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   This file is part of systemd.
   7
   8   Copyright 2012 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd-halt.service">
  25
  26   <refentryinfo>
  27     <title>systemd-halt.service</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>systemd-halt.service</refentrytitle>
  42     <manvolnum>8</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>systemd-halt.service</refname>
  47     <refname>systemd-poweroff.service</refname>
  48     <refname>systemd-reboot.service</refname>
  49     <refname>systemd-kexec.service</refname>
  50     <refname>systemd-shutdown</refname>
  51     <refpurpose>System shutdown logic</refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <para><filename>systemd-halt.service</filename></para>
  56     <para><filename>systemd-poweroff.service</filename></para>
  57     <para><filename>systemd-reboot.service</filename></para>
  58     <para><filename>systemd-kexec.service</filename></para>
  59     <para><filename>/usr/lib/systemd/systemd-shutdown</filename></para>
  60     <para><filename>/usr/lib/systemd/system-shutdown/</filename></para>
  61   </refsynopsisdiv>
  62
  63   <refsect1>
  64     <title>Description</title>
  65
  66     <para><filename>systemd-halt.service</filename> is a system
  67     service that is pulled in by <filename>halt.target</filename> and
  68     is responsible for the actual system halt. Similarly,
  69     <filename>systemd-poweroff.service</filename> is pulled in by
  70     <filename>poweroff.target</filename>,
  71     <filename>systemd-reboot.service</filename> by
  72     <filename>reboot.target</filename> and
  73     <filename>systemd-kexec.service</filename> by
  74     <filename>kexec.target</filename> to execute the respective
  75     actions.</para>
  76
  77     <para>When these services are run, they ensure that PID 1 is
  78     replaced by the
  79     <filename>/usr/lib/systemd/systemd-shutdown</filename> tool which
  80     is then responsible for the actual shutdown. Before shutting down,
  81     this binary will try to unmount all remaining file systems,
  82     disable all remaining swap devices, detach all remaining storage
  83     devices and kill all remaining processes.</para>
  84
  85     <para>It is necessary to have this code in a separate binary
  86     because otherwise rebooting after an upgrade might be broken — the
  87     running PID 1 could still depend on libraries which are not
  88     available any more, thus keeping the file system busy, which then
  89     cannot be re-mounted read-only.</para>
  90
  91     <para>Immediately before executing the actual system
  92     halt/poweroff/reboot/kexec <filename>systemd-shutdown</filename>
  93     will run all executables in
  94     <filename>/usr/lib/systemd/system-shutdown/</filename> and pass
  95     one arguments to them: either <literal>halt</literal>,
  96     <literal>poweroff</literal>, <literal>reboot</literal> or
  97     <literal>kexec</literal>, depending on the chosen action. All
  98     executables in this directory are executed in parallel, and
  99     execution of the action is not continued before all executables
 100     finished.</para>
 101
 102     <para>Note that <filename>systemd-halt.service</filename> (and the
 103     related units) should never be executed directly. Instead, trigger
 104     system shutdown with a command such as <literal>systemctl
 105     halt</literal> or suchlike.</para>
 106   </refsect1>
 107
 108   <refsect1>
 109     <title>See Also</title>
 110     <para>
 111       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 112       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 113       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 114       <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 115       <citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 116     </para>
 117   </refsect1>
 118
 119 </refentry>