service: make main pid guessing optional, and reread pid file after reloads

[thirdparty/systemd.git] / man / systemd.service.xml

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<refentry id="systemd.service">
        <refentryinfo>
                <title>systemd.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.service</refentrytitle>
                <manvolnum>5</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd.service</refname>
                <refpurpose>systemd service configuration files</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <para><filename>systemd.service</filename></para>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para>A unit configuration file whose name ends in
                <filename>.service</filename> encodes information
                about a process controlled and supervised by
                systemd.</para>

                <para>This man page lists the configuration options
                specific to this unit type. See
                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                for the common options of all unit configuration
                files. The common configuration items are configured
                in the generic <literal>[Unit]</literal> and
                <literal>[Install]</literal> sections. The service
                specific configuration options are configured in the
                <literal>[Service]</literal> section.</para>

                <para>Additional options are listed in
                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                which define the execution environment the commands
                are executed in.</para>

                <para>Unless <varname>DefaultDependencies=</varname>
                is set to <option>false</option>, service units will
                implicitly have dependencies of type
                <varname>Requires=</varname> and
                <varname>After=</varname> on
                <filename>basic.target</filename> as well as
                dependencies of type <varname>Conflicts=</varname> and
                <varname>Before=</varname> on
                <filename>shutdown.target</filename>. These ensure
                that normal service units pull in basic system
                initialization, and are terminated cleanly prior to
                system shutdown. Only services involved with early
                boot or late system shutdown should disable this
                option.</para>

                <para>If a service is requested under a certain name
                but no unit configuration file is found, systemd looks
                for a SysV init script by the same name (with the
                <filename>.service</filename> suffix removed) and
                dynamically creates a service unit from that
                script. This is useful for compatibility with
                SysV.</para>
        </refsect1>

        <refsect1>
                <title>Options</title>

                <para>Service files must include a
                <literal>[Service]</literal> section, which carries
                information about the service and the process it
                supervises. A number of options that may be used in
                this section are shared with other unit types. These
                options are documented in
                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
                options specific to the <literal>[Service]</literal>
                section of service units are the following:</para>

                <variablelist>
                        <varlistentry>
                                <term><varname>Type=</varname></term>

                                <listitem><para>Configures the process
                                start-up type for this service
                                unit. One of <option>simple</option>,
                                <option>forking</option>,
                                <option>oneshot</option>,
                                <option>dbus</option>,
                                <option>notify</option>.</para>

                                <para>If set to
                                <option>simple</option> (the default
                                value) it is expected that the process
                                configured with
                                <varname>ExecStart=</varname> is the
                                main process of the service. In this
                                mode, if the process offers
                                functionality to other processes on
                                the system its communication channels
                                should be installed before the daemon
                                is started up (e.g. sockets set up by
                                systemd, via socket activation), as
                                systemd will immediately proceed
                                starting follow-up units.</para>

                                <para>If set to
                                <option>forking</option> it is
                                expected that the process configured
                                with <varname>ExecStart=</varname>
                                will call <function>fork()</function>
                                as part of its start-up. The parent process is
                                expected to exit when start-up is
                                complete and all communication
                                channels set up. The child continues
                                to run as the main daemon
                                process. This is the behaviour of
                                traditional UNIX daemons. If this
                                setting is used, it is recommended to
                                also use the
                                <varname>PIDFile=</varname> option, so
                                that systemd can identify the main
                                process of the daemon. systemd will
                                proceed starting follow-up units as
                                soon as the parent process
                                exits.</para>

                                <para>Behaviour of
                                <option>oneshot</option> is similar
                                to <option>simple</option>, however
                                it is expected that the process has to
                                exit before systemd starts follow-up
                                units. <varname>RemainAfterExit=</varname>
                                is particularly useful for this type
                                of service.</para>

                                <para>Behaviour of
                                <option>dbus</option> is similar to
                                <option>simple</option>, however it is
                                expected that the daemon acquires a
                                name on the D-Bus bus, as configured
                                by
                                <varname>BusName=</varname>. systemd
                                will proceed starting follow-up units
                                after the D-Bus bus name has been
                                acquired. Service units with this
                                option configured implicitly gain
                                dependencies on the
                                <filename>dbus.target</filename>
                                unit.</para>

                                <para>Behaviour of
                                <option>notify</option> is similar to
                                <option>simple</option>, however it is
                                expected that the daemon sends a
                                notification message via
                                <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                or an equivalent call when it finished
                                starting up. systemd will proceed
                                starting follow-up units after this
                                notification message has been sent. If
                                this option is used
                                <varname>NotifyAccess=</varname> (see
                                below) should be set to open access to
                                the notification socket provided by
                                systemd. If
                                <varname>NotifyAccess=</varname> is not
                                set, it will implicitly be set to
                                <option>main</option>.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>RemainAfterExit=</varname></term>

