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>Automatic Dependencies</title>
  84
  85     <para>Unless <varname>DefaultDependencies=</varname> is set to
  86     <option>no</option> in either of related units or an explicit ordering
  87     dependency is already defined, target units will implicitly complement all
  88     configured dependencies of type <varname>Wants=</varname> or
  89     <varname>Requires=</varname> with dependencies of type
  90     <varname>After=</varname>. Note that <varname>Wants=</varname> or
  91     <varname>Requires=</varname> must be defined in the target unit itself — if
  92     you for example define <varname>Wants=</varname>some.target in
  93     some.service, the implicit ordering will not be added.</para>
  94
  95     <para>All target units automatically gain <varname>Conflicts=</varname>
  96     dependency against shutdown.target unless <varname>DefaultDependencies=</varname>
  97     is set to <option>no</option>.</para>
  98
  99   </refsect1>
 100
 101   <refsect1>
 102     <title>Example</title>
 103
 104     <example>
 105       <title>Simple standalone target</title>
 106
 107       <programlisting># emergency-net.target
 108
 109 [Unit]
 110 Description=Emergency Mode with Networking
 111 Requires=emergency.target systemd-networkd.service
 112 After=emergency.target systemd-networkd.service
 113 AllowIsolate=yes</programlisting>
 114
 115       <para>When adding dependencies to other units, it's important to check if they set
 116       <varname>DefaultDependencies=</varname>. Service units, unless they set
 117       <varname>DefaultDependencies=no</varname>, automatically get a dependency on
 118       <filename>sysinit.target</filename>. In this case, both
 119       <filename>emergency.target</filename> and <filename>systemd-networkd.service</filename>
 120       have <varname>DefaultDependencies=no</varname>, so they are suitable for use
 121       in this target, and do not pull in <filename>sysinit.target</filename>.</para>
 122
 123       <para>You can now switch into this emergency mode by running <varname>systemctl
 124       isolate emergency-net.target</varname> or by passing the option
 125       <varname>systemd.unit=emergency-net.target</varname> on the kernel command
 126       line.</para>
 127
 128       <para>Other units can have <varname>WantedBy=emergency-net.target</varname> in the
 129       <varname>[Install]</varname> section. After they are enabled using
 130       <command>systemctl enable</command>, they will be started before
 131       <varname>emergency-net.target</varname> is started. It is also possible to add
 132       arbitrary units as dependencies of <filename>emergency.target</filename> without
 133       modifying them by using <command>systemctl add-wants</command>.
 134       </para>
 135     </example>
 136   </refsect1>
 137
 138   <refsect1>
 139       <title>See Also</title>
 140       <para>
 141         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 142         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 143         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 144         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 145         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 146       </para>
 147   </refsect1>
 148
 149 </refentry>