systemd.service(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | SERVICE TEMPLATES | AUTOMATIC DEPENDENCIES | OPTIONS | COMMAND LINES | EXAMPLES | SEE ALSO | NOTES | COLOPHON

SYSTEMD.SERVICE(5)           systemd.service          SYSTEMD.SERVICE(5)

NAME         top

       systemd.service - Service unit configuration

SYNOPSIS         top

       service.service

DESCRIPTION         top

       A unit configuration file whose name ends in ".service" encodes
       information about a process controlled and supervised by systemd.

       This man page lists the configuration options specific to this
       unit type. See systemd.unit(5) for the common options of all unit
       configuration files. The common configuration items are
       configured in the generic [Unit] and [Install] sections. The
       service specific configuration options are configured in the
       [Service] section.

       Additional options are listed in systemd.exec(5), which define
       the execution environment the commands are executed in, and in
       systemd.kill(5), which define the way the processes of the
       service are terminated, and in systemd.resource-control(5), which
       configure resource control settings for the processes of the
       service.

       If SysV init compat is enabled, systemd automatically creates
       service units that wrap SysV init scripts (the service name is
       the same as the name of the script, with a ".service" suffix
       added); see systemd-sysv-generator(8).

       The systemd-run(1) command allows creating .service and .scope
       units dynamically and transiently from the command line.

SERVICE TEMPLATES         top

       It is possible for systemd services to take a single argument via
       the "service@argument.service" syntax. Such services are called
       "instantiated" services, while the unit definition without the
       argument parameter is called a "template". An example could be a
       dhcpcd@.service service template which takes a network interface
       as a parameter to form an instantiated service. Within the
       service file, this parameter or "instance name" can be accessed
       with %-specifiers. See systemd.unit(5) for details.

AUTOMATIC DEPENDENCIES         top

   Implicit Dependencies
       The following dependencies are implicitly added:

       •   Services with Type=dbus set automatically acquire
           dependencies of type Requires= and After= on dbus.socket.

       •   Socket activated services are automatically ordered after
           their activating .socket units via an automatic After=
           dependency. Services also pull in all .socket units listed in
           Sockets= via automatic Wants= and After= dependencies.

       Additional implicit dependencies may be added as result of
       execution and resource control parameters as documented in
       systemd.exec(5) and systemd.resource-control(5).

   Default Dependencies
       The following dependencies are added unless
       DefaultDependencies=no is set:

       •   Service units will have dependencies of type Requires= and
           After= on sysinit.target, a dependency of type After= on
           basic.target as well as dependencies of type Conflicts= and
           Before= on shutdown.target. 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.

       •   Instanced service units (i.e. service units with an "@" in
           their name) are assigned by default a per-template slice unit
           (see systemd.slice(5)), named after the template unit,
           containing all instances of the specific template. This slice
           is normally stopped at shutdown, together with all template
           instances. If that is not desired, set DefaultDependencies=no
           in the template unit, and either define your own per-template
           slice unit file that also sets DefaultDependencies=no, or set
           Slice=system.slice (or another suitable slice) in the
           template unit. Also see systemd.resource-control(5).

OPTIONS         top

       Service unit files may include [Unit] and [Install] sections,
       which are described in systemd.unit(5).

       Service unit files must include a [Service] 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
       systemd.exec(5), systemd.kill(5) and systemd.resource-control(5).
       The options specific to the [Service] section of service units
       are the following:

       Type=
           Configures the mechanism via which the service notifies the
           manager that the service start-up has finished. One of
           simple, exec, forking, oneshot, dbus, notify, notify-reload,
           or idle:

           •   If set to simple (the default if ExecStart= is specified
               but neither Type= nor BusName= are), the service manager
               will consider the unit started immediately after the main
               service process has been forked off (i.e. immediately
               after fork(), and before various process attributes have
               been configured and in particular before the new process
               has called execve() to invoke the actual service binary).
               Typically, Type=exec is the better choice, see below.

               It is expected that the process configured with
               ExecStart= 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 service is started up
               (e.g. sockets set up by systemd, via socket activation),
               as the service manager will immediately proceed starting
               follow-up units, right after creating the main service
               process, and before executing the service's binary. Note
               that this means systemctl start command lines for simple
               services will report success even if the service's binary
               cannot be invoked successfully (for example because the
               selected User= doesn't exist, or the service binary is
               missing).

           •   The exec type is similar to simple, but the service
               manager will consider the unit started immediately after
               the main service binary has been executed. The service
               manager will delay starting of follow-up units until that
               point. (Or in other words: simple proceeds with further
               jobs right after fork() returns, while exec will not
               proceed before both fork() and execve() in the service
               process succeeded.) Note that this means systemctl start
               command lines for exec services will report failure when
               the service's binary cannot be invoked successfully (for
               example because the selected User= doesn't exist, or the
               service binary is missing).

           •   If set to forking, the manager will consider the unit
               started immediately after the binary that forked off by
               the manager exits.  The use of this type is discouraged,
               use notify, notify-reload, or dbus instead.

               It is expected that the process configured with
               ExecStart= will call fork() as part of its start-up. The
               parent process is expected to exit when start-up is
               complete and all communication channels are set up. The
               child continues to run as the main service process, and
               the service manager will consider the unit started when
               the parent process exits. This is the behavior of
               traditional UNIX services. If this setting is used, it is
               recommended to also use the PIDFile= option, so that
               systemd can reliably identify the main process of the
               service. The manager will proceed with starting follow-up
               units after the parent process exits.

           •   Behavior of oneshot is similar to simple; however, the
               service manager will consider the unit up after the main
               process exits. It will then start follow-up units.
               RemainAfterExit= is particularly useful for this type of
               service.  Type=oneshot is the implied default if neither
               Type= nor ExecStart= are specified. Note that if this
               option is used without RemainAfterExit= the service will
               never enter "active" unit state, but will directly
               transition from "activating" to "deactivating" or "dead",
               since no process is configured that shall run
               continuously. In particular this means that after a
               service of this type ran (and which has RemainAfterExit=
               not set) it will not show up as started afterwards, but
               as dead.

           •   Behavior of dbus is similar to simple; however, units of
               this type must have the BusName= specified and the
               service manager will consider the unit up when the
               specified bus name has been acquired. This type is the
               default if BusName= is specified.

