systemd/man/systemd.target.xml

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<refentry id="systemd.target">
  <refentryinfo>
    <title>systemd.target</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.target</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.target</refname>
    <refpurpose>Target unit configuration</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>target</replaceable>.target</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>A unit configuration file whose name ends in <literal>.target</literal> encodes information about a
    target unit of systemd. Target units are used to group units and to set synchronization points for
    ordering dependencies with other unit files.</para>

    <para>This unit type has no specific options. See
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for the
    common options of all unit configuration files. The common configuration items are configured in the
    generic [Unit] and [Install] sections. A separate [Target] section does not exist, since no
    target-specific options may be configured.</para>

    <para>Target units do not offer any additional functionality on top of the generic functionality provided
    by units. They merely group units, allowing a single target name to be used in <varname>Wants=</varname>
    and <varname>Requires=</varname> settings to establish a dependency on a set of units defined by the
    target, and in <varname>Before=</varname> and <varname>After=</varname> settings to establish ordering.
    Targets establish standardized names for synchronization points during boot and shutdown. Importantly,
    see <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
    for examples and descriptions of standard systemd targets.</para>

    <para>Target units provide a more flexible replacement for SysV runlevels in the classic SysV init
    system. For compatibility reasons special target units such as <filename>runlevel3.target</filename>
    exist which are used by the SysV runlevel compatibility code in systemd, see
    <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
    details.</para>

    <para>Note that a target unit file must not be empty, lest it be considered a masked unit. It is
    recommended to provide a [Unit] section which includes informative <varname>Description=</varname> and
    <varname>Documentation=</varname> options.</para>
  </refsect1>

  <refsect1>
    <title>Automatic Dependencies</title>

    <refsect2>
      <title>Implicit Dependencies</title>

      <para>There are no implicit dependencies for target units.</para>
    </refsect2>

    <refsect2>
      <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.</para>

        <para>Note that the reverse is not true. For example, defining <option>Wants=that.target</option> in
        <filename index='false'>some.service</filename> will not automatically add the
        <option>After=that.target</option> ordering dependency for <filename>some.service</filename>.
        Instead, <filename>some.service</filename> should use the primary synchronization function of target
        type units, by setting a specific <option>After=that.target</option> or
        <option>Before=that.target</option> ordering dependency in its .service unit file.
        </para></listitem>

        <listitem><para>Target units automatically gain <varname>Conflicts=</varname>
        and <varname>Before=</varname> dependencies against
        <filename>shutdown.target</filename>.</para></listitem>
      </itemizedlist>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Target unit files may include [Unit] and [Install] sections, which are described in
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    No options specific to this file type are supported.</para>
  </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>
      <title>See Also</title>
      <para>
        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
      </para>
  </refsect1>

</refentry>