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