.

The plain zypper patch command does not apply patches from third party repositories. To update also the third party repositories, use the with-update command option as follows: 

> sudo zypper patch --with-update

To install also optional patches, use: 

> sudo zypper patch --with-optional

To install all patches relating to a specific Bugzilla issue, use: 

> sudo zypper patch --bugzilla=NUMBER

To install all patches relating to a specific CVE database entry, use: 

> sudo zypper patch --cve=NUMBER

For example, to install a security patch with the CVE number CVE-2010-2713, execute: 

> sudo zypper patch --cve=CVE-2010-2713

To install only patches which affect Zypper and the package management itself, use: 

> sudo zypper patch --updatestack-only

Bear in mind that other command options that would also update other repositories will be dropped if you use the updatestack-only command option.

6.1.4.2 Listing patches

  

To find out whether patches are available, Zypper allows viewing the following information:

Number of needed patches

To list the number of needed patches (patches that apply to your system but are not yet installed), use patch-check: 

> zypper patch-check
Loading repository data...
Reading installed packages...
5 patches needed (1 security patch)

This command can be combined with the --updatestack-only option to list only the patches which affect Zypper and the package management itself.

List of needed patches

To list all needed patches (patches that apply to your system but are not yet installed), use zypper list-patches.

List of all patches

To list all patches available for SUSE Linux Enterprise Server, regardless of whether they are already installed or apply to your installation, use zypper patches.

It is also possible to list and install patches relevant to specific issues. To list specific patches, use the zypper list-patches command with the following options:

By Bugzilla issues

To list all needed patches that relate to Bugzilla issues, use the option --bugzilla.

To list patches for a specific bug, you can also specify a bug number: --bugzilla=NUMBER. To search for patches relating to multiple Bugzilla issues, add commas between the bug numbers, for example: 

> zypper list-patches --bugzilla=972197,956917
By CVE number

To list all needed patches that relate to an entry in the CVE database (Common Vulnerabilities and Exposures), use the option --cve.

To list patches for a specific CVE database entry, you can also specify a CVE number: --cve=NUMBER. To search for patches relating to multiple CVE database entries, add commas between the CVE numbers, for example: 

> zypper list-patches --bugzilla=CVE-2016-2315,CVE-2016-2324
List retracted patches

In the SUSE Linux Enterprise 15 codestream, some patches are automatically retracted. Maintenance updates are carefully tested, because there is a risk that an update contains a new bug. If an update proves to contain a bug, a new update (with a higher version number) is issued to revert the buggy update, and the buggy update is blocked from being installed again. You can list retracted patches with zypper: 

> zypper lp --all |grep retracted
SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-1965 
 | recommended | important | ---    | retracted  | Recommended update for multipath-tools 
SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-2689 
 | security    | important | ---    | retracted  | Security update for cpio
SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-3655 
 | security    | important | reboot | retracted  | Security update for the Linux Kernel

See complete information on a retracted (or any) patch: 

> zypper patch-info SUSE-SLE-Product-SLES-15-2021-2689
Loading repository data...
Reading installed packages...

Information for patch SUSE-SLE-Product-SLES-15-2021-2689:
---------------------------------------------------------
Repository  : SLE-Product-SLES15-LTSS-Updates
Name        : SUSE-SLE-Product-SLES-15-2021-2689
Version     : 1
Arch        : noarch
Vendor      : maint-coord@suse.de
Status      : retracted
Category    : security
Severity    : important
Created On  : Mon 16 Aug 2021 03:44:00 AM PDT
Interactive : ---
Summary     : Security update for cpio
Description : 
    This update for cpio fixes the following issues:

    It was possible to trigger Remote code execution due to a integer overflow 
    (CVE-2021-38185, bsc#1189206)

    UPDATE:
    This update was buggy and could lead to hangs, so it has been retracted. 
    There will be a follow up update.
    [...]
Patch with conflicting packages
Information for patch openSUSE-SLE-15.3-2022-333:
-------------------------------------------------
Repository  : Update repository with updates from SUSE Linux Enterprise 15
Name        : openSUSE-SLE-15.3-2022-333
Version     : 1
Arch        : noarch
Vendor      : maint-coord@suse.de
Status      : needed
Category    : security
Severity    : important
Created On  : Fri Feb  4 09:30:32 2022
Interactive : reboot
Summary     : Security update for xen
Description :
    This update for xen fixes the following issues:

    - CVE-2022-23033: Fixed guest_physmap_remove_page not removing the p2m mappings. (XSA-393) (bsc#1194576)
    - CVE-2022-23034: Fixed possible DoS by a PV guest Xen while unmapping a grant. (XSA-394) (bsc#1194581)
    - CVE-2022-23035: Fixed insufficient cleanup of passed-through device IRQs. (XSA-395) (bsc#1194588)
Provides    : patch:openSUSE-SLE-15.3-2022-333 = 1
Conflicts   : [22]
    xen.src < 4.14.3_06-150300.3.18.2
    xen.noarch < 4.14.3_06-150300.3.18.2
    xen.x86_64 < 4.14.3_06-150300.3.18.2
    xen-devel.x86_64 < 4.14.3_06-150300.3.18.2
    xen-devel.noarch < 4.14.3_06-150300.3.18.2
[...]

The above patch conflicts with the affected or vulnerable versions of 22 packages. If any of these affected or vulnerable packages are installed, it triggers a conflict, and the patch is classified as needed. zypper patch tries to install all available patches. If it encounters problems, it reports them, thus informing you that not all updates are installed. The conflict can be resolved by either updating the affected or vulnerable packages or by removing them. Because SUSE update repositories also ship fixed packages, updating is a standard way to resolve conflicts. If the package cannot be updated—for example, due to dependency issues or package locks—it is deleted after the user's approval.

To list all patches regardless of whether they are needed, use the option --all additionally. For example, to list all patches with a CVE number assigned, use: 

> zypper list-patches --all --cve
Issue | No.           | Patch             | Category    | Severity  | Status
------+---------------+-------------------+-------------+-----------+----------
cve   | CVE-2019-0287 | SUSE-SLE-Module.. | recommended | moderate  | needed
cve   | CVE-2019-3566 | SUSE-SLE-SERVER.. | recommended | moderate  | not needed
[...]

6.1.4.3 Installing new package versions

  

If a repository contains only new packages, but does not provide patches, zypper patch does not show any effect. To update all installed packages with newer available versions, use the following command: 

> sudo zypper update
Important
Important

zypper update ignores problematic packages. For example, if a package is locked, zypper update omits the package, even if a higher version of it is available. Conversely, zypper patch reports a conflict if the package is considered vulnerable.

To update individual packages, specify the package with either the update or install command: 

> sudo zypper update PACKAGE_NAME
> sudo zypper install PACKAGE_NAME

A list of all new installable packages can be obtained with the command: 

> zypper list-updates

Note that this command only lists packages that match the following criteria:

  • has the same vendor like the already installed package,

  • is provided by repositories with at least the same priority than the already installed package,

  • is installable (all dependencies are satisfied).

A list of all new available packages (regardless whether installable or not) can be obtained with: 

> sudo zypper list-updates --all

To find out why a new package cannot be installed, use the zypper install or zypper update command as described above.

6.1.4.4 Identifying orphaned packages

  

Whenever you remove a repository from Zypper or upgrade your system, some packages can get in an “orphaned” state. These orphaned packages belong to no active repository anymore. The following command gives you a list of these: 

> sudo zypper packages --orphaned

With this list, you can decide if a package is still needed or can be removed safely.

6.1.5 Identifying processes and services using deleted files

  

When patching, updating or removing packages, there may be running processes on the system which continue to use files having been deleted by the update or removal. Use zypper ps to list processes using deleted files. In case the process belongs to a known service, the service name is listed, making it easy to restart the service. By default zypper ps shows a table: 

> zypper ps
PID   | PPID | UID | User  | Command      | Service      | Files
------+------+-----+-------+--------------+--------------+-------------------
814   | 1    | 481 | avahi | avahi-daemon | avahi-daemon | /lib64/ld-2.19.s->
      |      |     |       |              |              | /lib64/libdl-2.1->
      |      |     |       |              |              | /lib64/libpthrea->
      |      |     |       |              |              | /lib64/libc-2.19->
[...]
PID: ID of the process
PPID: ID of the parent process
UID: ID of the user running the process
Login: Login name of the user running the process
Command: Command used to execute the process
Service: Service name (only if command is associated with a system service)
Files: The list of the deleted files

The output format of zypper ps can be controlled as follows:

zypper ps-s

Create a short table not showing the deleted files. 

> zypper ps -s
PID   | PPID | UID  | User    | Command      | Service
------+------+------+---------+--------------+--------------
814   | 1    | 481  | avahi   | avahi-daemon | avahi-daemon
817   | 1    | 0    | root    | irqbalance   | irqbalance
1567  | 1    | 0    | root    | sshd         | sshd
1761  | 1    | 0    | root    | master       | postfix
1764  | 1761 | 51   | postfix | pickup       | postfix
1765  | 1761 | 51   | postfix | qmgr         | postfix
2031  | 2027 | 1000 | tux     | bash         |
zypper ps-ss

Show only processes associated with a system service. 

PID   | PPID | UID  | User    | Command      | Service
------+------+------+---------+--------------+--------------
814   | 1    | 481  | avahi   | avahi-daemon | avahi-daemon
817   | 1    | 0    | root    | irqbalance   | irqbalance
1567  | 1    | 0    | root    | sshd         | sshd
1761  | 1    | 0    | root    | master       | postfix
1764  | 1761 | 51   | postfix | pickup       | postfix
1765  | 1761 | 51   | postfix | qmgr         | postfix
zypper ps-sss

Only show system services using deleted files. 

avahi-daemon
irqbalance
postfix
sshd
zypper ps--print "systemctl status %s"

Show the commands to retrieve status information for services which might need a restart. 

systemctl status avahi-daemon
systemctl status irqbalance
systemctl status postfix
systemctl status sshd

For more information about service handling refer to Chapter 15, The systemd daemon.

6.1.6 Managing repositories with Zypper

  

All installation or patch commands of Zypper rely on a list of known repositories. To list all repositories known to the system, use the command: 

> zypper repos

The result will look similar to the following output:

Example 6.1: Zypper—list of known repositories
  
> zypper repos
# | Alias        | Name          | Enabled | Refresh
--+--------------+---------------+---------+--------
1 | SLEHA-15-GEO | SLEHA-15-GEO  | Yes     | No
2 | SLEHA-15     | SLEHA-15      | Yes     | No
3 | SLES15       | SLES15        | Yes     | No

When specifying repositories in various commands, an alias, URI or repository number from the zypper repos command output can be used. A repository alias is a short version of the repository name for use in repository handling commands. Note that the repository numbers can change after modifying the list of repositories. The alias will never change by itself.

By default, details such as the URI or the priority of the repository are not displayed. Use the following command to list all details: 

> zypper repos -d

6.1.6.1 Adding repositories

  

To add a repository, run 

> sudo zypper addrepo URI ALIAS

URI can either be an Internet repository, a network resource, a directory or a CD or DVD (see https://en.opensuse.org/openSUSE:Libzypp_URIs for details). The ALIAS is a shorthand and unique identifier of the repository. You can freely choose it, with the only exception that it needs to be unique. Zypper will issue a warning if you specify an alias that is already in use.

6.1.6.2 Refreshing repositories

  

zypper enables you to fetch changes in packages from configured repositories. To fetch the changes, run: 

> sudo zypper refresh
Note
Note: Default behavior of zypper

By default, some commands perform refresh automatically, so you do not need to run the command explicitly.

The refresh command enables you to view changes also in disabled repositories, by using the --plus-content option: 

> sudo zypper --plus-content refresh

This option fetches changes in repositories, but keeps the disabled repositories in the same state—disabled.

6.1.6.3 Removing repositories

  

To remove a repository from the list, use the command zypper removerepo together with the alias or number of the repository you want to delete. For example, to remove the repository SLEHA-12-GEO from Example 6.1, “Zypper—list of known repositories”, use one of the following commands: 

> sudo zypper removerepo 1
> sudo zypper removerepo "SLEHA-12-GEO"

6.1.6.4 Modifying repositories

  

Enable or disable repositories with zypper modifyrepo. You can also alter the repository's properties (such as refreshing behavior, name or priority) with this command. The following command will enable the repository named updates, turn on auto-refresh and set its priority to 20: 

> sudo zypper modifyrepo -er -p 20 'updates'

Modifying repositories is not limited to a single repository—you can also operate on groups:

-a: all repositories
-l: local repositories
-t: remote repositories
-m TYPE: repositories of a certain type (where TYPE can be one of the following: http, https, ftp, cd, dvd, dir, file, cifs, smb, nfs, hd, iso)

To rename a repository alias, use the renamerepo command. The following example changes the alias from Mozilla Firefox to firefox: 

> sudo zypper renamerepo 'Mozilla Firefox' firefox

6.1.7 Querying repositories and packages with Zypper

  

Zypper offers various methods to query repositories or packages. To get lists of all products, patterns, packages or patches available, use the following commands: 

> zypper products
> zypper patterns
> zypper packages
> zypper patches

To query all repositories for certain packages, use search. To get information regarding particular packages, use the info command.

6.1.7.2 Searching for packages across all SLE modules

  

To search for packages both within and outside of currently enabled SLE modules, use the search-packages subcommand. This command contacts the SUSE Customer Center and searches all modules for matching packages, for example: 

> zypper search-packages package1 package2

zypper search-packages provides the following options:

  • Search for an exact match of your search string: -x, --match-exact

  • Group the results by module (default: group by package): -g, --group-by-module

  • Display more detailed information about packages: -d, --details

  • Output search results in XML: --xmlout

6.1.7.3 Searching for specific capability

  

To search for packages which provide a special capability, use the command what-provides. For example, if you want to know which package provides the Perl module SVN::Core, use the following command: 

> zypper what-provides 'perl(SVN::Core)'

The what-provides PACKAGE_NAME is similar to rpm -q --whatprovides PACKAGE_NAME, but RPM is only able to query the RPM database (that is the database of all installed packages). Zypper, on the other hand, will tell you about providers of the capability from any repository, not only those that are installed.

6.1.7.4 Showing package information

  

To query single packages, use info with an exact package name as an argument. This displays detailed information about a package. In case the package name does not match any package name from repositories, the command outputs detailed information for non-package matches. If you request a specific type (by using the -t option) and the type does not exist, the command outputs other available matches but without detailed information.

If you specify a source package, the command displays binary packages built from the source package. If you specify a binary package, the command outputs the source packages used to build the binary package.

To also show what is required/recommended by the package, use the options --requires and --recommends: 

> zypper info --requires MozillaFirefox

6.1.8 Showing lifecycle information

  

SUSE products are generally supported for 10 years. Often, you can extend that standard lifecycle by using the extended support offerings of SUSE which add three years of support. Depending on your product, find the exact support lifecycle at https://www.suse.com/lifecycle.

To check the lifecycle of your product and the supported package, use the zypper lifecycle command as shown below: 

# zypper lifecycle
    Product end of support
Codestream: SUSE Linux Enterprise Server 15             2028-07-31
    Product: SUSE Linux Enterprise Server 15 SP3        n/a*

Module end of support
Basesystem Module                                       n/a*
Desktop Applications Module                             n/a*
Server Applications Module                              n/a*

Package end of support if different from product:
autofs                                   Now, installed 5.1.3-7.3.1, update available 5.1.3-7.6.1

6.1.9 Configuring Zypper

  

Zypper now comes with a configuration file, allowing you to permanently change Zypper's behavior (either system-wide or user-specific). For system-wide changes, edit /etc/zypp/zypper.conf. For user-specific changes, edit ~/.zypper.conf. If ~/.zypper.conf does not yet exist, you can use /etc/zypp/zypper.conf as a template: copy it to ~/.zypper.conf and adjust it to your liking. Refer to the comments in the file for help about the available options.

6.1.10 Troubleshooting

  

If you have trouble accessing packages from configured repositories (for example, Zypper cannot find a certain package even though you know it exists in one of the repositories), refreshing the repositories may help: 

> sudo zypper refresh

If that does not help, try 

> sudo zypper refresh -fdb

This forces a complete refresh and rebuild of the database, including a forced download of raw metadata.

6.1.11 Zypper rollback feature on Btrfs file system

  

If the Btrfs file system is used on the root partition and snapper is installed, Zypper automatically calls snapper when committing changes to the file system to create appropriate file system snapshots. These snapshots can be used to revert any changes made by Zypper. See Chapter 7, System recovery and snapshot management with Snapper for more information.

6.1.12 More information

  

For more information on managing software from the command line, enter zypper help, zypper help  COMMAND or refer to the zypper(8) man page. For a complete and detailed command reference, cheat sheets with the most important commands, and information on how to use Zypper in scripts and applications, refer to https://en.opensuse.org/SDB:Zypper_usage. A list of software changes for the latest SUSE Linux Enterprise Server version can be found at https://en.opensuse.org/openSUSE:Zypper_versions.

6.2 RPM—the package manager

  

RPM (RPM Package Manager) is used for managing software packages. Its main commands are rpm and rpmbuild. The powerful RPM database can be queried by the users, system administrators and package builders for detailed information about the installed software.

rpm has five modes: installing, uninstalling (or updating) software packages, rebuilding the RPM database, querying RPM bases or individual RPM archives, integrity checking of packages and signing packages. rpmbuild can be used to build installable packages from pristine sources.

Installable RPM archives are packed in a special binary format. These archives consist of the program files to install and certain meta information used during the installation by rpm to configure the software package or stored in the RPM database for documentation purposes. RPM archives normally have the extension .rpm.

Tip
Tip: Software development packages

For several packages, the components needed for software development (libraries, headers, include files, etc.) have been put into separate packages. These development packages are only needed if you want to compile software yourself (for example, the most recent GNOME packages). They can be identified by the name extension -devel, such as the packages alsa-devel and gimp-devel.

6.2.1 Verifying package authenticity

  

RPM packages have a GPG signature. To verify the signature of an RPM package, use the command rpm --checksig  PACKAGE-1.2.3.rpm to determine whether the package originates from SUSE or from another trustworthy facility. This is especially recommended for update packages from the Internet.

While fixing issues in the operating system, you might need to install a Problem Temporary Fix (PTF) into a production system. The packages provided by SUSE are signed against a special PTF key. However, in contrast to SUSE Linux Enterprise 11, this key is not imported by default on SUSE Linux Enterprise 12 systems. To manually import the key, use the following command: 

> sudo rpm --import \
/usr/share/doc/packages/suse-build-key/suse_ptf_key.asc

After importing the key, you can install PTF packages on your system.

6.2.2 Managing packages: install, update, and uninstall

  

Normally, the installation of an RPM archive is quite simple: rpm -i PACKAGE.rpm. With this command the package is installed, but only if its dependencies are fulfilled and if there are no conflicts with other packages. With an error message, rpm requests those packages that need to be installed to meet dependency requirements. In the background, the RPM database ensures that no conflicts arise—a specific file can only belong to one package. By choosing different options, you can force rpm to ignore these defaults, but this is only for experts. Otherwise, you risk compromising the integrity of the system and possibly jeopardize the ability to update the system.

The options -U or --upgrade and -F or --freshen can be used to update a package (for example, rpm -F PACKAGE.rpm). This command removes the files of the old version and immediately installs the new files. The difference between the two versions is that -U installs packages that previously did not exist in the system, while -F merely updates previously installed packages. When updating, rpm updates configuration files carefully using the following strategy:

  • If a configuration file was not changed by the system administrator, rpm installs the new version of the appropriate file. No action by the system administrator is required.

  • If a configuration file was changed by the system administrator before the update, rpm saves the changed file with the extension .rpmorig or .rpmsave (backup file) and installs the version from the new package. This is done only if the originally installed file and the newer version are different. If this is the case, compare the backup file (.rpmorig or .rpmsave) with the newly installed file and make your changes again in the new file. Afterward, delete all .rpmorig and .rpmsave files to avoid problems with future updates.

  • .rpmnew files appear if the configuration file already exists and if 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.

6.2.3 Delta RPM packages

  

Delta RPM packages contain the difference between an old and a new version of an RPM package. Applying a delta RPM onto an old RPM results in a completely new RPM. It is not necessary to have a copy of the old RPM because a delta RPM can also work with an installed RPM. The delta RPM packages are even smaller in size than patch RPMs, which is an advantage when transferring update packages over the Internet. The drawback is that update operations with delta RPMs involved consume considerably more CPU cycles than plain or patch RPMs.

The makedeltarpm and applydelta binaries are part of the delta RPM suite (package deltarpm) and help you create and apply delta RPM packages. With the following commands, you can create a delta RPM called new.delta.rpm. The following command assumes that old.rpm and new.rpm are present: 

> sudo makedeltarpm old.rpm new.rpm new.delta.rpm

Using applydeltarpm, you can reconstruct the new RPM from the file system if the old package is already installed: 

> sudo applydeltarpm new.delta.rpm new.rpm

To derive it from the old RPM without accessing the file system, use the -r option: 

> sudo applydeltarpm -r old.rpm new.delta.rpm new.rpm

See /usr/share/doc/packages/deltarpm/README for technical details.

6.2.4 RPM queries

  

With the -q option rpm initiates queries, making it possible to inspect an RPM archive (by adding the option -p) and to query the RPM database of installed packages. Several switches are available to specify the type of information required. See Table 6.1, “Essential RPM query options”.

Table 6.1: Essential RPM query options
  

-i

Package information

-l

File list

-f FILE

Query the package that contains the file FILE (the full path must be specified with FILE)

-s

File list with status information (implies -l)

-d

List only documentation files (implies -l)

-c

List only configuration files (implies -l)

--dump

File list with complete details (to be used with -l, -c, or -d)

--provides

List features of the package that another package can request with --requires

--requires, -R

Capabilities the package requires

--scripts

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”.

Example 6.2: rpm -q -i wget
  
Name        : wget
Version     : 1.14
Release     : 17.1
Architecture: x86_64
Install Date: Mon 30 Jan 2017 14:01:29 CET
Group       : Productivity/Networking/Web/Utilities
Size        : 2046483
License     : GPL-3.0+
Signature   : RSA/SHA256, Thu 08 Dec 2016 07:48:44 CET, Key ID 70af9e8139db7c82
Source RPM  : wget-1.14-17.1.src.rpm
Build Date  : Thu 08 Dec 2016 07:48:34 CET
Build Host  : sheep09
Relocations : (not relocatable)
Packager    : https://www.suse.com/
Vendor      : SUSE LLC <https://www.suse.com/>
URL         : http://www.gnu.org/software/wget/
Summary     : A Tool for Mirroring FTP and HTTP Servers
Description :
Wget enables you to retrieve WWW documents or FTP files from a server.
This can be done in script files or via the command line.
Distribution: SUSE Linux Enterprise 15

The option -f only works if you specify the complete file name with its full path. Provide as many file names as desired. For example: 

> rpm -q -f /bin/rpm /usr/bin/wget
rpm-4.14.1-lp151.13.10.x86_64
wget-1.19.5-lp151.4.1.x86_64

If only part of the file name is known, use a shell script as shown in Example 6.3, “Script to search for packages”. Pass the partial file name to the script shown as a parameter when running it.

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:

Table 6.2: RPM verify options
  

5

MD5 check sum

S

File size

L

Symbolic link

T

Modification time

D

Major and minor device numbers

U

Owner

G

Group

M

Mode (permissions and file type)

In the case of configuration files, the letter c is printed. For example, for changes to /etc/wgetrc (wget package): 

> rpm -V wget
S.5....T c /etc/wgetrc

The files of the RPM database are placed in /var/lib/rpm. If the partition /usr has a size of 1 GB, this database can occupy nearly 30 MB, especially after a complete update. If the database is much larger than expected, it is useful to rebuild the database with the option --rebuilddb. Before doing this, make a backup of the old database. The cron script cron.daily makes daily copies of the database (packed with gzip) and stores them in /var/adm/backup/rpmdb. The number of copies is controlled by the variable MAX_RPMDB_BACKUPS (default: 5) in /etc/sysconfig/backup. The size of a single backup is approximately 1 MB for 1 GB in /usr.

6.2.5 Installing and compiling source packages

  

All source packages carry a .src.rpm extension (source RPM).

Note
Note: Installed source packages

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.

Warning
Warning: System integrity

Do not experiment with system components (glibc, rpm, etc.), because this endangers the stability of your system.

The following example uses the wget.src.rpm package. After installing the source package, you should have files similar to those in the following list: 

/usr/src/packages/SOURCES/wget-1.19.5.tar.bz2
/usr/src/packages/SOURCES/wgetrc.patch
/usr/src/packages/SPECS/wget.spec

rpmbuild -bX /usr/src/packages/SPECS/wget.spec starts the compilation. X is a wild card for various stages of the build process (see the output of --help or the RPM documentation for details). The following is merely a brief explanation:

-bp

Prepare sources in /usr/src/packages/BUILD: unpack and patch.

-bc

Do the same as -bp, but with additional compilation.

-bi

Do the same as -bp, but with additional installation of the built software. Caution: if the package does not support the BuildRoot feature, you might overwrite configuration files.

-bb

Do the same as -bi, but with the additional creation of the binary package. If the compile was successful, the binary should be in /usr/src/packages/RPMS.

-ba

Do the same as -bb, but with the additional creation of the source RPM. If the compilation was successful, the binary should be in /usr/src/packages/SRPMS.

--short-circuit

Skip some steps.

