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![Lennart Poettering](/assets/img/avatar_default.png)
This part of the copyright blurb stems from the GPL use recommendations: https://www.gnu.org/licenses/gpl-howto.en.html The concept appears to originate in times where version control was per file, instead of per tree, and was a way to glue the files together. Ultimately, we nowadays don't live in that world anymore, and this information is entirely useless anyway, as people are very welcome to copy these files into any projects they like, and they shouldn't have to change bits that are part of our copyright header for that. hence, let's just get rid of this old cruft, and shorten our codebase a bit.
149 lines
5.8 KiB
XML
149 lines
5.8 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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Copyright 2010 Lennart Poettering
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-->
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<refentry id="systemd.target">
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<refentryinfo>
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<title>systemd.target</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.target</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.target</refname>
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<refpurpose>Target unit configuration</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename><replaceable>target</replaceable>.target</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>A unit configuration file whose name ends in
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<literal>.target</literal> encodes information about a target unit
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of systemd, which is used for grouping units and as well-known
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synchronization points during start-up.</para>
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<para>This unit type has no specific options. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for the common options of all unit configuration files. The common
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configuration items are configured in the generic [Unit] and
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[Install] sections. A separate [Target] section does not exist,
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since no target-specific options may be configured.</para>
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<para>Target units do not offer any additional functionality on
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top of the generic functionality provided by units. They exist
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merely to group units via dependencies (useful as boot targets),
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and to establish standardized names for synchronization points
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used in dependencies between units. Among other things, target
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units are a more flexible replacement for SysV runlevels in the
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classic SysV init system. (And for compatibility reasons special
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target units such as <filename>runlevel3.target</filename> exist
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which are used by the SysV runlevel compatibility code in systemd.
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See
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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for details).</para>
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</refsect1>
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<refsect1>
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<title>Automatic Dependencies</title>
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<refsect2>
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<title>Implicit Dependencies</title>
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<para>There are no implicit dependencies for target units.</para>
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</refsect2>
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<refsect2>
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<title>Default Dependencies</title>
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<para>The following dependencies are added unless
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<varname>DefaultDependencies=no</varname> is set:</para>
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<itemizedlist>
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<listitem><para>Target units will automatically complement all
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configured dependencies of type <varname>Wants=</varname> or
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<varname>Requires=</varname> with dependencies of type
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<varname>After=</varname> unless <varname>DefaultDependencies=no</varname>
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is set in the specified units. Note that <varname>Wants=</varname> or
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<varname>Requires=</varname> must be defined in the target unit itself — if
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you for example define <varname>Wants=</varname>some.target in
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some.service, the automatic ordering will not be added.</para></listitem>
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<listitem><para>Target units automatically gain <varname>Conflicts=</varname>
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dependency against <filename>shutdown.target</filename>.</para></listitem>
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</itemizedlist>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<example>
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<title>Simple standalone target</title>
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<programlisting># emergency-net.target
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[Unit]
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Description=Emergency Mode with Networking
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Requires=emergency.target systemd-networkd.service
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After=emergency.target systemd-networkd.service
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AllowIsolate=yes</programlisting>
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<para>When adding dependencies to other units, it's important to check if they set
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<varname>DefaultDependencies=</varname>. Service units, unless they set
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<varname>DefaultDependencies=no</varname>, automatically get a dependency on
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<filename>sysinit.target</filename>. In this case, both
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<filename>emergency.target</filename> and <filename>systemd-networkd.service</filename>
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have <varname>DefaultDependencies=no</varname>, so they are suitable for use
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in this target, and do not pull in <filename>sysinit.target</filename>.</para>
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<para>You can now switch into this emergency mode by running <varname>systemctl
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isolate emergency-net.target</varname> or by passing the option
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<varname>systemd.unit=emergency-net.target</varname> on the kernel command
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line.</para>
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<para>Other units can have <varname>WantedBy=emergency-net.target</varname> in the
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<varname>[Install]</varname> section. After they are enabled using
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<command>systemctl enable</command>, they will be started before
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<varname>emergency-net.target</varname> is started. It is also possible to add
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arbitrary units as dependencies of <filename>emergency.target</filename> without
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modifying them by using <command>systemctl add-wants</command>.
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</para>
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</example>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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