path: root/man/systemd.xml

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<refentry id="systemd">

        <refentryinfo>
                <title>systemd</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</refentrytitle>
                <manvolnum>1</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd</refname>
                <refname>init</refname>
                <refpurpose>systemd System and Session Manager</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <cmdsynopsis>
                        <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
                </cmdsynopsis>
                <cmdsynopsis>
                        <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
                </cmdsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para>systemd is a system and session manager for
                Linux operating systems. When run as first process on
                boot (as PID 1), it acts as init system that brings
                up and maintains userspace services.</para>

                <para>For compatibility with SysV, if systemd is called
                as <command>init</command> and a PID that is not
                1, it will execute <command>telinit</command> and pass
                all command line arguments unmodified. That means
                <command>init</command> and <command>telinit</command>
                are mostly equivalent when invoked from normal login sessions. See
                <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                for more information.</para>
        </refsect1>

        <refsect1>
                <title>Options</title>

                <para>The following options are understood:</para>

                <variablelist>
                        <varlistentry>
                                <term><option>-h</option></term>
                                <term><option>--help</option></term>

                                <listitem><para>Prints a short help
                                text and exits.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--unit=</option></term>

                                <listitem><para>Set default unit to
                                activate on startup. If not specified
                                defaults to
                                <filename>default.target</filename>.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--running-as=</option></term>

                                <listitem><para>Tell systemd to run in
                                a particular mode. Argument is one of
                                <option>system</option>,
                                <option>session</option>. Normally it
                                should not be necessary to pass this
                                option, as systemd automatically
                                detects the mode it is started
                                in. This call is hence of little use
                                except for
                                debugging.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--test</option></term>

                                <listitem><para>Determine startup
                                sequence, dump it and exit. This is an
                                option useful for debugging
                                only.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--dump-configuration-items</option></term>

                                <listitem><para>Dump understood unit
                                configuration items. This outputs a
                                terse but complete list of
                                configuration items understood in unit
                                definition files.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--confirm-spawn</option></term>

                                <listitem><para>Ask for confirmation when spawning processes.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--introspect=</option></term>

                                <listitem><para>Extract D-Bus
                                interface introspection data. This is
                                mostly useful at build at install time
                                to generate data suitable for the
                                D-Bus interfaces
                                repository. Optionally the interface
                                name for the introspection data may be
                                specified. If omitted, the
                                introspection data for all interfaces
                                is dumped.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--log-level=</option></term>

                                <listitem><para>Set log level. As
                                argument this accepts a numerical log
                                level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                symbolic names (lowercase):
                                <option>emerg</option>,
                                <option>alert</option>,
                                <option>crit</option>,
                                <option>err</option>,
                                <option>warning</option>,
                                <option>notice</option>,
                                <option>info</option>,
                                <option>debug</option>.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--log-target=</option></term>

                                <listitem><para>Set log
                                target. Argument must be one of
                                <option>console</option>,
                                <option>syslog</option>,
                                <option>kmsg</option>,
                                <option>syslog-or-kmsg</option>,
                                <option>null</option>.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--log-color=</option></term>

                                <listitem><para>Highlight important
                                log messages. Argument is a boolean
                                value. If the argument is omitted it
                                defaults to
                                <option>true</option>.</para></listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><option>--log-location=</option></term>

                                <listitem><para>Include code location
                                in log messages. This is mostly
                                relevant for debugging
                                purposes. Argument is a boolean
                                value. If the argument is omitted
                                it defaults to
                                <option>true</option>.</para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Concepts</title>

                <para>systemd provides a dependency system between
                various entities called "units". Units encapsulate
                various objects that are relevant for system boot-up
                and maintainance. The majority of units are configured
                in unit configuration files, whose syntax and basic
                set of options is described in
                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                however some are created automatically from other
                configuration or dynamically from system state. Units
                may be active (meaning started, bound, plugged in, ...
                depending on the unit type), or inactive (meaning
                stopped, unbound, unplugged, ...), as well is in the
                process of being activated or deactivated,
                i.e. between the two states. The following unit types
                are available:</para>

                <orderedlist>
                        <listitem><para>Service units, which control
                        daemons and the processes they consist of. For
                        details see
                        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Socket units, which
                        encapsulate local IPC or network sockets in
                        the system, useful for socket-based
                        activation. For details about socket units see
                        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        for details on socket-based activation and
                        other forms of activation, see
                        <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Target units are useful to
                        group units, or provide well-known
                        synchronization points during boot-up, see
                        <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Device units expose kernel
                        devices in systemd and may be used to
                        implement device-based activation. For details
                        see
                        <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Mount units control mount
                        points in the file system, for details see
                        <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Automount units provide
                        automount capabilities, for on-demand mounting
                        of file systems as well as parallelized
                        boot-up. See
                        <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Snapshot units can be used to
                        temporarily save the state of the set of
                        systemd units, which later may be restored by
                        activating the saved snapshot unit. For more
                        information see
                        <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Timer units are useful for
                        triggering activation of other units based on
                        timers. You may find details in
                        <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Swap units are very similar to
                        mount units and encapsulated memory swap
                        partitions or files of the operating
                        systemd. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                        <listitem><para>Path units may be used
                        activate other services when file system
                        objects change or are modified. See
                        <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>