The binary RPM created can now be installed with rpm -i or, preferably, with rpm -U. Installation with rpm makes it appear in the RPM database.

Keep in mind that the BuildRoot directive in the spec file is deprecated. If you still need this feature, use the --buildroot option as a workaround.

6.2.6 Compiling RPM packages with build

  

The danger with many packages is that unwanted files are added to the running system during the build process. To prevent this use build, which creates a defined environment in which the package is built. To establish this chroot environment, the build script must be provided with a complete package tree. This tree can be made available on the hard disk, via NFS, or from DVD. Set the position with build --rpms DIRECTORY. Unlike rpm, the build command looks for the .spec file in the source directory. To build wget (like in the above example) with the DVD mounted in the system under /media/dvd, use the following commands as root: 

# cd /usr/src/packages/SOURCES/
# mv ../SPECS/wget.spec .
# build --rpms /media/dvd/suse/ wget.spec

Subsequently, a minimum environment is established at /var/tmp/build-root. The package is built in this environment. Upon completion, the resulting packages are located in /var/tmp/build-root/usr/src/packages/RPMS.

The build script offers several additional options. For example, cause the script to prefer your own RPMs, omit the initialization of the build environment or limit the rpm command to one of the above-mentioned stages. Access additional information with build --help and by reading the build man page.

6.2.7 Tools for RPM archives and the RPM database

  

Midnight Commander (mc) can display the contents of RPM archives and copy parts of them. It represents archives as virtual file systems, offering all usual menu options of Midnight Commander. Display the HEADER with F3. View the archive structure with the cursor keys and Enter. Copy archive components with F5.

A full-featured package manager is available as a YaST module. For details, see Book “Deployment Guide”, Chapter 21 “Installing or removing software”.

7 System recovery and snapshot management with Snapper

  

Snapper allows creating and managing file system snapshots. File system snapshots allow keeping a copy of the state of a file system at a certain point of time. The standard setup of Snapper is designed to allow rolling back system changes. However, you can also use it to create on-disk backups of user data. As the basis for this functionality, Snapper uses the Btrfs file system or thinly-provisioned LVM volumes with an XFS or Ext4 file system.

Snapper has a command-line interface and a YaST interface. Snapper lets you create and manage file system snapshots on the following types of file systems:

  • Btrfs, a copy-on-write file system for Linux that natively supports file system snapshots of subvolumes. (Subvolumes are separately mountable file systems within a physical partition.)

    You can also boot from Btrfs snapshots. For more information, see Section 7.3, “System rollback by booting from snapshots”.

  • Thinly-provisioned LVM volumes formatted with XFS or Ext4.

Using Snapper, you can perform the following tasks:

7.1 Default setup

  

Snapper on SUSE Linux Enterprise Server is set up as an undo and recovery tool for system changes. By default, the root partition (/) of SUSE Linux Enterprise Server is formatted with Btrfs. Taking snapshots is automatically enabled if the root partition (/) is big enough (more than approximately 16 GB). By default, snapshots are disabled on partitions other than /.

Tip
Tip: Enabling Snapper in the installed system

If you disabled Snapper during the installation, you can enable it at any time later. To do so, create a default Snapper configuration for the root file system by running: 

> sudo snapper -c root create-config /

Afterward enable the different snapshot types as described in Section 7.1.4.1, “Disabling/enabling snapshots”.

Note that on a Btrfs root file system, snapshots require a file system with subvolumes set up as proposed by the installer and a partition size of at least 16 GB.

When a snapshot is created, both the snapshot and the original point to the same blocks in the file system. So, initially a snapshot does not occupy additional disk space. If data in the original file system is modified, changed data blocks are copied while the old data blocks are kept for the snapshot. Therefore, a snapshot occupies the same amount of space as the data modified. So, over time, the amount of space a snapshot allocates, constantly grows. As a consequence, deleting files from a Btrfs file system containing snapshots may not free disk space!

Note
Note: Snapshot location

Snapshots always reside on the same partition or subvolume on which the snapshot has been taken. It is not possible to store snapshots on a different partition or subvolume.

As a result, partitions containing snapshots need to be larger than partitions not containing snapshots. The exact amount depends strongly on the number of snapshots you keep and the amount of data modifications. As a rule of thumb, give partitions twice as much space as you normally would. To prevent disks from running out of space, old snapshots are automatically cleaned up. Refer to Section 7.1.4.4, “Controlling snapshot archiving” for details.

7.1.1 Default settings

  
Disks larger than 16 GB

  • Configuration file: /etc/snapper/configs/root

  • USE_SNAPPER=yes

  • TIMELINE_CREATE=no

Disks smaller than 16 GB

  • Configuration file: not created

  • USE_SNAPPER=no

  • TIMELINE_CREATE=yes

7.1.2 Types of snapshots

  

Although snapshots themselves do not differ in a technical sense, we distinguish between three types of snapshots, based on the events that trigger them:

Timeline snapshots

A single snapshot is created every hour. Using the YaST OS installation method (default), timeline snapshots are enabled, except for the root file system. You can configure timeline snapshots to be taken at different intervals: hourly, daily, weekly, monthly and yearly. Old snapshots are automatically deleted. By default, the first snapshot of the last ten days, months and years is kept.

Installation snapshots

Whenever one or more packages are installed with Zypper or YaST, three installation snapshots are created. In case an important system component such as the kernel has been installed, the snapshot pair is marked as important. Old snapshots are automatically deleted. Installation snapshots are enabled by default.

Administration snapshots

Whenever you make changes to the system using Zypper or YaST, a pair of snapshots is created: one prior to the system change (“pre”) and the other one after the system change (“post”). Old snapshots are automatically deleted. Administration snapshots are enabled by default.

7.1.3 Directories that are excluded from snapshots

  

Some directories need to be excluded from snapshots for different reasons. The following list shows all directories that are excluded:

/boot/grub2/i386-pc, /boot/grub2/x86_64-efi, /boot/grub2/powerpc-ieee1275, /boot/grub2/s390x-emu

A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The first two directories are present on AMD64/Intel 64 machines, the latter two on IBM POWER and on IBM Z, respectively.

/home

If /home does not reside on a separate partition, it is excluded to avoid data loss on rollbacks.

/opt

Third-party products usually get installed to /opt. It is excluded to avoid uninstalling these applications on rollbacks.

/srv

Contains data for Web and FTP servers. It is excluded to avoid data loss on rollbacks.

/tmp

All directories containing temporary files and caches are excluded from snapshots.

/usr/local

This directory is used when manually installing software. It is excluded to avoid uninstalling these installations on rollbacks.

/var

This directory contains many variable files, including logs, temporary caches, third party products in /var/opt, and is the default location for virtual machine images and databases. Therefore this subvolume is created to exclude all of this variable data from snapshots and has Copy-On-Write disabled.

7.1.4 Customizing the setup

  

SUSE Linux Enterprise Server comes with a reasonable default setup, which should be sufficient for most use cases. However, all aspects of taking automatic snapshots and snapshot keeping can be configured according to your needs.

7.1.4.1 Disabling/enabling snapshots

  

Each of the three snapshot types (timeline, installation, administration) can be enabled or disabled independently.

Disabling/enabling timeline snapshots

Enabling.  snapper -c root set-config "TIMELINE_CREATE=yes"

Disabling.  snapper -c root set-config "TIMELINE_CREATE=no"

Using the YaST OS installation method (default), timeline snapshots are enabled, except for the root file system.

Disabling/enabling installation snapshots

Enabling: Install the package snapper-zypp-plugin

Disabling: Uninstall the package snapper-zypp-plugin

Installation snapshots are enabled by default.

Disabling/enabling administration snapshots

Enabling: Set USE_SNAPPER to yes in /etc/sysconfig/yast2.

Disabling: Set USE_SNAPPER to no in /etc/sysconfig/yast2.

Administration snapshots are enabled by default.

7.1.4.2 Controlling installation snapshots

  

Taking snapshot pairs upon installing packages with YaST or Zypper is handled by the snapper-zypp-plugin. An XML configuration file, /etc/snapper/zypp-plugin.conf defines, when to make snapshots. By default the file looks like the following: 

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <snapper-zypp-plugin-conf>
 3  <solvables>
 4   <solvable match="w"1 important="true"2>kernel-*3</solvable>
 5   <solvable match="w" important="true">dracut</solvable>
 6   <solvable match="w" important="true">glibc</solvable>
 7   <solvable match="w" important="true">systemd*</solvable>
 8   <solvable match="w" important="true">udev</solvable>
 9   <solvable match="w">*</solvable>4
10  </solvables>
11 </snapper-zypp-plugin-conf>

1

The match attribute defines whether the pattern is a Unix shell-style wild card (w) or a Python regular expression (re).

2

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.

3

Pattern to match a package name. Based on the setting of the match attribute, special characters are either interpreted as shell wild cards or regular expressions. This pattern matches all package names starting with kernel-.

4

This line unconditionally matches all packages.

With this configuration snapshot, pairs are made whenever a package is installed (line 9). When the kernel, dracut, glibc, systemd, or udev packages marked as important are installed, the snapshot pair will also be marked as important (lines 4 to 8). All rules are evaluated.

To disable a rule, either delete it or deactivate it using XML comments. To prevent the system from making snapshot pairs for every package installation for example, comment line 9: 

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <snapper-zypp-plugin-conf>
 3  <solvables>
 4   <solvable match="w" important="true">kernel-*</solvable>
 5   <solvable match="w" important="true">dracut</solvable>
 6   <solvable match="w" important="true">glibc</solvable>
 7   <solvable match="w" important="true">systemd*</solvable>
 8   <solvable match="w" important="true">udev</solvable>
 9   <!-- <solvable match="w">*</solvable> -->
10  </solvables>
11 </snapper-zypp-plugin-conf>

7.1.4.3 Creating and mounting new subvolumes

  

Creating a new subvolume underneath the / hierarchy and permanently mounting it is supported. Such a subvolume will be excluded from snapshots. You need to make sure not to create it inside an existing snapshot, since you would not be able to delete snapshots anymore after a rollback.

SUSE Linux Enterprise Server is configured with the /@/ subvolume which serves as an independent root for permanent subvolumes such as /opt, /srv, /home and others. Any new subvolumes you create and permanently mount need to be created in this initial root file system.

To do so, run the following commands. In this example, a new subvolume /usr/important is created from /dev/sda2. 

> sudo mount /dev/sda2 -o subvol=@ /mnt
> sudo btrfs subvolume create /mnt/usr/important
> sudo umount /mnt

The corresponding entry in /etc/fstab needs to look like the following: 

/dev/sda2 /usr/important btrfs subvol=@/usr/important 0 0
Tip
Tip: Disable copy-on-write (cow)

A subvolume may contain files that constantly change, such as virtualized disk images, database files, or log files. If so, consider disabling the copy-on-write feature for this volume, to avoid duplication of disk blocks. Use the nodatacow mount option in /etc/fstab to do so: 

/dev/sda2 /usr/important btrfs nodatacow,subvol=@/usr/important 0 0

To alternatively disable copy-on-write for single files or directories, use the command chattr +C PATH.

7.1.4.4 Controlling snapshot archiving

  

Snapshots occupy disk space. To prevent disks from running out of space and thus causing system outages, old snapshots are automatically deleted. By default, up to ten important installation and administration snapshots and up to ten regular installation and administration snapshots are kept. If these snapshots occupy more than 50% of the root file system size, additional snapshots will be deleted. A minimum of four important and two regular snapshots are always kept.

Refer to Section 7.5.1, “Managing existing configurations” for instructions on how to change these values.

7.1.4.5 Using Snapper on thinly provisioned LVM volumes

  

Apart from snapshots on Btrfs file systems, Snapper also supports taking snapshots on thinly-provisioned LVM volumes (snapshots on regular LVM volumes are not supported) formatted with XFS, Ext4 or Ext3. For more information and setup instructions on LVM volumes, refer to Book “Deployment Guide”, Chapter 10 “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: 

> sudo snapper -c lvm create-config --fstype="lvm(xfs)" /thin_lvm

You can adjust this configuration according to your needs as described in Section 7.5.1, “Managing existing configurations”.

7.2 Using Snapper to undo changes

  

Snapper on SUSE Linux Enterprise Server is preconfigured to serve as a tool that lets you undo changes made by zypper and YaST. For this purpose, Snapper is configured to create a pair of snapshots before and after each run of zypper and YaST. Snapper also lets you restore system files that have been accidentally deleted or modified. Timeline snapshots for the root partition need to be enabled for this purpose—see Section 7.1.4.1, “Disabling/enabling snapshots” for details.

By default, automatic snapshots as described above are configured for the root partition and its subvolumes. To make snapshots available for other partitions such as /home for example, you can create custom configurations.

Important
Important: Undoing changes compared to rollback

When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:

Undoing changes

When undoing changes as described in the following, two snapshots are being compared and the changes between these two snapshots are made undone. Using this method also allows to explicitly select the files that should be restored.

Rollback

When doing rollbacks as described in Section 7.3, “System rollback by booting from snapshots”, the system is reset to the state at which the snapshot was taken.

When undoing changes, it is also possible to compare a snapshot against the current system. When restoring all files from such a comparison, this will have the same result as doing a rollback. However, using the method described in Section 7.3, “System rollback by booting from snapshots” for rollbacks should be preferred, since it is faster and allows you to review the system before doing the rollback.

Warning
Warning: Data consistency

There is no mechanism to ensure data consistency when creating a snapshot. Whenever a file (for example, a database) is written at the same time as the snapshot is being created, it will result in a corrupted or partly written file. Restoring such a file will cause problems. Furthermore, some system files such as /etc/mtab must never be restored. Therefore it is strongly recommended to always closely review the list of changed files and their diffs. Only restore files that really belong to the action you want to revert.

7.2.1 Undoing YaST and Zypper changes

  

If you set up the root partition with Btrfs during the installation, Snapper—preconfigured for doing rollbacks of YaST or Zypper changes—will automatically be installed. Every time you start a YaST module or a Zypper transaction, two snapshots are created: a “pre-snapshot” capturing the state of the file system before the start of the module and a “post-snapshot” after the module has been finished.

Using the YaST Snapper module or the snapper command line tool, you can undo the changes made by YaST/Zypper by restoring files from the “pre-snapshot”. Comparing two snapshots the tools also allow you to see which files have been changed. You can also display the differences between two versions of a file (diff).

Procedure 7.1: Undoing changes using the YaST Snapper module
  

  1. Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper.

  2. Make sure Current Configuration is set to root. This is always the case unless you have manually added own Snapper configurations.

  3. Choose a pair of pre- and post-snapshots from the list. Both, YaST and Zypper snapshot pairs are of the type Pre & Post. YaST snapshots are labeled as zypp(y2base) in the Description column; Zypper snapshots are labeled zypp(zypper).

    Snapshots

  4. Click Show Changes to open the list of files that differ between the two snapshots.

    Snapshot changes

  5. Review the list of files. To display a “diff” between the pre- and post-version of a file, select it from the list.

    File diff

  6. To restore one or more files, select the relevant files or directories by activating the respective check box. Click Restore Selected and confirm the action by clicking Yes.

    Restore files

    To restore a single file, activate its diff view by clicking its name. Click Restore From First and confirm your choice with Yes.

Procedure 7.2: Undoing changes using the snapper command
  

  1. 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 Description column; Zypper snapshots are labeled zypp(zypper). 

    > sudo snapper list -t pre-post
Pre # | Post # | Pre Date                      | Post Date                     | Description
------+--------+-------------------------------+-------------------------------+--------------
311   | 312    | Tue 06 May 2018 14:05:46 CEST | Tue 06 May 2018 14:05:52 CEST | zypp(y2base)
340   | 341    | Wed 07 May 2018 16:15:10 CEST | Wed 07 May 2018 16:15:16 CEST | zypp(zypper)
342   | 343    | Wed 07 May 2018 16:20:38 CEST | Wed 07 May 2018 16:20:42 CEST | zypp(y2base)
344   | 345    | Wed 07 May 2018 16:21:23 CEST | Wed 07 May 2018 16:21:24 CEST | zypp(zypper)
346   | 347    | Wed 07 May 2018 16:41:06 CEST | Wed 07 May 2018 16:41:10 CEST | zypp(y2base)
348   | 349    | Wed 07 May 2018 16:44:50 CEST | Wed 07 May 2018 16:44:53 CEST | zypp(y2base)
350   | 351    | Wed 07 May 2018 16:46:27 CEST | Wed 07 May 2018 16:46:38 CEST | zypp(y2base)

  2. Get a list of changed files for a snapshot pair with snapper status PRE..POST. Files with content changes are marked with c, files that have been added are marked with + and deleted files are marked with -. 

    > sudo snapper status 350..351
+..... /usr/share/doc/packages/mikachan-fonts
+..... /usr/share/doc/packages/mikachan-fonts/COPYING
+..... /usr/share/doc/packages/mikachan-fonts/dl.html
c..... /usr/share/fonts/truetype/fonts.dir
c..... /usr/share/fonts/truetype/fonts.scale
+..... /usr/share/fonts/truetype/みかちゃん-p.ttf
+..... /usr/share/fonts/truetype/みかちゃん-pb.ttf
+..... /usr/share/fonts/truetype/みかちゃん-ps.ttf
+..... /usr/share/fonts/truetype/みかちゃん.ttf
c..... /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4
c..... /var/lib/rpm/Basenames
c..... /var/lib/rpm/Dirnames
c..... /var/lib/rpm/Group
c..... /var/lib/rpm/Installtid
c..... /var/lib/rpm/Name
c..... /var/lib/rpm/Packages
c..... /var/lib/rpm/Providename
c..... /var/lib/rpm/Requirename
c..... /var/lib/rpm/Sha1header
c..... /var/lib/rpm/Sigmd5

  3. 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. 

    > 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
[...]

  4. To restore one or more files run snapper -v undochange PRE..POST FILENAMES. If you do not specify a FILENAMES, all changed files will be restored. 

    > sudo snapper -v undochange 350..351
     create:0 modify:13 delete:7
     undoing change...
     deleting /usr/share/doc/packages/mikachan-fonts
     deleting /usr/share/doc/packages/mikachan-fonts/COPYING
     deleting /usr/share/doc/packages/mikachan-fonts/dl.html
     deleting /usr/share/fonts/truetype/みかちゃん-p.ttf
     deleting /usr/share/fonts/truetype/みかちゃん-pb.ttf
     deleting /usr/share/fonts/truetype/みかちゃん-ps.ttf
     deleting /usr/share/fonts/truetype/みかちゃん.ttf
     modifying /usr/share/fonts/truetype/fonts.dir
     modifying /usr/share/fonts/truetype/fonts.scale
     modifying /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4
     modifying /var/lib/rpm/Basenames
     modifying /var/lib/rpm/Dirnames
     modifying /var/lib/rpm/Group
     modifying /var/lib/rpm/Installtid
     modifying /var/lib/rpm/Name
     modifying /var/lib/rpm/Packages
     modifying /var/lib/rpm/Providename
     modifying /var/lib/rpm/Requirename
     modifying /var/lib/rpm/Sha1header
     modifying /var/lib/rpm/Sigmd5
     undoing change done
Warning
Warning: Reverting user additions

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 User and Group Management tool to remove users.

7.2.2 Using Snapper to restore files

  

Apart from the installation and administration snapshots, Snapper creates timeline snapshots. You can use these backup snapshots to restore files that have accidentally been deleted or to restore a previous version of a file. By using Snapper's diff feature you can also find out which modifications have been made at a certain point of time.

Being able to restore files is especially interesting for data, which may reside on subvolumes or partitions for which snapshots are not taken by default. To be able to restore files from home directories, for example, create a separate Snapper configuration for /home doing automatic timeline snapshots. See Section 7.5, “Creating and modifying Snapper configurations” for instructions.

Warning
Warning: Restoring files compared to rollback

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!

Procedure 7.3: Restoring files using the YaST Snapper module
  

  1. Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper.

  2. Choose the Current Configuration from which to choose a snapshot.

  3. Select a timeline snapshot from which to restore a file and choose Show Changes. Timeline snapshots are of the type Single with a description value of timeline.

  4. 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.

  5. Click Restore Selected and confirm the action by clicking Yes.

Procedure 7.4: Restoring files using the snapper command
  

  1. Get a list of timeline snapshots for a specific configuration by running the following command: 

    > 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.

  2. Get a list of changed files for a given snapshot by running the following command: 

    > 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).

  3. Optionally list the differences between the current file version and the one from the snapshot by running 

    > sudo snapper -c CONFIG diff SNAPSHOT_ID..0 FILE NAME

    If you do not specify <FILE NAME>, the difference for all files are shown.

  4. To restore one or more files, run 

    > sudo snapper -c CONFIG -v undochange SNAPSHOT_ID..0 FILENAME1 FILENAME2

    If you do not specify file names, all changed files will be restored.

7.3 System rollback by booting from snapshots

  

The GRUB 2 version included on SUSE Linux Enterprise Server can boot from Btrfs snapshots. Together with Snapper's rollback feature, this allows to recover a misconfigured system. Only snapshots created for the default Snapper configuration (root) are bootable.

Important
Important: Supported configuration

As of SUSE Linux Enterprise Server 15 SP3 system rollbacks are only supported if the default subvolume configuration of the root partition has not been changed.

When booting a snapshot, the parts of the file system included in the snapshot are mounted read-only; all other file systems and parts that are excluded from snapshots are mounted read-write and can be modified.

Important
Important: Undoing changes compared to rollback

When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:

Undoing changes

When undoing changes as described in Section 7.2, “Using Snapper to undo changes”, two snapshots are compared and the changes between these two snapshots are reverted. Using this method also allows to explicitly exclude selected files from being restored.

Rollback

When doing rollbacks as described in the following, the system is reset to the state at which the snapshot was taken.

To do a rollback from a bootable snapshot, the following requirements must be met. When doing a default installation, the system is set up accordingly.

Requirements for a rollback from a bootable snapshot
  

  • The root file system needs to be Btrfs. Booting from LVM volume snapshots is not supported.

  • The root file system needs to be on a single device. To check, run sudo /sbin/btrfs filesystem show. It needs to report Total devices 1. If more than 1 device is listed, your setup is not supported.

    Note
    Note: Directories excluded from snapshots

    Directories that are excluded from snapshots such as /srv (see Section 7.1.3, “Directories that are excluded from snapshots” for a full list) may reside on separate devices.

  • The system needs to be bootable via the installed boot loader.

  • Only contents of the subvolume / will be rolled back. It is not possible to include other subvolumes.

To perform a rollback from a bootable snapshot, do as follows:

  1. Boot the system. In the boot menu choose Bootable snapshots and select the snapshot you want to boot. The list of snapshots is listed by date—the most recent snapshot is listed first.

  2. 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.

  3. Depending on whether you want to perform the rollback or not, choose your next step:

    1. 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.

    2. To perform the rollback, run 

      > 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
Tip
Tip: Rolling back to a specific installation state

If snapshots are not disabled during installation, an initial bootable snapshot is created at the end of the initial system installation. You can go back to that state at any time by booting this snapshot. The snapshot can be identified by the description after installation.

A bootable snapshot is also created when starting a system upgrade to a service pack or a new major release (provided snapshots are not disabled).

7.3.1 Snapshots after rollback

  

Before a rollback is performed, a snapshot of the running file system is created. The description references the ID of the snapshot that was restored in the rollback.

Snapshots created by rollbacks receive the value number for the Cleanup attribute. The rollback snapshots are therefore automatically deleted when the set number of snapshots is reached. Refer to Section 7.7, “Automatic snapshot clean-up” for details. If the snapshot contains important data, extract the data from the snapshot before it is removed.

7.3.1.1 Example of rollback snapshot

  

For example, after a fresh installation the following snapshots are available on the system: 

# snapper --iso list
Type   | # |     | Cleanup | Description           | Userdata
-------+---+ ... +---------+-----------------------+--------------
single | 0 |     |         | current               |
single | 1 |     |         | first root filesystem |
single | 2 |     | number  | after installation    | important=yes

After running sudo snapper rollback snapshot 3 is created and contains the state of the system before the rollback was executed. Snapshot 4 is the new default Btrfs subvolume and thus the system after a reboot. 

# snapper --iso list
Type   | # |     | Cleanup | Description           | Userdata
-------+---+ ... +---------+-----------------------+--------------
single | 0 |     |         | current               |
single | 1 |     | number  | first root filesystem |
single | 2 |     | number  | after installation    | important=yes
single | 3 |     | number  | rollback backup of #1 | important=yes
single | 4 |     |         |                       |

7.3.2 Accessing and identifying snapshot boot entries

  

To boot from a snapshot, reboot your machine and choose Start Bootloader from a read-only snapshot. A screen listing all bootable snapshots opens. The most recent snapshot is listed first, the oldest last. Use the keys ↓ 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.

Boot loader: snapshots
Figure 7.1: Boot loader: snapshots
  
Warning
Warning: Booting Xen from a Btrfs snapshot using UEFI currently fails

Refer to https://www.suse.com/support/kb/doc/?id=000020602 for more details.

Each snapshot entry in the boot loader follows a naming scheme which makes it possible to identify it easily: 

[*]1OS2 (KERNEL3,DATE4TTIME5,DESCRIPTION6)

1

If the snapshot was marked important, the entry is marked with a *.

2

Operating system label.

4

Date in the format YYYY-MM-DD.

5

Time in the format HH:MM.

6

This field contains a description of the snapshot. In case of a manually created snapshot this is the string created with the option --description or a custom string (see Tip: Setting a custom description for boot loader snapshot entries). In case of an automatically created snapshot, it is the tool that was called, for example zypp(zypper) or yast_sw_single. Long descriptions may be truncated, depending on the size of the boot screen.

