man/systemd-halt.service.xml

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  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         </refsynopsisdiv>
  61
  62         <refsect1>
  63                 <title>Description</title>
  64
  65                 <para><filename>systemd-halt.service</filename> is a
  66                 system service that is pulled in by
  67                 <filename>halt.target</filename> and is responsible
  68                 for the actual system halt. Similarly,
  69                 <filename>systemd-poweroff.service</filename> is
  70                 pulled in by <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
  75                 respective actions.</para>
  76
  77                 <para>When these services are run, they ensure that PID
  78                 1 is replaced by the
  79                 <filename>/usr/lib/systemd/systemd-shutdown</filename>
  80                 tool which is then responsible for the actual
  81                 shutdown. Before shutting down, this binary will try to
  82                 unmount all remaining file systems, disable all
  83                 remaining swap devices, detach all remaining storage
  84                 devices and kill all remaining processes.</para>
  85
  86                 <para>It is necessary to have this code in a separate binary
  87                 because otherwise rebooting after an upgrade might be broken —
  88                 the running PID 1 could still depend on libraries which are not
  89                 available any more, thus keeping the file system busy, which
  90                 then cannot be re-mounted read-only.</para>
  91
  92                 <para>Immediately before executing the actual system
  93                 halt/poweroff/reboot/kexec
  94                 <filename>systemd-shutdown</filename> will run all
  95                 executables in
  96                 <filename>/usr/lib/systemd/system-shutdown/</filename>
  97                 and pass one arguments to them: either
  98                 <literal>halt</literal>,
  99                 <literal>poweroff</literal>,
 100                 <literal>reboot</literal> or
 101                 <literal>kexec</literal>, depending on the chosen
 102                 action. All executables in this directory are executed
 103                 in parallel, and execution of the action is not
 104                 continued before all executables finished.</para>
 105
 106                 <para>Note that
 107                 <filename>systemd-halt.service</filename> (and the
 108                 related units) should never be executed
 109                 directly. Instead, trigger system shutdown with a
 110                 command such as <literal>systemctl halt</literal> or
 111                 suchlike.</para>
 112         </refsect1>
 113
 114         <refsect1>
 115                 <title>See Also</title>
 116                 <para>
 117                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 118                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 119                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 120                         <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 121                         <citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 122                 </para>
 123         </refsect1>
 124
 125 </refentry>