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https://github.com/systemd/systemd
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91 lines
5.0 KiB
XML
91 lines
5.0 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-poweroff.service">
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<refentryinfo>
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<title>systemd-poweroff.service</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-poweroff.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-poweroff.service</refname>
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<refname>systemd-halt.service</refname>
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<refname>systemd-reboot.service</refname>
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<refname>systemd-kexec.service</refname>
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<refname>systemd-shutdown</refname>
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<refpurpose>System shutdown logic</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-poweroff.service</filename></para>
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<para><filename>systemd-halt.service</filename></para>
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<para><filename>systemd-reboot.service</filename></para>
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<para><filename>systemd-kexec.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-shutdown</filename></para>
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<para><filename>/usr/lib/systemd/system-shutdown/</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-poweroff.service</filename> is a system service that is pulled in by
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<filename>poweroff.target</filename> and is responsible for the actual system power-off
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operation. Similarly, <filename>systemd-halt.service</filename> is pulled in by
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<filename>halt.target</filename>, <filename>systemd-reboot.service</filename> by
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<filename>reboot.target</filename> and <filename>systemd-kexec.service</filename> by
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<filename>kexec.target</filename> to execute the respective actions.</para>
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<para>When these services are run, they ensure that PID 1 is replaced by the
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<filename>/usr/lib/systemd/systemd-shutdown</filename> tool which is then responsible for the actual
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shutdown. Before shutting down, this binary will try to unmount all remaining file systems (or at least
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remount them read-only), disable all remaining swap devices, detach all remaining storage devices and
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kill all remaining processes.</para>
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<para>It is necessary to have this code in a separate binary because otherwise rebooting after an upgrade
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might be broken — the running PID 1 could still depend on libraries which are not available any more,
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thus keeping the file system busy, which then cannot be re-mounted read-only.</para>
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<para>Shortly before executing the actual system power-off/halt/reboot/kexec
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<filename>systemd-shutdown</filename> will run all executables in
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<filename>/usr/lib/systemd/system-shutdown/</filename> and pass one arguments to them: either
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<literal>poweroff</literal>, <literal>halt</literal>, <literal>reboot</literal>, or
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<literal>kexec</literal>, depending on the chosen action. All executables in this directory are executed
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in parallel, and execution of the action is not continued before all executables finished. Note that
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these executables are run <emphasis>after</emphasis> all services have been shut down, and after most
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mounts have been unmounted (the root file system as well as <filename>/run/</filename> and various API
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file systems are still around though). This means any programs dropped into this directory must be
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prepared to run in such a limited execution environment and not rely on external services or hierarchies
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such as <filename>/var/</filename> to be around (or writable).</para>
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<para>Note that <filename>systemd-poweroff.service</filename> (and the related units) should never be
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executed directly. Instead, trigger system shutdown with a command such as <literal>systemctl
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poweroff</literal>.</para>
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<para>Another form of shutdown is provided by the
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<citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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functionality. It reboots only the OS userspace, leaving the kernel, firmware, and hardware as it is.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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