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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-10 20:49:52 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-10 20:49:52 +0000
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Adding upstream version 255.4.upstream/255.4
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="systemd-poweroff.service">
+
+ <refentryinfo>
+ <title>systemd-poweroff.service</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>systemd-poweroff.service</refentrytitle>
+ <manvolnum>8</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>systemd-poweroff.service</refname>
+ <refname>systemd-halt.service</refname>
+ <refname>systemd-reboot.service</refname>
+ <refname>systemd-kexec.service</refname>
+ <refname>systemd-shutdown</refname>
+ <refpurpose>System shutdown logic</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename>systemd-poweroff.service</filename></para>
+ <para><filename>systemd-halt.service</filename></para>
+ <para><filename>systemd-reboot.service</filename></para>
+ <para><filename>systemd-kexec.service</filename></para>
+ <para><filename>/usr/lib/systemd/systemd-shutdown</filename></para>
+ <para><filename>/usr/lib/systemd/system-shutdown/</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><filename>systemd-poweroff.service</filename> is a system service that is pulled in by
+ <filename>poweroff.target</filename> and is responsible for the actual system power-off
+ operation. Similarly, <filename>systemd-halt.service</filename> is pulled in by
+ <filename>halt.target</filename>, <filename>systemd-reboot.service</filename> by
+ <filename>reboot.target</filename> and <filename>systemd-kexec.service</filename> by
+ <filename>kexec.target</filename> to execute the respective actions.</para>
+
+ <para>When these services are run, they ensure that PID 1 is replaced by the
+ <filename>/usr/lib/systemd/systemd-shutdown</filename> tool which is then responsible for the actual
+ shutdown. Before shutting down, this binary will try to unmount all remaining file systems (or at least
+ remount them read-only), disable all remaining swap devices, detach all remaining storage devices and
+ kill all remaining processes.</para>
+
+ <para>It is necessary to have this code in a separate binary because otherwise rebooting after an upgrade
+ might be broken — the running PID 1 could still depend on libraries which are not available any more,
+ thus keeping the file system busy, which then cannot be re-mounted read-only.</para>
+
+ <para>Shortly before executing the actual system power-off/halt/reboot/kexec
+ <filename>systemd-shutdown</filename> will run all executables in
+ <filename>/usr/lib/systemd/system-shutdown/</filename> and pass one arguments to them: either
+ <literal>poweroff</literal>, <literal>halt</literal>, <literal>reboot</literal>, or
+ <literal>kexec</literal>, depending on the chosen action. All executables in this directory are executed
+ in parallel, and execution of the action is not continued before all executables finished. Note that
+ these executables are run <emphasis>after</emphasis> all services have been shut down, and after most
+ mounts have been detached (the root file system as well as <filename>/run/</filename> and various API
+ file systems are still around though). This means any programs dropped into this directory must be
+ prepared to run in such a limited execution environment and not rely on external services or hierarchies
+ such as <filename>/var/</filename> to be around (or writable).</para>
+
+ <para>Note that <filename>systemd-poweroff.service</filename> (and the related units) should never be
+ executed directly. Instead, trigger system shutdown with a command such as <literal>systemctl
+ poweroff</literal>.</para>
+
+ <para>Another form of shutdown is provided by the
+ <citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ functionality. It reboots only the OS userspace, leaving the kernel, firmware, and hardware as it is.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>