man/systemd-halt.service.xml

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