Tip
Tip: Setting a custom description for boot loader snapshot entries

It is possible to replace the default string in the description field of a snapshot with a custom string. This is for example useful if an automatically created description is not sufficient, or a user-provided description is too long. To set a custom string STRING for snapshot NUMBER, use the following command: 

> sudo snapper modify --userdata "bootloader=STRING" NUMBER

The description should be no longer than 25 characters—everything that exceeds this size will not be readable on the boot screen.

7.3.3 Limitations

  

A complete system rollback, restoring the complete system to the identical state as it was in when a snapshot was taken, is not possible.

7.3.3.1 Directories excluded from snapshots

  

Root file system snapshots do not contain all directories. See Section 7.1.3, “Directories that are excluded from snapshots” for details and reasons. As a general consequence, data from these directories is not restored, resulting in the following limitations.

Add-ons and third-party software may be unusable after a rollback

Applications and add-ons installing data in subvolumes excluded from the snapshot, such as /opt, may not work after a rollback, if others parts of the application data are also installed on subvolumes included in the snapshot. Re-install the application or the add-on to solve this problem.

File access problems

If an application had changed file permissions and/or ownership in between snapshot and current system, the application may not be able to access these files. Reset permissions and/or ownership for the affected files after the rollback.

Incompatible data formats

If a service or an application has established a new data format in between snapshot and current system, the application may not be able to read the affected data files after a rollback.

Subvolumes with a mixture of code and data

Subvolumes like /srv may contain a mixture of code and data. A rollback may result in non-functional code. A downgrade of the PHP version, for example, may result in broken PHP scripts for the Web server.

User data

If a rollback removes users from the system, data that is owned by these users in directories excluded from the snapshot, is not removed. If a user with the same user ID is created, this user will inherit the files. Use a tool like find to locate and remove orphaned files.

7.3.3.2 No rollback of boot loader data

  

A rollback of the boot loader is not possible, since all “stages” of the boot loader must fit together. This cannot be guaranteed when doing rollbacks of /boot.

7.4 Enabling Snapper in user home directories

  

You may enable snapshots for users' /home directories, which supports a number of use cases:

  • Individual users may manage their own snapshots and rollbacks.

  • System users, for example database, system, and network admins who want to track copies of configuration files, documentation, and so on.

  • Samba shares with home directories and Btrfs back-end.

Each user's directory is a Btrfs subvolume of /home. It is possible to set this up manually (see Section 7.4.3, “Manually enabling snapshots in home directories”). However, a more convenient way is to use pam_snapper. The pam_snapper package installs the pam_snapper.so module and helper scripts, which automate user creation and Snapper configuration.

pam_snapper provides integration with the useradd command, pluggable authentication modules (PAM), and Snapper. By default it creates snapshots at user login and logout, and also creates time-based snapshots as some users remain logged in for extended periods of time. You may change the defaults using the normal Snapper commands and configuration files.

7.4.1 Installing pam_snapper and creating users

  

The easiest way is to start with a new /home directory formatted with Btrfs, and no existing users. Install pam_snapper: 

# zypper in pam_snapper

Add this line to /etc/pam.d/common-session: 

session optional pam_snapper.so

Use the /usr/lib/pam_snapper/pam_snapper_useradd.sh script to create a new user and home directory. By default the script performs a dry run. Edit the script to change DRYRUN=1 to DRYRUN=0. Now you can create a new user: 

# /usr/lib/pam_snapper/pam_snapper_useradd.sh \
username group passwd=password
Create subvolume '/home/username'
useradd: warning: the home directory already exists.
Not copying any file from skel directory into it.

The files from /etc/skel will be copied into the user's home directory at their first login. Verify that the user's configuration was created by listing your Snapper configurations: 

# snapper list --all
Config: home_username, subvolume: /home/username
Type   | # | Pre # | Date | User | Cleanup | Description | Userdata
-------+---+-------+------+------+---------+-------------+---------
single | 0 |       |      | root |         | current     |

Over time, this output will become populated with a list of snapshots, which the user can manage with the standard Snapper commands.

7.4.2 Removing users

  

Remove users with the /usr/lib/pam_snapper/pam_snapper_userdel.sh script. By default it performs a dry run, so edit it to change DRYRUN=1 to DRYRUN=0. This removes the user, the user's home subvolume, Snapper configuration, and deletes all snapshots. 

# /usr/lib/pam_snapper/pam_snapper_userdel.sh username

7.4.3 Manually enabling snapshots in home directories

  

These are the steps for manually setting up users' home directories with Snapper. /home must be formatted with Btrfs, and the users not yet created. 

# btrfs subvol create /home/username
# snapper -c home_username create-config /home/username
# sed -i -e "s/ALLOW_USERS=\"\"/ALLOW_USERS=\"username\"/g" \
/etc/snapper/configs/home_username
# yast users add username=username home=/home/username password=password
# chown username.group /home/username
# chmod 755 /home/username/.snapshots

7.5 Creating and modifying Snapper configurations

  

The way Snapper behaves is defined in a configuration file that is specific for each partition or Btrfs subvolume. These configuration files reside under /etc/snapper/configs/.

In case the root file system is big enough (approximately 12 GB), snapshots are automatically enabled for the root file system / upon installation. The corresponding default configuration is named root. It creates and manages the YaST and Zypper snapshot. See Section 7.5.1.1, “Configuration data” for a list of the default values.

Note
Note: Minimum root file system size for enabling snapshots

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 Snapper module to restore files from these snapshots. In YaST you need to select your Current Configuration, while you need to specify your configuration for snapper with the global switch -c (for example, snapper -c myconfig list).

To create a new Snapper configuration, run snapper create-config: 

> sudo snapper -c www-data1 create-config /srv/www2

1

Name of configuration file.

2

Mount point of the partition or Btrfs subvolume on which to take snapshots.

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.

Tip
Tip: Configuration defaults

Default values for a new configuration are taken from /etc/snapper/config-templates/default. To use your own set of defaults, create a copy of this file in the same directory and adjust it to your needs. To use it, specify the -t option with the create-config command: 

> sudo snapper -c www-data create-config -t MY_DEFAULTS /srv/www

7.5.1 Managing existing configurations

  

The snapper command offers several subcommands for managing existing configurations. You can list, show, delete and modify them:

Listing configurations

Use the subcommand snapper list-configs to get all existing configurations: 

> sudo snapper list-configs
Config | Subvolume
-------+----------
root   | /
usr    | /usr
local  | /local
Showing a configuration

Use the subcommand snapper -c CONFIG get-config to display the specified configuration. Replace CONFIG with one of the configuration names shown 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: 

> sudo snapper -c root get-config
Modifying a configuration

Use the subcommand snapper -c CONFIG set-config OPTION=VALUE to modify an option in the specified configuration. Replace CONFIG with one of the configuration names shown by snapper list-configs. Possible values for OPTION and VALUE are listed in Section 7.5.1.1, “Configuration data”.

Deleting a configuration

Use the subcommand snapper -c CONFIG delete-config to delete a configuration. Replace CONFIG with one of the configuration names shown by snapper list-configs.

7.5.1.1 Configuration data

  

Each configuration contains a list of options that can be modified from the command line. The following list provides details for each option. To change a value, run snapper -c CONFIG set-config "KEY=VALUE".

ALLOW_GROUPS, ALLOW_USERS

Granting permissions to use snapshots to regular users. See Section 7.5.1.2, “Using Snapper as regular user” for more information.

The default value is "".

BACKGROUND_COMPARISON

Defines whether pre and post snapshots should be compared in the background after creation.

The default value is "yes".

EMPTY_*

Defines the clean-up algorithm for snapshots pairs with identical pre and post snapshots. See Section 7.7.3, “Cleaning up snapshot pairs that do not differ” for details.

FSTYPE

File system type of the partition. Do not change.

The default value is "btrfs".

NUMBER_*

Defines the clean-up algorithm for installation and admin snapshots. See Section 7.7.1, “Cleaning up numbered snapshots” for details.

QGROUP / SPACE_LIMIT

Adds quota support to the clean-up algorithms. See Section 7.7.5, “Adding disk quota support” for details.

SUBVOLUME

Mount point of the partition or subvolume to snapshot. Do not change.

The default value is "/".

SYNC_ACL

If Snapper is used by regular users (see Section 7.5.1.2, “Using Snapper as regular user”), the users must be able to access the .snapshot directories and to read files within them. If SYNC_ACL is set 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.

7.5.1.2 Using Snapper as regular user

  

By default Snapper can only be used by root. However, there are cases in which certain groups or users need to be able to create snapshots or undo changes by reverting to a snapshot:

  • Web site administrators who want to take snapshots of /srv/www

  • Users who want to take a snapshot of their home directory

For these purposes, you can create Snapper configurations that grant permissions to users or/and groups. The corresponding .snapshots directory needs to be readable and accessible by the specified users. The easiest way to achieve this is to set the SYNC_ACL option to yes.

Procedure 7.5: Enabling regular users to use Snapper
  

Note that all steps in this procedure need to be run by root.

  1. If a Snapper configuration does not exist yet, create one for the partition or subvolume on which the user should be able to use Snapper. Refer to Section 7.5, “Creating and modifying Snapper configurations” for instructions. Example: 

    > sudo snapper --config web_data create /srv/www

  2. 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”.

  3. 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: 

    > sudo snapper -c web_data set-config "ALLOW_USERS=www_admin" SYNC_ACL="yes"

  4. The given Snapper configuration can now be used by the specified user(s) and/or group(s). You can test it with the list command, for example: 

    www_admin:~ > snapper -c web_data list

7.6 Manually creating and managing snapshots

  

Snapper is not restricted to creating and managing snapshots automatically by configuration; you can also create snapshot pairs (“before and after”) or single snapshots manually using either the command-line tool or the YaST module.

All Snapper operations are carried out for an existing configuration (see Section 7.5, “Creating and modifying Snapper configurations” for details). You can only take snapshots of partitions or volumes for which a configuration exists. By default the system configuration (root) is used. To create or manage snapshots for your own configuration you need to explicitly choose it. Use the Current Configuration drop-down box in YaST or specify the -c on the command line (snapper -c MYCONFIG COMMAND).

7.6.1 Snapshot metadata

  

Each snapshot consists of the snapshot itself and some metadata. When creating a snapshot you also need to specify the metadata. Modifying a snapshot means changing its metadata—you cannot modify its content. Use snapper list to show existing snapshots and their metadata:

snapper --config home list

Lists snapshots for the configuration home. To list snapshots for the default configuration (root), 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.

7.6.1.1 Snapshot types

  

Snapper knows three different types of snapshots: pre, post, and single. Physically they do not differ, but Snapper handles them differently.

pre

Snapshot of a file system before a modification. Each pre snapshot corresponds to 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.

7.6.1.2 Cleanup algorithms

  

Snapper provides three algorithms to clean up old snapshots. The algorithms are executed in a daily cron job. It is possible to define the number of different types of snapshots to keep in the Snapper configuration (see Section 7.5.1, “Managing existing configurations” for details).

number

Deletes old snapshots when a certain snapshot count is reached.

timeline

Deletes old snapshots having passed a certain age, but keeps several hourly, daily, monthly, and yearly snapshots.

empty-pre-post

Deletes pre/post snapshot pairs with empty diffs.

7.6.2 Creating snapshots

  

To create a snapshot, run snapper create or click Create in the YaST module Snapper. 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.

Tip
Tip: Snapshot description

Always specify a meaningful description to later be able to identify its purpose. You can also specify additional information via the option --userdata.

snapper create --from 17 --description "with package2"

Creates a stand-alone snapshot (type single) from an existing snapshot, which is specified by the snapshot's number from snapper list. (This applies to Snapper version 0.8.4 and newer.)

snapper create --description "Snapshot for week 2 2014"

Creates a stand-alone snapshot (type single) for the default (root) configuration with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.

snapper --config home create --description "Cleanup in ~tux"

Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.

snapper --config home create --description "Daily data backup" --cleanup-algorithm timeline>

Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. The snapshot will automatically be deleted when it meets the criteria specified for the timeline cleanup-algorithm in the configuration.

snapper create --type pre --print-number --description "Before the Apache config cleanup" --userdata "important=yes"

Creates a snapshot of the type pre and prints the snapshot number. First command needed to create a pair of snapshots used to save a “before” and “after” state. The snapshot is marked as important.

snapper create --type post --pre-number 30 --description "After the Apache config cleanup" --userdata "important=yes"

Creates a snapshot of the type post paired with 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.

7.6.3 Modifying snapshot metadata

  

Snapper allows you to modify the description, the cleanup algorithm, and the user data of a snapshot. All other metadata cannot be changed. The following examples explain how to modify snapshots from the command line. It should be easy to adopt them when using the YaST interface.

To modify a snapshot on the command line, you need to know its number. Use snapper list to display all snapshots and their numbers.

The YaST Snapper module already lists all snapshots. Choose one from the list and click Modify.

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.

7.6.4 Deleting snapshots

  

To delete a snapshot with the YaST Snapper module, choose a snapshot from the list and click Delete.

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.

Tip
Tip: Deleting snapshot pairs

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.

Tip
Tip: Delete unreferenced snapshots

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
Tip
Tip: Old snapshots occupy more disk space

If you delete snapshots to free space on your hard disk, make sure to delete old snapshots first. The older a snapshot is, the more disk space it occupies.

Snapshots are also automatically deleted by a daily cron job. Refer to Section 7.6.1.2, “Cleanup algorithms” for details.

7.7 Automatic snapshot clean-up

  

Snapshots occupy disk space and over time the amount of disk space occupied by the snapshots may become large. To prevent disks from running out of space, Snapper offers algorithms to automatically delete old snapshots. These algorithms differentiate between timeline snapshots and numbered snapshots (administration plus installation snapshot pairs). You can specify the number of snapshots to keep for each type.

In addition to that, you can optionally specify a disk space quota, defining the maximum amount of disk space the snapshots may occupy. It is also possible to automatically delete pre and post snapshots pairs that do not differ.

A clean-up algorithm is always bound to a single Snapper configuration, so you need to configure algorithms for each configuration. To prevent certain snapshots from being automatically deleted, refer to Can a snapshot be protected from deletion? .

The default setup (root) is configured to do clean-up for numbered snapshots and empty pre and post snapshot pairs. Quota support is enabled—snapshots may not occupy more than 50% of the available disk space of the root partition. Timeline snapshots are disabled by default, therefore the timeline clean-up algorithm is also disabled.

7.7.1 Cleaning up numbered snapshots

  

Cleaning up numbered snapshots—administration plus installation snapshot pairs—is controlled by the following parameters of a Snapper configuration.

NUMBER_CLEANUP

Enables or disables clean-up of installation and admin snapshot pairs. If enabled, snapshot pairs are deleted when the total snapshot count exceeds a number specified with NUMBER_LIMIT and/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: 

> sudo snapper -c CONFIG set-config "NUMBER_CLEANUP=no"
NUMBER_LIMIT / NUMBER_LIMIT_IMPORTANT

Defines how many regular and/or important installation and administration snapshot pairs to keep. Ignored if NUMBER_CLEANUP is set to "no".

The default value is "2-10" for NUMBER_LIMIT and "4-10" for NUMBER_LIMIT_IMPORTANT. The cleaning algorithms delete snapshots above the specified maximum value, without taking the snapshot and file system space into account. The algorithms also delete snapshots above the minimum value until the limits for the snapshot and file system are reached.

Example command to change or set: 

> sudo snapper -c CONFIG set-config "NUMBER_LIMIT=10"
Important
Important: Ranged compared to constant values

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: 

> sudo snapper -c CONFIG set-config "NUMBER_MIN_AGE=864000"
Note
Note: Limit and age

NUMBER_LIMIT, NUMBER_LIMIT_IMPORTANT and NUMBER_MIN_AGE are always evaluated. Snapshots are only deleted when all conditions are met.

If you always want to keep the number of snapshots defined with NUMBER_LIMIT* regardless of their age, set NUMBER_MIN_AGE to 0.

The following example shows a configuration to keep the last 10 important and regular snapshots regardless of age: 

NUMBER_CLEANUP=yes
NUMBER_LIMIT_IMPORTANT=10
NUMBER_LIMIT=10
NUMBER_MIN_AGE=0

On the other hand, if you do not want to keep snapshots beyond a certain age, set NUMBER_LIMIT* to 0 and provide the age with NUMBER_MIN_AGE.

The following example shows a configuration to only keep snapshots younger than ten days: 

NUMBER_CLEANUP=yes
NUMBER_LIMIT_IMPORTANT=0
NUMBER_LIMIT=0
NUMBER_MIN_AGE=864000

7.7.2 Cleaning up timeline snapshots

  

Cleaning up timeline snapshots is controlled by the following parameters of a Snapper configuration.

TIMELINE_CLEANUP

Enables or disables clean-up of timeline snapshots. If enabled, snapshots are deleted when the total snapshot count exceeds a number specified with TIMELINE_LIMIT_* and an age specified with TIMELINE_MIN_AGE. Valid values: yes, no.

The default value is "yes".

Example command to change or set: 

> sudo snapper -c CONFIG set-config "TIMELINE_CLEANUP=yes"
TIMELINE_LIMIT_DAILY, TIMELINE_LIMIT_HOURLY, TIMELINE_LIMIT_MONTHLY, TIMELINE_LIMIT_WEEKLY, TIMELINE_LIMIT_YEARLY

Number of snapshots to keep for hour, day, month, week, and year.

The default value for each entry is "10", except 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".

Example 7.1: Example timeline configuration
  
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.

Snapshots to be kept
  

  • Hourly: The last 24 snapshots that have been made.

  • Daily: The first daily snapshot that has been made is kept from the last seven days.

  • Monthly: The first snapshot made on the last day of the month is kept for the last twelve months.

  • Weekly: The first snapshot made on the last day of the week is kept from the last four weeks.

  • Yearly: The first snapshot made on the last day of the year is kept for the last two years.

7.7.3 Cleaning up snapshot pairs that do not differ

  

As explained in Section 7.1.2, “Types of snapshots”, whenever you run a YaST module or execute Zypper, a pre snapshot is created on start-up and a post snapshot is created when exiting. In case you have not made any changes there will be no difference between the pre and post snapshots. Such “empty” snapshot pairs can be automatically be deleted by setting the following parameters in a Snapper configuration:

EMPTY_PRE_POST_CLEANUP

If set to yes, pre and post snapshot pairs that do not differ will be deleted.

The default value is "yes".

EMPTY_PRE_POST_MIN_AGE

Defines the minimum age in seconds a pre and post snapshot pair that does not differ must have before it can automatically be deleted.

The default value is "1800".

7.7.4 Cleaning up manually created snapshots

  

Snapper does not offer custom clean-up algorithms for manually created snapshots. However, you can assign the number or timeline clean-up algorithm to a manually created snapshot. If you do so, the snapshot will join the “clean-up queue” for the algorithm you specified. You can specify a clean-up algorithm when creating a snapshot, or by modifying an existing snapshot:

snapper create --description "Test" --cleanup-algorithm number

Creates a stand-alone snapshot (type single) for the default (root) configuration and assigns the number clean-up algorithm.

snapper modify --cleanup-algorithm "timeline" 25

Modifies the snapshot with the number 25 and assigns the clean-up algorithm timeline.

7.7.5 Adding disk quota support

  

In addition to the number and/or timeline clean-up algorithms described above, Snapper supports quotas. You can define what percentage of the available space snapshots are allowed to occupy. This percentage value always applies to the Btrfs subvolume defined in the respective Snapper configuration.

Btrfs quotas are applied to subvolumes, not to users. You may apply disk space quotas to users and groups (for example, with the quota command) in addition to using Btrfs quotas.

If Snapper was enabled during the installation, quota support is automatically enabled. In case you manually enable Snapper at a later point in time, you can enable quota support by running snapper setup-quota. This requires a valid configuration (see Section 7.5, “Creating and modifying Snapper configurations” for more information).

Quota support is controlled by the following parameters of a Snapper configuration.

QGROUP

The Btrfs quota group used by Snapper. If not set, run snapper setup-quota. If already set, only change if you are familiar 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.

7.8 Showing exclusive disk space used by snapshots

  

Snapshots share data, for efficient use of storage space, so using ordinary commands like du and df won't measure used disk space accurately. When you want to free up disk space on Btrfs with quotas enabled, you need to know how much exclusive disk space is used by each snapshot, rather than shared space. Snapper 0.6 and up reports the used disk space for each snapshot in the Used Space column: 

# snapper --iso list
  # | Type   | Pre # | Date                | User | Used Space | Cleanup | Description           | Userdata     
----+--------+-------+---------------------+------+------------+---------+-----------------------+--------------
 0  | single |       |                     | root |            |         | current               |              
 1* | single |       | 2019-07-22 13:08:38 | root |  16.00 KiB |         | first root filesystem |              
 2  | single |       | 2019-07-22 14:21:05 | root |  14.23 MiB | number  | after installation    | important=yes
 3  | pre    |       | 2019-07-22 14:26:03 | root | 144.00 KiB | number  | zypp(zypper)          | important=no 
 4  | post   |     3 | 2019-07-22 14:26:04 | root | 112.00 KiB | number  |                       | important=no 
 5  | pre    |       | 2019-07-23 08:19:36 | root | 128.00 KiB | number  | zypp(zypper)          | important=no 
 6  | post   |     5 | 2019-07-23 08:19:43 | root |  80.00 KiB | number  |                       | important=no 
 7  | pre    |       | 2019-07-23 08:20:50 | root | 256.00 KiB | number  | yast sw_single        |              
 8  | pre    |       | 2019-07-23 08:23:22 | root | 112.00 KiB | number  | zypp(ruby.ruby2.5)    | important=no 
 9  | post   |     8 | 2019-07-23 08:23:35 | root |  64.00 KiB | number  |                       | important=no 
10  | post   |     7 | 2019-07-23 08:24:05 | root |  16.00 KiB | number  |                       |

The btrfs command provides another view of space used by snapshots: 

# btrfs qgroup show -p /
qgroupid         rfer         excl parent  
--------         ----         ---- ------  
0/5          16.00KiB     16.00KiB ---     
[...]    
0/272         3.09GiB     14.23MiB 1/0     
0/273         3.11GiB    144.00KiB 1/0     
0/274         3.11GiB    112.00KiB 1/0     
0/275         3.11GiB    128.00KiB 1/0     
0/276         3.11GiB     80.00KiB 1/0     
0/277         3.11GiB    256.00KiB 1/0     
0/278         3.11GiB    112.00KiB 1/0     
0/279         3.12GiB     64.00KiB 1/0     
0/280         3.12GiB     16.00KiB 1/0     
1/0           3.33GiB    222.95MiB ---

The qgroupid column displays the identification number for each subvolume, assigning a qgroup level/ID combination.

The rfer column displays the total amount of data referred to in the subvolume.

The excl column displays the exclusive data in each subvolume.

The parent column shows the parent qgroup of the subvolumes.

The final item, 1/0, shows the totals for the parent qgroup. In the above example, 222.95 MiB will be freed if all subvolumes are removed. Run the following command to see which snapshots are associated with each subvolume: 

# btrfs subvolume list -st /
ID	gen	top level	path	
--	---	---------	----	
267	298	266		@/.snapshots/1/snapshot
272	159	266		@/.snapshots/2/snapshot
273	170	266		@/.snapshots/3/snapshot
274	171	266		@/.snapshots/4/snapshot
275	287	266		@/.snapshots/5/snapshot
276	288	266		@/.snapshots/6/snapshot
277	292	266		@/.snapshots/7/snapshot
278	296	266		@/.snapshots/8/snapshot
279	297	266		@/.snapshots/9/snapshot
280	298	266		@/.snapshots/10/snapshot

Doing an upgrade from one service pack to another results in snapshots occupying a lot of disk space on the system subvolumes. Manually deleting these snapshots after they are no longer needed is recommended. See Section 7.6.4, “Deleting snapshots” for details.

7.9 Frequently asked questions

  
Q: Why does Snapper never show changes in /var/log, /tmp and other directories?

For some directories we decided to exclude them from snapshots. See Section 7.1.3, “Directories that are excluded from snapshots” for a list and reasons. To exclude a path from snapshots we create a subvolume for that path.

Q: Can I boot a snapshot from the boot loader?

Yes—refer to Section 7.3, “System rollback by booting from snapshots” for details.

Q: Can a snapshot be protected from deletion?

Currently Snapper does not offer means to prevent a snapshot from being deleted manually. However, you can prevent snapshots from being automatically deleted by clean-up algorithms. Manually created snapshots (see Section 7.6.2, “Creating snapshots”) have no clean-up algorithm assigned unless you specify one with --cleanup-algorithm. Automatically created snapshots always either have the number or timeline algorithm assigned. To remove such an assignment from one or more snapshots, proceed as follows:

  1. List all available snapshots: 

    > sudo snapper list -a

  2. Memorize the number of the snapshot(s) you want to prevent from being deleted.

  3. Run the following command and replace the number placeholders with the number(s) you memorized: 

    > sudo snapper modify --cleanup-algorithm "" #1 #2 #n

  4. Check the result by running snapper list -a again. The entry in the column Cleanup should now be empty for the snapshots you modified.

Q: Where can I get more information on Snapper?

See the Snapper home page at http://snapper.io/.

8 Live kernel patching with KLP

  

This document describes the basic principles of the Kernel Live Patching (KLP) technology, and provides usage guidelines for the SLE Live Patching service.

