man/systemd.target.xml

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   8   Copyright 2010 Lennart Poettering
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  10
  11 <refentry id="systemd.target">
  12   <refentryinfo>
  13     <title>systemd.target</title>
  14     <productname>systemd</productname>
  15
  16     <authorgroup>
  17       <author>
  18         <contrib>Developer</contrib>
  19         <firstname>Lennart</firstname>
  20         <surname>Poettering</surname>
  21         <email>lennart@poettering.net</email>
  22       </author>
  23     </authorgroup>
  24   </refentryinfo>
  25
  26   <refmeta>
  27     <refentrytitle>systemd.target</refentrytitle>
  28     <manvolnum>5</manvolnum>
  29   </refmeta>
  30
  31   <refnamediv>
  32     <refname>systemd.target</refname>
  33     <refpurpose>Target unit configuration</refpurpose>
  34   </refnamediv>
  35
  36   <refsynopsisdiv>
  37     <para><filename><replaceable>target</replaceable>.target</filename></para>
  38   </refsynopsisdiv>
  39
  40   <refsect1>
  41     <title>Description</title>
  42
  43     <para>A unit configuration file whose name ends in
  44     <literal>.target</literal> encodes information about a target unit
  45     of systemd, which is used for grouping units and as well-known
  46     synchronization points during start-up.</para>
  47
  48     <para>This unit type has no specific options. See
  49     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  50     for the common options of all unit configuration files. The common
  51     configuration items are configured in the generic [Unit] and
  52     [Install] sections. A separate [Target] section does not exist,
  53     since no target-specific options may be configured.</para>
  54
  55     <para>Target units do not offer any additional functionality on
  56     top of the generic functionality provided by units. They exist
  57     merely to group units via dependencies (useful as boot targets),
  58     and to establish standardized names for synchronization points
  59     used in dependencies between units. Among other things, target
  60     units are a more flexible replacement for SysV runlevels in the
  61     classic SysV init system. (And for compatibility reasons special
  62     target units such as <filename>runlevel3.target</filename> exist
  63     which are used by the SysV runlevel compatibility code in systemd.
  64     See
  65     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  66     for details).</para>
  67   </refsect1>
  68
  69   <refsect1>
  70     <title>Automatic Dependencies</title>
  71
  72     <refsect2>
  73       <title>Implicit Dependencies</title>
  74
  75       <para>There are no implicit dependencies for target units.</para>
  76     </refsect2>
  77
  78     <refsect2>
  79       <title>Default Dependencies</title>
  80
  81       <para>The following dependencies are added unless
  82       <varname>DefaultDependencies=no</varname> is set:</para>
  83
  84       <itemizedlist>
  85         <listitem><para>Target units will automatically complement all
  86         configured dependencies of type <varname>Wants=</varname> or
  87         <varname>Requires=</varname> with dependencies of type
  88         <varname>After=</varname> unless <varname>DefaultDependencies=no</varname>
  89         is set in the specified units. Note that <varname>Wants=</varname> or
  90         <varname>Requires=</varname> must be defined in the target unit itself — if
  91         you for example define <varname>Wants=</varname>some.target in
  92         some.service, the automatic ordering will not be added.</para></listitem>
  93
  94         <listitem><para>Target units automatically gain <varname>Conflicts=</varname>
  95         dependency against <filename>shutdown.target</filename>.</para></listitem>
  96       </itemizedlist>
  97     </refsect2>
  98   </refsect1>
  99
 100   <refsect1>
 101     <title>Example</title>
 102
 103     <example>
 104       <title>Simple standalone target</title>
 105
 106       <programlisting># emergency-net.target
 107
 108 [Unit]
 109 Description=Emergency Mode with Networking
 110 Requires=emergency.target systemd-networkd.service
 111 After=emergency.target systemd-networkd.service
 112 AllowIsolate=yes</programlisting>
 113
 114       <para>When adding dependencies to other units, it's important to check if they set
 115       <varname>DefaultDependencies=</varname>. Service units, unless they set
 116       <varname>DefaultDependencies=no</varname>, automatically get a dependency on
 117       <filename>sysinit.target</filename>. In this case, both
 118       <filename>emergency.target</filename> and <filename>systemd-networkd.service</filename>
 119       have <varname>DefaultDependencies=no</varname>, so they are suitable for use
 120       in this target, and do not pull in <filename>sysinit.target</filename>.</para>
 121
 122       <para>You can now switch into this emergency mode by running <varname>systemctl
 123       isolate emergency-net.target</varname> or by passing the option
 124       <varname>systemd.unit=emergency-net.target</varname> on the kernel command
 125       line.</para>
 126
 127       <para>Other units can have <varname>WantedBy=emergency-net.target</varname> in the
 128       <varname>[Install]</varname> section. After they are enabled using
 129       <command>systemctl enable</command>, they will be started before
 130       <varname>emergency-net.target</varname> is started. It is also possible to add
 131       arbitrary units as dependencies of <filename>emergency.target</filename> without
 132       modifying them by using <command>systemctl add-wants</command>.
 133       </para>
 134     </example>
 135   </refsect1>
 136
 137   <refsect1>
 138       <title>See Also</title>
 139       <para>
 140         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 141         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 142         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 143         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 144         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 145       </para>
 146   </refsect1>
 147
 148 </refentry>