systemd-halt.service.xml 5.73 KB
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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">

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  This file is part of systemd.

  Copyright 2012 Lennart Poettering

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<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
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                for the actual system halt. Similarly,
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                <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>

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                <para>When these services are run, they ensure that PID
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                1 is replaced by the
                <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
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                unmount all remaining file systems, disable all
                remaining swap devices, detach all remaining storage
                devices and 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 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>

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                <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
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                <literal>halt</literal>,
                <literal>poweroff</literal>,
                <literal>reboot</literal> or
                <literal>kexec</literal>, depending on the chosen
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                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
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                command such as <literal>systemctl halt</literal> or
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                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>