KLP makes it possible to apply the latest security updates to Linux kernels without rebooting. This maximizes system uptime and availability, which is especially important for mission-critical systems.

The information provided in this document relates to the AMD64/Intel 64, POWER, and IBM Z architectures.

8.1 Advantages of Kernel Live Patching

  

KLP offers several benefits.

  • Keeping a large number of servers automatically up to date is essential for organizations obtaining or maintaining certain compliance certifications. KLP can help achieve compliance, while reducing the need for costly maintenance windows.

  • Companies that work with service-level agreement contracts must guarantee a specific level of their system accessibility and uptime. Live patching makes it possible to patch systems without incurring downtime.

  • Since KLP is part of the standard system update mechanism, there is no need for specialized training or introduction of complicated maintenance routines.

8.2 Kernel Live Patching overview

  

Kernel live patches are delivered as packages with modified code that are separate from the main kernel package. The live patches are cumulative, so the latest patch contains all fixes from the previous ones for the kernel package. Each kernel live package is tied to the exact kernel revision for which it is issued. The live patch package version number increases with every addition of fixes.

Note
Note: Live patches and the running kernel

After a live patch is applied, the lp-HASH string is added to the version of the running kernel as reported by the uname -a command. 

> uname -a
Linux sle15-sp3 5.3.18-150300.59.101-default #1 SMP \
Tue Nov 1 11:32:03 UTC 2022 (b2a976e/lp-cd28ef5) x86_64 x86_64 x86_64 GNU/Linux

To determine the kernel patching status, use the klp -v patches command.

Important
Important: Live patches vs. kernel updates

Live patches contain only critical fixes, and they do not replace regular kernel updates that require a reboot. Consider live patches as temporary measures that protect the kernel until a proper kernel update and a reboot are performed.

The diagram below illustrates the overall relationship between live patches and kernel updates. The list of CVEs and defect reports addressed by the currently active live patch can be viewed using the klp -v patches command.

Relationship between live patches and kernel updates

It is possible to have multiple versions of the kernel package installed along with their live patches. These packages do not conflict. You can install updated kernel packages along with live patches for the running kernel. In this case, you may be prompted to reboot the system. Users with SLE Live Patching subscriptions are eligible for technical support as long as there are live patch updates for the running kernel (see Section 8.5.1, “Checking expiration date of the live patch”).

With KLP activated, every kernel update comes with a live patch package. This live patch does not contain any fixes and serves as a seed for future live patches for the corresponding kernel. These empty seed patches are called initial patches.

8.2.1 Kernel Live Patching scope

  

The scope of SLE Live Patching includes fixes for SUSE Common Vulnerability Scoring System (CVSS; SUSE CVSS is based on the CVSS v3.0 system) level 7+ vulnerabilities and bug fixes related to system stability or data corruption. However, it may not be technically feasible to create live patches for all fixes that fall under the specified categories. SUSE therefore reserves the right to skip fixes in situations where creating a kernel live patch is not possible for technical reasons. Currently, over 95% of qualifying fixes are released as live patches. For more information on CVSS (the base for the SUSE CVSS rating), see Common Vulnerability Scoring System SIG.

8.2.2 Kernel Live Patching limitations

  

KLP involves replacing functions and gracefully handling replacement of interdependent function sets. This is done by redirecting calls to old code to updated code in a different memory location. Changes in data structures make the situation more complicated, as the data remain in place and cannot be extended or reinterpreted. While there are techniques that allow indirect alteration of data structures, some fixes cannot be converted to live patches. In this situation, a system restart is the only way to apply the fixes.

8.3 Activating Kernel Live Patching using YaST

  

To activate KLP on your system, you need to have active SLES and SLE Live Patching subscriptions. Visit SUSE Customer Center to check the status of your subscriptions and obtain a registration code for the SLE Live Patching subscription.

To activate Kernel Live Patching on your system, follow these steps:

  1. Run the yast2 registration command and click Select Extensions.

  2. Select SUSE Linux Enterprise Live Patching 15 in the list of available extensions and click Next.

  3. Confirm the license terms and click Next.

  4. Enter your SLE Live Patching registration code and click Next.

  5. Check the Installation Summary and selected Patterns. The patterns Live Patching and SLE Live Patching Lifecycle Data should be automatically selected for installation along with additional packages to satisfy dependencies.

  6. Click Accept to complete the installation. This will install the base Kernel Live Patching components on your system, the initial live patch, and the required dependencies.

8.4 Activating Kernel Live Patching from the command line

  

To activate Kernel Live Patching, you need to have active SLES and SLES Live Patching subscriptions. Visit SUSE Customer Center to check the status of your subscriptions and obtain a registration code for the SLES Live Patching subscription.

  1. Run sudo SUSEConnect --list-extensions. Note the exact activation command for SLES Live Patching. Example command output (abbreviated): 

    $ SUSEConnect --list-extensions
...
SUSE Linux Enterprise Live Patching 15 SP3 x86_64
Activate with: SUSEConnect -p sle-module-live-patching/15.3/x86_64 \
  -r ADDITIONAL REGCODE

  2. Activate SLES Live Patching using the obtained command followed by -r LIVE_PATCHING_REGISTRATION_CODE, for example: 

    SUSEConnect -p sle-module-live-patching/15.3/x86_64 \
  -r LIVE_PATCHING_REGISTRATION_CODE

  3. Install the required packages and dependencies using the command zypper install -t pattern lp_sles

At this point, the system has already been live-patched.

Here is how the process works behind the scenes: When the package installation system detects that there is an installed kernel that can be live-patched, and that there is a live patch for it in the software channel, the system selects the live patch for installation. The kernel then receives the live patch fixes as part of the package installation. The kernel gets live-patched even before the product installation is complete.

8.5 Performing Kernel Live Patching

  

Kernel live patches are installed as part of regular system updates. However, there are several things you should be aware of.

  • The kernel is live-patched if a kernel-livepatch-* package has been installed for the running kernel. You can use the command zypper se --details kernel-livepatch-* to check what kernel live patch packages are installed on your system.

  • When the kernel-default package is installed, the update manager prompts you to reboot the system. To prevent this message from appearing, you can filter out kernel updates from the patching operation. This can be done by adding package locks with Zypper. SUSE Manager also makes it possible to filter channel contents (see Live Patching with SUSE Manager).

  • You can check patching status using the klp status command. To examine installed patches, run the klp -v patches command.

  • Keep in mind that while there may be multiple kernel packages installed on the system, only one of them is running at any given time. Similarly, there may be multiple live patch packages installed, but only one live patch is loaded into the kernel.

  • The active live patch is included in the initrd. This means that in case of an unexpected reboot, the system comes up with the live patch fixes applied, so there is no need to perform patching again.

8.5.1 Checking expiration date of the live patch

  

Make sure that the lifecycle-data-sle-module-live-patching is installed, then run the zypper lifecycle command. You should see expiration dates for live patches in the Package end of support if different from product section of the output.

Every live patch receives updates for one year from the release of the underlying kernel package. The Maintained kernels, patch updates and lifecycle page allows you to check expiration dates based on the running kernel version without installing the product extension.

8.6 Troubleshooting Kernel Live Patching issues

  

8.6.1 Manual patch downgrade

  

If you find the latest live patch problematic, you can downgrade the currently installed live patch back to its previous version. We recommend performing patch downgrade before the system starts exhibiting issues. Keep in mind that a system with kernel warnings or kernel error traces in the system log may not be suitable for the patch downgrade procedure. If you are unsure whether the system meets the requirements for a patch downgrade, contact SUSE Technical Support for help.

Procedure 8.1: Manual patch downgrade
  

  1. Identify the running live patch using the klp -v patches command. You can see the currently running patch on the line starting with RPM:. For example: 

    RPM: kernel-livepatch-5_3_18-24_29-default-2-2.1.x86_64

    The 5_3_18-24_29-default in the example above denotes the exact running kernel version.

  2. Use the command zypper search -s kernel-livepatch-RUNNING_KERNEL_VERSION-default to search for previous versions of the patch. The command returns a list of available package versions. Keep in mind that for every new live patch package release, the version number increases by one. Make sure that you choose the version number one release lower than the current one.

  3. Install the desired version with the command zypper in --oldpackage kernel-livepatch-RUNNING_KERNEL_VERSION-default=DESIRED_VERSION.

9 Transactional updates

  

Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root file system is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not affect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the admin must decide if a reboot is more expensive than disturbing running services. If reboots are too expensive then do not use transactional updates.

Transactional updates are run daily by the transactional-update script. The script checks for available updates. If there are any updates, it creates a new snapshot of the root file system in the background, and then fetches updates from the release channels. After the new snapshot is completely updated, it is marked as active and will be the new default root file system after the next reboot of the system. When transactional-update is set to run automatically (which is the default behavior) it also reboots the system. Both the time that the update runs and the reboot maintenance window are configurable.

Only packages that are part of the snapshot of the root file system can be updated. If packages contain files that are not part of the snapshot, the update could fail or break the system.

RPMs that require a license to be accepted cannot be updated.

9.1 Limitations of technology preview

  

As a technology preview, there are certain limitations in functionality. The following packages will not work with transactional-update:

  • The nginx default index.html page may not be available

  • tomcat-webapps and tomcat-admin-webapps

  • phpMyAdmin

  • sca-appliance-*

  • mpi-selector

  • emacs works except for Emacs games

  • bind and bind-chrootenv

  • docbook*

  • sblim-sfcb*

  • texlive*

  • iso_ent

  • openjade

  • opensp

  • pcp

  • plymouth

  • postgresql-server-10

  • pulseaudio-gdm-hooks

  • smartmontools

The updater component of the system installer does not work with a read-only file system as it has no support for transactional updates.

Further considerations:

  • In general it is a good idea to minimize the time between updating the system and rebooting the machine.

  • Only one update can be applied at a time. Be sure to reboot after an update, and before the next update is applied.

  • update-alternatives should not be run after a transactional update until the machine has been rebooted.

  • Do not create new system users or system groups after a transactional update until after reboot. It is acceptable to create normal users and groups (UID > 1000, GID > 1000).

  • YaST is not yet aware of transactional updates. If a YaST module needs to install additional packages, this will not work. Normal system operations only modifying configuration files in /etc will work.

  • For php7-fastcgi, you must manually create a symlink, /srv/www/cgi-bin/php, that points to /usr/bin/php-cgi.

  • ntpis part of the Legacy Module for migration from older SLES versions. It is not supported on a new SUSE Linux Enterprise Server installation, and has been replaced by chrony. If you continue to use ntp, a fresh installation is required to work correctly with transactional updates.

  • sblim-sfcb: The whole sblim ecosystem is incompatible with transactional update.

  • btrfs-defrag from the btrfsmaintenance package does not work with a read-only root file system.

  • For btrfs-balance, the 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.

9.2 Enabling transactional-update

  

You must enable the Transactional Server Module during system installation, and then select the Transactional Server System Role. Installing any package from the Transactional Server Module later in a running system is NOT supported and may break the system.

Note that changing the subvolume layout of the root partition, or putting sub-directories or subvolumes of the root partition on their own partitions (except /home, /var, /srv, and /opt) is not supported, and will most likely break the system.

9.3 Managing automatic updates

  

Automatic updates are controlled by a systemd.timer that runs once per day. This applies all updates, and informs rebootmgrd that the machine should be rebooted. You may adjust the time when the update runs, see systemd.timer(5). To adjust the maintenance window, which is when rebootmgrd reboots the system, see rebootmgrd(8).

You can disable automatic transactional updates with this command: 

# systemctl --now disable transactional-update.timer

9.4 The transactional-update command

  

The transactional-update command enables atomic installation or removal of updates; updates are applied only if all of them can be successfully installed. transactional-update creates a snapshot of your system before the update is applied, and you can restore this snapshot. All changes become active only after reboot.

--continue

The --continue option is for making multiple changes to an existing snapshot without rebooting.

The default transactional-update behavior is to create a new snapshot from the current root file system. If you forget something, such as installing a new package, you have to reboot to apply your previous changes, run transactional-update again to install the forgotten package, and reboot again. You cannot run the transactional-update command multiple times without rebooting to add more changes to the snapshot, because that creates separate independent snapshots that do not include changes from the previous snapshots.

Use the --continue option to make as many changes as you want without rebooting. A separate snapshot is made each time, and each snapshot contains all the changes you made in the previous snapshots, plus your new changes. Repeat this process as many times as you want, and when the final snapshot includes everything you want reboot the system, and your final snapshot becomes the new root file system.

Another useful feature of the --continue option is you may select any existing snapshot as the base for your new snapshot. The following example demonstrates running transactional-update to install a new package in a snapshot based on snapshot 13, and then running it again to install another package: 

# transactional-update pkg install package_1
# transactional-update --continue 13 pkg install package_2

The --continue [num] option calls snapper create --from, see Section 7.6.2, “Creating snapshots”.

cleanup

If the current root filesystem is identical to the active root filesystem (after a reboot, before transactional-update creates a new snapshot with updates), all old snapshots without a cleanup algorithm get a cleanup algorithm set. This ensures that old snapshots will be deleted by Snapper. (See the section about cleanup algorithms in snapper(8).) This also removes all unreferenced (and thus unused) /etc overlay directories in /var/lib/overlay: 

# transactional-update cleanup
pkg in/install

Installs individual packages from the available channels using the zypper install command. This command can also be used to install Program Temporary Fix (PTF) RPM files. 

# transactional-update pkg install package_name

or 

# transactional-update pkg install rpm1 rpm2
pkg rm/remove

Removes individual packages from the active snapshot using the zypper remove command. This command can also be used to remove PTF RPM files. 

# transactional-update pkg remove package_name
pkg up/update

Updates individual packages from the active snapshot using the zypper update command. Only packages that are part of the snapshot of the base file system can be updated. 

# transactional-update pkg update package_name
up/update

If there are new updates available, a new snapshot is created and zypper up/update updates the snapshot. 

# transactional-update up
dup

If there are new updates available, a new snapshot is created and zypper dup –no-allow-vendor-change updates the snapshot. The snapshot is activated afterwards and becomes the new root file system after reboot. 

# transactional-update dup
patch

If there are new updates available, a new snapshot is created and zypper patch updates the snapshot. 

# transactional-update patch
rollback

This sets the default subvolume. On systems with a read-write file system snapper rollback is called. On a read-only file system and without any argument, the current system is set to a new default root file system. If you specify a number, that snapshot is used as the default root file system. On a read-only file system, it does not create any additional snapshots. 

# transactional-update rollback snapshot_number
grub.cfg

This creates a new GRUB2 configuration. Sometimes it is necessary to adjust the boot configuration, for example adding additional kernel parameters. Edit /etc/default/grub, run transactional-update grub.cfg, and then reboot to activate the change. You must immediately reboot, or the new GRUB2 configuration will be overwritten with the default by the next transactional-update. 

# transactional-update grub.cfg
reboot

This parameter triggers a reboot after the action is completed. 

# transactional-update dup reboot
--help

This prints a help screen with options and subcommands. 

# transactional-update --help

9.5 Troubleshooting

  

If the upgrade fails, run supportconfig to collect log data. Provide the resulting files, including /var/log/transactional-update.log to SUSE Support.

10 Remote graphical sessions with VNC

  

Virtual Network Computing (VNC) enables you to access a remote computer via a graphical desktop, and run remote graphical applications. VNC is platform-independent and accesses the remote machine from any operating system. This chapter describes how to connect to a VNC server with the desktop clients vncviewer and Remmina, and how to operate a VNC server.

SUSE Linux Enterprise Server supports two different kinds of VNC sessions: One-time sessions that “live” as long as the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated.

A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.

10.1 The vncviewer client

  

To connect to a VNC service provided by a server, a client is needed. The default in SUSE Linux Enterprise Server is vncviewer, provided by the tigervnc package.

10.1.1 Connecting using the vncviewer CLI

  

To start your VNC viewer and initiate a session with the server, use the command: 

> vncviewer jupiter.example.com:1

Instead of the VNC display number you can also specify the port number with two colons: 

> vncviewer jupiter.example.com::5901
Note
Note: Display and port number

The actual display or port number you specify in the VNC client must be the same as the display or port number picked by the vncserver command on the target machine. See Section 10.4, “Configuring persistent VNC server sessions” for further info.

10.1.2 Connecting using the vncviewer GUI

  

By running vncviewer without specifying --listen or a host to connect to, it will show a window to ask for connection details. Enter the host into the VNC server field like in Section 10.1.1, “Connecting using the vncviewer CLI” and click Connect.

vncviewer asking for connection details
Figure 10.1: vncviewer
  

10.1.3 Notification of unencrypted connections

  

The VNC protocol supports different kinds of encrypted connections, not to be confused with password authentication. If a connection does not use TLS, the text “(Connection not encrypted!)” can be seen in the window title of the VNC viewer.

10.2 Remmina: the remote desktop client

  

Remmina is a modern and feature rich remote desktop client. It supports several access methods, for example VNC, SSH, RDP, and Spice.

10.2.1 Installation

  

To use Remmina, verify whether the remmina package is installed on your system, and install it if not. Remember to install the VNC plug-in for Remmina as well: 

# zypper in remmina remmina-plugin-vnc

10.2.2 Main window

  

Run Remmina by entering the remmina command.

Remmina's main window
Figure 10.2: Remmina's main window
  

The main application window shows the list of stored remote sessions. Here you can add and save a new remote session, quick-start a new session without saving it, start a previously saved session, or set Remmina's global preferences.

10.2.3 Adding remote sessions

  

To add and save a new remote session, click Add new session in the top left of the main window. The Remote Desktop Preference window opens.

Remote desktop preference
Figure 10.3: Remote desktop preference
  

Complete the fields that specify your newly added remote session profile. The most important are:

Name

Name of the profile. It will be listed in the main window.

Protocol

The protocol to use when connecting to the remote session, for example VNC.

Server

The IP or DNS address and display number of the remote server.

User name, password

Credentials to use for remote authentication. Leave empty for no authentication.

Color depth, quality

Select the best options according to your connection speed and quality.

Select the Advanced tab to enter more specific settings.

Tip
Tip: Disable encryption

If the communication between the client and the remote server is not encrypted, activate Disable encryption, otherwise the connection fails.

Select the SSH tab for advanced SSH tunneling and authentication options.

Confirm with Save. Your new profile will be listed in the main window.

10.2.4 Starting remote sessions

  

You can either start a previously saved session, or quick-start a remote session without saving the connection details.

10.2.4.1 Quick-starting remote sessions

  

To start a remote session quickly without adding and saving connection details, use the drop-down box and text box at the top of the main window.

Quick-starting
Figure 10.4: Quick-starting
  

Select the communication protocol from the drop-down box, for example 'VNC', then enter the VNC server DNS or IP address followed by a colon and a display number, and confirm with Enter.

10.2.4.2 Opening saved remote sessions

  

To open a specific remote session, double-click it from the list of sessions.

10.2.4.3 Remote sessions window

  

Remote sessions are opened in tabs of a separate window. Each tab hosts one session. The toolbar on the left of the window helps you manage the windows/sessions, such as toggle fullscreen mode, resize the window to match the display size of the session, send specific keystrokes to the session, take screenshots of the session, or set the image quality.

Remmina viewing remote session
Figure 10.5: Remmina viewing remote session
  

10.2.5 Editing, copying, and deleting saved sessions

  

To edit a saved remote session, right-click its name in Remmina's main window and select Edit. 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 Copy. In the Remote Desktop Preference window, change the name of the profile, optionally adjust relevant options, and confirm with Save.

To Delete a saved remote session, right-click its name in Remmina's main window and select Delete. Confirm with Yes in the next dialog.

10.2.6 Running remote sessions from the command line

  

If you need to open a remote session from the command line or from a batch file without first opening the main application window, use the following syntax: 

 > remmina -c profile_name.remmina

Remmina's profile files are stored in the .local/share/remmina/ directory in your home directory. To determine which profile file belongs to the session you want to open, run Remmina, click the session name in the main window, and read the path to the profile file in the window's status line at the bottom.

Reading path to the profile file
Figure 10.6: Reading path to the profile file
  

While Remmina is not running, you can rename the profile file to a more reasonable file name, such as sle15.remmina. You can even copy the profile file to your custom directory and run it using the remmina -c command from there.

10.3 Configuring one-time sessions on the VNC server

  

A one-time session is initiated by the remote client. It starts a graphical login screen on the server. This way you can choose the user which starts the session and, if supported by the login manager, the desktop environment. When you terminate the client connection to such a VNC session, all applications started within that session will be terminated, too. One-time VNC sessions cannot be shared, but it is possible to have multiple sessions on a single host at the same time.

Procedure 10.1: Enabling one-time VNC sessions
  

  1. Start YaST › Network Services › Remote Administration (VNC).

  2. Check Allow Remote Administration Without Session Management.

  3. Activate Enable access using a web browser if you plan to access the VNC session in a Web browser window.

  4. If necessary, also check Open Port in Firewall (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 Firewall Details.

  5. Confirm your settings with Next.

  6. In case not all needed packages are available yet, you need to approve the installation of missing packages.

    Tip
    Tip: Restart the display manager

    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.

Remote administration
Figure 10.7: Remote administration
  

10.3.1 Available configurations

  

The default configuration on SUSE Linux Enterprise Server serves sessions with a resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are available on ports 5901 for “regular” VNC viewers (equivalent to VNC display 1) and on port 5801 for Web browsers.

Other configurations can be made available on different ports, see Section 10.3.3, “Configuring one-time VNC sessions”.

VNC display numbers and X display numbers are independent in one-time sessions. A VNC display number is manually assigned to every configuration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the configurations, it automatically gets a free X display number.

By default, both the VNC client and server try to communicate securely via a self-signed SSL certificate, which is generated after installation. You can either use the default one, or replace it with your own. When using the self-signed certificate, you need to confirm its signature before the first connection—both in the VNC viewer and the Web browser.

Tip
Tip

Some VNC clients refuse to establish a secure connection via the default self-signed certificate. For example, the Vinagre client verifies the certification against the GnuTLS global trust store and fails if the certificate is self-signed. In such a case, either use an encryption method other than x509, or generate a properly signed certificate for the VNC server and import it to the client's system trust store.

10.3.2 Initiating a one-time VNC session

  

To connect to a one-time VNC session, a VNC viewer must be installed, see also Section 10.1, “The vncviewer client”. Alternatively use a JavaScript-capable Web browser to view the VNC session by entering the following URL: http://jupiter.example.com:5801

10.3.3 Configuring one-time VNC sessions

  

You can skip this section, if you do not need or want to modify the default configuration.

One-time VNC sessions are started via the systemd socket xvnc.socket. By default it offers six configuration blocks: three for VNC viewers (vnc1 to vnc3), and three serving a JavaScript client (vnchttpd1 to vnchttpd3). By default only vnc1 and vnchttpd1 are active.

To activate the VNC server socket at boot time, run the following command: 

> sudo  systemctl enable xvnc.socket

To start the socket immediately, run: 

> sudo  systemctl start xvnc.socket

The Xvnc server can be configured via the server_args option. For a list of options, see Xvnc --help.

When adding custom configurations, make sure they are not using ports that are already in use by other configurations, other services, or existing persistent VNC sessions on the same host.

Activate configuration changes by entering the following command: 

> sudo systemctl reload xvnc.socket
Important
Important: Firewall and VNC ports

When activating Remote Administration as described in Procedure 10.1, “Enabling one-time VNC sessions”, the ports 5801 and 5901 are opened in the firewall. If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the respective ports when activating additional ports for VNC sessions. See Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls” for instructions.

10.4 Configuring persistent VNC server sessions

  

A persistent session can be accessed from multiple clients simultaneously. This is ideal for demonstration purposes where one client has full access and all other clients have view-only access. Another use case are training sessions where the trainer might need access to the trainee's desktop.

Tip
Tip: Connecting to a persistent VNC session

To connect to a persistent VNC session, a VNC viewer must be installed. Refer to Section 10.1, “The vncviewer client” for more details. Alternatively use a JavaScript-capable Web browser to view the VNC session by entering the following URL: http://jupiter.example.com:5801

There are two types of persistent VNC sessions:

10.4.1 VNC session initiated using vncserver

  

This type of persistent VNC session is initiated on the server. The session and all applications started in this session run regardless of client connections until the session is terminated. Access to persistent sessions is protected by two possible types of passwords:

  • a regular password that grants full access or

  • an optional view-only password that grants a non-interactive (view-only) access.

A session can have multiple client connections of both kinds at once.

Procedure 10.2: Starting a persistent VNC session using vncserver
  

  1. Open a shell and make sure you are logged in as the user that should own the VNC session.

  2. If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the port used by your session in the firewall. If starting multiple sessions you may alternatively open a range of ports. See Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls” for details on how to configure the firewall.

    vncserver uses the 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.

  3. 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.

Important
Important: Security considerations

Make sure to use strong passwords of significant length (eight or more characters). Do not share these passwords.

To terminate the session shut down the desktop environment that runs inside the VNC session from the VNC viewer as you would shut it down if it was a regular local X session.

If you prefer to manually terminate a session, open a shell on the VNC server and make sure you are logged in as the user that owns the VNC session you want to terminate. Run the following command to terminate the session that runs on display :1: vncserver -kill :1

10.4.1.1 Configuring persistent VNC sessions

  

Persistent VNC sessions can be configured by editing $HOME/.vnc/xstartup. By default this shell script starts the same GUI/window manager it was started from. In SUSE Linux Enterprise Server this will either be GNOME or IceWM. If you want to start your session with a window manager of your choice, set the variable WINDOWMANAGER: 

WINDOWMANAGER=gnome vncserver -geometry 1024x768
WINDOWMANAGER=icewm vncserver -geometry 1024x768
Note
Note: One configuration for each user

Persistent VNC sessions are configured in a single per-user configuration. Multiple sessions started by the same user will all use the same start-up and password files.

