man/systemd-halt.service.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2012 Lennart Poettering
  11 -->
  12
  13 <refentry id="systemd-halt.service">
  14
  15   <refentryinfo>
  16     <title>systemd-halt.service</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>systemd-halt.service</refentrytitle>
  31     <manvolnum>8</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>systemd-halt.service</refname>
  36     <refname>systemd-poweroff.service</refname>
  37     <refname>systemd-reboot.service</refname>
  38     <refname>systemd-kexec.service</refname>
  39     <refname>systemd-shutdown</refname>
  40     <refpurpose>System shutdown logic</refpurpose>
  41   </refnamediv>
  42
  43   <refsynopsisdiv>
  44     <para><filename>systemd-halt.service</filename></para>
  45     <para><filename>systemd-poweroff.service</filename></para>
  46     <para><filename>systemd-reboot.service</filename></para>
  47     <para><filename>systemd-kexec.service</filename></para>
  48     <para><filename>/usr/lib/systemd/systemd-shutdown</filename></para>
  49     <para><filename>/usr/lib/systemd/system-shutdown/</filename></para>
  50   </refsynopsisdiv>
  51
  52   <refsect1>
  53     <title>Description</title>
  54
  55     <para><filename>systemd-halt.service</filename> is a system
  56     service that is pulled in by <filename>halt.target</filename> and
  57     is responsible for the actual system halt. Similarly,
  58     <filename>systemd-poweroff.service</filename> is pulled in by
  59     <filename>poweroff.target</filename>,
  60     <filename>systemd-reboot.service</filename> by
  61     <filename>reboot.target</filename> and
  62     <filename>systemd-kexec.service</filename> by
  63     <filename>kexec.target</filename> to execute the respective
  64     actions.</para>
  65
  66     <para>When these services are run, they ensure that PID 1 is
  67     replaced by the
  68     <filename>/usr/lib/systemd/systemd-shutdown</filename> tool which
  69     is then responsible for the actual shutdown. Before shutting down,
  70     this binary will try to unmount all remaining file systems,
  71     disable all remaining swap devices, detach all remaining storage
  72     devices and kill all remaining processes.</para>
  73
  74     <para>It is necessary to have this code in a separate binary
  75     because otherwise rebooting after an upgrade might be broken — the
  76     running PID 1 could still depend on libraries which are not
  77     available any more, thus keeping the file system busy, which then
  78     cannot be re-mounted read-only.</para>
  79
  80     <para>Immediately before executing the actual system
  81     halt/poweroff/reboot/kexec <filename>systemd-shutdown</filename>
  82     will run all executables in
  83     <filename>/usr/lib/systemd/system-shutdown/</filename> and pass
  84     one arguments to them: either <literal>halt</literal>,
  85     <literal>poweroff</literal>, <literal>reboot</literal> or
  86     <literal>kexec</literal>, depending on the chosen action. All
  87     executables in this directory are executed in parallel, and
  88     execution of the action is not continued before all executables
  89     finished.</para>
  90
  91     <para>Note that <filename>systemd-halt.service</filename> (and the
  92     related units) should never be executed directly. Instead, trigger
  93     system shutdown with a command such as <literal>systemctl
  94     halt</literal> or suchlike.</para>
  95   </refsect1>
  96
  97   <refsect1>
  98     <title>See Also</title>
  99     <para>
 100       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 101       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 102       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 103       <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 104       <citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 105       <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 106     </para>
 107   </refsect1>
 108
 109 </refentry>