<?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>
