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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<sect1 id="ch-scripts-systemd-custom" revision="systemd">
<?dbhtml filename="systemd-custom.html"?>
<title>Systemd Usage and Configuration</title>
<indexterm zone="ch-scripts-systemd-custom">
<primary sortas="e-Systemd">Systemd Customization</primary>
</indexterm>
<sect2>
<title>Basic Configuration</title>
<para>The <filename>/etc/systemd/system.conf</filename> file contains a set
of options to control basic systemd operations. The default file has all
entries commented out with the default settings indicated. This file is
where the log level may be changed as well as some basic logging settings.
See <filename>systemd-system.conf(5)</filename> manual page for details on
each configuration option.</para>
</sect2>
<sect2>
<title>Disabling Screen Clearing at Boot Time</title>
<para>The normal behavior for systemd is to clear the screen at
the end of the boot sequence. If desired, this behavior may be
changed by running the following command:</para>
<screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/getty@tty1.service.d
cat > /etc/systemd/system/getty@tty1.service.d/noclear.conf << EOF
<literal>[Service]
TTYVTDisallocate=no</literal>
EOF</userinput></screen>
<para>The boot messages can always be reviewed by using the
<userinput>journalctl -b</userinput> command as the root user.</para>
</sect2>
<sect2>
<title>Disabling tmpfs for /tmp</title>
<para>By default, <filename class="directory">/tmp</filename> is created as
a tmpfs. If this is not desired, it can be overridden by the following:</para>
<screen role="nodump"><userinput>ln -sfv /dev/null /etc/systemd/system/tmp.mount</userinput></screen>
<para>This is not necessary if there is a separate partition for
<filename class="directory">/tmp</filename> specified in
<filename>/etc/fstab</filename>.</para>
</sect2>
<sect2>
<title>Configuring Automatic File Creation and Deletion</title>
<para>There are several services that create or delete files or
directories:</para>
<itemizedlist>
<listitem><para>systemd-tmpfiles-clean.service</para></listitem>
<listitem><para>systemd-tmpfiles-setup-dev.service</para></listitem>
<listitem><para>systemd-tmpfiles-setup.service</para></listitem>
</itemizedlist>
<para>The system location for the configuration files is
<filename>/usr/lib/tmpfiles.d/*.conf</filename>. The local
configuration files are in
<filename class="directory">/etc/tmpfiles.d</filename>. Files in
<filename class="directory">/etc/tmpfiles.d</filename> override
files with the same name in
<filename class="directory">/usr/lib/tmpfiles.d</filename>. See
<filename>tmpfiles.d(5)</filename> manual page for file format
details.</para>
</sect2>
<sect2>
<title>Overriding Default Services Behavior</title>
<para>The parameter of a unit can be overriden by creating a directory
and a configuration file in <filename
class="directory">/etc/systemd/system</filename>. For example:</para>
<screen role="nodump"><userinput>mkdir -pv /etc/systemd/system/foobar.service.d
cat > /etc/systemd/system/foobar.service.d/foobar.conf << EOF
<literal>[Service]
Restart=always
RestartSec=30</literal>
EOF</userinput></screen>
<para>See <filename>systemd.unit(5)</filename> manual page for more
information. After creating the configuration file, run
<userinput>systemctl daemon-reload</userinput> and <userinput>systemctl
restart foobar</userinput> to activate the changes to a service.</para>
</sect2>
<sect2>
<title>Debugging the Boot Sequence</title>
<para>Rather than plain shell scripts used in SysVinit or BSD style init
systems, systemd uses a unified format for different types of startup
files (or units). The command <command>systemctl</command> is used to
enable, disable, control state, and obtain status of unit files. Here
are some examples of frequently used commands:</para>
<itemizedlist>
<listitem>
<para><command>systemctl list-units -t <replaceable><service></replaceable> [--all]</command>:
lists loaded unit files of type service.</para>
</listitem>
<listitem>
<para><command>systemctl list-units -t <replaceable><target></replaceable> [--all]</command>:
lists loaded unit files of type target.</para>
</listitem>
<listitem>
<para><command>systemctl show -p Wants <replaceable><multi-user.target></replaceable></command>:
shows all units that depend on the multi-user target. Targets are
special unit files that are anogalous to runlevels under
SysVinit.</para>
</listitem>
<listitem>
<para><command>systemctl status <replaceable><servicename.service></replaceable></command>:
shows the status of the servicename service. The .service extension
can be omitted if there are no other unit files with the same name,
such as .socket files (which create a listening socket that provides
similar functionality to inetd/xinetd).</para>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>Working with the Systemd Journal</title>
<para>Logging on a system booted with systemd is handled with
systemd-journald (by default), rather than a typical unix syslog daemon.
You can also add a normal syslog daemon and have both work side by
side if desired. The systemd-journald program stores journal entries in a
binary format rather than a plain text log file. To assist with
parsing the file, the command <command>journalctl</command> is provided.
Here are some examples of frequently used commands:</para>
<itemizedlist>
<listitem>
<para><command>journalctl -r</command>: shows all contents of the
journal in reverse chronological order.</para>
</listitem>
<listitem>
<para><command>journalctl -u <replaceable>UNIT</replaceable></command>:
shows the journal entries associated with the specified UNIT
file.</para>
</listitem>
<listitem>
<para><command>journalctl -b[=ID] -r</command>: shows the journal
entries since last successful boot (or for boot ID) in reverse
chronological order.</para>
</listitem>
<listitem>
<para><command>journalctl -f</command>: povides functionality similar
to tail -f (follow).</para>
</listitem>
</itemizedlist>
</sect2>
<sect2>
<title>Long Running Processes</title>
<para>Beginning with systemd-230, all user processes are killed when a
user session is ended, even if nohup is used, or the process uses
<function>daemon()</function> or <function>setsid()</function>. This is a
deliberate change from a historically permissive environment to a more
restrictive one. The new behavior may cause issues if you depend on long
running programs (e.g., <command>screen</command> or
<command>tmux</command>) to remain active after ending your user
session. There are three ways to enable lingering processes to remain after
a user session is ended.</para>
<itemizedlist>
<listitem>
<para>
<emphasis>Enable process lingering for only needed users</emphasis>:
normal users have permission to enable process lingering
with the command <command>loginctl enable-linger</command> for their
own user. System administrators can use the same command with a
<parameter>user</parameter> argument to enable for a user. That user
can then use the <command>systemd-run</command> command to start
long running processes. For example: <command>systemd-run --scope
--user /usr/bin/screen</command>. If you enable lingering for your
user, the user@.service will remain even after all login sessions are
closed, and will automatically start at system boot. This has the
advantage of explicitly allowing and disallowing processes to run
after the user session has ended, but breaks backwards compatibility
with tools like <command>nohup</command> and utilities that use
<function>deamon()</function>.
</para>
</listitem>
<listitem>
<para>
<emphasis>Enable system-wide process lingering</emphasis>:
you can set <parameter>KillUserProcesses=no</parameter> in
<filename>/etc/logind.conf</filename> to enable process lingering
globally for all users. This has the benefit of leaving the old
method available to all users at the expense of explicit control.
</para>
</listitem>
<listitem>
<para>
<emphasis>Disable at build-time</emphasis>: You can enable
lingering by default while building systemd by adding the switch
<parameter>--without-kill-user-processes</parameter> to the
<command>configure</command> command for systemd. This completely
disables the ability of systemd to kill user processes at session
end.
</para>
</listitem>
</itemizedlist>
</sect2>
</sect1>
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