path: root/man/systemd.special.xml

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<refentry id="systemd.special">

        <refentryinfo>
                <title>systemd.special</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.special</refentrytitle>
                <manvolnum>7</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd.special</refname>
                <refpurpose>Special systemd units</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <para><filename>basic.target</filename>,
                <filename>ctrl-alt-del.target</filename>,
                <filename>dbus.service</filename>,
                <filename>dbus.socket</filename>,
                <filename>default.target</filename>,
                <filename>display-manager.service</filename>,
                <filename>emergency.target</filename>,
                <filename>exit.service</filename>,
                <filename>final.service</filename>,
                <filename>graphical.target</filename>,
                <filename>hibernate.target</filename>,
                <filename>http-daemon.target</filename>,
                <filename>halt.target</filename>,
                <filename>kbrequest.target</filename>,
                <filename>kexec.target</filename>,
                <filename>local-fs.target</filename>,
                <filename>local-fs-pre.target</filename>,
                <filename>mail-transfer-agent.target</filename>,
                <filename>multi-user.target</filename>,
                <filename>network.target</filename>,
                <filename>nss-lookup.target</filename>,
                <filename>poweroff.target</filename>,
                <filename>reboot.target</filename>,
                <filename>remote-fs.target</filename>,
                <filename>remote-fs-pre.target</filename>,
                <filename>rescue.target</filename>,
                <filename>rpcbind.target</filename>,
                <filename>runlevel2.target</filename>,
                <filename>runlevel3.target</filename>,
                <filename>runlevel4.target</filename>,
                <filename>runlevel5.target</filename>,
                <filename>shutdown.target</filename>,
                <filename>sigpwr.target</filename>,
                <filename>sleep.target</filename>,
                <filename>sockets.target</filename>,
                <filename>suspend.target</filename>,
                <filename>swap.target</filename>,
                <filename>sysinit.target</filename>,
                <filename>syslog.service</filename>,
                <filename>syslog.socket</filename>,
                <filename>syslog.target</filename>,
                <filename>time-sync.target</filename>,
                <filename>umount.target</filename></para>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para>A few units are treated specially by
                systemd. They have special internal semantics and
                cannot be renamed.</para>
        </refsect1>

        <refsect1>
                <title>Special System Units</title>

                <variablelist>
                        <varlistentry>
                                <term><filename>basic.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        covering early boot-up.</para>
                                        <para>systemd automatically
                                        adds dependencies of the types
                                        Requires and After for this
                                        target unit to all SysV
                                        service units configured for
                                        runlevel 1 to 5.</para>
                                        <para>Usually this should pull-in
                                        all sockets, mount points,
                                        swap devices and other basic
                                        initialization necessary for
                                        the general purpose
                                        daemons. Most normal daemons
                                        should have dependencies of
                                        type After and Requires on
                                        this unit.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>ctrl-alt-del.target</filename></term>
                                <listitem>
                                        <para>systemd starts this
                                        target whenever
                                        Control+Alt+Del is pressed on
                                        the console. Usually this
                                        should be aliased (symlinked)
                                        to
                                        <filename>reboot.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>dbus.service</filename></term>
                                <listitem>
                                        <para>A special unit for the
                                        D-Bus system bus. As soon as
                                        this service is fully started
                                        up systemd will connect to it
                                        and register its
                                        service.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>dbus.socket</filename></term>
                                <listitem>
                                        <para>A special unit for the
                                        D-Bus system bus socket. All
                                        units with
                                        <literal>Type=dbus</literal>
                                        automatically gain a
                                        dependency on this
                                        unit.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>default.target</filename></term>
                                <listitem>
                                        <para>The default unit systemd
                                        starts at bootup. Usually this
                                        should be aliased (symlinked)
                                        to
                                        <filename>multi-user.target</filename>
                                        or
                                        <filename>graphical.target</filename>.</para>
                                        <para>The default unit systemd
                                        starts at bootup can be
                                        overridden with the
                                        <varname>systemd.unit=</varname>
                                        kernel command line option.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>display-manager.service</filename></term>
                                <listitem>
                                        <para>The display manager
                                        service. Usually this should
                                        be aliased (symlinked) to
                                        <filename>gdm.service</filename>
                                        or a similar display manager
                                        service.</para>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with a LSB header
                                        referring to the
                                        <literal>$x-display-manager</literal>
                                        facility, for compatibility
                                        with Debian.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>emergency.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        that starts an emergency
                                        shell on the main
                                        console. This unit is supposed
                                        to be used with the kernel
                                        command line option
                                        <varname>systemd.unit=</varname>
                                        and has otherwise little use.
                                        </para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>final.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        that is used during the
                                        shutdown logic and may be used
                                        to pull in late services after
                                        all normal services are
                                        already terminated and all
                                        mounts unmounted.
                                        </para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>graphical.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for setting up a graphical
                                        login screen. This pulls in
                                        <filename>multi-user.target</filename>.</para>

