man/systemd-poweroff.service.xml

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   5
   6 <refentry id="systemd-poweroff.service">
   7
   8   <refentryinfo>
   9     <title>systemd-poweroff.service</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd-poweroff.service</refentrytitle>
  15     <manvolnum>8</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd-poweroff.service</refname>
  20     <refname>systemd-halt.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-poweroff.service</filename></para>
  29     <para><filename>systemd-halt.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-poweroff.service</filename> is a system service that is pulled in by
  40     <filename>poweroff.target</filename> and is responsible for the actual system power-off
  41     operation. Similarly, <filename>systemd-halt.service</filename> is pulled in by
  42     <filename>halt.target</filename>, <filename>systemd-reboot.service</filename> by
  43     <filename>reboot.target</filename> and <filename>systemd-kexec.service</filename> by
  44     <filename>kexec.target</filename> to execute the respective actions.</para>
  45
  46     <para>When these services are run, they ensure that PID 1 is replaced by the
  47     <filename>/usr/lib/systemd/systemd-shutdown</filename> tool which is then responsible for the actual
  48     shutdown. Before shutting down, this binary will try to unmount all remaining file systems (or at least
  49     remount them read-only), disable all remaining swap devices, detach all remaining storage devices and
  50     kill all remaining processes.</para>
  51
  52     <para>It is necessary to have this code in a separate binary because otherwise rebooting after an upgrade
  53     might be broken — the running PID 1 could still depend on libraries which are not available any more,
  54     thus keeping the file system busy, which then cannot be re-mounted read-only.</para>
  55
  56     <para>Shortly before executing the actual system power-off/halt/reboot/kexec
  57     <filename>systemd-shutdown</filename> will run all executables in
  58     <filename>/usr/lib/systemd/system-shutdown/</filename> and pass one arguments to them: either
  59     <literal>poweroff</literal>, <literal>halt</literal>, <literal>reboot</literal>, or
  60     <literal>kexec</literal>, depending on the chosen action. All executables in this directory are executed
  61     in parallel, and execution of the action is not continued before all executables finished. Note that
  62     these executables are run <emphasis>after</emphasis> all services have been shut down, and after most
  63     mounts have been unmounted (the root file system as well as <filename>/run/</filename> and various API
  64     file systems are still around though). This means any programs dropped into this directory must be
  65     prepared to run in such a limited execution environment and not rely on external services or hierarchies
  66     such as <filename>/var/</filename> to be around (or writable).</para>
  67
  68     <para>Note that <filename>systemd-poweroff.service</filename> (and the related units) should never be
  69     executed directly. Instead, trigger system shutdown with a command such as <literal>systemctl
  70     poweroff</literal>.</para>
  71
  72     <para>Another form of shutdown is provided by the
  73     <citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  74     functionality. It reboots only the OS userspace, leaving the kernel, firmware, and hardware as it is.</para>
  75   </refsect1>
  76
  77   <refsect1>
  78     <title>See Also</title>
  79     <para><simplelist type="inline">
  80       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
  81       <member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
  82       <member><citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
  83       <member><citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
  84       <member><citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
  85       <member><citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
  86       <member><citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
  87     </simplelist></para>
  88   </refsect1>
  89
  90 </refentry>