               Service units with this option configured implicitly gain
               dependencies on the dbus.socket unit. A service unit of
               this type is considered to be in the activating state
               until the specified bus name is acquired. It is
               considered activated while the bus name is taken. Once
               the bus name is released the service is considered being
               no longer functional which has the effect that the
               service manager attempts to terminate any remaining
               processes belonging to the service. Services that drop
               their bus name as part of their shutdown logic thus
               should be prepared to receive a SIGTERM (or whichever
               signal is configured in KillSignal=) as result.

           •   Behavior of notify is similar to exec; however, it is
               expected that the service sends a "READY=1" notification
               message via sd_notify(3) or an equivalent call when it
               has finished starting up. systemd will proceed with
               starting follow-up units after this notification message
               has been sent. If this option is used, NotifyAccess= (see
               below) should be set to open access to the notification
               socket provided by systemd. If NotifyAccess= is missing
               or set to none, it will be forcibly set to main.

               If the service supports reloading, and uses a signal to
               start the reload, using notify-reload instead is
               recommended.

           •   Behavior of notify-reload is similar to notify, with one
               difference: the SIGHUP UNIX process signal is sent to the
               service's main process when the service is asked to
               reload and the manager will wait for a notification about
               the reload being finished.

               When initiating the reload process the service is
               expected to reply with a notification message via
               sd_notify(3) that contains the "RELOADING=1" field in
               combination with "MONOTONIC_USEC=" set to the current
               monotonic time (i.e.  CLOCK_MONOTONIC in
               clock_gettime(2)) in μs, formatted as decimal string.
               Once reloading is complete another notification message
               must be sent, containing "READY=1". Using this service
               type and implementing this reload protocol is an
               efficient alternative to providing an ExecReload= command
               for reloading of the service's configuration.

               The signal to send can be tweaked via ReloadSignal=, see
               below.

           •   Behavior of idle is very similar to simple; however,
               actual execution of the service program is delayed until
               all active jobs are dispatched. This may be used to avoid
               interleaving of output of shell services with the status
               output on the console. Note that this type is useful only
               to improve console output, it is not useful as a general
               unit ordering tool, and the effect of this service type
               is subject to a 5s timeout, after which the service
               program is invoked anyway.

           It is recommended to use Type=exec for long-running services,
           as it ensures that process setup errors (e.g. errors such as
           a missing service executable, or missing user) are properly
           tracked. However, as this service type won't propagate the
           failures in the service's own startup code (as opposed to
           failures in the preparatory steps the service manager
           executes before execve()) and doesn't allow ordering of other
           units against completion of initialization of the service
           code itself (which for example is useful if clients need to
           connect to the service through some form of IPC, and the IPC
           channel is only established by the service itself — in
           contrast to doing this ahead of time through socket or bus
           activation or similar), it might not be sufficient for many
           cases. If so, notify, notify-reload, or dbus (the latter only
           in case the service provides a D-Bus interface) are the
           preferred options as they allow service program code to
           precisely schedule when to consider the service started up
           successfully and when to proceed with follow-up units. The
           notify/notify-reload service types require explicit support
           in the service codebase (as sd_notify() or an equivalent API
           needs to be invoked by the service at the appropriate time) —
           if it's not supported, then forking is an alternative: it
           supports the traditional heavy-weight UNIX service start-up
           protocol. Note that using any type other than simple possibly
           delays the boot process, as the service manager needs to wait
           for at least some service initialization to complete. (Also
           note it is generally not recommended to use idle or oneshot
           for long-running services.)

           Note that various service settings (e.g.  User=, Group=
           through libc NSS) might result in "hidden" blocking IPC calls
           to other services when used. Sometimes it might be advisable
           to use the simple service type to ensure that the service
           manager's transaction logic is not affected by such
           potentially slow operations and hidden dependencies, as this
           is the only service type where the service manager will not
           wait for such service execution setup operations to complete
           before proceeding.

       ExitType=
           Specifies when the manager should consider the service to be
           finished. One of main or cgroup:

           •   If set to main (the default), the service manager will
               consider the unit stopped when the main process, which is
               determined according to the Type=, exits. Consequently,
               it cannot be used with Type=oneshot.

           •   If set to cgroup, the service will be considered running
               as long as at least one process in the cgroup has not
               exited.

           It is generally recommended to use ExitType=main when a
           service has a known forking model and a main process can
           reliably be determined.  ExitType= cgroup is meant for
           applications whose forking model is not known ahead of time
           and which might not have a specific main process. It is well
           suited for transient or automatically generated services,
           such as graphical applications inside of a desktop
           environment.

           Added in version 250.

       RemainAfterExit=
           Takes a boolean value that specifies whether the service
           shall be considered active even when all its processes
           exited. Defaults to no.

       GuessMainPID=
           Takes a boolean value that specifies whether systemd should
           try to guess the main PID of a service if it cannot be
           determined reliably. This option is ignored unless
           Type=forking is set and PIDFile= 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 yes.

       PIDFile=
           Takes a path referring to the PID file of the service. Usage
           of this option is recommended for services where Type= is set
           to forking. The path specified typically points to a file
           below /run/. If a relative path is specified it is hence
           prefixed with /run/. The service manager will read the PID of
           the main process of the service from this file after start-up
           of the service. The service manager will not write to the
           file configured here, although it will remove the file after
           the service has shut down if it still exists. The PID file
           does not need to be owned by a privileged user, but if it is
           owned by an unprivileged user additional safety restrictions
           are enforced: the file may not be a symlink to a file owned
           by a different user (neither directly nor indirectly), and
           the PID file must refer to a process already belonging to the
           service.

           Note that PID files should be avoided in modern projects. Use
           Type=notify, Type=notify-reload or Type=simple where
           possible, which does not require use of PID files to
           determine the main process of a service and avoids needless
           forking.

       BusName=
           Takes a D-Bus destination name that this service shall use.
           This option is mandatory for services where Type= is set to
           dbus. It is recommended to always set this property if known
           to make it easy to map the service name to the D-Bus
           destination. In particular, systemctl
           service-log-level/service-log-target verbs make use of this.

       ExecStart=
           Commands that are executed when this service is started. The
           value is split into zero or more command lines according to
           the rules described in the section "Command Lines" below.