                                <listitem><para>Takes a boolean value
                                that specifies whether the service
                                shall be considered active even when
                                all its processes exited. Defaults to
                                <option>no</option>.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>GuessMainPID=</varname></term>

                                <listitem><para>Takes a boolean value
                                that specifies whether systemd should
                                try to guess the main PID of a service
                                should if it cannot be determined
                                reliably. This option is ignored
                                unless <option>Type=forking</option>
                                is set and <option>PIDFile=</option>
                                is unset because for the other types
                                or with an explicitly configured PID
                                file the main PID is always known. The
                                guessing algorithm might come to
                                incorrect conclusions if a daemon
                                consists of more than one process. If
                                the main PID cannot be determined
                                failure detection and automatic
                                restarting of a service will not work
                                reliably. Defaults to
                                <option>yes</option>.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>PIDFile=</varname></term>

                                <listitem><para>Takes an absolute file
                                name pointing to the PID file of this
                                daemon. Use of this option is
                                recommended for services where
                                <varname>Type=</varname> is set to
                                <option>forking</option>. systemd will
                                read the PID of the main process of
                                the daemon after start-up of the
                                service. systemd will not write to the
                                file configured here.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>BusName=</varname></term>

                                <listitem><para>Takes a D-Bus bus
                                name, where this service is reachable
                                as. This option is mandatory for
                                services where
                                <varname>Type=</varname> is set to
                                <option>dbus</option>, but its use
                                is otherwise recommended as well if
                                the process takes a name on the D-Bus
                                bus.</para>
                                </listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>ExecStart=</varname></term>
                                <listitem><para>Takes a command line
                                that is executed when this service
                                shall be started up. The first token
                                of the command line must be an
                                absolute file name, then followed by
                                arguments for the process. It is
                                mandatory to set this option for all
                                services. This option may not be
                                specified more than once, except when
                                <varname>Type=oneshot</varname> is
                                used in which case more than one
                                <varname>ExecStart=</varname> line is
                                accepted which are then invoked one by
                                one, sequentially in the order they
                                appear in the unit file.</para>

