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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">
<!--
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>
</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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