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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
This file is part of systemd.
Copyright 2012 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="systemd-halt.service">
<refentryinfo>
<title>systemd-halt.service</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-halt.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-halt.service</refname>
<refname>systemd-poweroff.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-halt.service</filename></para>
<para><filename>systemd-poweroff.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-halt.service</filename> is a system
service that is pulled in by <filename>halt.target</filename> and
is responsible for the actual system halt. Similarly,
<filename>systemd-poweroff.service</filename> is pulled in by
<filename>poweroff.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,
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>Immediately before executing the actual system
halt/poweroff/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>halt</literal>,
<literal>poweroff</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.</para>
<para>Note that <filename>systemd-halt.service</filename> (and the
related units) should never be executed directly. Instead, trigger
system shutdown with a command such as <literal>systemctl
halt</literal> or suchlike.</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>
</para>
</refsect1>
</refentry>
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