                                <para>Optionally, if the absolute file
                                name is prefixed with
                                <literal>@</literal>, the second token
                                will be passed as
                                <literal>argv[0]</literal> to the
                                executed process, followed by the
                                further arguments specified. If the
                                first token is prefixed with
                                <literal>-</literal> an exit code of
                                the command normally considered a
                                failure (i.e. non-zero exit status or
                                abnormal exit due to signal) is ignored
                                and considered success. If both
                                <literal>-</literal> and
                                <literal>@</literal> are used for the
                                same command the former must precede
                                the latter. Unless
                                <varname>Type=forking</varname> is
                                set, the process started via this
                                command line will be considered the
                                main process of the daemon. The
                                command line accepts % specifiers as
                                described in
                                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. On
                                top of that basic environment variable
                                substitution is supported, where
                                <literal>${FOO}</literal> is replaced
                                by the string value of the environment
                                variable of the same name. Also
                                <literal>$FOO</literal> may appear as
                                separate word on the command line in
                                which case the variable is replaced by
                                its value split at whitespaces. Note
                                that the first argument (i.e. the
                                binary to execute) may not be a
                                variable, and must be a literal and
                                absolute path name.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>ExecStartPre=</varname></term>
                                <term><varname>ExecStartPost=</varname></term>
                                <listitem><para>Additional commands
                                that are executed before (resp. after)
                                the command in
                                <varname>ExecStart=</varname>. Multiple
                                command lines may be concatenated in a
                                single directive, by separating them
                                by semicolons (these semicolons must
                                be passed as separate words). In that
                                case, the commands are executed one
                                after the other,
                                serially. Alternatively, these
                                directives may be specified more than
                                once with the same effect. However,
                                the latter syntax is not recommended
                                for compatibility with parsers
                                suitable for XDG
                                <filename>.desktop</filename> files.
                                Use of these settings is
                                optional. Specifier and environment
                                variable substitution is
                                supported.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>ExecReload=</varname></term>
                                <listitem><para>Commands to execute to
                                trigger a configuration reload in the
                                service. This argument takes multiple
                                command lines, following the same
                                scheme as pointed out for
                                <varname>ExecStartPre=</varname>
                                above. Use of this setting is
                                optional. Specifier and environment
                                variable substitution is supported
                                here following the same scheme as for
                                <varname>ExecStart=</varname>. One
                                special environment variable is set:
                                if known <literal>$MAINPID</literal> is
                                set to the main process of the
                                daemon, and may be used for command
                                lines like the following:
                                <command>/bin/kill -HUP
                                $MAINPID</command>.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>ExecStop=</varname></term>
                                <listitem><para>Commands to execute to
                                stop the service started via
                                <varname>ExecStart=</varname>. This
                                argument takes multiple command lines,
                                following the same scheme as pointed
                                out for
                                <varname>ExecStartPre=</varname>
                                above. Use of this setting is
                                optional. All processes remaining for
                                a service after the commands
                                configured in this option are run are
                                terminated according to the
                                <varname>KillMode=</varname> setting
                                (see below). If this option is not
                                specified the process is terminated
                                right-away when service stop is
                                requested. Specifier and environment
                                variable substitution is supported
                                (including
                                <literal>$MAINPID</literal>, see
                                above).</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>ExecStopPost=</varname></term>
                                <listitem><para>Additional commands
                                that are executed after the service
                                was stopped using the commands
                                configured in
                                <varname>ExecStop=</varname>. This
                                argument takes multiple command lines,
                                following the same scheme as pointed
                                out for
                                <varname>ExecStartPre</varname>. Use
                                of these settings is
                                optional. Specifier and environment
                                variable substitution is
                                supported.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>RestartSec=</varname></term>
                                <listitem><para>Configures the time to
                                sleep before restarting a service (as
                                configured with
                                <varname>Restart=</varname>). Takes a
                                unit-less value in seconds, or a time
                                span value such as "5min
                                20s". Defaults to
                                100ms.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>TimeoutSec=</varname></term>
                                <listitem><para>Configures the time to
                                wait for start-up and stop. If a
                                daemon service does not signal
                                start-up completion within the
                                configured time the service will be
                                considered failed and be shut down
                                again. If a service is asked to stop
                                but does not terminate in the
                                specified time it will be terminated
                                forcibly via SIGTERM, and after
                                another delay of this time with
                                SIGKILL. (See
                                <varname>KillMode=</varname>
                                below.) Takes a unit-less value in seconds, or a
                                time span value such as "5min
                                20s". Pass 0 to disable the timeout
                                logic. Defaults to
                                60s.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>Restart=</varname></term>
                                <listitem><para>Configures whether the
                                main service process shall be
                                restarted when it exits. Takes one of
                                <option>no</option>,
                                <option>on-success</option>,
                                <option>on-failure</option>,
                                <option>on-abort</option> or
                                <option>always</option>. If set to
                                <option>no</option> (the default) the
                                service will not be restarted when it
                                exits. If set to
                                <option>on-success</option> it will be
                                restarted only when it exited cleanly,
                                i.e. terminated with an exit code of
                                0. If set to
                                <option>on-failure</option> it will be
                                restarted only when it exited with an
                                exit code not equalling 0, or when
                                terminated by a signal. If set to
                                <option>on-abort</option> it will be
                                restarted only if it exits due to
                                reception of an uncaught signal. If
                                set to <option>always</option> the
                                service will be restarted regardless
                                whether it exited cleanly or not, or
                                got terminated abnormally by a
                                signal.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>PermissionsStartOnly=</varname></term>
                                <listitem><para>Takes a boolean
                                argument. If true, the permission
                                related execution options as
                                configured with
                                <varname>User=</varname> and similar
                                options (see
                                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                for more information) are only applied
                                to the process started with
                                <varname>ExecStart=</varname>, and not
                                to the various other
                                <varname>ExecStartPre=</varname>,
                                <varname>ExecStartPost=</varname>,
                                <varname>ExecReload=</varname>,
                                <varname>ExecStop=</varname>,
                                <varname>ExecStopPost=</varname>
                                commands. If false, the setting is
                                applied to all configured commands the
                                same way. Defaults to
                                false.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>RootDirectoryStartOnly=</varname></term>
                                <listitem><para>Takes a boolean
                                argument. If true, the root directory
                                as configured with the
                                <varname>RootDirectory=</varname>
                                option (see
                                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                for more information) is only applied
                                to the process started with
                                <varname>ExecStart=</varname>, and not
                                to the various other
                                <varname>ExecStartPre=</varname>,
                                <varname>ExecStartPost=</varname>,
                                <varname>ExecReload=</varname>,
                                <varname>ExecStop=</varname>,
                                <varname>ExecStopPost=</varname>
                                commands. If false, the setting is
                                applied to all configured commands the
                                same way. Defaults to
                                false.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>SysVStartPriority=</varname></term>
                                <listitem><para>Set the SysV start
                                priority to use to order this service
                                in relation to SysV services lacking
                                LSB headers. This option is only
                                necessary to fix ordering in relation
                                to legacy SysV services, that have no
                                ordering information encoded in the
                                script headers. As such it should only
                                be used as temporary compatibility
                                option, and not be used in new unit
                                files. Almost always it is a better
                                choice to add explicit ordering
                                directives via
                                <varname>After=</varname> or
                                <varname>Before=</varname>,
                                instead. For more details see
                                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. If
                                used, pass an integer value in the
                                range 0-99.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>KillMode=</varname></term>
                                <listitem><para>Specifies how
                                processes of this service shall be
                                killed. One of
                                <option>control-group</option>,
                                <option>process-group</option>,
                                <option>process</option>,
                                <option>none</option>.</para>