           Unless Type= is oneshot, exactly one command must be given.
           When Type=oneshot is used, zero or more commands may be
           specified. Commands may be specified by providing multiple
           command lines in the same directive, or alternatively, this
           directive may be specified more than once with the same
           effect. If the empty string is assigned to this option, the
           list of commands to start is reset, prior assignments of this
           option will have no effect. If no ExecStart= is specified,
           then the service must have RemainAfterExit=yes and at least
           one ExecStop= line set. (Services lacking both ExecStart= and
           ExecStop= are not valid.)

           If more than one command is specified, the commands are
           invoked sequentially in the order they appear in the unit
           file. If one of the commands fails (and is not prefixed with
           "-"), other lines are not executed, and the unit is
           considered failed.

           Unless Type=forking is set, the process started via this
           command line will be considered the main process of the
           daemon.

       ExecStartPre=, ExecStartPost=
           Additional commands that are executed before or after the
           command in ExecStart=, respectively. Syntax is the same as
           for ExecStart=, except that multiple command lines are
           allowed and the commands are executed one after the other,
           serially.

           If any of those commands (not prefixed with "-") fail, the
           rest are not executed and the unit is considered failed.

           ExecStart= commands are only run after all ExecStartPre=
           commands that were not prefixed with a "-" exit successfully.

           ExecStartPost= commands are only run after the commands
           specified in ExecStart= have been invoked successfully, as
           determined by Type= (i.e. the process has been started for
           Type=simple or Type=idle, the last ExecStart= process exited
           successfully for Type=oneshot, the initial process exited
           successfully for Type=forking, "READY=1" is sent for
           Type=notify/Type=notify-reload, or the BusName= has been
           taken for Type=dbus).

           Note that ExecStartPre= may not be used to start long-running
           processes. All processes forked off by processes invoked via
           ExecStartPre= will be killed before the next service process
           is run.

           Note that if any of the commands specified in ExecStartPre=,
           ExecStart=, or ExecStartPost= fail (and are not prefixed with
           "-", see above) or time out before the service is fully up,
           execution continues with commands specified in ExecStopPost=,
           the commands in ExecStop= are skipped.

           Note that the execution of ExecStartPost= is taken into
           account for the purpose of Before=/After= ordering
           constraints.

       ExecCondition=
           Optional commands that are executed before the commands in
           ExecStartPre=. Syntax is the same as for ExecStart=, except
           that multiple command lines are allowed and the commands are
           executed one after the other, serially.

           The behavior is like an ExecStartPre= and condition check
           hybrid: when an ExecCondition= command exits with exit code 1
           through 254 (inclusive), the remaining commands are skipped
           and the unit is not marked as failed. However, if an
           ExecCondition= command exits with 255 or abnormally (e.g.
           timeout, killed by a signal, etc.), the unit will be
           considered failed (and remaining commands will be skipped).
           Exit code of 0 or those matching SuccessExitStatus= will
           continue execution to the next commands.

           The same recommendations about not running long-running
           processes in ExecStartPre= also applies to ExecCondition=.
           ExecCondition= will also run the commands in ExecStopPost=,
           as part of stopping the service, in the case of any non-zero
           or abnormal exits, like the ones described above.

           Added in version 243.

       ExecReload=
           Commands to execute to trigger a configuration reload in the
           service. This argument takes multiple command lines,
           following the same scheme as described for ExecStart= above.
           Use of this setting is optional. Specifier and environment
           variable substitution is supported here following the same
           scheme as for ExecStart=.

           One additional, special environment variable is set: if
           known, $MAINPID is set to the main process of the daemon, and
           may be used for command lines like the following:

               ExecReload=kill -HUP $MAINPID

           Note however that reloading a daemon by enqueuing a signal
           (as with the example line above) is usually not a good
           choice, because this is an asynchronous operation and hence
           not suitable when ordering reloads of multiple services
           against each other. It is thus strongly recommended to either
           use Type=notify-reload in place of ExecReload=, or to set
           ExecReload= to a command that not only triggers a
           configuration reload of the daemon, but also synchronously
           waits for it to complete. For example, dbus-broker(1) uses
           the following:

               ExecReload=busctl call org.freedesktop.DBus \
                       /org/freedesktop/DBus org.freedesktop.DBus \
                       ReloadConfig

       ExecStop=
           Commands to execute to stop the service started via
           ExecStart=. This argument takes multiple command lines,
           following the same scheme as described for ExecStart= above.
           Use of this setting is optional. After the commands
           configured in this option are run, it is implied that the
           service is stopped, and any processes remaining for it are
           terminated according to the KillMode= setting (see
           systemd.kill(5)). If this option is not specified, the
           process is terminated by sending the signal specified in
           KillSignal= or RestartKillSignal= when service stop is
           requested. Specifier and environment variable substitution is
           supported (including $MAINPID, see above).

           Note that it is usually not sufficient to specify a command
           for this setting that only asks the service to terminate (for
           example, by sending some form of termination signal to it),
           but does not wait for it to do so. Since the remaining
           processes of the services are killed according to KillMode=
           and KillSignal= or RestartKillSignal= as described above
           immediately after the command exited, this may not result in
           a clean stop. The specified command should hence be a
           synchronous operation, not an asynchronous one.

           Note that the commands specified in ExecStop= are only
           executed when the service started successfully first. They
           are not invoked if the service was never started at all, or
           in case its start-up failed, for example because any of the
           commands specified in ExecStart=, ExecStartPre= or
           ExecStartPost= failed (and weren't prefixed with "-", see
           above) or timed out. Use ExecStopPost= to invoke commands
           when a service failed to start up correctly and is shut down
           again. Also note that the stop operation is always performed
           if the service started successfully, even if the processes in
           the service terminated on their own or were killed. The stop
           commands must be prepared to deal with that case.  $MAINPID
           will be unset if systemd knows that the main process exited
           by the time the stop commands are called.

           Service restart requests are implemented as stop operations
           followed by start operations. This means that ExecStop= and
           ExecStopPost= are executed during a service restart
           operation.

           It is recommended to use this setting for commands that
           communicate with the service requesting clean termination.
           For post-mortem clean-up steps use ExecStopPost= instead.

       ExecStopPost=
           Additional commands that are executed after the service is
           stopped. This includes cases where the commands configured in
           ExecStop= were used, where the service does not have any
           ExecStop= defined, or where the service exited unexpectedly.
           This argument takes multiple command lines, following the
           same scheme as described for ExecStart=. Use of these
           settings is optional. Specifier and environment variable
           substitution is supported. Note that – unlike ExecStop= –
           commands specified with this setting are invoked when a
           service failed to start up correctly and is shut down again.

