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94 lines
4.0 KiB
XML
94 lines
4.0 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/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-halt.service">
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<refentryinfo>
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<title>systemd-halt.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-halt.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-halt.service</refname>
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<refname>systemd-poweroff.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-halt.service</filename></para>
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<para><filename>systemd-poweroff.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-halt.service</filename> is a system
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service that is pulled in by <filename>halt.target</filename> and
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is responsible for the actual system halt. Similarly,
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<filename>systemd-poweroff.service</filename> is pulled in by
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<filename>poweroff.target</filename>,
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<filename>systemd-reboot.service</filename> by
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<filename>reboot.target</filename> and
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<filename>systemd-kexec.service</filename> by
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<filename>kexec.target</filename> to execute the respective
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actions.</para>
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<para>When these services are run, they ensure that PID 1 is
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replaced by the
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<filename>/usr/lib/systemd/systemd-shutdown</filename> tool which
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is then responsible for the actual shutdown. Before shutting down,
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this binary will try to unmount all remaining file systems,
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disable all remaining swap devices, detach all remaining storage
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devices and kill all remaining processes.</para>
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<para>It is necessary to have this code in a separate binary
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because otherwise rebooting after an upgrade might be broken — the
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running PID 1 could still depend on libraries which are not
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available any more, thus keeping the file system busy, which then
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cannot be re-mounted read-only.</para>
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<para>Immediately before executing the actual system
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halt/poweroff/reboot/kexec <filename>systemd-shutdown</filename>
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will run all executables in
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<filename>/usr/lib/systemd/system-shutdown/</filename> and pass
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one arguments to them: either <literal>halt</literal>,
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<literal>poweroff</literal>, <literal>reboot</literal> or
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<literal>kexec</literal>, depending on the chosen action. All
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executables in this directory are executed in parallel, and
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execution of the action is not continued before all executables
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finished.</para>
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<para>Note that <filename>systemd-halt.service</filename> (and the
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related units) should never be executed directly. Instead, trigger
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system shutdown with a command such as <literal>systemctl
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halt</literal> or suchlike.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-suspend.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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