man/systemd-halt.service.xml

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