           It is recommended to use this setting for clean-up operations
           that shall be executed even when the service failed to start
           up correctly. Commands configured with this setting need to
           be able to operate even if the service failed starting up
           half-way and left incompletely initialized data around. As
           the service's processes have been terminated already when the
           commands specified with this setting are executed they should
           not attempt to communicate with them.

           Note that all commands that are configured with this setting
           are invoked with the result code of the service, as well as
           the main process' exit code and status, set in the
           $SERVICE_RESULT, $EXIT_CODE and $EXIT_STATUS environment
           variables, see systemd.exec(5) for details.

           Note that the execution of ExecStopPost= is taken into
           account for the purpose of Before=/After= ordering
           constraints.

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

       RestartSteps=
           Configures the number of steps to take to increase the
           interval of auto-restarts from RestartSec= to
           RestartMaxDelaySec=. Takes a positive integer or 0 to disable
           it. Defaults to 0.

           This setting is effective only if RestartMaxDelaySec= is also
           set.

           Added in version 254.

       RestartMaxDelaySec=
           Configures the longest time to sleep before restarting a
           service as the interval goes up with RestartSteps=. Takes a
           value in the same format as RestartSec=, or "infinity" to
           disable the setting. Defaults to "infinity".

           This setting is effective only if RestartSteps= is also set.

           Added in version 254.

       TimeoutStartSec=
           Configures the time to wait for start-up. If a daemon service
           does not signal start-up completion within the configured
           time, the service will be considered failed and will be shut
           down again. The precise action depends on the
           TimeoutStartFailureMode= option. Takes a unit-less value in
           seconds, or a time span value such as "5min 20s". Pass
           "infinity" to disable the timeout logic. Defaults to
           DefaultTimeoutStartSec= set in the manager, except when
           Type=oneshot is used, in which case the timeout is disabled
           by default (see systemd-system.conf(5)).

           If a service of Type=notify/Type=notify-reload sends
           "EXTEND_TIMEOUT_USEC=...", this may cause the start time to
           be extended beyond TimeoutStartSec=. The first receipt of
           this message must occur before TimeoutStartSec= is exceeded,
           and once the start time has extended beyond TimeoutStartSec=,
           the service manager will allow the service to continue to
           start, provided the service repeats "EXTEND_TIMEOUT_USEC=..."
           within the interval specified until the service startup
           status is finished by "READY=1". (see sd_notify(3)).

           Added in version 188.

       TimeoutStopSec=
           This option serves two purposes. First, it configures the
           time to wait for each ExecStop= command. If any of them times
           out, subsequent ExecStop= commands are skipped and the
           service will be terminated by SIGTERM. If no ExecStop=
           commands are specified, the service gets the SIGTERM
           immediately. This default behavior can be changed by the
           TimeoutStopFailureMode= option. Second, it configures the
           time to wait for the service itself to stop. If it doesn't
           terminate in the specified time, it will be forcibly
           terminated by SIGKILL (see KillMode= in systemd.kill(5)).
           Takes a unit-less value in seconds, or a time span value such
           as "5min 20s". Pass "infinity" to disable the timeout logic.
           Defaults to DefaultTimeoutStopSec= from the manager
           configuration file (see systemd-system.conf(5)).

           If a service of Type=notify/Type=notify-reload sends
           "EXTEND_TIMEOUT_USEC=...", this may cause the stop time to be
           extended beyond TimeoutStopSec=. The first receipt of this
           message must occur before TimeoutStopSec= is exceeded, and
           once the stop time has extended beyond TimeoutStopSec=, the
           service manager will allow the service to continue to stop,
           provided the service repeats "EXTEND_TIMEOUT_USEC=..."
           within the interval specified, or terminates itself (see
           sd_notify(3)).

           Added in version 188.

       TimeoutAbortSec=
           This option configures the time to wait for the service to
           terminate when it was aborted due to a watchdog timeout (see
           WatchdogSec=). If the service has a short TimeoutStopSec=
           this option can be used to give the system more time to write
           a core dump of the service. Upon expiration the service will
           be forcibly terminated by SIGKILL (see KillMode= in
           systemd.kill(5)). The core file will be truncated in this
           case. Use TimeoutAbortSec= to set a sensible timeout for the
           core dumping per service that is large enough to write all
           expected data while also being short enough to handle the
           service failure in due time.

           Takes a unit-less value in seconds, or a time span value such
           as "5min 20s". Pass an empty value to skip the dedicated
           watchdog abort timeout handling and fall back
           TimeoutStopSec=. Pass "infinity" to disable the timeout
           logic. Defaults to DefaultTimeoutAbortSec= from the manager
           configuration file (see systemd-system.conf(5)).

           If a service of Type=notify/Type=notify-reload handles
           SIGABRT itself (instead of relying on the kernel to write a
           core dump) it can send "EXTEND_TIMEOUT_USEC=..."  to extended
           the abort time beyond TimeoutAbortSec=. The first receipt of
           this message must occur before TimeoutAbortSec= is exceeded,
           and once the abort time has extended beyond TimeoutAbortSec=,
           the service manager will allow the service to continue to
           abort, provided the service repeats "EXTEND_TIMEOUT_USEC=..."
           within the interval specified, or terminates itself (see
           sd_notify(3)).

           Added in version 243.

       TimeoutSec=
           A shorthand for configuring both TimeoutStartSec= and
           TimeoutStopSec= to the specified value.

       TimeoutStartFailureMode=, TimeoutStopFailureMode=
           These options configure the action that is taken in case a
           daemon service does not signal start-up within its configured
           TimeoutStartSec=, respectively if it does not stop within
           TimeoutStopSec=. Takes one of terminate, abort and kill. Both
           options default to terminate.

           If terminate is set the service will be gracefully terminated
           by sending the signal specified in KillSignal= (defaults to
           SIGTERM, see systemd.kill(5)). If the service does not
           terminate the FinalKillSignal= is sent after TimeoutStopSec=.
           If abort is set, WatchdogSignal= is sent instead and
           TimeoutAbortSec= applies before sending FinalKillSignal=.
           This setting may be used to analyze services that fail to
           start-up or shut-down intermittently. By using kill the
           service is immediately terminated by sending FinalKillSignal=
           without any further timeout. This setting can be used to
           expedite the shutdown of failing services.

           Added in version 246.