                                <para>If set to
                                <option>control-group</option> all
                                remaining processes in the control
                                group of this service will be
                                terminated on service stop, after the
                                stop command (as configured with
                                <varname>ExecStop=</varname>) is
                                executed. If set to
                                <option>process-group</option> only
                                the members of the process group of
                                the main service process are
                                killed. If set to
                                <option>process</option> only the main
                                process itself is killed. If set to
                                <option>none</option> no process is
                                killed. In this case only the stop
                                command will be executed on service
                                stop, but no process be killed
                                otherwise. Processes remaining alive
                                after stop are left in their control
                                group and the control group continues
                                to exist after stop unless it is
                                empty. Defaults to
                                <option>control-group</option>.</para>

                                <para>Processes will first be
                                terminated via SIGTERM (unless the
                                signal to send is changed via
                                <varname>KillSignal=</varname>). If
                                then after a delay (configured via the
                                <varname>TimeoutSec=</varname> option)
                                processes still remain, the
                                termination request is repeated with
                                the SIGKILL signal (unless this is
                                disabled via the
                                <varname>SendSIGKILL=</varname>
                                option). See
                                <citerefentry><refentrytitle>kill</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                                for more
                                information.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>KillSignal=</varname></term>
                                <listitem><para>Specifies which signal
                                to use when killing a
                                service. Defaults to SIGTERM.
                                </para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>SendSIGKILL=</varname></term>
                                <listitem><para>Specifies whether to
                                send SIGKILL to remaining processes
                                after a timeout, if the normal
                                shutdown procedure left processes of
                                the service around. Takes a boolean
                                value. Defaults to "yes".
                                </para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>NonBlocking=</varname></term>
                                <listitem><para>Set O_NONBLOCK flag
                                for all file descriptors passed via
                                socket-based activation. If true, all
                                file descriptors >= 3 (i.e. all except
                                STDIN/STDOUT/STDERR) will have
                                the O_NONBLOCK flag set and hence are in
                                non-blocking mode. This option is only
                                useful in conjunction with a socket
                                unit, as described in
                                <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Defaults
                                to false.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>NotifyAccess=</varname></term>
                                <listitem><para>Controls access to the
                                service status notification socket, as
                                accessible via the
                                <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                call. Takes one of
                                <option>none</option> (the default),
                                <option>main</option> or
                                <option>all</option>. If
                                <option>none</option> no daemon status
                                updates are accepted from the service
                                processes, all status update messages
                                are ignored. If <option>main</option>
                                only service updates sent from the
                                main process of the service are
                                accepted. If <option>all</option> all
                                services updates from all members of
                                the service's control group are
                                accepted. This option must be set to
                                open access to the notification socket
                                when using
                                <varname>Type=notify</varname> (see above).</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>Sockets=</varname></term>
                                <listitem><para>Specifies the name of
                                the socket units this service shall
                                inherit the sockets from when the
                                service (ignoring the different suffix
                                of course) is started. Normally it
                                should not be necessary to use this
                                setting as all sockets whose unit
                                shares the same name as the service
                                are passed to the spawned
                                process.</para>

                                <para>Note that the same socket may be
                                passed to multiple processes at the
                                same time. Also note that a different
                                service may be activated on incoming
                                traffic than inherits the sockets. Or
                                in other words: The
                                <varname>Service=</varname> setting of
                                <filename>.socket</filename> units
                                doesn't have to match the inverse of the
                                <varname>Sockets=</varname> setting of
                                the <filename>.service</filename> it
                                refers to.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>FsckPassNo=</varname></term>
                                <listitem><para>Set the fsck passno
                                priority to use to order this service
                                in relation to other file system
                                checking services. This option is only
                                necessary to fix ordering in relation
                                to fsck jobs automatically created for
                                all <filename>/etc/fstab</filename>
                                entries with a value in the fs_passno
                                column > 0. As such it should only be
                                used as option for fsck
                                services. Almost always it is a better
                                choice to add explicit ordering
                                directives via
                                <varname>After=</varname> or
                                <varname>Before=</varname>,
                                instead. For more details see
                                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. If
                                used, pass an integer value in the
                                same range as
                                <filename>/etc/fstab</filename>'s
                                fs_passno column. See
                                <citerefentry><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                for details.</para></listitem>
                        </varlistentry>

                </variablelist>
        </refsect1>

        <refsect1>
                  <title>See Also</title>
                  <para>
                          <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                  </para>
        </refsect1>

</refentry>