man/systemd.target.xml

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  23
  24 <refentry id="systemd.target">
  25   <refentryinfo>
  26     <title>systemd.target</title>
  27     <productname>systemd</productname>
  28
  29     <authorgroup>
  30       <author>
  31         <contrib>Developer</contrib>
  32         <firstname>Lennart</firstname>
  33         <surname>Poettering</surname>
  34         <email>lennart@poettering.net</email>
  35       </author>
  36     </authorgroup>
  37   </refentryinfo>
  38
  39   <refmeta>
  40     <refentrytitle>systemd.target</refentrytitle>
  41     <manvolnum>5</manvolnum>
  42   </refmeta>
  43
  44   <refnamediv>
  45     <refname>systemd.target</refname>
  46     <refpurpose>Target unit configuration</refpurpose>
  47   </refnamediv>
  48
  49   <refsynopsisdiv>
  50     <para><filename><replaceable>target</replaceable>.target</filename></para>
  51   </refsynopsisdiv>
  52
  53   <refsect1>
  54     <title>Description</title>
  55
  56     <para>A unit configuration file whose name ends in
  57     <literal>.target</literal> encodes information about a target unit
  58     of systemd, which is used for grouping units and as well-known
  59     synchronization points during start-up.</para>
  60
  61     <para>This unit type has no specific options. See
  62     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  63     for the common options of all unit configuration files. The common
  64     configuration items are configured in the generic [Unit] and
  65     [Install] sections. A separate [Target] section does not exist,
  66     since no target-specific options may be configured.</para>
  67
  68     <para>Target units do not offer any additional functionality on
  69     top of the generic functionality provided by units. They exist
  70     merely to group units via dependencies (useful as boot targets),
  71     and to establish standardized names for synchronization points
  72     used in dependencies between units. Among other things, target
  73     units are a more flexible replacement for SysV runlevels in the
  74     classic SysV init system. (And for compatibility reasons special
  75     target units such as <filename>runlevel3.target</filename> exist
  76     which are used by the SysV runlevel compatibility code in systemd.
  77     See
  78     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  79     for details).</para>
  80   </refsect1>
  81
  82   <refsect1>
  83     <title>Implicit Dependencies</title>
  84
  85     <para>There are no implicit dependencies for target units.</para>
  86   </refsect1>
  87
  88   <refsect1>
  89     <title>Default Dependencies</title>
  90
  91     <para>The following dependencies are added unless
  92     <varname>DefaultDependencies=no</varname> is set:</para>
  93
  94     <itemizedlist>
  95       <listitem><para>Target units will automatically complement all
  96       configured dependencies of type <varname>Wants=</varname> or
  97       <varname>Requires=</varname> with dependencies of type
  98       <varname>After=</varname> unless <varname>DefaultDependencies=no</varname>
  99       is set in the specified units. Note that <varname>Wants=</varname> or
 100       <varname>Requires=</varname> must be defined in the target unit itself — if
 101       you for example define <varname>Wants=</varname>some.target in
 102       some.service, the automatic ordering will not be added.</para></listitem>
 103
 104       <listitem><para>Target units automatically gain <varname>Conflicts=</varname>
 105       dependency against <filename>shutdown.target</filename>.</para></listitem>
 106     </itemizedlist>
 107   </refsect1>
 108
 109   <refsect1>
 110     <title>Example</title>
 111
 112     <example>
 113       <title>Simple standalone target</title>
 114
 115       <programlisting># emergency-net.target
 116
 117 [Unit]
 118 Description=Emergency Mode with Networking
 119 Requires=emergency.target systemd-networkd.service
 120 After=emergency.target systemd-networkd.service
 121 AllowIsolate=yes</programlisting>
 122
 123       <para>When adding dependencies to other units, it's important to check if they set
 124       <varname>DefaultDependencies=</varname>. Service units, unless they set
 125       <varname>DefaultDependencies=no</varname>, automatically get a dependency on
 126       <filename>sysinit.target</filename>. In this case, both
 127       <filename>emergency.target</filename> and <filename>systemd-networkd.service</filename>
 128       have <varname>DefaultDependencies=no</varname>, so they are suitable for use
 129       in this target, and do not pull in <filename>sysinit.target</filename>.</para>
 130
 131       <para>You can now switch into this emergency mode by running <varname>systemctl
 132       isolate emergency-net.target</varname> or by passing the option
 133       <varname>systemd.unit=emergency-net.target</varname> on the kernel command
 134       line.</para>
 135
 136       <para>Other units can have <varname>WantedBy=emergency-net.target</varname> in the
 137       <varname>[Install]</varname> section. After they are enabled using
 138       <command>systemctl enable</command>, they will be started before
 139       <varname>emergency-net.target</varname> is started. It is also possible to add
 140       arbitrary units as dependencies of <filename>emergency.target</filename> without
 141       modifying them by using <command>systemctl add-wants</command>.
 142       </para>
 143     </example>
 144   </refsect1>
 145
 146   <refsect1>
 147       <title>See Also</title>
 148       <para>
 149         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 150         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 151         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 152         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 153         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 154       </para>
 155   </refsect1>
 156
 157 </refentry>