       RuntimeMaxSec=
           Configures a maximum time for the service to run. If this is
           used and the service has been active for longer than the
           specified time it is terminated and put into a failure state.
           Note that this setting does not have any effect on
           Type=oneshot services, as they terminate immediately after
           activation completed. Pass "infinity" (the default) to
           configure no runtime limit.

           If a service of Type=notify/Type=notify-reload sends
           "EXTEND_TIMEOUT_USEC=...", this may cause the runtime to be
           extended beyond RuntimeMaxSec=. The first receipt of this
           message must occur before RuntimeMaxSec= is exceeded, and
           once the runtime has extended beyond RuntimeMaxSec=, the
           service manager will allow the service to continue to run,
           provided the service repeats "EXTEND_TIMEOUT_USEC=..."
           within the interval specified until the service shutdown is
           achieved by "STOPPING=1" (or termination). (see
           sd_notify(3)).

           Added in version 229.

       RuntimeRandomizedExtraSec=
           This option modifies RuntimeMaxSec= by increasing the maximum
           runtime by an evenly distributed duration between 0 and the
           specified value (in seconds). If RuntimeMaxSec= is
           unspecified, then this feature will be disabled.

           Added in version 250.

       WatchdogSec=
           Configures the watchdog timeout for a service. The watchdog
           is activated when the start-up is completed. The service must
           call sd_notify(3) regularly with "WATCHDOG=1" (i.e. the
           "keep-alive ping"). If the time between two such calls is
           larger than the configured time, then the service is placed
           in a failed state and it will be terminated with SIGABRT (or
           the signal specified by WatchdogSignal=). By setting Restart=
           to on-failure, on-watchdog, on-abnormal or always, the
           service will be automatically restarted. The time configured
           here will be passed to the executed service process in the
           WATCHDOG_USEC= environment variable. This allows daemons to
           automatically enable the keep-alive pinging logic if watchdog
           support is enabled for the service. If this option is used,
           NotifyAccess= (see below) should be set to open access to the
           notification socket provided by systemd. If NotifyAccess= is
           not set, it will be implicitly set to main. Defaults to 0,
           which disables this feature. The service can check whether
           the service manager expects watchdog keep-alive
           notifications. See sd_watchdog_enabled(3) for details.
           sd_event_set_watchdog(3) may be used to enable automatic
           watchdog notification support.

       Restart=
           Configures whether the service shall be restarted when the
           service process exits, is killed, or a timeout is reached.
           The service process may be the main service process, but it
           may also be one of the processes specified with
           ExecStartPre=, ExecStartPost=, ExecStop=, ExecStopPost=, or
           ExecReload=. When the death of the process is a result of
           systemd operation (e.g. service stop or restart), the service
           will not be restarted. Timeouts include missing the watchdog
           "keep-alive ping" deadline and a service start, reload, and
           stop operation timeouts.

           Takes one of no, on-success, on-failure, on-abnormal,
           on-watchdog, on-abort, or always. If set to no (the default),
           the service will not be restarted. If set to on-success, it
           will be restarted only when the service process exits
           cleanly. In this context, a clean exit means any of the
           following:

           •   exit code of 0;

           •   for types other than Type=oneshot, one of the signals
               SIGHUP, SIGINT, SIGTERM, or SIGPIPE;

           •   exit statuses and signals specified in
               SuccessExitStatus=.

           If set to on-failure, the service will be restarted when the
           process exits with a non-zero exit code, is terminated by a
           signal (including on core dump, but excluding the
           aforementioned four signals), when an operation (such as
           service reload) times out, and when the configured watchdog
           timeout is triggered. If set to on-abnormal, the service will
           be restarted when the process is terminated by a signal
           (including on core dump, excluding the aforementioned four
           signals), when an operation times out, or when the watchdog
           timeout is triggered. If set to on-abort, the service will be
           restarted only if the service process exits due to an
           uncaught signal not specified as a clean exit status. If set
           to on-watchdog, the service will be restarted only if the
           watchdog timeout for the service expires. If set to always,
           the service will be restarted regardless of whether it exited
           cleanly or not, got terminated abnormally by a signal, or hit
           a timeout.

           Table 1. Exit causes and the effect of the Restart= settings
           ┌───────────────┬────┬────────┬────────────┬────────────┬─────────────┬──────────┬─────────────┐
           │ Restart       no always on-success on-failure on-abnormal on-abort on-watchdog │
           │ settings/Exit │    │        │            │            │             │          │             │
           │ causes        │    │        │            │            │             │          │             │
           ├───────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
           │ Clean exit    │    │ X      │ X          │            │             │          │             │
           │ code or       │    │        │            │            │             │          │             │
           │ signal        │    │        │            │            │             │          │             │
           ├───────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
           │ Unclean exit  │    │ X      │            │ X          │             │          │             │
           │ code          │    │        │            │            │             │          │             │
           ├───────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
           │ Unclean       │    │ X      │            │ X          │ X           │ X        │             │
           │ signal        │    │        │            │            │             │          │             │
           ├───────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
           │ Timeout       │    │ X      │            │ X          │ X           │          │             │
           ├───────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
           │ Watchdog      │    │ X      │            │ X          │ X           │          │ X           │
           └───────────────┴────┴────────┴────────────┴────────────┴─────────────┴──────────┴─────────────┘

           As exceptions to the setting above, the service will not be
           restarted if the exit code or signal is specified in
           RestartPreventExitStatus= (see below) or the service is
           stopped with systemctl stop or an equivalent operation. Also,
           the services will always be restarted if the exit code or
           signal is specified in RestartForceExitStatus= (see below).

           Note that service restart is subject to unit start rate
           limiting configured with StartLimitIntervalSec= and
           StartLimitBurst=, see systemd.unit(5) for details.

           Setting this to on-failure is the recommended choice for
           long-running services, in order to increase reliability by
           attempting automatic recovery from errors. For services that
           shall be able to terminate on their own choice (and avoid
           immediate restarting), on-abnormal is an alternative choice.

       RestartMode=
           Takes a string value that specifies how a service should
           restart:

           •   If set to normal (the default), the service restarts by
               going through a failed/inactive state.

           •   If set to direct, the service transitions to the
               activating state directly during auto-restart, skipping
               failed/inactive state.  ExecStopPost= is invoked.
               OnSuccess= and OnFailure= are skipped.

           This option is useful in cases where a dependency can fail
           temporarily but we don't want these temporary failures to
           make the dependent units fail. When this option is set to
           direct, dependent units are not notified of these temporary
           failures.