                </orderedlist>

                <para>Units are named as their configuration
                files. Some units have special semantics. A detailed
                list you may find in
                <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>

                <para>On boot systemd activates the target unit
                <filename>default.target</filename> whose job it is to
                activate on-boot services and other on-boot units by
                pulling them in via dependencies. Usually the unit
                name is just an alias (symlink) for either
                <filename>graphical.target</filename> (for
                fully-featured boots into the UI) or
                <filename>multi-user.target</filename> (for limited
                console-only boots for use in embedded or server
                environments, or similar; a subset of
                graphical.target). However it is at the discretion of
                the administrator to configure it as an alias to any
                other target unit. See
                <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                for details about these target units.</para>

                <para>For more information about the concepts and
                ideas behind systemd please refer to the <ulink
                url="http://0pointer.de/blog/projects/systemd.html">Original
                Announcement Document</ulink>.</para>
        </refsect1>

        <refsect1>
                <title>Directories</title>

                <variablelist>
                        <varlistentry>
                                <term>System unit directories</term>

                                <listitem><para>The systemd system
                                manager reads unit configuration from
                                various directories. Packages that
                                want to install unit files shall place
                                them in the directory returned by
                                <command>pkg-config systemd
                                --variable=systemdsystemunitdir</command>. Other
                                directories checked are
                                <filename>/usr/local/share/systemd/system</filename>
                                and
                                <filename>/usr/share/systemd/system</filename>. User
                                configuration always takes
                                precedence. <command>pkg-config
                                systemd
                                --variable=systemdsystemconfdir</command>
                                returns the path of the system
                                configuration directory. Packages
                                should alter the content of these directories
                                only with the
                                <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                                tool.</para></listitem>
                        </varlistentry>
                </variablelist>

                <variablelist>
                        <varlistentry>
                                <term>Session unit directories</term>

                                <listitem><para>Similar rules apply
                                for the session unit
                                directories. However, here the <ulink
                                url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
                                Base Directory specification</ulink>
                                is followed to find
                                units. Applications should place their
                                unit files in the directory returned
                                by <command>pkg-config systemd
                                --variable=systemdsessionunitdir</command>. Global
                                configuration is done in the
                                directory reported by
                                <command>pkg-config systemd
                                --variable=systemdsessionconfdir</command>. The
                                <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                                tool can handle both global (i.e. for
                                all users) and private (for one user)
                                enabling/disabling of
                                units.</para></listitem>
                        </varlistentry>
                </variablelist>

                <variablelist>
                        <varlistentry>
                                <term>SysV init scripts directory</term>

                                <listitem><para>The location of the
                                SysV init script directory varies
                                between distributions. If systemd
                                cannot find a native unit file for a
                                requested service, it will look for a
                                SysV init script of the same name
                                (with the
                                <filename>.service</filename> suffix
                                removed).</para></listitem>
                        </varlistentry>
                </variablelist>

                <variablelist>
                        <varlistentry>
                                <term>SysV runlevel link farm directory</term>

                                <listitem><para>The location of the
                                SysV runlevel link farm directory
                                varies between distributions. systemd
                                will take the link farm into account
                                when figuring out whether a service
                                shall be enabled. Note that a service
                                unit with a native unit configuration
                                file can be started by activating it
                                in the SysV runlevel link
                                farm.</para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Signals</title>

                <variablelist>
                        <varlistentry>
                                <term>SIGTERM</term>

                                <listitem><para>Upon receiving this
                                signal the systemd system manager
                                serializes its state, reexecutes
                                itself and deserializes the saved
                                state again. This is mostly equivalent
                                to <command>systemctl
                                daemon-reexec</command>.</para>

                                <para>systemd session managers will
                                start the
                                <filename>exit.target</filename> unit
                                when this signal is received. This is
                                mostly equivalent to
                                <command>systemctl --session start
                                exit.target</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGINT</term>

                                <listitem><para>Upon receiving this
                                signal the systemd system manager will
                                start the
                                <filename>ctrl-alt-del.target</filename> unit. This
                                is mostly equivalent to
                                <command>systemctl start
                                ctl-alt-del.target</command>.</para>

                                <para>systemd session managers
                                treat this signal the same way as
                                SIGTERM.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGWINCH</term>

                                <listitem><para>When this signal is
                                received the systemd system manager
                                will start the
                                <filename>kbrequest.target</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl start
                                kbrequest.target</command>.</para>

                                <para>This signal is ignored by
                                systemd session
                                managers.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGPWR</term>

                                <listitem><para>When this signal is
                                received the systemd manager
                                will start the
                                <filename>sigpwr.target</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl start
                                sigpwr.target</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGUSR1</term>

