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Target units gain both Conflicts= and Before= against shutdown.target (not only Conflicts=).
139 lines
5.6 KiB
XML
139 lines
5.6 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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-->
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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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</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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and <varname>Before=</varname> dependencies against
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<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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