                                        <para>Units that are needed
                                        for graphical login shall add
                                        Wants dependencies for their
                                        unit to this unit (or
                                        <filename>multi-user.target</filename>)
                                        during installation.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>hibernate.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for hibernating the
                                        system. This pulls in
                                        <filename>sleep.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>http-daemon.target</filename></term>
                                <listitem>
                                        <para>A target for pulling in
                                        an HTTP server if there is
                                        any.</para>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with a LSB header
                                        referring to the
                                        <literal>$httpd</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>halt.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for shutting down and halting the system.</para>

                                        <para>Applications wanting to
                                        halt the system should start
                                        this unit.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>kbrequest.target</filename></term>
                                <listitem>
                                        <para>systemd starts this
                                        target whenever Alt+ArrowUp is
                                        pressed on the console. This
                                        is a good candidate to be
                                        aliased (symlinked) to
                                        <filename>rescue.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>kexec.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for shutting down and rebooting the system via kexec.</para>

                                        <para>Applications wanting to
                                        reboot the system with kexec should start
                                        this unit.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>local-fs.target</filename></term>
                                <listitem>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        After to all mount units that
                                        refer to local mount points
                                        for this target unit. In
                                        addition, systemd adds
                                        dependencies of type Wants to
                                        this target unit for those
                                        mounts listed in
                                        <filename>/etc/fstab</filename>
                                        that have the
                                        <option>auto</option> and
                                        <option>comment=systemd.mount</option>
                                        mount options set.</para>

                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with an LSB header
                                        referring to the
                                        <literal>$local_fs</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>local-fs-pre.target</filename></term>
                                <listitem>
                                        <para>This target unit is
                                        automatically ordered before
                                        all local mount points marked
                                        with <option>auto</option>
                                        (see above). It can be used to
                                        execute certain units before
                                        all local mounts.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>mail-transfer-agent.target</filename></term>
                                <listitem>
                                        <para>The mail transfer agent
                                        (MTA) service. Usually this
                                        should pull-in all units
                                        necessary for
                                        sending/receiving mails on the
                                        local host.</para>

                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with an LSB header
                                        referring to the
                                        <literal>$mail-transfer-agent</literal>
                                        or
                                        <literal>$mail-transport-agent</literal>
                                        facilities, for compatibility
                                        with Debian.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>multi-user.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for setting up a multi-user
                                        system (non-graphical). This
                                        is pulled in by
                                        <filename>graphical.target</filename>.</para>

                                        <para>Units that are needed
                                        for a multi-user system shall
                                        add Wants dependencies to
                                        this unit for their unit during
                                        installation.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>network.target</filename></term>
                                <listitem>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with an LSB header
                                        referring to the
                                        <literal>$network</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>nss-lookup.target</filename></term>
                                <listitem>
                                        <para>A target that should be
                                        used as synchronization point
                                        for all host/network name
                                        service lookups. Note that
                                        this is independent of
                                        user/group name lookups for
                                        which
                                        <filename>nss-user-lookup.target</filename>
                                        should be used. systemd
                                        automatically adds
                                        dependencies of type After for
                                        this target unit to all SysV
                                        init script service units with
                                        an LSB header referring to the
                                        <literal>$named</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>nss-user-lookup.target</filename></term>
                                <listitem>
                                        <para>A target that should be
                                        used as synchronization point
                                        for all user/group name
                                        service lookups. Note that
                                        this is independent of
                                        host/network name lookups for
                                        which
                                        <filename>nss-lookup.target</filename>
                                        should be used. </para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>poweroff.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for shutting down and powering off the system.</para>

                                        <para>Applications wanting to
                                        power off the system should start
                                        this unit.</para>

                                        <para><filename>runlevel0.target</filename>
                                        is an alias for this target
                                        unit, for compatibility with SysV.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>reboot.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for shutting down and rebooting the system.</para>

                                        <para>Applications wanting to
                                        reboot the system should start
                                        this unit.</para>

                                        <para><filename>runlevel6.target</filename>
                                        is an alias for this target
                                        unit, for compatibility with SysV.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>remote-fs.target</filename></term>
                                <listitem>
                                        <para>Similar to
                                        <filename>local-fs.target</filename>,
                                        but for remote mount
                                        points.</para>

                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with an LSB header
                                        referring to the
                                        <literal>$remote_fs</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>remote-fs-pre.target</filename></term>
                                <listitem>
                                        <para>This target unit is
                                        automatically ordered before
                                        all remote mount points marked
                                        with <option>auto</option>
                                        (see above). It can be used to
                                        execute certain units before
                                        all remote mounts.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>rescue.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for setting up the base system
                                        and a rescue shell.</para>