10.4.2 VNC session initiated using vncmanager

  
Procedure 10.3: Enabling persistent VNC sessions
  

  1. Start YaST › Network Services › Remote Administration (VNC).

  2. Activate Allow Remote Administration With Session Management.

  3. Activate Enable access using a web browser if you plan to access the VNC session in a Web browser window.

  4. If necessary, also check Open Port in Firewall (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 Firewall Details.

  5. Confirm your settings with Next.

  6. In case not all needed packages are available yet, you need to approve the installation of missing packages.

    Tip
    Tip: Restart the display manager

    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.

10.4.2.1 Configuring persistent VNC sessions

  

After you enable the VNC session management as described in Procedure 10.3, “Enabling persistent VNC sessions”, you can normally connect to the remote session with your favorite VNC viewer, such as vncviewer or Remmina. You will be presented with the login screen. After you log in, the 'VNC' icon will appear in the system tray of your desktop environment. Click the icon to open the VNC Session window. If it does not appear or if your desktop environment does not support icons in the system tray, run vncmanager-controller manually.

VNC session settings
Figure 10.8: VNC session settings
  

There are several settings that influence the VNC session's behavior:

Non-persistent, private

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.

Persistent, visible

The session is visible to other users and keeps running even after you disconnect from it.

Session name

Here you can specify the name of the persistent session so that it is easily identified when reconnecting.

No password required

The session will be freely accessible without having to log in under user credentials.

Require user login

You need to log in with a valid user name and password to access the session. Lists the valid user names in the Allowed users text box.

Allow one client at a time

Prevents multiple users from joining the session at the same time.

Allow multiple clients at a time

Allows multiple users to join the persistent session at the same time. Useful for remote presentations or training sessions.

Confirm with OK.

10.4.2.2 Joining persistent VNC sessions

  

After you set up a persistent VNC session as described in Section 10.4.2.1, “Configuring persistent VNC sessions”, you can join it with your VNC viewer. After your VNC client connects to the server, you will be prompted to choose whether you want to create a new session, or join the existing one:

Joining a persistent VNC session
Figure 10.9: Joining a persistent VNC session
  

After you click the name of the existing session, you may be asked for login credentials, depending on the persistent session settings.

10.5 Configuring encryption on the VNC server

  

If the VNC server is set up properly, all communication between the VNC server and the client is encrypted. The authentication happens at the beginning of the session; the actual data transfer only begins afterward.

Whether for a one-time or a persistent VNC session, security options are configured via the -securitytypes parameter of the /usr/bin/Xvnc command located on the server_args line. The -securitytypes parameter selects both authentication method and encryption. It has the following options:

Authentications
  
None, TLSNone, x509None

No authentication.

VncAuth, TLSVnc, x509Vnc

Authentication using custom password.

Plain, TLSPlain, x509Plain

Authentication using PAM to verify user's password.

Encryptions
  
None, vncAuth, plain

No encryption.

TLSNone, TLSVnc, TLSPlain

Anonymous TLS encryption. Everything is encrypted, but there is no verification of the remote host. So you are protected against passive attackers, but not against man-in-the-middle attackers.

X509None, x509Vnc, x509Plain

TLS encryption with certificate. If you use a self-signed certificate, you will be asked to verify it on the first connection. On subsequent connections you will be warned only if the certificate changed. So you are protected against everything except man-in-the-middle on the first connection (similar to typical SSH usage). If you use a certificate signed by a certificate authority matching the machine name, then you get full security (similar to typical HTTPS usage).

Tip
Tip

Some VNC clients refuse to establish a secure connection via the default self-signed certificate. For example, the Vinagre client verifies the certification against the GnuTLS global trust store and fails if the certificate is self-signed. In such a case, either use an encryption method other than x509, or generate a properly signed certificate for the VNC server and import it to the client's system trust store.

Tip
Tip: Path to certificate and key

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).

10.6 Compatibility with Wayland

  

The Remote Administration (VNC) feature relies on X11 and may result in an empty screen if Wayland is enabled. The display manager must be configured to use X11 instead of Wayland. For gdm, edit /etc/gdm/custom.conf. In the [daemon] section, add WaylandEnable=false to the configuration file. When logging in, the user must choose an X11-compatible session as well. If you wish to remove the Wayland option for GNOME, you can remove and lock the gnome-session-wayland package.

11 File copying with RSync

  

Today, a typical user has several computers: home and workplace machines, a laptop, a smartphone or a tablet. This makes the task of keeping files and documents in synchronization across multiple devices all the more important.

Warning
Warning: Risk of data loss

Before you start using a synchronization tool, you should familiarize yourself with its features and functionality. Make sure to back up your important files.

11.1 Conceptual overview

  

For synchronizing a large amount of data over a slow network connection, Rsync offers a reliable method of transmitting only changes within files. This applies not only to text files but also binary files. To detect the differences between files, Rsync subdivides the files into blocks and computes check sums over them.

Detecting changes requires some computing power. So make sure that machines on both ends have enough resources, including RAM.

Rsync can be particularly useful when large amounts of data containing only minor changes need to be transmitted regularly. This is often the case when working with backups. Rsync can also be useful for mirroring staging servers that store complete directory trees of Web servers to a Web server in a DMZ.

Despite its name, Rsync is not a synchronization tool. Rsync is a tool that copies data only in one direction at a time. It does not and cannot do the reverse. If you need a bidirectional tool which can synchronize both source and destination, use Csync.

11.2 Basic syntax

  

Rsync is a command-line tool that has the following basic syntax: 

rsync [OPTION] SOURCE [SOURCE]... DEST

You can use Rsync on any local or remote machine, provided you have access and write permissions. It is possible to have multiple SOURCE entries. The SOURCE and DEST placeholders can be paths, URLs, or both.

Below are the most common Rsync options:

-v

Outputs more verbose text

-a

Archive mode; copies files recursively and preserves time stamps, user/group ownership, file permissions, and symbolic links

-z

Compresses the transmitted data

Note
Note: Trailing slashes count

When working with Rsync, you should pay particular attention to trailing slashes. A trailing slash after the directory denotes the content of the directory. No trailing slash denotes the directory itself.

11.3 Copying files and directories locally

  

The following description assumes that the current user has write permissions to the directory /var/backup. To copy a single file from one directory on your machine to another path, use the following command: 

> rsync -avz backup.tar.xz /var/backup/

The file backup.tar.xz is copied to /var/backup/; the absolute path will be /var/backup/backup.tar.xz.

Do not forget to add the trailing slash after the /var/backup/ directory! If you do not insert the slash, the file backup.tar.xz is copied to /var/backup (file) not inside the directory /var/backup/!

Copying a directory is similar to copying a single file. The following example copies the directory tux/ and its content into the directory /var/backup/: 

> rsync -avz tux /var/backup/

Find the copy in the absolute path /var/backup/tux/.

11.4 Copying files and directories remotely

  

The Rsync tool is required on both machines. To copy files from or to remote directories requires an IP address or a domain name. A user name is optional if your current user names on the local and remote machine are the same.

To copy the file file.tar.xz from your local host to the remote host 192.168.1.1 with same users (being local and remote), use the following command: 

> rsync -avz file.tar.xz  tux@192.168.1.1:

Depending on what you prefer, these commands are also possible and equivalent: 

> rsync -avz file.tar.xz 192.168.1.1:~
> rsync -avz file.tar.xz 192.168.1.1:/home/tux

In all cases with standard configuration, you will be prompted to enter your passphrase of the remote user. This command will copy file.tar.xz to the home directory of user tux (usually /home/tux).

Copying a directory remotely is similar to copying a directory locally. The following example copies the directory tux/ and its content into the remote directory /var/backup/ on the 192.168.1.1 host: 

> rsync -avz tux 192.168.1.1:/var/backup/

Assuming you have write permissions on the host 192.168.1.1, you will find the copy in the absolute path /var/backup/tux.

11.5 Configuring and using an rsync server

  

Rsync can run as a daemon (rsyncd) listening on default port 873 for incoming connections. This daemon can receive “copying targets”.

The following description explains how to create an Rsync server on a jupiter host with a backup target. This target can be used to store your backups. To create an Rsync server, do the following:

Procedure 11.1: Setting up an rsync server
  

  1. On jupiter, create a directory to store all your backup files. In this example, we use /var/backup: 

    # mkdir /var/backup

  2. Specify ownership. In this case, the directory is owned by user tux in group users: 

    # chown tux.users /var/backup

  3. 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:

    1. Create a directory /etc/rsyncd.d/: 

      # mkdir /etc/rsyncd.d/

    2. 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

      1

      Merges global values from /etc/rsyncd.d/*.inc files into the main configuration file.

      2

      Loads any modules (or targets) from /etc/rsyncd.d/*.conf files. These files should not contain any references to global values.

    3. 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

      1

      The backup target. You can use any name you like. However, it is a good idea to name a target according to its purpose and use the same name in your *.conf file.

      2

      Specifies the user name or group name that is used when the file transfer takes place.

      3

      Defines the path to store your backups (from Step 1).

      4

      Specifies a comma-separated list of allowed users. In its simplest form, it contains the user names that are allowed to connect to this module. In our case, only user tux is allowed.

      5

      Specifies the path of a file that contains lines with user names and plain passwords.

    4. Create the /etc/rsyncd.secrets file with the following content and replace PASSPHRASE: 

      # user:passwd
tux:PASSPHRASE

    5. Make sure the file is only readable by root: 

      # chmod 0600 /etc/rsyncd.secrets

  4. Start and enable the rsyncd daemon with: 

    # systemctl enable rsyncd
# systemctl start rsyncd

  5. Test the access to your Rsync server: 

    > rsync jupiter::

    You should see a response that looks like this: 

    backup          Our backup target

    Otherwise, check your configuration file, firewall and network settings.

The above steps create an Rsync server that can now be used to store backups. The example also creates a log file listing all connections. This file is stored in /var/log/rsyncd.log. This is useful if you want to debug your transfers.

To list the content of your backup target, use the following command: 

> rsync -avz jupiter::backup

This command lists all files present in the directory /var/backup on the server. This request is also logged in the log file /var/log/rsyncd.log. To start an actual transfer, provide a source directory. Use . for the current directory. For example, the following command copies the current directory to your Rsync backup server: 

> rsync -avz . jupiter::backup

By default, Rsync does not delete files and directories when it runs. To enable deletion, the additional option --delete must be stated. To ensure that no newer files are deleted, the option --update can be used instead. Any conflicts that arise must be resolved manually.

11.6 More information

  
Csync

Bidirectional file synchronization tool, see https://csync.org/.

RSnapshot

Creates incremental backups, see https://rsnapshot.org.

Unison

A file synchronization tool similar to CSync but with a graphical interface, see https://github.com/bcpierce00/unison.

Rear

A disaster recovery framework, see the Administration Guide of the SUSE Linux Enterprise High Availability, chapter Disaster Recovery with Rear (Relax-and-Recover).

Part II Booting a Linux system

  
  • 12 Introduction to the boot process

    • Booting a Linux system involves different components and tasks. After a firmware and hardware initialization process, which depends on the machine's architecture, the kernel is started by means of the boot loader GRUB 2. After this point, the boot process is completely controlled by the operating system and handled by systemd. systemd provides a set of “targets” that boot configurations for everyday usage, maintenance or emergencies.

  • 13 UEFI (Unified Extensible Firmware Interface)

    • UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.

  • 14 The boot loader GRUB 2

    • This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 12, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 13, UEFI (Unified Extensible Firmware Interface).

  • 15 The systemd daemon

    • systemd initializes the system. It has the process ID 1. systemd is started directly by the kernel and resists signal 9, which normally terminates processes. All other programs are started directly by systemd or by one of its child processes. systemd is a replacement for the System V init daemon and…

12 Introduction to the boot process

  

Booting a Linux system involves different components and tasks. After a firmware and hardware initialization process, which depends on the machine's architecture, the kernel is started by means of the boot loader GRUB 2. After this point, the boot process is completely controlled by the operating system and handled by systemd. systemd provides a set of “targets” that boot configurations for everyday usage, maintenance or emergencies.

12.1 Terminology

  

This chapter uses terms that can be interpreted ambiguously. To understand how they are used here, read the definitions below:

init

Two different processes are commonly named “init”:

  • The initramfs process mounting the root file 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.

12.2 The Linux boot process

  

The Linux boot process consists of several stages, each represented by a different component:

  1. Section 12.2.1, “The initialization and boot loader phase”

  2. Section 12.2.2, “The kernel phase”

  3. Section 12.2.3, “The init on initramfs phase”

  4. Section 12.2.4, “The systemd phase”

12.2.1 The initialization and boot loader phase

  

During the initialization phase the machine's hardware is set up and the devices are prepared. This process differs significantly between hardware architectures.

SUSE Linux Enterprise Server uses the boot loader GRUB 2 on all architectures. Depending on the architecture and firmware, starting the GRUB 2 boot loader can be a multi-step process. The purpose of the boot loader is to load the kernel and the initial, RAM-based file system (initramfs). For more information about GRUB 2, refer to Chapter 14, The boot loader GRUB 2.

12.2.1.1 Initialization and boot loader phase on AArch64 and AMD64/Intel 64

  

After turning on the computer, the BIOS or the UEFI initializes the screen and keyboard, and tests the main memory. Up to this stage, the machine does not access any mass storage media. Subsequently, the information about the current date, time, and the most important peripherals are loaded from the CMOS values. When the boot media and its geometry are recognized, the system control passes from the BIOS/UEFI to the boot loader.

On a machine equipped with a traditional BIOS, only code from the first physical 512-byte data sector (the Master Boot Record, MBR) of the boot disk can be loaded. Only a minimal GRUB 2 fits into the MBR. Its sole purpose is to load a GRUB 2 core image containing file system drivers from the gap between the MBR and the first partition (MBR partition table) or from the BIOS boot partition (GPT partition table). This image contains file system drivers and therefore is able to access /boot located on the root file system. /boot contains additional modules for GRUB 2 core as well as the kernel and the initramfs image. Once it has access to this partition, GRUB 2 loads the kernel and the initramfs image into memory and hands control over to the kernel.

When booting a BIOS system from an encrypted file system that includes an encrypted /boot partition, you need to enter the password for decryption twice. It is first needed by GRUB 2 to decrypt /boot and then for systemd to mount the encrypted volumes.

On machines with UEFI the boot process is much simpler than on machines with a traditional BIOS. The firmware is able to read from a FAT formatted system partition of disks with a GPT partition table. This EFI system-partition (in the running system mounted as /boot/efi) holds enough space to host a fully-fledged GRUB 2 which is directly loaded and executed by the firmware.

If the BIOS/UEFI supports network booting, it is also possible to configure a boot server that provides the boot loader. The system can then be booted via PXE. The BIOS/UEFI acts as the boot loader. It gets the boot image from the boot server and starts the system. This is completely independent of local hard disks.

12.2.1.2 Initialization and boot loader phase on IBM Z

  

On IBM Z the boot process must be initialized by a boot loader called zipl (z initial program load). Although zipl supports reading from various file systems, it does not support the SLE default file system (Btrfs) or booting from snapshots. SUSE Linux Enterprise Server therefore uses a two-stage boot process that ensures full Btrfs support at boot-time:

  1. zipl boots from the partition /boot/zipl, which can be formatted with the Ext2, Ext3, Ext4, or XFS file system. This partition contains a minimal kernel and an initramfs that are loaded into memory. The initramfs contains a Btrfs driver (among others) and the boot loader GRUB 2. The kernel is started with a parameter initgrub, which tells it to start GRUB 2.

  2. The kernel mounts the root file system, so /boot becomes accessible. Now GRUB 2 is started from the initramfs. It reads its configuration from /boot/grub2/grub.cfg and loads the final kernel and initramfs from /boot. The new kernel now gets loaded via Kexec.

12.2.2 The kernel phase

  

When the boot loader has passed on system control, the boot process is the same on all architectures. The boot loader loads both the kernel and an initial RAM-based file system (initramfs) into memory and the kernel takes over.

After the kernel has set up memory management and has detected the CPU type and its features, it initializes the hardware and mounts the temporary root file system from the memory that was loaded with the initramfs.

12.2.2.1 The initramfs file

  

initramfs (initial RAM file system) is a small cpio archive that the kernel can load into a RAM disk. It is located at /boot/initrd. It can be created with a tool called dracut—refer to man 8 dracut for details.

The initramfs provides a minimal Linux environment that enables the execution of programs before the actual root file system is mounted. This minimal Linux environment is loaded into memory by BIOS or UEFI routines and does not have specific hardware requirements other than sufficient memory. The initramfs archive must always provide an executable named init that executes the systemd daemon on the root file system for the boot process to proceed.

Before the root file system can be mounted and the operating system can be started, the kernel needs the corresponding drivers to access the device on which the root file system is located. These drivers may include special drivers for certain kinds of hard disks or even network drivers to access a network file system. The needed modules for the root file system are loaded by init on initramfs. After the modules are loaded, udev provides the initramfs with the needed devices. Later in the boot process, after changing the root file system, it is necessary to regenerate the devices. This is done by the systemd unit systemd-udev-trigger.service.

12.2.2.1.1 Regenerating the initramfs
  

Because the initramfs contains drivers, it needs to be updated whenever a new version of one of its drivers is available. This is done automatically when installing the package containing the driver update. YaST or zypper will inform you about this by showing the output of the command that generates the initramfs. However, there are some occasions when you need to regenerate an initramfs manually:

Adding drivers because of hardware changes

If you need to change hardware, for example, hard disks, and this hardware requires different drivers to be in the kernel at boot time, you must update the initramfs file.

Open or create /etc/dracut.conf.d/10-DRIVER.conf and add the following line (mind the leading whitespace): 

force_drivers+=" DRIVER1 "

Replace DRIVER1 with the module name of the driver. If you need to add more than one driver, list them space-separated: 

force_drivers+=" DRIVER1 DRIVER2 "

Proceed with Procedure 12.1, “Generate an initramfs”.

Moving system directories to a RAID or LVM

Whenever you move swap files, or system directories like /usr in a running system to a RAID or logical volume, you need to create 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”.

Adding disks to an LVM group or Btrfs RAID containing the root file system

Whenever you add (or remove) a disk to a logical volume group or a Btrfs RAID containing the root file system, you need to create an initramfs that contains support for the enlarged volume. Follow the instructions at Procedure 12.1, “Generate an initramfs”.

Proceed with Procedure 12.1, “Generate an initramfs”.

Changing kernel variables

If you change the values of kernel variables via the sysctl interface by editing related files (/etc/sysctl.conf or /etc/sysctl.d/*.conf), the change will be lost on the next system reboot. Even if you load the values 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”.

Adding or removing swap devices, re-creating swap area

Whenever you add or remove a swap device, or re-create a swap area with a different UUID, update the initramfs as outlined in Procedure 12.1, “Generate an initramfs”. You may also need to update GRUB_CMDLINE_* variables that include the resume= option in /etc/default/grub, and then regenerate /boot/grub2/grub.cfg as outlined in Section 14.2.1, “The file /boot/grub2/grub.cfg”.

Procedure 12.1: Generate an initramfs
  

Note that all commands in the following procedure need to be executed as the root user.

  1. Enter your /boot directory: 

    # cd /boot

  2. Generate a new initramfs file with dracut, replacing MY_INITRAMFS with a file name of your choice: 

    # dracut MY_INITRAMFS

    Alternatively, run dracut -f FILENAME to replace an existing init file.

  3. (Skip this step if you ran dracut -f in the previous step.) Create a symlink from the initramfs file you created in the previous step to initrd: 

    #  ln -sf MY_INITRAMFS initrd

  4. On the IBM IBM Z architecture, additionally run grub2-install.

12.2.3 The init on initramfs phase

  

The temporary root file system mounted by the kernel from the initramfs contains the executable systemd (which is called init on initramfs in the following, also see Section 12.1, “Terminology”. This program performs all actions needed to mount the proper root file system. It provides kernel functionality for the needed file system and device drivers for mass storage controllers with udev.

The main purpose of init on initramfs is to prepare the mounting of and access to the real root file system. Depending on your system configuration, init on initramfs is responsible for the following tasks.

Loading kernel modules

Depending on your hardware configuration, special drivers may be needed to access the hardware components of your computer (the most important component being your hard disk). To access the final root file system, the kernel needs to load the proper file system drivers.

Providing block special files

The kernel generates device events depending on loaded modules. udev handles these events and generates the required special block files on a RAM file system in /dev. Without those special files, the file system and other devices would not be accessible.

Managing RAID and LVM setups

If you configured your system to hold the root file system under RAID or LVM, init on initramfs sets up LVM or RAID to enable access to the root file system later.

Managing the network configuration

If you configured your system to use a network-mounted root file system (mounted via NFS), init must make sure that the proper network drivers are loaded and that they are set up to allow access to the root file system.

If the file system resides on a network block device like iSCSI or SAN, the connection to the storage server is also set up by init 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 15 “Mass storage over IP networks: iSCSI”, Section 15.3.1 “Using YaST for the iSCSI initiator configuration”.

Note
Note: Handling of mount failures

If the root file system fails to mount from within the boot environment, it must be checked and repaired before the boot can continue. The file system checker will be automatically started for Ext3 and Ext4 file systems. The repair process is not automated for XFS and Btrfs file systems, and the user is presented with information describing the options available to repair the file system. When the file system has been successfully repaired, exiting the boot environment will cause the system to retry mounting the root file system. If successful, the boot will continue normally.

12.2.3.1 The init on initramfs phase in the installation process

  

When init on initramfs is called during the initial boot as part of the installation process, its tasks differ from those mentioned above. Note that the installation system also does not start systemd from initramfs—these tasks are performed by linuxrc.

Finding the installation medium

When starting the installation process, your machine loads an installation kernel and a special init containing the YaST installer. The YaST installer is running in a RAM file system and needs to have information about the location of the installation medium to access it for installing the operating system.

Initiating hardware recognition and loading appropriate kernel modules

As mentioned in Section 12.2.2.1, “The initramfs file”, the boot process starts with a minimum set of drivers that can be used with most hardware configurations. On AArch64, POWER, and AMD64/Intel 64 machines, linuxrc starts an initial hardware scanning process that determines the set of drivers suitable for your hardware configuration. On IBM Z, a list of drivers and their parameters needs to be provided, for example via linuxrc or a parmfile.

These drivers are used to generate a custom initramfs that is needed to boot the system. If the modules are not needed for boot but for coldplug, the modules can be loaded with systemd; for more information, see Section 15.6.4, “Loading kernel modules”.

Loading the installation system

When the hardware is properly recognized, the appropriate drivers are loaded. The udev program creates the special device files and linuxrc starts the installation system with the YaST installer.

Starting YaST

Finally, linuxrc starts YaST, which starts the package installation and the system configuration.

12.2.4 The systemd phase

  

After the “real” root file system has been found, it is checked for errors and mounted. If this is successful, the initramfs is cleaned and the systemd daemon on the root file system is executed. systemd is Linux's system and service manager. It is the parent process that is started as PID 1 and acts as an init system which brings up and maintains user space services. See Chapter 15, The systemd daemon for details.

13 UEFI (Unified Extensible Firmware Interface)

  

UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.

UEFI is becoming more and more available on PC systems and thus is replacing the traditional PC-BIOS. UEFI, for example, properly supports 64-bit systems and offers secure booting (“Secure Boot”, firmware version 2.3.1c or better required), which is one of its most important features. Lastly, with UEFI a standard firmware will become available on all x86 platforms.

UEFI additionally offers the following advantages:

  • Booting from large disks (over 2 TiB) with a GUID Partition Table (GPT).

  • CPU-independent architecture and drivers.

  • Flexible pre-OS environment with network capabilities.

  • CSM (Compatibility Support Module) to support booting legacy operating systems via a PC-BIOS-like emulation.

For more information, see http://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface. The following sections are not meant as a general UEFI overview; these are only hints about how some features are implemented in SUSE Linux Enterprise Server.

13.1 Secure boot

  

In the world of UEFI, securing the bootstrapping process means establishing a chain of trust. The “platform” is the root of this chain of trust; in the context of SUSE Linux Enterprise Server, the mainboard and the on-board firmware could be considered the “platform”. In other words, it is the hardware vendor, and the chain of trust flows from that hardware vendor to the component manufacturers, the OS vendors, etc.

The trust is expressed via public key cryptography. The hardware vendor puts a so-called Platform Key (PK) into the firmware, representing the root of trust. The trust relationship with operating system vendors and others is documented by signing their keys with the Platform Key.

Finally, security is established by requiring that no code will be executed by the firmware unless it has been signed by one of these “trusted” keys—be it an OS boot loader, some driver located in the flash memory of some PCI Express card or on disk, or be it an update of the firmware itself.

To use Secure Boot, you need to have your OS loader signed with a key trusted by the firmware, and you need the OS loader to verify that the kernel it loads can be trusted.

Key Exchange Keys (KEK) can be added to the UEFI key database. This way, you can use other certificates, as long as they are signed with the private part of the PK.

13.1.1 Implementation on SUSE Linux Enterprise Server

  

Microsoft’s Key Exchange Key (KEK) is installed by default.