           Added in version 254.

       SuccessExitStatus=
           Takes a list of exit status definitions that, when returned
           by the main service process, will be considered successful
           termination, in addition to the normal successful exit status
           0 and, except for Type=oneshot, the signals SIGHUP, SIGINT,
           SIGTERM, and SIGPIPE. Exit status definitions can be numeric
           termination statuses, termination status names, or
           termination signal names, separated by spaces. See the
           Process Exit Codes section in systemd.exec(5) for a list of
           termination status names (for this setting only the part
           without the "EXIT_" or "EX_" prefix should be used). See
           signal(7) for a list of signal names.

           Note that this setting does not change the mapping between
           numeric exit statuses and their names, i.e. regardless how
           this setting is used 0 will still be mapped to "SUCCESS" (and
           thus typically shown as "0/SUCCESS" in tool outputs) and 1 to
           "FAILURE" (and thus typically shown as "1/FAILURE"), and so
           on. It only controls what happens as effect of these exit
           statuses, and how it propagates to the state of the service
           as a whole.

           This option may appear more than once, in which case the list
           of successful exit statuses is merged. If the empty string is
           assigned to this option, the list is reset, all prior
           assignments of this option will have no effect.

           Example 1. A service with the SuccessExitStatus= setting

               SuccessExitStatus=TEMPFAIL 250 SIGKILL

           Exit status 75 (TEMPFAIL), 250, and the termination signal
           SIGKILL are considered clean service terminations.

           Note: systemd-analyze exit-status may be used to list exit
           statuses and translate between numerical status values and
           names.

           Added in version 189.

       RestartPreventExitStatus=
           Takes a list of exit status definitions that, when returned
           by the main service process, will prevent automatic service
           restarts, regardless of the restart setting configured with
           Restart=. Exit status definitions can either be numeric exit
           codes or termination signal names, and are separated by
           spaces. Defaults to the empty list, so that, by default, no
           exit status is excluded from the configured restart logic.
           For example:

               RestartPreventExitStatus=1 6 SIGABRT

           ensures that exit codes 1 and 6 and the termination signal
           SIGABRT will not result in automatic service restarting. This
           option may appear more than once, in which case the list of
           restart-preventing statuses is merged. If the empty string is
           assigned to this option, the list is reset and all prior
           assignments of this option will have no effect.

           Note that this setting has no effect on processes configured
           via ExecStartPre=, ExecStartPost=, ExecStop=, ExecStopPost=
           or ExecReload=, but only on the main service process, i.e.
           either the one invoked by ExecStart= or (depending on Type=,
           PIDFile=, ...) the otherwise configured main process.

           Added in version 189.

       RestartForceExitStatus=
           Takes a list of exit status definitions that, when returned
           by the main service process, will force automatic service
           restarts, regardless of the restart setting configured with
           Restart=. The argument format is similar to
           RestartPreventExitStatus=.

           Added in version 215.

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

       NonBlocking=
           Set the 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), excluding those
           passed in via the file descriptor storage logic (see
           FileDescriptorStoreMax= for details), 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 systemd.socket(5) and has no effect on file
           descriptors which were previously saved in the
           file-descriptor store for example. Defaults to false.

           Note that if the same socket unit is configured to be passed
           to multiple service units (via the Sockets= setting, see
           below), and these services have different NonBlocking=
           configurations, the precise state of O_NONBLOCK depends on
           the order in which these services are invoked, and will
           possibly change after service code already took possession of
           the socket file descriptor, simply because the O_NONBLOCK
           state of a socket is shared by all file descriptors
           referencing it. Hence it is essential that all services
           sharing the same socket use the same NonBlocking=
           configuration, and do not change the flag in service code
           either.

       NotifyAccess=
           Controls access to the service status notification socket, as
           accessible via the sd_notify(3) call. Takes one of none (the
           default), main, exec or all. If none, no daemon status
           updates are accepted from the service processes, all status
           update messages are ignored. If main, only service updates
           sent from the main process of the service are accepted. If
           exec, only service updates sent from any of the main or
           control processes originating from one of the Exec*= commands
           are accepted. If all, all services updates from all members
           of the service's control group are accepted. This option
           should be set to open access to the notification socket when
           using Type=notify/Type=notify-reload or WatchdogSec= (see
           above). If those options are used but NotifyAccess= is not
           configured, it will be implicitly set to main.

           Note that sd_notify() notifications may be attributed to
           units correctly only if either the sending process is still
           around at the time PID 1 processes the message, or if the
           sending process is explicitly runtime-tracked by the service
           manager. The latter is the case if the service manager
           originally forked off the process, i.e. on all processes that
           match main or exec. Conversely, if an auxiliary process of
           the unit sends an sd_notify() message and immediately exits,
           the service manager might not be able to properly attribute
           the message to the unit, and thus will ignore it, even if
           NotifyAccess=all is set for it.

           Hence, to eliminate all race conditions involving lookup of
           the client's unit and attribution of notifications to units
           correctly, sd_notify_barrier() may be used. This call acts as
           a synchronization point and ensures all notifications sent
           before this call have been picked up by the service manager
           when it returns successfully. Use of sd_notify_barrier() is
           needed for clients which are not invoked by the service
           manager, otherwise this synchronization mechanism is
           unnecessary for attribution of notifications to the unit.

       Sockets=
           Specifies the name of the socket units this service shall
           inherit socket file descriptors from when the service is
           started. Normally, it should not be necessary to use this
           setting, as all socket file descriptors whose unit shares the
           same name as the service (subject to the different unit name
           suffix of course) are passed to the spawned process.

           Note that the same socket file descriptors may be passed to
           multiple processes simultaneously. Also note that a different
           service may be activated on incoming socket traffic than the
           one which is ultimately configured to inherit the socket file
           descriptors. Or, in other words: the Service= setting of
           .socket units does not have to match the inverse of the
           Sockets= setting of the .service it refers to.

           This option may appear more than once, in which case the list
           of socket units is merged. Note that once set, clearing the
           list of sockets again (for example, by assigning the empty
           string to this option) is not supported.

