man/systemd-halt.service.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="systemd-halt.service">
  10
  11   <refentryinfo>
  12     <title>systemd-halt.service</title>
  13     <productname>systemd</productname>
  14
  15     <authorgroup>
  16       <author>
  17         <contrib>Developer</contrib>
  18         <firstname>Lennart</firstname>
  19         <surname>Poettering</surname>
  20         <email>lennart@poettering.net</email>
  21       </author>
  22     </authorgroup>
  23   </refentryinfo>
  24
  25   <refmeta>
  26     <refentrytitle>systemd-halt.service</refentrytitle>
  27     <manvolnum>8</manvolnum>
  28   </refmeta>
  29
  30   <refnamediv>
  31     <refname>systemd-halt.service</refname>
  32     <refname>systemd-poweroff.service</refname>
  33     <refname>systemd-reboot.service</refname>
  34     <refname>systemd-kexec.service</refname>
  35     <refname>systemd-shutdown</refname>
  36     <refpurpose>System shutdown logic</refpurpose>
  37   </refnamediv>
  38
  39   <refsynopsisdiv>
  40     <para><filename>systemd-halt.service</filename></para>
  41     <para><filename>systemd-poweroff.service</filename></para>
  42     <para><filename>systemd-reboot.service</filename></para>
  43     <para><filename>systemd-kexec.service</filename></para>
  44     <para><filename>/usr/lib/systemd/systemd-shutdown</filename></para>
  45     <para><filename>/usr/lib/systemd/system-shutdown/</filename></para>
  46   </refsynopsisdiv>
  47
  48   <refsect1>
  49     <title>Description</title>
  50
  51     <para><filename>systemd-halt.service</filename> is a system
  52     service that is pulled in by <filename>halt.target</filename> and
  53     is responsible for the actual system halt. Similarly,
  54     <filename>systemd-poweroff.service</filename> is pulled in by
  55     <filename>poweroff.target</filename>,
  56     <filename>systemd-reboot.service</filename> by
  57     <filename>reboot.target</filename> and
  58     <filename>systemd-kexec.service</filename> by
  59     <filename>kexec.target</filename> to execute the respective
  60     actions.</para>
  61
  62     <para>When these services are run, they ensure that PID 1 is
  63     replaced by the
  64     <filename>/usr/lib/systemd/systemd-shutdown</filename> tool which
  65     is then responsible for the actual shutdown. Before shutting down,
  66     this binary will try to unmount all remaining file systems,
  67     disable all remaining swap devices, detach all remaining storage
  68     devices and kill all remaining processes.</para>
  69
  70     <para>It is necessary to have this code in a separate binary
  71     because otherwise rebooting after an upgrade might be broken — the
  72     running PID 1 could still depend on libraries which are not
  73     available any more, thus keeping the file system busy, which then
  74     cannot be re-mounted read-only.</para>
  75
  76     <para>Immediately before executing the actual system
  77     halt/poweroff/reboot/kexec <filename>systemd-shutdown</filename>
  78     will run all executables in
  79     <filename>/usr/lib/systemd/system-shutdown/</filename> and pass
  80     one arguments to them: either <literal>halt</literal>,
  81     <literal>poweroff</literal>, <literal>reboot</literal> or
  82     <literal>kexec</literal>, depending on the chosen action. All
  83     executables in this directory are executed in parallel, and
  84     execution of the action is not continued before all executables
  85     finished.</para>
  86
  87     <para>Note that <filename>systemd-halt.service</filename> (and the
  88     related units) should never be executed directly. Instead, trigger
  89     system shutdown with a command such as <literal>systemctl
  90     halt</literal> or suchlike.</para>
  91   </refsect1>
  92
  93   <refsect1>
  94     <title>See Also</title>
  95     <para>
  96       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  97       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  98       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
  99       <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 100       <citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 101       <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 102     </para>
 103   </refsect1>
 104
 105 </refentry>