Note
Note: GUID partitioning table (GPT) required

The Secure Boot feature is enabled by default on UEFI/x86_64 installations. You can find the Enable Secure Boot Support option in the Boot Code Options tab of the Boot Loader Settings dialog. It supports booting when the secure boot is activated in the firmware, while making it possible to boot when it is deactivated.

Secure boot support
Figure 13.1: Secure boot support
  

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).

UEFI: secure boot process
Figure 13.2: UEFI: secure boot process
  

At the implementation layer, SUSE uses the shim loader which is installed by default. It is a smart solution that avoids legal issues, and simplifies the certification and signing step considerably. The shim loader’s job is to load a boot loader such as GRUB 2 and verify it; this boot loader in turn will load kernels signed by a SUSE key only. SUSE provides this functionality since SLE11 SP3 on fresh installations with UEFI Secure Boot enabled.

There are two types of trusted users:

  • First, those who hold the keys. The Platform Key (PK) allows almost everything. The Key Exchange Key (KEK) allows all a PK can except changing the PK.

  • Second, anyone with physical access to the machine. A user with physical access can reboot the machine, and configure UEFI.

UEFI offers two types of variables to fulfill the needs of those users:

  • The first is the so-called “Authenticated Variables”, which can be updated from both within the boot process (the so-called Boot Services Environment) and the running OS. This can be done only when the new value of the variable is signed with the same key that the old value of the variable was signed with. And they can only be appended to or changed to a value with a higher serial number.

  • The second is the so-called “Boot Services Only Variables”. These variables are accessible to any code that runs during the boot process. After the boot process ends and before the OS starts, the boot loader must call the ExitBootServices call. After that, these variables are no longer accessible, and the OS cannot touch them.

The various UEFI key lists are of the first type, as this allows online updating, adding, and blacklisting of keys, drivers, and firmware fingerprints. It is the second type of variable, the “Boot Services Only Variable”, that helps to implement Secure Boot in a secure and open source-friendly manner, and thus compatible with GPLv3.

SUSE starts with shim—a small and simple EFI boot loader signed by SUSE and Microsoft.

This allows shim to load and execute.

shim then goes on to verify that the boot loader it wants to load is trusted. In a default situation shim will use an independent SUSE certificate embedded in its body. In addition, shim will allow to “enroll” additional keys, overriding the default SUSE key. In the following, we call them “Machine Owner Keys” or MOKs for short.

Next the boot loader will verify and then boot the kernel, and the kernel will do the same on the modules.

13.1.2 MOK (Machine Owner Key)

  

To replace specific kernels, drivers, or other components that are part of the boot process, you have to use Machine Owner Keys (MOKs). The mokutil tool can help you to manage MOKs.

You can create a MOK enrollment request with mokutil. The request is stored in a UEFI runtime (RT) variable called MokNew. During the next boot, the shim bootloader detects MokNew and loads MokManager, which presents you with several options. You can use the Enroll key from disk and Enroll hash from disk options to add the key to the MokList. Use the Enroll MOK option to copy the key from the MokNew variable.

Enrolling a key from disk is usually done when the shim fails to load grub2 and falls back to loading MokManager. As MokNew does not exist yet, you have the option of locating the key on the UEFI partition.

13.1.3 Booting a custom kernel

  

The following is based on https://en.opensuse.org/openSUSE:UEFI#Booting_a_custom_kernel.

Secure Boot does not prevent you from using a self-compiled kernel. You must sign it with your own certificate and make that certificate known to the firmware or MOK.

  1. Create a custom X.509 key and certificate used for signing: 

    openssl req -new -x509 -newkey rsa:2048 -keyout key.asc \
  -out cert.pem -nodes -days 666 -subj "/CN=$USER/"

    For more information about creating certificates, see https://en.opensuse.org/openSUSE:UEFI_Image_File_Sign_Tools#Create_Your_Own_Certificate.

  2. Package the key and the certificate as a PKCS#12 structure: 

    > openssl pkcs12 -export -inkey key.asc -in cert.pem \
  -name kernel_cert -out cert.p12

  3. Generate an NSS database for use with pesign: 

    > certutil -d . -N

  4. Import the key and the certificate contained in PKCS#12 into the NSS database: 

    > pk12util -d . -i cert.p12

  5. “Bless” the kernel with the new signature using pesign: 

    > pesign -n . -c kernel_cert -i arch/x86/boot/bzImage \
  -o vmlinuz.signed -s

  6. List the signatures on the kernel image: 

    > pesign -n . -S -i vmlinuz.signed

    At that point, you can install the kernel in /boot as usual. Because the kernel now has a custom signature the certificate used for signing needs to be imported into the UEFI firmware or MOK.

  7. Convert the certificate to the DER format for import into the firmware or MOK: 

    > openssl x509 -in cert.pem -outform der -out cert.der

  8. Copy the certificate to the ESP for easier access: 

    > sudo cp cert.der /boot/efi/

  9. Use mokutil to launch the MOK list automatically.

      1. Import the certificate to MOK: 

        > mokutil --root-pw --import cert.der

        The --root-pw option enables usage of the root user directly.

      2. Check the list of certificates that are prepared to be enrolled: 

        > mokutil --list-new

      3. 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.

      4. Check if the newly imported key was enrolled: 

        > mokutil --list-enrolled

      1. Alternatively, this is the procedure if you want to launch MOK manually:

        Reboot

      2. In the GRUB 2 menu press the 'c' key.

      3. Type: 

        chainloader $efibootdir/MokManager.efi
boot

      4. Select Enroll key from disk.

      5. Navigate to the cert.der file and press Enter.

      6. Follow the instructions to enroll the key. Normally this should be pressing '0' and then 'y' to confirm.

        Alternatively, the firmware menu may provide ways to add a new key to the Signature Database.

13.1.4 Using non-inbox drivers

  

There is no support for adding non-inbox drivers (that is, drivers that do not come with SUSE Linux Enterprise Server) during installation with Secure Boot enabled. The signing key used for SolidDriver/PLDP is not trusted by default.

It is possible to install third party drivers during installation with Secure Boot enabled in two different ways. In both cases:

  • Add the needed keys to the firmware database via firmware/system management tools before the installation. This option depends on the specific hardware you are using. Consult your hardware vendor for more information.

  • Use a bootable driver ISO from https://drivers.suse.com/ or your hardware vendor to enroll the needed keys in the MOK list at first boot.

To use the bootable driver ISO to enroll the driver keys to the MOK list, follow these steps:

  1. Burn the ISO image above to an empty CD/DVD medium.

  2. 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.

  3. An initrd containing updated drivers will be used for installation.

For more information, see https://drivers.suse.com/doc/Usage/Secure_Boot_Certificate.html.

13.1.5 Features and limitations

  

When booting in Secure Boot mode, the following features apply:

  • Installation to UEFI default boot loader location, a mechanism to keep or restore the EFI boot entry.

  • Reboot via UEFI.

  • Xen hypervisor will boot with UEFI when there is no legacy BIOS to fall back to.

  • UEFI IPv6 PXE boot support.

  • UEFI videomode support, the kernel can retrieve video mode from UEFI to configure KMS mode with the same parameters.

  • UEFI booting from USB devices is supported.

  • Since SUSE Linux Enterprise Server 15 SP3, Kexec and Kdump are supported in Secure Boot mode.

When booting in Secure Boot mode, the following limitations apply:

  • To ensure that Secure Boot cannot be easily circumvented, some kernel features are disabled when running under Secure Boot.

  • Boot loader, kernel, and kernel modules must be signed.

  • Hibernation (suspend on disk) is disabled.

  • Access to /dev/kmem and /dev/mem is not possible, not even as root user.

  • Access to the I/O port is not possible, not even as root user. All X11 graphical drivers must use a kernel driver.

  • PCI BAR access through sysfs is not possible.

  • custom_method in ACPI is not available.

  • debugfs for asus-wmi module is not available.

  • the acpi_rsdp parameter does not have any effect on the kernel.

13.2 More information

  

14 The boot loader GRUB 2

  

This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring the most important settings. The boot procedure as a whole is outlined in Chapter 12, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 13, UEFI (Unified Extensible Firmware Interface).

14.1 Main differences between GRUB legacy and GRUB 2

  

  • The configuration is stored in different files.

  • More file systems are supported (for example, Btrfs).

  • Can directly read files stored on LVM or RAID devices.

  • The user interface can be translated and altered with themes.

  • Includes a mechanism for loading modules to support additional features, such as file systems, etc.

  • Automatically searches for and generates boot entries for other kernels and operating systems, such as Windows.

  • Includes a minimal Bash-like console.

14.2 Configuration file structure

  

The configuration of GRUB 2 is based on the following files:

/boot/grub2/grub.cfg

This file contains the configuration of the GRUB 2 menu items. It replaces menu.lst used in GRUB Legacy. grub.cfg should not be edited—it is automatically generated by the 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 12 SP2 these entries are also parsed when using grub-once.

/etc/default/grub

This file controls the user settings of GRUB 2 and normally includes additional environmental settings such as backgrounds and themes.

Scripts under /etc/grub.d/

The scripts in this directory are read during execution of the command grub2-mkconfig -o /boot/grub2/grub.cfg. Their instructions are integrated into the main configuration file /boot/grub/grub.cfg.

/etc/sysconfig/bootloader

This configuration file holds certain basic settings like the boot loader type and whether to enable UEFI Secure Boot support.

/boot/grub2/x86_64-efi, /boot/grub2/power-ieee1275, /boot/grub2/s390x

These configuration files contain architecture-specific options.

GRUB 2 can be controlled in various ways. Boot entries from an existing configuration can be selected from the graphical menu (splash screen). The configuration is loaded from the file /boot/grub2/grub.cfg which is compiled from other configuration files (see below). All GRUB 2 configuration files are considered system files, and you need root privileges to edit them.

Note
Note: Activating configuration changes

After having manually edited GRUB 2 configuration files, you need to run grub2-mkconfig -o /boot/grub2/grub.cfg to activate the changes. However, this is not necessary when changing the configuration with YaST, because YaST automatically runs this command.

14.2.1 The file /boot/grub2/grub.cfg

  

The graphical splash screen with the boot menu is based on the GRUB 2 configuration file /boot/grub2/grub.cfg, which contains information about all partitions or operating systems that can be booted by the menu.

Every time the system is booted, GRUB 2 loads the menu file directly from the file system. For this reason, GRUB 2 does not need to be re-installed after changes to the configuration file. grub.cfg is automatically rebuilt with kernel installations or removals.

grub.cfg is compiled from the file /etc/default/grub and scripts found in the /etc/grub.d/ directory when running the command grub2-mkconfig -o /boot/grub2/grub.cfg. Therefore you should never edit the file manually. Instead, edit the related source files or use the YaST Boot Loader module to modify the configuration as described in Section 14.3, “Configuring the boot loader with YaST”.

14.2.2 The file /etc/default/grub

  

More general options of GRUB 2 belong in this file, such as the time the menu is displayed, or the default OS to boot. To list all available options, see the output of the following command: 

> grep "export GRUB_DEFAULT" -A50 /usr/sbin/grub2-mkconfig | grep GRUB_

You can introduce custom variables and use them later in the scripts found in the /etc/grub.d directory.

After having edited /etc/default/grub, update the main configuration file with grub2-mkconfig -o /boot/grub2/grub.cfg.

Note
Note: Scope

All options specified in this file are general options that affect all boot entries. Options specific to a Xen hypervisor include the _XEN_ substring.

Important
Important: Escaping inner quotes

More complex options with spaces require quoting so that they are processed as one option. Such inner quotes need to be correctly escaped, for example: 

GRUB_CMDLINE_LINUX_XEN="debug loglevel=9 log_buf_len=5M \"ddebug_query=file drivers/xen/xen-acpi-processor.c +p\""
GRUB_DEFAULT

Sets the boot menu entry that is booted by default. Its value can be a numeric value, the complete name of a menu entry, or “saved”.

GRUB_DEFAULT=2 boots the third (counted from zero) boot menu entry.

GRUB_DEFAULT="2>0" boots the first submenu entry of the third top-level menu entry.

GRUB_DEFAULT="Example boot menu entry" boots the menu entry with the title “Example boot menu entry”.

GRUB_DEFAULT=saved boots the entry specified by 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 causes the menu to be displayed until you select the boot entry manually.

GRUB_CMDLINE_LINUX

Entries on this line are added at the end of the boot entries for normal and recovery modes. Use it to add kernel parameters to the boot entry.

GRUB_CMDLINE_LINUX_DEFAULT

Same as GRUB_CMDLINE_LINUX but the entries are appended in the normal mode only.

GRUB_CMDLINE_LINUX_RECOVERY

Same as GRUB_CMDLINE_LINUX but the entries are appended in the recovery mode only.

GRUB_CMDLINE_LINUX_XEN_REPLACE

This entry replaces the GRUB_CMDLINE_LINUX parameters for all Xen boot entries.

GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT

Same as GRUB_CMDLINE_LINUX_XEN_REPLACE but it only replaces parameters of GRUB_CMDLINE_LINUX_DEFAULT.

GRUB_CMDLINE_XEN

These entries are passed to the Xen hypervisor Xen menu entries for normal and recovery modes. For example: 

GRUB_CMDLINE_XEN="loglvl=all guest_loglvl=all"
Tip
Tip: Xen hypervisor options

Find a complete list of Xen hypervisor options in https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html

GRUB_CMDLINE_XEN_DEFAULT

Same as GRUB_CMDLINE_XEN but the entries are appended in the normal mode only.

GRUB_TERMINAL

Enables and specifies an input/output terminal device. Can be console (PC BIOS and EFI consoles), serial (serial terminal), ofconsole (Open Firmware console), or the 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. 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 is scaled to fit the screen.

GRUB_DISABLE_OS_PROBER

If this option is set to true, automatic searching for other operating systems is disabled. Only the kernel images in /boot/ and the options from your own scripts in /etc/grub.d/ are detected.

SUSE_BTRFS_SNAPSHOT_BOOTING

If this option is set to true, GRUB 2 can boot directly into Snapper snapshots. For more information, see Section 7.3, “System rollback by booting from snapshots”.

For a complete list of options, see the GNU GRUB manual.

14.2.3 Scripts in /etc/grub.d

  

The scripts in this directory are read during execution of the command grub2-mkconfig -o /boot/grub2/grub.cfg. Their instructions are incorporated into /boot/grub2/grub.cfg. The order of menu items in grub.cfg is determined by the order in which the files in this directory are run. Files with a leading numeral are executed first, beginning with the lowest number. 00_header is run before 10_linux, which would run before 40_custom. If files with alphabetic names are present, they are executed after the numerically named files. Only executable files generate output to grub.cfg during execution of grub2-mkconfig. By default all files in the /etc/grub.d directory are executable.

Tip
Tip: Persistent custom content in grub.cfg

Because /boot/grub2/grub.cfg is recompiled each time grub2-mkconfig is run, any custom content is lost. To insert your lines directly into /boot/grub2/grub.cfg without losing them after grub2-mkconfig is run, insert them between 

### BEGIN /etc/grub.d/90_persistent ###

and 

### END /etc/grub.d/90_persistent ###

The 90_persistent script ensures that such content is preserved.

A list of the most important scripts follows:

00_header

Sets environmental variables such as system file locations, display settings, themes and previously saved entries. It also imports preferences stored in the /etc/default/grub. Normally you do not need to make changes to this file.

10_linux

Identifies Linux kernels on the root device and creates relevant menu entries. This includes the associated recovery mode option if enabled. Only the latest kernel is displayed on the main menu page, with additional kernels included in a submenu.

30_os-prober

This script uses os-prober to search for Linux and other operating systems and places the results in the GRUB 2 menu. There are sections to identify specific other operating systems, such as Windows or macOS.

40_custom

This file provides a simple way to include custom boot entries into grub.cfg. Make sure that you do not change 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.

Tip
Tip: /boot/grub2/custom.cfg

If you create /boot/grub2/custom.cfg and fill it with content, it is automatically included into /boot/grub2/grub.cfg right after 40_custom at boot time.

14.2.4 Mapping between BIOS drives and Linux devices

  

In GRUB Legacy, the device.map configuration file was used to derive Linux device names from BIOS drive numbers. The mapping between BIOS drives and Linux devices cannot always be guessed correctly. For example, GRUB Legacy would get a wrong order if the boot sequence of IDE and SCSI drives is exchanged in the BIOS configuration.

GRUB 2 avoids this problem by using device ID strings (UUIDs) or file system labels when generating grub.cfg. GRUB 2 utilities create a temporary device map on the fly, which is normally sufficient, particularly for single-disk systems.

However, if you need to override the GRUB 2's automatic device mapping mechanism, create your custom mapping file /boot/grub2/device.map. The following example changes the mapping to make DISK 3 the boot disk. GRUB 2 partition numbers start with 1 and not with 0 as in GRUB 2 Legacy. 

(hd1)  /dev/disk-by-id/DISK3 ID
(hd2)  /dev/disk-by-id/DISK1 ID
(hd3)  /dev/disk-by-id/DISK2 ID

14.2.5 Editing menu entries during the boot procedure

  

Being able to directly edit menu entries is useful when the system does not boot anymore because of a faulty configuration. It can also be used to test new settings without altering the system configuration.

  1. In the graphical boot menu, select the entry you want to edit with the arrow keys.

  2. Press E to open the text-based editor.

  3. Use the arrow keys to move to the line you want to edit.

    GRUB 2 boot editor
    Figure 14.1: GRUB 2 boot editor
      

    Now you have two options:

    1. Add space-separated parameters to the end of the line starting with linux or linuxefi to edit the kernel parameters. A complete list of parameters is available at https://en.opensuse.org/Linuxrc.

    2. Or edit the general options to change, for example, the kernel version. The →| key suggests all possible completions.

  4. Press F10 to boot the system with the changes you made or press Esc to discard your edits and return to the GRUB 2 menu.

Changes made this way only apply to the current boot process and are not saved permanently.

Important
Important: Keyboard layout during the boot procedure

The US keyboard layout is the only one available when booting. See Book “Deployment Guide”, Chapter 12 “Troubleshooting”, Section 12.3 “Booting from installation media fails”, US keyboard layout.

Note
Note: Boot loader on the installation media

The Boot Loader of the installation media on systems with a traditional BIOS is still GRUB Legacy. To add boot parameters, select an entry and start typing. Additions you make to the installation boot entry are permanently saved in the installed system.

Note
Note: Editing GRUB 2 menu entries on IBM Z

Cursor movement and editing commands on IBM Z differ—see Section 14.4, “Differences in terminal usage on IBM Z” for details.

14.2.6 Setting a boot password

  

Even before the operating system is booted, GRUB 2 enables access to file systems. Users without root permissions can access files in your Linux system to which they have no access after the system is booted. To block this kind of access or to prevent users from booting certain menu entries, set a boot password.

Important
Important: Booting requires a 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 (Protect Boot Loader with Password ).

  1. Encrypt the password using grub2-mkpasswd-pbkdf2: 

    > sudo grub2-mkpasswd-pbkdf2
Password: ****
Reenter password: ****
PBKDF2 hash of your password is grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A...

  2. 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...

  3. To import the changes into the main configuration file, run: 

    > sudo grub2-mkconfig -o /boot/grub2/grub.cfg

After you reboot, GRUB 2 prompts you for a user name and a password when trying to boot a menu entry. Enter root and the password you typed during the grub2-mkpasswd-pbkdf2 command. If the credentials are correct, the system boots the selected boot entry.

For more information, see https://www.gnu.org/software/grub/manual/grub.html#Security.

14.2.7 Authorized access to boot menu entries

  

You can configure GRUB 2 to allow access to boot menu entries depending on the level of authorization. You can configure multiple user accounts protected with passwords and assign them access to different menu entries. To configure authorization in GRUB 2, follow these steps:

  1. Create and encrypt one password for each user account you want to use in GRUB 2. Use the grub2-mkpasswd-pbkdf2 command as described in Section 14.2.6, “Setting a boot password”.

  2. Delete the content of the /etc/grub.d/10_linux file and save it. This prevents outputting the default GRUB 2 menu entries.

  3. Edit the /boot/grub2/custom.cfg file and add custom menu entries manually. The following template is just an example, adjust it to better match your use case: 

    set superusers=admin
password admin ADMIN_PASSWORD
password maintainer MAINTAINER_PASSWORD

menuentry 'Operational mode' {
  insmod ext2
  set root=hd0,1
  echo 'Loading Linux ...'
  linux /boot/vmlinuz root=/dev/vda1 $GRUB_CMDLINE_LINUX_DEFAULT $GRUB_CMDLINE_LINUX mode=operation
  echo 'Loading Initrd ...'
  initrd /boot/initrd
}

menuentry 'Maintenance mode' --users maintainer {
  insmod ext2
  set root=hd0,1
  echo 'Loading Linux ...'
  linux /boot/vmlinuz root=/dev/vda1 $GRUB_CMDLINE_LINUX_DEFAULT $GRUB_CMDLINE_LINUX mode=maintenance
  echo 'Loading Initrd ...'
  initrd /boot/initrd
}

  4. Import the changes into the main configuration file: 

    > sudo grub2-mkconfig -o /boot/grub2/grub.cfg

In the above example:

  • The GRUB 2 menu has two entries, Operational mode and Maintenance mode.

  • If no user is specified, both boot menu entries are accessible, but no one can access GRUB 2 command line nor edit existing menu entries.

  • admin user can access GRUB 2 command line and edit existing menu entries.

  • maintenance user can select the recovery menu item.

14.3 Configuring the boot loader with YaST

  

The easiest way to configure general options of the boot loader in your SUSE Linux Enterprise Server system is to use the YaST module. In the YaST Control Center, select System › Boot Loader. The module shows the current boot loader configuration of your system and allows you to make changes.

Use the Boot Code Options 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.

Boot code options
Figure 14.2: Boot code options
  
Important
Important: EFI systems require GRUB2-EFI

If you have an EFI system you can only install GRUB2-EFI, otherwise your system is no longer bootable.

Important
Important: Reinstalling the boot loader

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 GRUB2 first and then immediately switch back to GRUB2-EFI.

Otherwise, the boot loader may only be partially reinstalled.

Note
Note: Custom boot loader

To use a boot loader other than the ones listed, select Do Not Install Any Boot Loader. Read the documentation of your boot loader carefully before choosing this option.

14.3.1 Boot loader location and boot code options

  

The default location of the boot loader depends on the partition setup and is either the Master Boot Record (MBR) or the boot sector of the / partition. To modify the location of the boot loader, follow these steps:

Procedure 14.1: Changing the boot loader location
  

  1. Select the Boot Code Options tab and then choose one of the following options for Boot Loader Location:

    Boot from Master Boot Record

    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.

    Boot from Root Partition

    This installs the boot loader in the boot sector of the / partition.

    Custom Root Partition

    Use this option to specify the location of the boot loader manually.

  2. Click OK to apply the changes.

Code options
Figure 14.3: Code options
  

The Boot Code Options tab includes the following additional options:

Set Active Flag in Partition Table for Boot Partition

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.

Write Generic Boot Code to MBR

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.

Enable Trusted Boot Support

Starts TrustedGRUB2, which supports trusted computing functionality (Trusted Platform Module (TPM)). For more information refer to https://github.com/Sirrix-AG/TrustedGRUB2.

The Protective MBR flag section includes the following options:

set

This is appropriate for traditional legacy BIOS booting.

remove

This is appropriate for UEFI booting.

do not change

This is usually the best choice if you have an already working system.

In most cases YaST defaults to the appropriate choice.

14.3.2 Adjusting the disk order

  

If your computer has more than one hard disk, you can specify the boot sequence of the disks. The first disk in the list is where GRUB 2 will be installed in the case of booting from MBR. It is the disk where SUSE Linux Enterprise Server is installed by default. The rest of the list is a hint for GRUB 2's device mapper (see Section 14.2.4, “Mapping between BIOS drives and Linux devices”).

Warning
Warning: Unbootable system

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.

Procedure 14.2: Setting the disk order
  

  1. Open the Boot Code Options tab.

  2. Click Edit Disk Boot Order.

  3. If more than one disk is listed, select a disk and click Up or Down to reorder the displayed disks.

  4. Click OK two times to save the changes.

14.3.3 Configuring advanced options

  

Advanced boot parameters can be configured via the Boot Loader Options tab.

14.3.3.1 Boot Loader Options tab

  
Boot loader options
Figure 14.4: Boot loader options
  
Boot Loader Time-Out

Change the value of Time-Out in Seconds by typing in a new value and clicking the appropriate arrow key with your mouse.

Probe Foreign OS

When selected, the boot loader searches for other systems like Windows or other Linux installations.

Hide Menu on Boot

Hides the boot menu and boots the default entry.

Adjusting the Default Boot 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.

Protect Boot Loader with Password

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 Protect Entry Modification Only. With this setting, anybody is allowed to select a boot entry and boot the system, whereas the password for the GRUB 2 root user is only required for modifying boot entries.

14.3.3.2 Kernel Parameters tab

  
Kernel parameters
Figure 14.5: Kernel parameters
  
Optional Kernel Command Line Parameter

Specify optional kernel parameters here to enable/disable system features, add drivers, etc.

CPU Mitigations

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:

Auto.  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.

Auto + No SMT.  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.

Off.  Disables all mitigations. Side-channel attacks against your CPU are possible, depending on the CPU model. This setting has no impact on performance.

Manual.  Does not set any mitigation level. Specify your CPU mitigations manually by using the kernel command line options.