       FileDescriptorStoreMax=
           Configure how many file descriptors may be stored in the
           service manager for the service using
           sd_pid_notify_with_fds(3)'s "FDSTORE=1" messages. This is
           useful for implementing services that can restart after an
           explicit request or a crash without losing state. Any open
           sockets and other file descriptors which should not be closed
           during the restart may be stored this way. Application state
           can either be serialized to a file in RuntimeDirectory=, or
           stored in a memfd_create(2) memory file descriptor. Defaults
           to 0, i.e. no file descriptors may be stored in the service
           manager. All file descriptors passed to the service manager
           from a specific service are passed back to the service's main
           process on the next service restart (see sd_listen_fds(3) for
           details about the precise protocol used and the order in
           which the file descriptors are passed). Any file descriptors
           passed to the service manager are automatically closed when
           POLLHUP or POLLERR is seen on them, or when the service is
           fully stopped and no job is queued or being executed for it
           (the latter can be tweaked with FileDescriptorStorePreserve=,
           see below). If this option is used, NotifyAccess= (see above)
           should be set to open access to the notification socket
           provided by systemd. If NotifyAccess= is not set, it will be
           implicitly set to main.

           The fdstore command of systemd-analyze(1) may be used to list
           the current contents of a service's file descriptor store.

           Note that the service manager will only pass file descriptors
           contained in the file descriptor store to the service's own
           processes, never to other clients via IPC or similar.
           However, it does allow unprivileged clients to query the list
           of currently open file descriptors of a service. Sensitive
           data may hence be safely placed inside the referenced files,
           but should not be attached to the metadata (e.g. included in
           filenames) of the stored file descriptors.

           If this option is set to a non-zero value the $FDSTORE
           environment variable will be set for processes invoked for
           this service. See systemd.exec(5) for details.

           For further information on the file descriptor store see the
           File Descriptor Store[1] overview.

           Added in version 219.

       FileDescriptorStorePreserve=
           Takes one of no, yes, restart and controls when to release
           the service's file descriptor store (i.e. when to close the
           contained file descriptors, if any). If set to no the file
           descriptor store is automatically released when the service
           is stopped; if restart (the default) it is kept around as
           long as the unit is neither inactive nor failed, or a job is
           queued for the service, or the service is expected to be
           restarted. If yes the file descriptor store is kept around
           until the unit is removed from memory (i.e. is not referenced
           anymore and inactive). The latter is useful to keep entries
           in the file descriptor store pinned until the service manager
           exits.

           Use systemctl clean --what=fdstore ...  to release the file
           descriptor store explicitly.

           Added in version 254.

       USBFunctionDescriptors=
           Configure the location of a file containing USB FunctionFS[2]
           descriptors, for implementation of USB gadget functions. This
           is used only in conjunction with a socket unit with
           ListenUSBFunction= configured. The contents of this file are
           written to the ep0 file after it is opened.

           Added in version 227.

       USBFunctionStrings=
           Configure the location of a file containing USB FunctionFS
           strings. Behavior is similar to USBFunctionDescriptors=
           above.

           Added in version 227.

       OOMPolicy=
           Configure the out-of-memory (OOM) killing policy for the
           kernel and the userspace OOM killer systemd-oomd.service(8).
           On Linux, when memory becomes scarce to the point that the
           kernel has trouble allocating memory for itself, it might
           decide to kill a running process in order to free up memory
           and reduce memory pressure. Note that systemd-oomd.service is
           a more flexible solution that aims to prevent out-of-memory
           situations for the userspace too, not just the kernel, by
           attempting to terminate services earlier, before the kernel
           would have to act.

           This setting takes one of continue, stop or kill. If set to
           continue and a process in the unit is killed by the OOM
           killer, this is logged but the unit continues running. If set
           to stop the event is logged but the unit is terminated
           cleanly by the service manager. If set to kill and one of the
           unit's processes is killed by the OOM killer the kernel is
           instructed to kill all remaining processes of the unit too,
           by setting the memory.oom.group attribute to 1; also see
           kernel page Control Group v2[3].

           Defaults to the setting DefaultOOMPolicy= in
           systemd-system.conf(5) is set to, except for units where
           Delegate= is turned on, where it defaults to continue.

           Use the OOMScoreAdjust= setting to configure whether
           processes of the unit shall be considered preferred or less
           preferred candidates for process termination by the Linux OOM
           killer logic. See systemd.exec(5) for details.

           This setting also applies to systemd-oomd.service(8).
           Similarly to the kernel OOM kills performed by the kernel,
           this setting determines the state of the unit after
           systemd-oomd kills a cgroup associated with it.

           Added in version 243.

       OpenFile=
           Takes an argument of the form "path[:fd-name:options]",
           where:

           •   "path" is a path to a file or an AF_UNIX socket in the
               file system;

           •   "fd-name" is a name that will be associated with the file
               descriptor; the name may contain any ASCII character, but
               must exclude control characters and ":", and must be at
               most 255 characters in length; it is optional and, if not
               provided, defaults to the file name;

           •   "options" is a comma-separated list of access options;
               possible values are "read-only", "append", "truncate",
               "graceful"; if not specified, files will be opened in rw
               mode; if "graceful" is specified, errors during
               file/socket opening are ignored. Specifying the same
               option several times is treated as an error.

           The file or socket is opened by the service manager and the
           file descriptor is passed to the service. If the path is a
           socket, we call connect() on it. See sd_listen_fds(3) for
           more details on how to retrieve these file descriptors.

           This setting is useful to allow services to access
           files/sockets that they can't access themselves (due to
           running in a separate mount namespace, not having privileges,
           ...).

           This setting can be specified multiple times, in which case
           all the specified paths are opened and the file descriptors
           passed to the service. If the empty string is assigned, the
           entire list of open files defined prior to this is reset.

           Added in version 253.

       ReloadSignal=
           Configures the UNIX process signal to send to the service's
           main process when asked to reload the service's
           configuration. Defaults to SIGHUP. This option has no effect
           unless Type=notify-reload is used, see above.

           Added in version 253.

       Check systemd.unit(5), systemd.exec(5), and systemd.kill(5) for
       more settings.

COMMAND LINES         top

       This section describes command line parsing and variable and
       specifier substitutions for ExecStart=, ExecStartPre=,
       ExecStartPost=, ExecReload=, ExecStop=, and ExecStopPost=
       options.

       Multiple command lines may be concatenated in a single directive
       by separating them with semicolons (these semicolons must be
       passed as separate words). Lone semicolons may be escaped as
       "\;".

       Each command line is unquoted using the rules described in
       "Quoting" section in systemd.syntax(7). The first item becomes
       the command to execute, and the subsequent items the arguments.

