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+ SPDX-License-Identifier: LGPL-2.1+
+
This file is part of systemd.
Copyright 2010 Lennart Poettering
See
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details).</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Implicit Dependencies</title>
+
+ <para>There are no implicit dependencies for target units.</para>
+ </refsect1>
- <para>Unless <varname>DefaultDependencies=</varname> is set to
- <option>false</option>, target units will implicitly complement
- all configured dependencies of type <varname>Wants=</varname>,
- <varname>Requires=</varname>,
- <varname>RequiresOverridable=</varname> with dependencies of type
- <varname>After=</varname> if the units in question also have
- <varname>DefaultDependencies=true</varname>.
- </para>
+ <refsect1>
+ <title>Default Dependencies</title>
+
+ <para>The following dependencies are added unless
+ <varname>DefaultDependencies=no</varname> is set:</para>
+
+ <itemizedlist>
+ <listitem><para>Target units will automatically complement all
+ configured dependencies of type <varname>Wants=</varname> or
+ <varname>Requires=</varname> with dependencies of type
+ <varname>After=</varname> unless <varname>DefaultDependencies=no</varname>
+ is set in the specified units. Note that <varname>Wants=</varname> or
+ <varname>Requires=</varname> must be defined in the target unit itself — if
+ you for example define <varname>Wants=</varname>some.target in
+ some.service, the automatic ordering will not be added.</para></listitem>
+
+ <listitem><para>Target units automatically gain <varname>Conflicts=</varname>
+ dependency against <filename>shutdown.target</filename>.</para></listitem>
+ </itemizedlist>
+ </refsect1>
+
+ <refsect1>
+ <title>Example</title>
+
+ <example>
+ <title>Simple standalone target</title>
+
+ <programlisting># emergency-net.target
+
+[Unit]
+Description=Emergency Mode with Networking
+Requires=emergency.target systemd-networkd.service
+After=emergency.target systemd-networkd.service
+AllowIsolate=yes</programlisting>
+
+ <para>When adding dependencies to other units, it's important to check if they set
+ <varname>DefaultDependencies=</varname>. Service units, unless they set
+ <varname>DefaultDependencies=no</varname>, automatically get a dependency on
+ <filename>sysinit.target</filename>. In this case, both
+ <filename>emergency.target</filename> and <filename>systemd-networkd.service</filename>
+ have <varname>DefaultDependencies=no</varname>, so they are suitable for use
+ in this target, and do not pull in <filename>sysinit.target</filename>.</para>
+
+ <para>You can now switch into this emergency mode by running <varname>systemctl
+ isolate emergency-net.target</varname> or by passing the option
+ <varname>systemd.unit=emergency-net.target</varname> on the kernel command
+ line.</para>
+
+ <para>Other units can have <varname>WantedBy=emergency-net.target</varname> in the
+ <varname>[Install]</varname> section. After they are enabled using
+ <command>systemctl enable</command>, they will be started before
+ <varname>emergency-net.target</varname> is started. It is also possible to add
+ arbitrary units as dependencies of <filename>emergency.target</filename> without
+ modifying them by using <command>systemctl add-wants</command>.
+ </para>
+ </example>
</refsect1>
<refsect1>