Use Graphical Console

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 Console resolution. The graphical theme definition file can be specified with the Console theme file chooser. Only change this if you want to apply your own, custom-made theme.

Use Serial Console

If your machine is controlled via a serial console, activate this option and specify which COM port to use at which speed. See info grub or http://www.gnu.org/software/grub/manual/grub.html#Serial-terminal

14.4 Differences in terminal usage on IBM Z

  

On 3215 and 3270 terminals there are some differences and limitations on how to move the cursor and how to issue editing commands within GRUB 2.

14.4.1 Limitations

  
Interactivity

Interactivity is strongly limited. Typing often does not result in visual feedback. To see where the cursor is, type an underscore (_).

Note
Note: 3270 compared to 3215

The 3270 terminal is much better at displaying and refreshing screens than the 3215 terminal.

Cursor movement

“Traditional” cursor movement is not possible. Alt, Meta, Ctrl and the cursor keys do not work. To move the cursor, use the key combinations listed in Section 14.4.2, “Key combinations”.

Caret

The caret (^) is used as a control character. To type a literal ^ followed by a letter, type ^, ^, LETTER.

Enter

The Enter key does not work, use ^–J instead.

14.4.2 Key combinations

  

Common Substitutes:

^–J

engage (“Enter”)

^–L

abort, return to previous “state”

^–I

tab completion (in edit and shell mode)

Keys Available in Menu Mode:

^–A

first entry

^–E

last entry

^–P

previous entry

^–N

next entry

^–G

previous page

^–C

next page

^–F

boot selected entry or enter submenu (same as ^–J)

E

edit selected entry

C

enter GRUB-Shell

Keys Available in Edit Mode:

^–P

previous line

^–N

next line

^–B

backward char

^–F

forward char

^–A

beginning of line

^–E

end of line

^–H

backspace

^–D

delete

^–K

kill line

^–Y

yank

^–O

open line

^–L

refresh screen

^–X

boot entry

^–C

enter GRUB-Shell

Keys Available in Command Line Mode:

^–P

previous command

^–N

next command from history

^–A

beginning of line

^–E

end of line

^–B

backward char

^–F

forward char

^–H

backspace

^–D

delete

^–K

kill line

^–U

discard line

^–Y

yank

14.5 Helpful GRUB 2 commands

  
grub2-mkconfig

Generates a new /boot/grub2/grub.cfg based on /etc/default/grub and the scripts from /etc/grub.d/.

Example 14.1: Usage of grub2-mkconfig
  
grub2-mkconfig -o /boot/grub2/grub.cfg
Tip
Tip: Syntax check

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.

Important
Important: grub2-mkconfig cannot repair UEFI Secure Boot tables

If you are using UEFI Secure Boot and your system is not reaching GRUB 2 correctly anymore, you may need to additionally reinstall the Shim and regenerate the UEFI boot table. To do so, use: 

# shim-install --config-file=/boot/grub2/grub.cfg
grub2-mkrescue

Creates a bootable rescue image of your installed GRUB 2 configuration.

Example 14.2: Usage of grub2-mkrescue
  
grub2-mkrescue -o save_path/name.iso iso
grub2-script-check

Checks the given file for syntax errors.

Example 14.3: Usage of grub2-script-check
  
grub2-script-check /boot/grub2/grub.cfg
grub2-once

Set the default boot entry for the next boot only. To get the list of available boot entries use the --list option.

Example 14.4: Usage of grub2-once
  
grub2-once number_of_the_boot_entry
Tip
Tip: grub2-once help

Call the program without any option to get a full list of all possible options.

14.6 Rescue mode

  

Rescue mode is a specific root user session for troubleshooting and repairing systems where the booting process fails. It offers a single-user environment with local file systems and core system services active. Network interfaces are not activated. To enter the rescue mode, follow these steps.

Procedure 14.3: Entering rescue mode
  

  1. Reboot the system. The boot screen appears, offering the GRUB 2 boot menu.

  2. Select the menu entry to boot and press e to edit the boot line.

  3. Append the following parameter to the line containing the kernel parameters: 

    systemd.unit=rescue.target

  4. Press Ctrl+X to boot with these settings.

  5. Enter the password for root.

  6. Make all the necessary changes.

  7. Enter normal operating target again by entering systemctl isolate multi-user.target or systemctl isolate graphical.target at the command line.

14.7 More information

  

Extensive information about GRUB 2 is available at https://www.gnu.org/software/grub/. Also refer to the grub info page. You can also search for the keyword “GRUB 2” in the Technical Information Search at https://www.suse.com/support to get information about special issues.

15 The systemd daemon

  

systemd initializes the system. It has the process ID 1. systemd is started directly by the kernel and resists signal 9, which normally terminates processes. All other programs are started directly by systemd or by one of its child processes. systemd is a replacement for the System V init daemon and is fully compatible with System V init (by supporting init scripts).

The main advantage of systemd is that it considerably speeds up boot time by parallelizing service starts. Furthermore, systemd only starts a service when it is really needed. Daemons are not started unconditionally at boot time, but when being required for the first time. systemd also supports Kernel Control Groups (cgroups), creating snapshots, and restoring the system state. For more details see http://www.freedesktop.org/wiki/Software/systemd/.

15.1 The systemd concept

  

The following section explains the concept behind systemd.

systemd is a system and session manager for Linux, compatible with System V and LSB init scripts. The main features of systemd include:

  • parallelization capabilities

  • socket and D-Bus activation for starting services

  • on-demand starting of daemons

  • tracking of processes using Linux cgroups

  • creating snapshots and restoring of the system state

  • maintains mount and automount points

  • implements an elaborate transactional dependency-based service control logic

15.1.1 Unit file

  

A unit configuration file contains information about a service, a socket, a device, a mount point, an automount point, a swap file or partition, a start-up target, a watched file system path, a timer controlled and supervised by systemd, a temporary system state snapshot, a resource management slice or a group of externally created processes.

“Unit file” is a generic term used by systemd for the following:

  • Service.  Information about a process (for example, running a daemon); file ends with .service

  • Targets.  Used for grouping units and as synchronization points during start-up; file ends with .target

  • Sockets.  Information about an IPC or network socket or a file system FIFO, for socket-based activation (like inetd); file ends with .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.  Normally auto-generated by the fstab generator; file ends with .mount

  • Automount point.  Information about a file system automount point; file ends with .automount

  • Swap.  Information about a swap device or file for memory paging; file ends with .swap

  • Device.  Information about a device unit as exposed in the sysfs/udev(7) device tree; file ends with .device

  • Scope / slice.  A concept for hierarchically managing resources of a group of processes; file ends with .scope/.slice

For more information about systemd unit files, see http://www.freedesktop.org/software/systemd/man/systemd.unit.html

15.2 Basic usage

  

The System V init system uses several commands to handle services—the init scripts, insserv, telinit and others. systemd makes it easier to manage services, because there is only one command to handle most service related tasks: systemctl. It uses the “command plus subcommand” notation like git or zypper: 

systemctl GENERAL OPTIONS SUBCOMMAND SUBCOMMAND OPTIONS

See man 1 systemctl for a complete manual.

Tip
Tip: Terminal output and Bash completion

If the output goes to a terminal (and not to a pipe or a file, for example), systemd commands send long output to a pager by default. Use the --no-pager option to turn off paging mode.

systemd also supports bash-completion, allowing you to enter the first letters of a subcommand and then press →|. This feature is only available in the bash shell and requires the installation of the package bash-completion.

15.2.1 Managing services in a running system

  

Subcommands for managing services are the same as for managing a service with System V init (start, stop, ...). The general syntax for service management commands is as follows:

systemd
systemctl reload|restart|start|status|stop|... MY_SERVICE(S)
System V init
rcMY_SERVICE(S) reload|restart|start|status|stop|...

systemd allows you to manage several services in one go. Instead of executing init scripts one after the other as with System V init, execute a command like the following: 

> sudo systemctl start MY_1ST_SERVICE MY_2ND_SERVICE

To list all services available on the system: 

> sudo systemctl list-unit-files --type=service

The following table lists the most important service management commands for systemd and System V init:

Table 15.1: Service management commands
  

Task

systemd Command

System V init Command

Starting. 

 
start
 
start

Stopping. 

 
stop
 
stop

Restarting.  Shuts down services and starts them afterward. If a service is not yet running, it is started. 

restart
 
restart

Restarting conditionally.  Restarts services if they are currently running. Does nothing for services that are not running. 

try-restart
 
try-restart

Reloading.  Tells services to reload their configuration files without interrupting operation. Use case: Tell Apache to reload a modified httpd.conf configuration file. Note that not all services support reloading. 

reload
 
reload

Reloading or restarting.  Reloads services if reloading is supported, otherwise restarts them. If a service is not yet running, it is started. 

reload-or-restart
 
n/a

Reloading or restarting conditionally.  Reloads services if reloading is supported, otherwise restarts them if currently running. Does nothing for services that are not running. 

reload-or-try-restart
 
n/a

Getting detailed status information.  Lists information about the status of services. The systemd command shows details such as description, executable, status, cgroup, and messages last issued by a service (see Section 15.6.9, “Debugging services”). The level of details displayed with the System V init differs from service to service. 

status
 
status

Getting short status information.  Shows whether services are active or not. 

is-active
 
status

15.2.2 Permanently enabling/disabling services

  

The service management commands mentioned in the previous section let you manipulate services for the current session. systemd also lets you permanently enable or disable services, so they are automatically started when requested or are always unavailable. You can either do this by using YaST, or on the command line.

15.2.2.1 Enabling/disabling services on the command line

  

The following table lists enabling and disabling commands for systemd and System V init:

Important
Important: Service start

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.

Table 15.2: Commands for enabling and disabling services
  

Task

systemd Command

System V init Command

Enabling. 

systemctl enable MY_SERVICE(S)

insserv MY_SERVICE(S), chkconfig -a MY_SERVICE(S)

Disabling. 

systemctl disable MY_SERVICE(S).service

insserv -r MY_SERVICE(S), chkconfig -d MY_SERVICE(S)

Checking.  Shows whether a service is enabled or not.

systemctl is-enabled MY_SERVICE

chkconfig MY_SERVICE

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.

systemctl reenable MY_SERVICE

n/a

Masking.  After “disabling” a service, it can still be started manually. To disable a service, you need to mask it. Use with care.

systemctl mask MY_SERVICE

n/a

Unmasking.  A service that has been masked can only be used again after it has been unmasked.

systemctl unmask MY_SERVICE

n/a

15.3 System start and target management

  

The entire process of starting the system and shutting it down is maintained by systemd. From this point of view, the kernel can be considered a background process to maintain all other processes and adjust CPU time and hardware access according to requests from other programs.

15.3.1 Targets compared to runlevels

  

With System V init the system was booted into a so-called “Runlevel”. A runlevel defines how the system is started and what services are available in the running system. Runlevels are numbered; the most commonly known ones are 0 (shutting down the system), 3 (multiuser with network) and 5 (multiuser with network and display manager).

systemd introduces a new concept by using so-called “target units”. However, it remains fully compatible with the runlevel concept. Target units are named rather than numbered and serve specific purposes. For example, the targets local-fs.target and swap.target mount local file systems and swap spaces.

The target graphical.target provides a multiuser system with network and display manager capabilities and is equivalent to runlevel 5. Complex targets, such as graphical.target act as “meta” targets by combining a subset of other targets. Since systemd makes it easy to create custom targets by combining existing targets, it offers great flexibility.

The following list shows the most important systemd target units. For a full list refer to man 7 systemd.special.

Selected systemd target units
  
default.target

The target that is booted by default. Not a “real” target, but rather a symbolic link to another target like graphic.target. Can be permanently changed via YaST (see Section 15.4, “Managing services with YaST”). To change it for a session, use the kernel parameter systemd.unit=MY_TARGET.target at the boot prompt.

emergency.target

Starts a minimal emergency root shell on the console. Only use it at the boot prompt 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 root session without network. Basic tools for system administration are available. The rescue target is suitable for solving multiple system problems, for example, failing logins or fixing issues with a display driver.

To remain compatible with the System V init runlevel system, systemd provides special targets named runlevelX.target mapping the corresponding runlevels numbered X.

To inspect the current target, use the command: systemctl get-default

Table 15.3: System V runlevels and systemd target units
  

System V runlevel

systemd target

Purpose

0

runlevel0.target, halt.target, poweroff.target

System shutdown

1, S

runlevel1.target, rescue.target,

Single-user mode

2

runlevel2.target, multi-user.target,

Local multiuser without remote network

3

runlevel3.target, multi-user.target,

Full multiuser with network

4

runlevel4.target

Unused/User-defined

5

runlevel5.target, graphical.target,

Full multiuser with network and display manager

6

runlevel6.target, reboot.target,

System reboot

Important
Important: systemd ignores /etc/inittab

The runlevels in a System V init system are configured in /etc/inittab. systemd does not use this configuration. Refer to Section 15.5.5, “Creating custom targets” for instructions on how to create your own bootable target.

15.3.1.1 Commands to change targets

  

Use the following commands to operate with target units:

Task

systemd Command

System V init Command

Change the current target/runlevel

systemctl isolate MY_TARGET.target

telinit X

Change to the default target/runlevel

systemctl default

n/a

Get the current target/runlevel

systemctl list-units --type=target

With systemd, there is usually more than one active target. The command lists all currently active targets.

who -r

or

runlevel

persistently change the default runlevel

Use the Services Manager or run the following command:

ln -sf /usr/lib/systemd/system/ MY_TARGET.target /etc/systemd/system/default.target

Use the Services Manager or change the line

id: X:initdefault:

in /etc/inittab

Change the default runlevel for the current boot process

Enter the following option at the boot prompt

systemd.unit= MY_TARGET.target

Enter the desired runlevel number at the boot prompt.

Show a target's/runlevel's dependencies

systemctl show -p "Requires" MY_TARGET.target

systemctl show -p "Wants" MY_TARGET.target

“Requires” lists the hard dependencies (the ones that must be resolved), whereas “Wants” lists the soft dependencies (the ones that get resolved if possible).

n/a

15.3.2 Debugging system start-up

  

systemd offers the means to analyze the system start-up process. You can review the list of all services and their status (rather than having to parse /var/log/). systemd also allows you to scan the start-up procedure to find out how much time each service start-up consumes.

15.3.2.1 Review start-up of services

  

To review the complete list of services that have been started since booting the system, enter the command systemctl. It lists all active services like shown below (shortened). To get more information on a specific service, use systemctl status MY_SERVICE.

Example 15.1: List active services
  
# 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:

Example 15.2: List failed services
  
# systemctl --failed
UNIT                   LOAD   ACTIVE SUB    JOB DESCRIPTION
apache2.service        loaded failed failed     apache
NetworkManager.service loaded failed failed     Network Manager
plymouth-start.service loaded failed failed     Show Plymouth Boot Screen

[...]

15.3.2.2 Debug start-up time

  

To debug system start-up time, systemd offers the systemd-analyze command. It shows the total start-up time, a list of services ordered by start-up time and can also generate an SVG graphic showing the time services took to start in relation to the other services.

Listing the system start-up time
# systemd-analyze
Startup finished in 2666ms (kernel) + 21961ms (userspace) = 24628ms
Listing the services start-up time
# systemd-analyze blame
    15.000s backup-rpmdb.service
    14.879s mandb.service
     7.646s backup-sysconfig.service
     4.940s postfix.service
     4.921s logrotate.service
     4.640s libvirtd.service
     4.519s display-manager.service
     3.921s btrfsmaintenance-refresh.service
     3.466s lvm2-monitor.service
     2.774s plymouth-quit-wait.service
     2.591s firewalld.service
     2.137s initrd-switch-root.service
     1.954s ModemManager.service
     1.528s rsyslog.service
     1.378s apparmor.service
    [...]
Services start-up time graphics
# systemd-analyze plot > jupiter.example.com-startup.svg
systemd startup

15.3.2.3 Review the complete start-up process

  

The commands above list the services that are started and their start-up times. For a more detailed overview, specify the following parameters at the boot prompt to instruct systemd to create a verbose log of the complete start-up procedure. 

systemd.log_level=debug systemd.log_target=kmsg

Now systemd writes its log messages into the kernel ring buffer. View that buffer with dmesg: 

> dmesg -T | less

15.3.3 System V compatibility

  

systemd is compatible with System V, allowing you to still use existing System V init scripts. However, there is at least one known issue where a System V init script does not work with systemd out of the box: starting a service as a different user via su or sudo in init scripts will result in a failure of the script, producing an “Access denied” error.

When changing the user with su or sudo, a PAM session is started. This session will be terminated after the init script is finished. As a consequence, the service that has been started by the init script will also be terminated. To work around this error, proceed as follows:

  1. 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.

    1

    Optional—only use if the init script starts a daemon.

    2

    multi-user.target also starts the init script when booting into graphical.target. If it should only be started when booting into the display manager, use graphical.target.

  2. Start the daemon with systemctl start APPLICATION.

15.4 Managing services with YaST

  

Basic service management can also be done with the YaST Services Manager module. It supports starting, stopping, enabling and disabling services. It also lets you show a service's status and change the default target. Start the YaST module with YaST › System › Services Manager.

Services Manager
Figure 15.1: Services Manager
  
Changing the Default system target

To change the target the system boots into, choose a target from the Default System Target drop-down box. The most often used targets are Graphical Interface (starting a graphical login screen) and Multi-User (starting the system in command line mode).

Starting or stopping a service

Select a service from the table. The State column shows whether it is currently running (Active) or not (Inactive). Toggle its status by choosing Start or Stop.

Starting or stopping a service changes its status for the currently running session. To change its status throughout a reboot, you need to enable or disable it.

Defining service start-up behavior

Services can either be started automatically at boot time or manually. Select a service from the table. The Start column shows whether it is currently started Manually or On Boot. Toggle its status by choosing Start Mode.

To change a service status in the current session, you need to start or stop it as described above.

View a status messages

To view the status message of a service, select it from the list and choose Show Details. The output is identical to the one generated by the command systemctl -l status MY_SERVICE.

15.5 Customizing systemd

  

The following sections describe how to customize systemd unit files.

15.5.1 Where are unit files stored?

  

systemd unit files shipped by SUSE are stored in /usr/lib/systemd/. Customized unit files and unit file drop-ins are stored in /etc/systemd/.

Warning
Warning: Preventing your customization from being overwritten

When customizing systemd, always use the directory /etc/systemd/ instead of /usr/lib/systemd/. Otherwise your changes will be overwritten by the next update of systemd.

15.5.2 Override with drop-in files

  

Drop-in files (or drop-ins) are partial unit files that override only specific settings of the unit file. Drop-ins have higher precedence over main configuration files. The command systemctl edit SERVICE starts the default text editor and creates a directory with an empty override.conf file in /etc/systemd/system/NAME.service.d/. The command also ensures that the running systemd process is notified about the changes.

For example, to change the amount of time that the system waits for MariaDB to start, run sudo systemctl edit mariadb.service and edit the opened file to include the modified lines only: 

# Configures the time to wait for start-up/stop
TimeoutSec=300

Adjust the TimeoutSec value and save the changes. To enable the changes, run sudo systemctl daemon-reload.

For further information, refer to the man pages that can be evoked with the man 1 systemctl command.

Warning
Warning: Creating a copy of a full unit file

If you use the --full option in the systemctl edit --full SERVICE command, a copy of the original unit file is created where you can modify specific options. We do not recommend such customization because when the unit file is updated by SUSE, its changes are overridden by the customized copy in the /etc/systemd/system/ directory. Moreover, if SUSE provides updates to distribution drop-ins, they will override the copy of the unit file created with --full. To prevent this confusion and always have your customization valid, use drop-ins.

15.5.3 Creating drop-in files manually

  

Apart from using the systemctl edit command, you can create drop-ins manually to have more control over their priority. Such drop-ins let you extend both unit and daemon configuration files without having to edit or override the files themselves. They are stored in the following directories:

/etc/systemd/*.conf.d/, /etc/systemd/system/*.service.d/

Drop-ins added and customized by system administrators.

/usr/lib/systemd/*.conf.d/, /usr/lib/systemd/system/*.service.d/

Drop-ins installed by customization packages to override upstream settings. For example, SUSE ships systemd-default-settings.

Tip
Tip

See the man page man 5 systemd.unit for the full list of unit search paths.

For example, to disable the rate limiting that is enforced by the default setting of systemd-journald, follow these steps:

  1. Create a directory called /etc/systemd/journald.conf.d. 

    > sudo mkdir /etc/systemd/journald.conf.d
    Note
    Note

    The directory name must follow the service name that you want to patch with the drop-in file.

  2. In that directory, create a file /etc/systemd/journald.conf.d/60-rate-limit.conf with the option that you want to override, for example: 

    > cat /etc/systemd/journald.conf.d/60-rate-limit.conf
# Disable rate limiting
RateLimitIntervalSec=0

  3. Save your changes and restart the service of the corresponding systemd daemon. 

    > sudo systemctl restart systemd-journald
Note
Note: Avoiding name conflicts

To avoid name conflicts between your drop-ins and files shipped by SUSE, it is recommended to prefix all drop-ins with a two-digit number and a dash, for example, 80-override.conf.

The following ranges are reserved:

  • 0-19 is reserved for systemd upstream.

  • 20-29 is reserved for systemd shipped by SUSE.

  • 30-39 is reserved for SUSE packages other than systemd.

  • 40-49 is reserved for third party packages.

  • 50 is reserved for unit drop-in files created with systemctl set-property.

Use a two-digit number above this range to ensure that none of the drop-ins shipped by SUSE can override your own drop-ins.

Tip
Tip

You can use systemctl cat $UNIT to list and verify which files are taken into account in the units configuration.

Tip
Tip

Because the configuration of systemd components can be scattered across different places on the file system, it might be hard to get a global overview. To inspect the configuration of a systemd component, use the following commands:

  • systemctl cat UNIT_PATTERN prints configuration files related to one or more systemd units, for example: 

    > systemctl cat atd.service

  • systemd-analyze cat-config DAEMON_NAME_OR_PATH copies the contents of a configuration file and drop-ins for a systemd daemon, for example: 

    > systemd-analyze cat-config systemd/journald.conf

15.5.4 Converting xinetd services to systemd

  

Since the release of SUSE Linux Enterprise Server 15, the xinetd infrastructure has been removed. This section outlines how to convert existing custom xinetd service files to systemd sockets.

For each xinetd service file, you need at least two systemd unit files: the socket file (*.socket) and an associated service file (*.service). The socket file tells systemd which socket to create, and the service file tells systemd which executable to start.

Consider the following example xinetd service file: 

# cat /etc/xinetd.d/example
service example
{
  socket_type = stream
  protocol = tcp
  port = 10085
  wait = no
  user = user
  group = users
  groups = yes
  server = /usr/libexec/example/exampled
  server_args = -auth=bsdtcp exampledump
  disable = no
}

To convert it to systemd, you need the following two matching files: 

# cat /usr/lib/systemd/system/example.socket
[Socket]
ListenStream=0.0.0.0:10085
Accept=false

[Install]
WantedBy=sockets.target
# cat /usr/lib/systemd/system/example.service
[Unit]
Description=example

[Service]
ExecStart=/usr/libexec/example/exampled -auth=bsdtcp exampledump
User=user
Group=users
StandardInput=socket

For a complete list of the systemd 'socket' and 'service' file options, refer to the systemd.socket and systemd.service manual pages (man 5 systemd.socket, man 5 systemd.service).

15.5.5 Creating custom targets

  

On System V init SUSE systems, runlevel 4 is unused to allow administrators to create their own runlevel configuration. systemd allows you to create any number of custom targets. It is suggested to start by adapting an existing target such as graphical.target.

  1. Copy the configuration file /usr/lib/systemd/system/graphical.target to /etc/systemd/system/MY_TARGET.target and adjust it according to your needs.

  2. 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.

  3. For each wanted service, create a symbolic link from /usr/lib/systemd/system into /etc/systemd/system/MY_TARGET.target.wants.

  4. When you have finished setting up the target, reload the systemd configuration to make the new target available: 

    > sudo systemctl daemon-reload

15.6 Advanced usage

  

The following sections cover advanced topics for system administrators. For even more advanced systemd documentation, refer to Lennart Pöttering's series about systemd for administrators at http://0pointer.de/blog/projects.

15.6.1 Cleaning temporary directories

  

systemd supports cleaning temporary directories regularly. The configuration from the previous system version is automatically migrated and active. tmpfiles.d—which is responsible for managing temporary files—reads its configuration from /etc/tmpfiles.d/*.conf, /run/tmpfiles.d/*.conf, and /usr/lib/tmpfiles.d/*.conf files. Configuration placed in /etc/tmpfiles.d/*.conf overrides related configurations from the other two directories (/usr/lib/tmpfiles.d/*.conf is where packages store their configuration files).

The configuration format is one line per path containing action and path, and optionally mode, ownership, age and argument fields, depending on the action. The following example unlinks the X11 lock files: 

Type Path               Mode UID  GID  Age Argument
r    /tmp/.X[0-9]*-lock

To get the status the tmpfile timer: 

> sudo systemctl status systemd-tmpfiles-clean.timer
systemd-tmpfiles-clean.timer - Daily Cleanup of Temporary Directories
 Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-clean.timer; static)
 Active: active (waiting) since Tue 2018-04-09 15:30:36 CEST; 1 weeks 6 days ago
   Docs: man:tmpfiles.d(5)
         man:systemd-tmpfiles(8)

Apr 09 15:30:36 jupiter systemd[1]: Starting Daily Cleanup of Temporary Directories.
Apr 09 15:30:36 jupiter systemd[1]: Started Daily Cleanup of Temporary Directories.

