man/systemd.target.xml

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  10   Copyright 2010 Lennart Poettering
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  25
  26 <refentry id="systemd.target">
  27   <refentryinfo>
  28     <title>systemd.target</title>
  29     <productname>systemd</productname>
  30
  31     <authorgroup>
  32       <author>
  33         <contrib>Developer</contrib>
  34         <firstname>Lennart</firstname>
  35         <surname>Poettering</surname>
  36         <email>lennart@poettering.net</email>
  37       </author>
  38     </authorgroup>
  39   </refentryinfo>
  40
  41   <refmeta>
  42     <refentrytitle>systemd.target</refentrytitle>
  43     <manvolnum>5</manvolnum>
  44   </refmeta>
  45
  46   <refnamediv>
  47     <refname>systemd.target</refname>
  48     <refpurpose>Target unit configuration</refpurpose>
  49   </refnamediv>
  50
  51   <refsynopsisdiv>
  52     <para><filename><replaceable>target</replaceable>.target</filename></para>
  53   </refsynopsisdiv>
  54
  55   <refsect1>
  56     <title>Description</title>
  57
  58     <para>A unit configuration file whose name ends in
  59     <literal>.target</literal> encodes information about a target unit
  60     of systemd, which is used for grouping units and as well-known
  61     synchronization points during start-up.</para>
  62
  63     <para>This unit type has no specific options. See
  64     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  65     for the common options of all unit configuration files. The common
  66     configuration items are configured in the generic [Unit] and
  67     [Install] sections. A separate [Target] section does not exist,
  68     since no target-specific options may be configured.</para>
  69
  70     <para>Target units do not offer any additional functionality on
  71     top of the generic functionality provided by units. They exist
  72     merely to group units via dependencies (useful as boot targets),
  73     and to establish standardized names for synchronization points
  74     used in dependencies between units. Among other things, target
  75     units are a more flexible replacement for SysV runlevels in the
  76     classic SysV init system. (And for compatibility reasons special
  77     target units such as <filename>runlevel3.target</filename> exist
  78     which are used by the SysV runlevel compatibility code in systemd.
  79     See
  80     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  81     for details).</para>
  82   </refsect1>
  83
  84   <refsect1>
  85     <title>Implicit Dependencies</title>
  86
  87     <para>There are no implicit dependencies for target units.</para>
  88   </refsect1>
  89
  90   <refsect1>
  91     <title>Default Dependencies</title>
  92
  93     <para>The following dependencies are added unless
  94     <varname>DefaultDependencies=no</varname> is set:</para>
  95
  96     <itemizedlist>
  97       <listitem><para>Target units will automatically complement all
  98       configured dependencies of type <varname>Wants=</varname> or
  99       <varname>Requires=</varname> with dependencies of type
 100       <varname>After=</varname> unless <varname>DefaultDependencies=no</varname>
 101       is set in the specified units. Note that <varname>Wants=</varname> or
 102       <varname>Requires=</varname> must be defined in the target unit itself — if
 103       you for example define <varname>Wants=</varname>some.target in
 104       some.service, the automatic ordering will not be added.</para></listitem>
 105
 106       <listitem><para>Target units automatically gain <varname>Conflicts=</varname>
 107       dependency against <filename>shutdown.target</filename>.</para></listitem>
 108     </itemizedlist>
 109   </refsect1>
 110
 111   <refsect1>
 112     <title>Example</title>
 113
 114     <example>
 115       <title>Simple standalone target</title>
 116
 117       <programlisting># emergency-net.target
 118
 119 [Unit]
 120 Description=Emergency Mode with Networking
 121 Requires=emergency.target systemd-networkd.service
 122 After=emergency.target systemd-networkd.service
 123 AllowIsolate=yes</programlisting>
 124
 125       <para>When adding dependencies to other units, it's important to check if they set
 126       <varname>DefaultDependencies=</varname>. Service units, unless they set
 127       <varname>DefaultDependencies=no</varname>, automatically get a dependency on
 128       <filename>sysinit.target</filename>. In this case, both
 129       <filename>emergency.target</filename> and <filename>systemd-networkd.service</filename>
 130       have <varname>DefaultDependencies=no</varname>, so they are suitable for use
 131       in this target, and do not pull in <filename>sysinit.target</filename>.</para>
 132
 133       <para>You can now switch into this emergency mode by running <varname>systemctl
 134       isolate emergency-net.target</varname> or by passing the option
 135       <varname>systemd.unit=emergency-net.target</varname> on the kernel command
 136       line.</para>
 137
 138       <para>Other units can have <varname>WantedBy=emergency-net.target</varname> in the
 139       <varname>[Install]</varname> section. After they are enabled using
 140       <command>systemctl enable</command>, they will be started before
 141       <varname>emergency-net.target</varname> is started. It is also possible to add
 142       arbitrary units as dependencies of <filename>emergency.target</filename> without
 143       modifying them by using <command>systemctl add-wants</command>.
 144       </para>
 145     </example>
 146   </refsect1>
 147
 148   <refsect1>
 149       <title>See Also</title>
 150       <para>
 151         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 152         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 153         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 154         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 155         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 156       </para>
 157   </refsect1>
 158
 159 </refentry>