                                        <para><filename>runlevel1.target</filename>
                                        is an alias for this target
                                        unit, for compatibility with SysV.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>rpcbind.target</filename></term>
                                <listitem>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with an LSB header
                                        referring to the
                                        <literal>$rpcbind</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>runlevel2.target</filename></term>
                                <listitem>
                                        <para>This is a target that is
                                        called whenever the SysV
                                        compatibility code asks for
                                        runlevel 2. It is a good idea
                                        to make this an alias for
                                        (i.e. symlink to)
                                        <filename>multi-user.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>runlevel3.target</filename></term>
                                <listitem>
                                        <para>This is a target that is
                                        called whenever the SysV
                                        compatibility code asks for
                                        runlevel 3. It is a good idea
                                        to make this an alias for
                                        (i.e. symlink to)
                                        <filename>multi-user.target</filename>
                                        or
                                        <filename>graphical.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>runlevel4.target</filename></term>
                                <listitem>
                                        <para>This is a target that is
                                        called whenever the SysV
                                        compatibility code asks for
                                        runlevel 4. It is a good idea
                                        to make this an alias for
                                        (i.e. symlink to)
                                        <filename>multi-user.target</filename>
                                        or
                                        <filename>graphical.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>runlevel5.target</filename></term>
                                <listitem>
                                        <para>This is a target that is
                                        called whenever the SysV
                                        compatibility code asks for
                                        runlevel 5. It is a good idea
                                        to make this an alias for
                                        (i.e. symlink to)
                                        <filename>multi-user.target</filename>
                                        or
                                        <filename>graphical.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>shutdown.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        that terminates the services
                                        on system shutdown.</para>

                                        <para>Services that shall be
                                        terminated on system shutdown
                                        shall add Conflicts
                                        dependencies to this unit for
                                        their service unit, which is
                                        implicitly done when
                                        <varname>DefaultDependencies=yes</varname>
                                        is set (the default).</para>

                                        <para>systemd automatically
                                        adds dependencies of type
                                        Conflicts to this target unit
                                        for all SysV init script
                                        service units that shall be
                                        terminated in SysV runlevels 0
                                        or 6.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>sigpwr.target</filename></term>
                                <listitem>
                                        <para>A special target that is
                                        started when systemd receives
                                        the SIGPWR process signal,
                                        which is normally sent by the
                                        kernel or UPS daemons when
                                        power fails.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>sleep.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        that is pulled in by
                                        <filename>suspend.target</filename>
                                        and
                                        <filename>hibernate.target</filename>
                                        and may be used to hook units
                                        into the sleep state
                                        logic.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>sockets.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        that sets up all service
                                        sockets.</para>

                                        <para>Services that can be
                                        socket-activated shall add
                                        Wants dependencies to this
                                        unit for their socket unit
                                        during installation.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>suspend.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for suspending the
                                        system. This pulls in
                                        <filename>sleep.target</filename>.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>swap.target</filename></term>
                                <listitem>
                                        <para>Similar to
                                        <filename>local-fs.target</filename>, but for swap
                                        partitions and swap
                                        files.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>sysinit.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        covering early boot-up scripts.</para>
                                        <para>systemd automatically
                                        adds dependencies of the types
                                        Wants and After for all
                                        SysV service units configured
                                        for runlevels that are not 0
                                        to 6 to this target unit.
                                        This covers the special
                                        boot-up runlevels some
                                        distributions have, such as S
                                        or b.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>syslog.service</filename></term>
                                <listitem>
                                        <para>The syslog service if
                                        any. Implementations should
                                        create a symlink from the
                                        actual syslog implementation
                                        to this generic name for
                                        activating it.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>syslog.socket</filename></term>
                                <listitem>
                                        <para>The socket unit where
                                        syslog implementations should
                                        listen on. All userspace log
                                        messages will be made
                                        available on this
                                        socket.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>syslog.target</filename></term>
                                <listitem>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with an LSB header
                                        referring to the
                                        <literal>$syslog</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>time-sync.target</filename></term>
                                <listitem>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        After for this target unit to
                                        all SysV init script service
                                        units with an LSB header
                                        referring to the
                                        <literal>$time</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>umount.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        that umounts all mount and
                                        automount points on system
                                        shutdown.</para>

                                        <para>Mounts that shall be
                                        unmounted on system shutdown
                                        shall add Conflicts
                                        dependencies to this unit for
                                        their mount unit, which is
                                        implicitly done when
                                        <varname>DefaultDependencies=yes</varname>
                                        is set (the default).</para>
                                </listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Special User Units</title>

                <para>When systemd runs as a user instance, the
                following special units are available, which have
                similar definitions as their system counterparts:
                <filename>default.target</filename>,
                <filename>shutdown.target</filename>,
                <filename>sockets.target</filename></para>

                <para>In addition the following special unit is
                understood only when systemd runs as service instance:</para>

                <variablelist>
                        <varlistentry>
                                <term><filename>exit.service</filename></term>
                                <listitem>
                                        <para>A special service unit
                                        for shutting down the
                                        user service manager.</para>

                                        <para>Applications wanting to
                                        terminate the user service
                                        manager should start this
                                        unit. If systemd receives
                                        SIGTERM or SIGINT when running
                                        as user service daemon it will
                                        start this unit.</para>

                                        <para>Normally, this pulls in
                                        <filename>shutdown.target</filename>
                                        which in turn should be
                                        conflicted by all units that
                                        want to be shut down on
                                        user service manager exit.</para>
                                </listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                  <title>See Also</title>
                  <para>
                          <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                  </para>
        </refsect1>

</refentry>