For more information on temporary files handling, see man 5 tmpfiles.d.

15.6.2 System log

  

Section 15.6.9, “Debugging services” explains how to view log messages for a given service. However, displaying log messages is not restricted to service logs. You can also access and query the complete log messages written by systemd—the so-called “Journal”. Use the command journalctl to display the complete log messages starting with the oldest entries. Refer to man 1 journalctl for options such as applying filters or changing the output format.

15.6.3 Snapshots

  

You can save the current state of systemd to a named snapshot and later revert to it with the isolate subcommand. This is useful when testing services or custom targets, because it allows you to return to a defined state at any time. A snapshot is only available in the current session and will automatically be deleted on reboot. A snapshot name must end in .snapshot.

Create a snapshot
> sudo systemctl snapshot MY_SNAPSHOT.snapshot
Delete a snapshot
> sudo systemctl delete MY_SNAPSHOT.snapshot
View a snapshot
> sudo systemctl show MY_SNAPSHOT.snapshot
Activate a snapshot
> sudo systemctl isolate MY_SNAPSHOT.snapshot

15.6.4 Loading kernel modules

  

With systemd, kernel modules can automatically be loaded at boot time via a configuration file in /etc/modules-load.d. The file should be named MODULE.conf and have the following content: 

# load module MODULE at boot time
MODULE

In case a package installs a configuration file for loading a kernel module, the file gets installed to /usr/lib/modules-load.d. If two configuration files with the same name exist, the one in /etc/modules-load.d tales precedence.

For more information, see the modules-load.d(5) man page.

15.6.5 Performing actions before loading a service

  

With System V init actions that need to be performed before loading a service, needed to be specified in /etc/init.d/before.local . This procedure is no longer supported with systemd. If you need to do actions before starting services, do the following:

Loading kernel modules

Create a drop-in file in /etc/modules-load.d directory (see man modules-load.d for the syntax)

Creating Files or Directories, Cleaning-up Directories, Changing Ownership

Create a drop-in file in /etc/tmpfiles.d (see man tmpfiles.d for the syntax)

Other tasks

Create a system service file, for example, /etc/systemd/system/before.service, from the following template: 

[Unit]
Before=NAME OF THE SERVICE YOU WANT THIS SERVICE TO BE STARTED BEFORE
[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=YOUR_COMMAND
# beware, executable is run directly, not through a shell, check the man pages
# systemd.service and systemd.unit for full syntax
[Install]
# target in which to start the service
WantedBy=multi-user.target
#WantedBy=graphical.target

When the service file is created, you should run the following commands (as root): 

> sudo systemctl daemon-reload
> sudo systemctl enable before

Every time you modify the service file, you need to run: 

> sudo systemctl daemon-reload

15.6.6 Kernel control groups (cgroups)

  

On a traditional System V init system, it is not always possible to match a process to the service that spawned it. Some services, such as Apache, spawn a lot of third-party processes (for example, CGI or Java processes), which themselves spawn more processes. This makes a clear assignment difficult or even impossible. Additionally, a service may not finish correctly, leaving certain children alive.

systemd solves this problem by placing each service into its own cgroup. cgroups are a kernel feature that allows aggregating processes and all their children into hierarchical organized groups. systemd names each cgroup after its service. Since a non-privileged process is not allowed to “leave” its cgroup, this provides an effective way to label all processes spawned by a service with the name of the service.

To list all processes belonging to a service, use the command systemd-cgls, for example:

Example 15.3: List all processes belonging to a service
  
# systemd-cgls --no-pager
├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 20
├─user.slice
│ └─user-1000.slice
│   ├─session-102.scope
│   │ ├─12426 gdm-session-worker [pam/gdm-password]
│   │ ├─15831 gdm-session-worker [pam/gdm-password]
│   │ ├─15839 gdm-session-worker [pam/gdm-password]
│   │ ├─15858 /usr/lib/gnome-terminal-server

[...]

└─system.slice
  ├─systemd-hostnamed.service
  │ └─17616 /usr/lib/systemd/systemd-hostnamed
  ├─cron.service
  │ └─1689 /usr/sbin/cron -n
  ├─postfix.service
  │ ├─ 1676 /usr/lib/postfix/master -w
  │ ├─ 1679 qmgr -l -t fifo -u
  │ └─15590 pickup -l -t fifo -u
  ├─sshd.service
  │ └─1436 /usr/sbin/sshd -D

[...]

See Book “System Analysis and Tuning Guide”, Chapter 10 “Kernel control groups” for more information about cgroups.

15.6.7 Terminating services (sending signals)

  

As explained in Section 15.6.6, “Kernel control groups (cgroups)”, it is not always possible to assign a process to its parent service process in a System V init system. This makes it difficult to terminate a service and all of its children. Child processes that have not been terminated will remain as zombie processes.

systemd's concept of confining each service into a cgroup makes it possible to clearly identify all child processes of a service and therefore allows you to send a signal to each of these processes. Use systemctl kill to send signals to services. For a list of available signals refer to man 7 signals.

Sending SIGTERM to a service

SIGTERM is the default signal that is sent. 

> sudo systemctl kill MY_SERVICE
Sending SIGNAL to a service

Use the -s option to specify the signal that should be sent. 

> sudo systemctl kill -s SIGNAL MY_SERVICE
Selecting processes

By default the kill command sends the signal 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: 

> sudo systemctl kill -s SIGHUP --kill-who=main MY_SERVICE

15.6.8 Important notes on the D-Bus service

  

The D-Bus service is the message bus for communication between systemd clients and the systemd manager that is running as pid 1. Even though dbus is a stand-alone daemon, it is an integral part of the init infrastructure.

Stopping dbus or restarting it in the running system is similar to an attempt to stop or restart PID 1. It breaks the systemd client/server communication and makes most systemd functions unusable.

Therefore, terminating or restarting dbus is neither recommended nor supported.

Updating the dbus or dbus-related packages requires a reboot. When in doubt whether a reboot is necessary, run the sudo zypper ps -s. If dbus appears among the listed services, you need to reboot the system.

Keep in mind that dbus is updated even when automatic updates are configured to skip the packages that require reboot.

15.6.9 Debugging services

  

By default, systemd is not overly verbose. If a service was started successfully, no output is produced. In case of a failure, a short error message is displayed. However, systemctl status provides a means to debug the start-up and operation of a service.

systemd comes with its own logging mechanism (“The Journal”) that logs system messages. This allows you to display the service messages together with status messages. The status command works similar to tail and can also display the log messages in different formats, making it a powerful debugging tool.

Show service start-up failure

Whenever a service fails to start, use systemctl status MY_SERVICE to get a detailed error message: 

# systemctl start apache2
Job failed. See system journal and 'systemctl status' for details.
# systemctl status apache2
   Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled)
   Active: failed (Result: exit-code) since Mon, 04 Apr 2018 16:52:26 +0200; 29s ago
   Process: 3088 ExecStart=/usr/sbin/start_apache2 -D SYSTEMD -k start (code=exited, status=1/FAILURE)
   CGroup: name=systemd:/system/apache2.service

Apr 04 16:52:26 g144 start_apache2[3088]: httpd2-prefork: Syntax error on line
205 of /etc/apache2/httpd.conf: Syntax error on li...alHost>
Show last N service messages

The default behavior of the status subcommand is to display the last ten messages a service issued. To change the number of messages to show, use the --lines=N parameter: 

> sudo systemctl status chronyd
> sudo systemctl --lines=20 status chronyd
Show service messages in append mode

To display a “live stream” of service messages, use the --follow option, which works like tail -f: 

> sudo systemctl --follow status chronyd
Messages output format

The --output=MODE parameter allows you to change the output format of service messages. The most important modes available are:

short

The default format. Shows the log messages with a human readable time stamp.

verbose

Full output with all fields.

cat

Terse output without time stamps.

15.7 systemd timer units

  

Similar to cron, systemd timer units provide a mechanism for scheduling jobs on Linux. Although systemd timer units serve the same purpose as cron, they offer several advantages.

  • Jobs scheduled using a timer unit can depend on other systemd services.

  • Timer units are treated as regular systemd services, so can be managed with systemctl.

  • Timers can be realtime and monotonic.

  • Time units are logged to the systemd journal, which makes it easier to monitor and troubleshoot them.

systemd timer units are identified by the .timer file name extension.

15.7.1 systemd timer types

  

Timer units can use monotonic and realtime timers.

  • Similar to cronjobs, realtime timers are triggered on calendar events. Realtime timers are defined using the option OnCalendar.

  • Monotonic timers are triggered at a specified time elapsed from a certain starting point. The latter could be a system boot or system unit activation event. There are several options for defining monotonic timers including OnBootSec, OnUnitActiveSec, and OnTypeSec. Monotonic timers are not persistent, and they are reset after each reboot.

15.7.2 systemd timers and service units

  

Every timer unit must have a corresponding systemd unit file it controls. In other words, a .timer file activates and manages the corresponding .service file. When used with a timer, the .service file does not require an [Install] section, as the service is managed by the timer.

15.7.3 Practical example

  

To understand the basics of systemd timer units, we set up a timer that triggers the foo.sh shell script.

First step is to create a systemd service unit that controls the shell script. To do this, open a new text file for editing and add the following service unit definition: 

[Unit]
Description="Foo shell script"

[Service]
ExecStart=/usr/local/bin/foo.sh

Save the file under the name foo.service in the directory /etc/systemd/system/.

Next, open a new text file for editing and add the following timer definition: 

[Unit]
Description="Run foo shell script"

[Timer]
OnBootSec=5min
OnUnitActiveSec=24h
Unit=foo.service

[Install]
WantedBy=multi-user.target

The [Timer] section in the example above specifies what service to trigger (foo.service) and when to trigger it. In this case, the option OnBootSec specifies a monotonic timer that triggers the service five minutes after the system boot, while the option OnUnitActiveSec triggers the service 24 hours after the service has been activated (that is, the timer triggers the service once a day). Finally, the option WantedBy specifies that the timer should start when the system has reached the multi-user target.

Instead of a monotonic timer, you can specify a real-time one using the option OnCalendar. The following realtime timer definition triggers the related service unit once a week, starting on Monday at 12:00. 

[Timer]
OnCalendar=weekly
Persistent=true

The option Persistent=true indicates that the service is triggered immediately after the timer activation if the timer missed the last start time (for example, because of the system being powered off).

The option OnCalendar can also be used to define specific dates times for triggering a service using the following format: DayOfWeek Year-Month-Day Hour:Minute:Second. The example below triggers a service at 5am every day: 

OnCalendar=*-*-* 5:00:00

You can use an asterisk to specify any value, and commas to list possible values. Use two values separated by .. to indicate a contiguous range. The following example triggers a service at 6pm on Friday of every month: 

OnCalendar=Fri *-*-1..7 18:00:00

To trigger a service at different times, you can specify several OnCalendar entries: 

OnCalendar=Mon..Fri 10:00
OnCalendar=Sat,Sun 22:00

In the example above, a service is triggered at 10am on week days and at 10pm on weekends.

When you are done editing the timer unit file, save it under the name foo.timer in the /etc/systemd/system/ directory. To check the correctness of the created unit files, run the following command: 

> sudo  systemd-analyze verify /etc/systemd/system/foo.*

If the command returns no output, the files have passed the verification successfully.

To start the timer, use the command sudo systemctl start foo.timer. To enable the timer on boot, run the command sudo systemctl enable foo.timer.

15.7.4 Managing systemd timers

  

Since timers are treated as regular systemd units, you can manage them using systemctl. You can start a timer with systemctl start, enable a timer with systemctl enable, and so on. In addition to that, you can list all active timers using the command systemctl list-timers. To list all timers, including inactive ones, run the command systemctl list-timers --all.

15.8 More information

  

For more information on systemd refer to the following online resources:

Homepage

http://www.freedesktop.org/wiki/Software/systemd

systemd for administrators

Lennart Pöttering, one of the systemd authors, has written a series of blog entries (13 at the time of writing this chapter). Find them at http://0pointer.de/blog/projects.

Part III System

  
  • 16 32-bit and 64-bit applications in a 64-bit system environment

    • SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. This chapter offers a brief overview of 32-bit support implementation on 64-bit SUSE Linux Enterprise Server platforms.

  • 17 journalctl: Query the systemd journal

    • systemd features its own logging system called journal. There is no need to run a syslog-based service, as all system events are written to the journal.

  • 18 update-alternatives: Managing multiple versions of commands and files

    • Often, there are several versions of the same tool installed on a system. To give administrators a choice and to make it possible to install and use different versions side by side, the alternatives system allows managing such versions consistently.

  • 19 Basic networking

    • Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.

  • 20 Printer operation

    • SUSE® Linux Enterprise Server supports printing with many types of printers, including remote network printers. Printers can be configured manually or with YaST. For configuration instructions, refer to Book “Deployment Guide”, Chapter 20 “Setting up hardware components with YaST”, Section 20.3 “Set…

  • 21 Graphical user interface

    • SUSE Linux Enterprise Server includes the X.org server and the GNOME desktop. This chapter describes the configuration of the graphical user interface for all users.

  • 22 Accessing file systems with FUSE

    • FUSE is the acronym for Filesystem in Userspace. This means you can configure and mount a file system as an unprivileged user. Normally, you need to be root for this task. FUSE alone is a kernel module. Combined with plug-ins, it allows you to extend FUSE to access almost all file systems like remote SSH connections, ISO images, and more.

  • 23 Managing kernel modules

    • Although Linux is a monolithic kernel, it can be extended using kernel modules. These are special objects that can be inserted into the kernel and removed on demand. In practical terms, kernel modules make it possible to add and remove drivers and interfaces that are not included in the kernel itsel…

  • 24 Dynamic kernel device management with udev

    • The kernel can add or remove almost any device in a running system. Changes in the device state (whether a device is plugged in or removed) need to be propagated to user space. Devices need to be configured when they are plugged in and recognized. Users of a certain device need to be informed about …

  • 25 Special system features

    • This chapter starts with information about various software packages, the virtual consoles and the keyboard layout. We talk about software components like bash, cron 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).

  • 26 Using NetworkManager

    • NetworkManager is the ideal solution for laptops and other portable computers. It supports state-of-the-art encryption types and standards for network connections, including connections to 802.1X protected networks. 802.1X is the “IEEE Standard for Local and Metropolitan Area Networks—Port-Based Net…

  • 27 Power management

    • The features and hardware described in this chapter do not exist on IBM Z, making this chapter irrelevant for these platforms.

  • 28 Persistent memory

    • This chapter contains additional information about using SUSE Linux Enterprise with non-volatile main memory, also known as Persistent Memory, comprising one or more NVDIMMs.

16 32-bit and 64-bit applications in a 64-bit system environment

  

SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. This chapter offers a brief overview of 32-bit support implementation on 64-bit SUSE Linux Enterprise Server platforms.

SUSE Linux Enterprise Server for the 64-bit platforms POWER, IBM Z and AMD64/Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment “out-of-the-box.” The corresponding 32-bit platforms are POWER for POWER, and x86 for AMD64/Intel 64. This support means that you can continue to use your preferred 32-bit applications without waiting for a corresponding 64-bit port to become available. The current POWER system runs most applications in 32-bit mode, but you can run 64-bit applications.

Note
Note: No support for building 32-bit applications

SUSE Linux Enterprise Server does not support compilation of 32-bit applications. It only offers runtime support for 32-bit binaries.

16.1 Runtime support

  
Important
Important: Conflicts between application versions

If an application is available for both 32-bit and 64-bit environments, installing both versions may cause problems. In such cases, decide on one version to install to avoid potential runtime errors.

An exception to this rule is PAM (pluggable authentication modules). SUSE Linux Enterprise Server uses PAM in the authentication process as a layer that mediates between user and application. Always install both PAM versions on 64-bit operating systems that also run 32-bit applications.

For correct execution, every application requires a range of libraries. Unfortunately, the names are identical for the 32-bit and 64-bit versions of these libraries. They must be differentiated from each other in another way.

To retain compatibility with 32-bit versions, 64-bit and 32-bit libraries are stored in the same location. The 32-bit version of libc.so.6 is located under /lib/libc.so.6 in both 32-bit and 64-bit environments.

All 64-bit libraries and object files are located in directories called lib64. The 64-bit object files normally found under /lib and /usr/lib are now found under /lib64 and /usr/lib64. This means that space is available for 32-bit libraries under /lib and /usr/lib, so the file name for both versions can remain unchanged.

If the data content of 32-bit subdirectories under /lib does not depend on word size, they are not moved. This scheme conforms to LSB (Linux Standards Base) and FHS (File System Hierarchy Standard).

16.2 Kernel specifications

  

The 64-bit kernels for AMD64/Intel 64, POWER and IBM Z offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical to the ABI for the corresponding 32-bit kernel. This means that communication between both 32-bit and 64-bit applications with 64-bit kernels are identical.

The 32-bit system call emulation for 64-bit kernels does not support all the APIs used by system programs. This depends on the platform. For this reason, few applications, like lspci, must be compiled on non-POWER platforms as 64-bit programs to function properly. On IBM Z, not all ioctls are available in the 32-bit kernel ABI.

A 64-bit kernel can only load 64-bit kernel modules. You must compile 64-bit modules specifically for 64-bit kernels. It is not possible to use 32-bit kernel modules with 64-bit kernels.

Tip
Tip: Kernel-loadable modules

Some applications require separate kernel-loadable modules. If you intend to use a 32-bit application in a 64-bit system environment, contact the provider of the application and SUSE. Make sure that the 64-bit version of the kernel-loadable module and the 32-bit compiled version of the kernel API are available for this module.

17 journalctl: Query the systemd journal

  

systemd features its own logging system called journal. There is no need to run a syslog-based service, as all system events are written to the journal.

The journal itself is a system service managed by systemd. Its full name is systemd-journald.service. It collects and stores logging data by maintaining structured indexed journals based on logging information received from the kernel, user processes, standard input, and system service errors. The systemd-journald service is on by default: 

> sudo systemctl status systemd-journald
systemd-journald.service - Journal Service
   Loaded: loaded (/usr/lib/systemd/system/systemd-journald.service; static)
   Active: active (running) since Mon 2014-05-26 08:36:59 EDT; 3 days ago
     Docs: man:systemd-journald.service(8)
           man:journald.conf(5)
 Main PID: 413 (systemd-journal)
   Status: "Processing requests..."
   CGroup: /system.slice/systemd-journald.service
           └─413 /usr/lib/systemd/systemd-journald
[...]

17.1 Making the journal persistent

  

The journal stores log data in /run/log/journal/ by default. Because the /run/ directory is volatile by nature, log data is lost at reboot. To make the log data persistent, create the directory /var/log/journal/ and make sure it has the correct access modes and ownership, so the systemd-journald service can store its data. To switch to persistent logging, execute the following commands: 

> sudo  mkdir /var/log/journal
> sudo  systemd-tmpfiles --create --prefix=/var/log/journal
> sudo  journalctl --flush

Any log data stored in /run/log/journal/ will be flushed into /var/log/journal/.

17.2 journalctl: Useful switches

  

This section introduces several common useful options to enhance the default journalctl behavior. All switches are described in the journalctl manual page, man 1 journalctl.

Tip
Tip: Messages related to a specific executable

To show all journal messages related to a specific executable, specify the full path to the executable: 

> sudo journalctl /usr/lib/systemd/systemd
-f

Shows only the most recent journal messages, and prints new log entries as they are added to the journal.

Prints the messages and jumps to the end of the journal, so that the latest entries are visible within the pager.

-r

Prints the messages of the journal in reverse order, so that the latest entries are listed first.

-k

Shows only kernel messages. This is equivalent to the field match _TRANSPORT=kernel (see Section 17.3.3, “Filtering based on fields”).

-u

Shows only messages for the specified systemd unit. This is equivalent to the field match _SYSTEMD_UNIT=UNIT (see Section 17.3.3, “Filtering based on fields”). 

> sudo journalctl -u apache2
[...]
Jun 03 10:07:11 pinkiepie systemd[1]: Starting The Apache Webserver...
Jun 03 10:07:12 pinkiepie systemd[1]: Started The Apache Webserver.

17.3 Filtering the journal output

  

When called without switches, journalctl shows the full content of the journal, the oldest entries listed first. The output can be filtered by specific switches and fields.

17.3.1 Filtering based on a boot number

  

journalctl can filter messages based on a specific system boot. To list all available boots, run 

> sudo journalctl --list-boots
-1 097ed2cd99124a2391d2cffab1b566f0 Mon 2014-05-26 08:36:56 EDT—Fri 2014-05-30 05:33:44 EDT
 0 156019a44a774a0bb0148a92df4af81b Fri 2014-05-30 05:34:09 EDT—Fri 2014-05-30 06:15:01 EDT

The first column lists the boot offset: 0 for the current boot, -1 for the previous one, -2 for the one prior to that, etc. The second column contains the boot ID followed by the limiting time stamps of the specific boot.

Show all messages from the current boot: 

> sudo journalctl -b

If you need to see journal messages from the previous boot, add an offset parameter. The following example outputs the previous boot messages: 

> sudo journalctl -b -1

Another way is to list boot messages based on the boot ID. For this purpose, use the _BOOT_ID field: 

> sudo journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b

17.3.2 Filtering based on time interval

  

You can filter the output of journalctl by specifying the starting and/or ending date. The date specification should be of the format "2014-06-30 9:17:16". If the time part is omitted, midnight is assumed. If seconds are omitted, ":00" is assumed. If the date part is omitted, the current day is assumed. Instead of numeric expression, you can specify the keywords "yesterday", "today", or "tomorrow". They refer to midnight of the day before the current day, of the current day, or of the day after the current day. If you specify "now", it refers to the current time. You can also specify relative times prefixed with - or +, referring to times before or after the current time.

Show only new messages since now, and update the output continuously: 

> sudo journalctl --since "now" -f

Show all messages since last midnight till 3:20am: 

> sudo journalctl --since "today" --until "3:20"

17.3.3 Filtering based on fields

  

You can filter the output of the journal by specific fields. The syntax of a field to be matched is FIELD_NAME=MATCHED_VALUE, such as _SYSTEMD_UNIT=httpd.service. You can specify multiple matches in a single query to filter the output messages even more. See man 7 systemd.journal-fields for a list of default fields.

Show messages produced by a specific process ID: 

> sudo journalctl _PID=1039

Show messages belonging to a specific user ID: 

# journalctl _UID=1000

Show messages from the kernel ring buffer (the same as dmesg produces): 

> sudo journalctl _TRANSPORT=kernel

Show messages from the service's standard or error output: 

> sudo journalctl _TRANSPORT=stdout

Show messages produced by a specified service only: 

> sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service

If two different fields are specified, only entries that match both expressions at the same time are shown: 

> sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1488

If two matches refer to the same field, all entries matching either expression are shown: 

> sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _SYSTEMD_UNIT=dbus.service

You can use the '+' separator to combine two expressions in a logical 'OR'. The following example shows all messages from the Avahi service process with the process ID 1480 together with all messages from the D-Bus service: 

> sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service

17.4 Investigating systemd errors

  

This section introduces a simple example to illustrate how to find and fix the error reported by systemd during apache2 start-up.

  1. Try to start the apache2 service: 

    # systemctl start apache2
Job for apache2.service failed. See 'systemctl status apache2' and 'journalctl -xn' for details.

  2. Let us see what the service's status says: 

    > sudo systemctl status apache2
apache2.service - The Apache Webserver
   Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled)
   Active: failed (Result: exit-code) since Tue 2014-06-03 11:08:13 CEST; 7min ago
  Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND \
           -k graceful-stop (code=exited, status=1/FAILURE)

    The ID of the process causing the failure is 11026.

  3. Show the verbose version of messages related to process ID 11026: 

    > sudo journalctl -o verbose _PID=11026
[...]
MESSAGE=AH00526: Syntax error on line 6 of /etc/apache2/default-server.conf:
[...]
MESSAGE=Invalid command 'DocumenttRoot', perhaps misspelled or defined by a module
[...]

  4. Fix the typo inside /etc/apache2/default-server.conf, start the apache2 service, and print its status: 

    > sudo systemctl start apache2 && systemctl status apache2
apache2.service - The Apache Webserver
   Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled)
   Active: active (running) since Tue 2014-06-03 11:26:24 CEST; 4ms ago
  Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND
           -k graceful-stop (code=exited, status=1/FAILURE)
 Main PID: 11263 (httpd2-prefork)
   Status: "Processing requests..."
   CGroup: /system.slice/apache2.service
           ├─11263 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11280 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11281 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11282 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11283 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           └─11285 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]

17.5 Journald configuration

  

The behavior of the systemd-journald service can be adjusted by modifying /etc/systemd/journald.conf. This section introduces only basic option settings. For a complete file description, see man 5 journald.conf. Note that you need to restart the journal for the changes to take effect with 

> sudo systemctl restart systemd-journald

17.5.1 Changing the journal size limit

  

If the journal log data is saved to a persistent location (see Section 17.1, “Making the journal persistent”), it uses up to 10% of the file system the /var/log/journal resides on. For example, if /var/log/journal is located on a 30 GB /var partition, the journal may use up to 3 GB of the disk space. To change this limit, change (and uncomment) the SystemMaxUse option: 

SystemMaxUse=50M

17.5.2 Forwarding the journal to /dev/ttyX

  

You can forward the journal to a terminal device to inform you about system messages on a preferred terminal screen, for example /dev/tty12. Change the following journald options to