                                <listitem><para>When this signal is
                                received the systemd manager will try
                                to reconnect to the D-Bus
                                bus.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGUSR2</term>

                                <listitem><para>When this signal is
                                received the systemd manager will log
                                its complete state in human readable
                                form. The data logged is the same as
                                printed by <command>systemctl
                                dump</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGHUP</term>

                                <listitem><para>Reloads the complete
                                daemon configuration. This is mostly
                                equivalent to <command>systemctl
                                daemon-reload</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGRTMIN+0</term>

                                <listitem><para>Enters default mode, starts the
                                <filename>default.target</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl start
                                default.target</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGRTMIN+1</term>

                                <listitem><para>Enters rescue mode,
                                starts the
                                <filename>rescue.target</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl isolate
                                rescue.target</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGRTMIN+2</term>

                                <listitem><para>Enters emergency mode,
                                starts the
                                <filename>emergency.service</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl isolate
                                emergency.service</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGRTMIN+3</term>

                                <listitem><para>Halts the machine,
                                starts the
                                <filename>halt.target</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl start
                                halt.target</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGRTMIN+4</term>

                                <listitem><para>Powers off the machine,
                                starts the
                                <filename>poweroff.target</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl start
                                poweroff.target</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term>SIGRTMIN+5</term>

                                <listitem><para>Reboots the machine,
                                starts the
                                <filename>reboot.target</filename>
                                unit. This is mostly equivalent to
                                <command>systemctl start
                                reboot.target</command>.</para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Environment</title>

                <variablelist>
                        <varlistentry>
                                <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
                                <listitem><para>systemd reads the
                                log level from this environment
                                variable. This can be overridden with
                                <option>--log-level=</option>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
                                <listitem><para>systemd reads the
                                log target from this environment
                                variable. This can be overridden with
                                <option>--log-target=</option>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
                                <listitem><para>Controls whether
                                systemd highlights important log
                                messages. This can be overridden with
                                <option>--log-color=</option>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
                                <listitem><para>Controls whether
                                systemd prints the code location along
                                with log messages. This can be
                                overridden with
                                <option>--log-location=</option>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$XDG_CONFIG_HOME</varname></term>
                                <term><varname>$XDG_CONFIG_DIRS</varname></term>
                                <term><varname>$XDG_DATA_HOME</varname></term>
                                <term><varname>$XDG_DATA_DIRS</varname></term>

                                <listitem><para>The systemd session
                                manager uses these variables in
                                accordance to the <ulink
                                url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
                                Base Directory specification</ulink>
                                to find its configuration.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$SYSTEMD_UNIT_PATH</varname></term>

                                <listitem><para>Controls where systemd
                                looks for unit
                                files.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>

                                <listitem><para>Controls where systemd
                                looks for SysV init scripts.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>

                                <listitem><para>Controls where systemd
                                looks for SysV init script runlevel link
                                farms.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$LISTEN_PID</varname></term>
                                <term><varname>$LISTEN_FDS</varname></term>

                                <listitem><para>Set by systemd for
                                supervised processes during
                                socket-based activation. See
                                <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                for more information.
                                </para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>$NOTIFY_SOCKET</varname></term>

                                <listitem><para>Set by systemd for
                                supervised processes for status and
                                start-up completion notification. See
                                <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                for more information.
                                </para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>Sockets and FIFOs</title>

                <variablelist>
                        <varlistentry>
                                <term><filename>@/org/freedesktop/systemd1/notify</filename></term>

                                <listitem><para>Daemon status
                                notification socket. This is an AF_UNIX
                                datagram socket in the Linux abstract
                                namespace, and is used to implement
                                the daemon notification logic as
                                implemented by
                                <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>

                        </varlistentry>

                        <varlistentry>
                                <term><filename>@/org/freedesktop/systemd1/logger</filename></term>

                                <listitem><para>Used internally by the
                                <filename>systemd-logger.service</filename>
                                unit to connect STDOUT and/or STDERR
                                of spawned processes to
                                <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                or the kernel log buffer. This is an
                                AF_UNIX stream socket in the Linux
                                abstract namespace.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><filename>@/org/freedesktop/systemd1/private</filename></term>

                                <listitem><para>Used internally as
                                communication channel between
                                <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                                and the systemd process. This is an
                                AF_UNIX stream socket in the Linux
                                abstract namespace. This interface is
                                private to systemd and should not be
                                used in external
                                projects.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><filename>/dev/initctl</filename></term>

                                <listitem><para>Limited compatibility
                                support for the SysV client interface,
                                as implemented by the
                                <filename>systemd-initctl.service</filename>
                                unit. This is a named pipe in the file
                                system. This interface is obsolete and
                                should not be used in new
                                applications.</para></listitem>
                        </varlistentry>
                </variablelist>
        </refsect1>

        <refsect1>
                <title>See Also</title>
                <para>
                        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>