       This syntax is inspired by shell syntax, but only the
       meta-characters and expansions described in the following
       paragraphs are understood, and the expansion of variables is
       different. Specifically, redirection using "<", "<<", ">", and
       ">>", pipes using "|", running programs in the background using
       "&", and other elements of shell syntax are not supported.

       The command to execute may contain spaces, but control characters
       are not allowed.

       Each command may be prefixed with a number of special characters:

       Table 2. Special executable prefixes
       ┌────────┬─────────────────────────────┐
       │ Prefix Effect                      │
       ├────────┼─────────────────────────────┤
       │ "@"    │ If the executable path      │
       │        │ is prefixed with "@",       │
       │        │ the second specified        │
       │        │ token will be passed as     │
       │        │ argv[0] to the executed     │
       │        │ process (instead of the     │
       │        │ actual filename),           │
       │        │ followed by the further     │
       │        │ arguments specified.        │
       ├────────┼─────────────────────────────┤
       │ "-"    │ If the executable path      │
       │        │ is prefixed with "-", an    │
       │        │ exit code of the command    │
       │        │ normally considered a       │
       │        │ failure (i.e. non-zero      │
       │        │ exit status or abnormal     │
       │        │ exit due to signal) is      │
       │        │ recorded, but has no        │
       │        │ further effect and is       │
       │        │ considered equivalent to    │
       │        │ success.                    │
       ├────────┼─────────────────────────────┤
       │ ":"    │ If the executable path      │
       │        │ is prefixed with ":",       │
       │        │ environment variable        │
       │        │ substitution (as            │
       │        │ described by the            │
       │        │ "Command Lines" section     │
       │        │ below) is not applied.      │
       ├────────┼─────────────────────────────┤
       │ "+"    │ If the executable path      │
       │        │ is prefixed with "+"        │
       │        │ then the process is         │
       │        │ executed with full          │
       │        │ privileges. In this mode    │
       │        │ privilege restrictions      │
       │        │ configured with User=,      │
       │        │ Group=,                     │
       │        │ CapabilityBoundingSet=      │
       │        │ or the various file         │
       │        │ system namespacing          │
       │        │ options (such as            │
       │        │ PrivateDevices=,            │
       │        │ PrivateTmp=) are not        │
       │        │ applied to the invoked      │
       │        │ command line (but still     │
       │        │ affect any other            │
       │        │ ExecStart=, ExecStop=,      │
       │        │ ... lines). However,        │
       │        │ note that this will not     │
       │        │ bypass options that         │
       │        │ apply to the whole          │
       │        │ control group, such as      │
       │        │ DevicePolicy=, see          │
       │        │ systemd.resource-control(5) │
       │        │ for the full list.          │
       ├────────┼─────────────────────────────┤
       │ "!"    │ Similar to the "+"          │
       │        │ character discussed above   │
       │        │ this permits invoking       │
       │        │ command lines with elevated │
       │        │ privileges. However, unlike │
       │        │ "+" the "!" character       │
       │        │ exclusively alters the      │
       │        │ effect of User=, Group= and │
       │        │ SupplementaryGroups=, i.e.  │
       │        │ only the stanzas that       │
       │        │ affect user and group       │
       │        │ credentials. Note that this │
       │        │ setting may be combined     │
       │        │ with DynamicUser=, in which │
       │        │ case a dynamic user/group   │
       │        │ pair is allocated before    │
       │        │ the command is invoked, but │
       │        │ credential changing is left │
       │        │ to the executed process     │
       │        │ itself.                     │
       ├────────┼─────────────────────────────┤
       │ "!!"   │ This prefix is very similar │
       │        │ to "!", however it only has │
       │        │ an effect on systems        │
       │        │ lacking support for ambient │
       │        │ process capabilities, i.e.  │
       │        │ without support for         │
       │        │ AmbientCapabilities=. It's  │
       │        │ intended to be used for     │
       │        │ unit files that take        │
       │        │ benefit of ambient          │
       │        │ capabilities to run         │
       │        │ processes with minimal      │
       │        │ privileges wherever         │
       │        │ possible while remaining    │
       │        │ compatible with systems     │
       │        │ that lack ambient           │
       │        │ capabilities support. Note  │
       │        │ that when "!!" is used, and │
       │        │ a system lacking ambient    │
       │        │ capability support is       │
       │        │ detected any configured     │
       │        │ SystemCallFilter= and       │
       │        │ CapabilityBoundingSet=      │
       │        │ stanzas are implicitly      │
       │        │ modified, in order to       │
       │        │ permit spawned processes to │
       │        │ drop credentials and        │
       │        │ capabilities themselves,    │
       │        │ even if this is configured  │
       │        │ to not be allowed.          │
       │        │ Moreover, if this prefix is │
       │        │ used and a system lacking   │
       │        │ ambient capability support  │
       │        │ is detected                 │
       │        │ AmbientCapabilities= will   │
       │        │ be skipped and not be       │
       │        │ applied. On systems         │
       │        │ supporting ambient          │
       │        │ capabilities, "!!" has no   │
       │        │ effect and is redundant.    │
       └────────┴─────────────────────────────┘

       "@", "-", ":", and one of "+"/"!"/"!!"  may be used together and
       they can appear in any order. However, only one of "+", "!", "!!"
       may be used at a time.

       For each command, the first argument must be either an absolute
       path to an executable or a simple file name without any slashes.
       If the command is not a full (absolute) path, it will be resolved
       to a full path using a fixed search path determined at
       compilation time. Searched directories include /usr/local/bin/,
       /usr/bin/, /bin/ on systems using split /usr/bin/ and /bin/
       directories, and their sbin/ counterparts on systems using split
       bin/ and sbin/. It is thus safe to use just the executable name
       in case of executables located in any of the "standard"
       directories, and an absolute path must be used in other cases.
       Hint: this search path may be queried using systemd-path
       search-binaries-default.

       The command line accepts "%" specifiers as described in
       systemd.unit(5).

       Basic environment variable substitution is supported. Use
       "${FOO}" as part of a word, or as a word of its own, on the
       command line, in which case it will be erased and replaced by the
       exact value of the environment variable (if any) including all
       whitespace it contains, always resulting in exactly a single
       argument. Use "$FOO" as a separate word on the command line, in
       which case it will be replaced by the value of the environment
       variable split at whitespace, resulting in zero or more
       arguments. For this type of expansion, quotes are respected when
       splitting into words, and afterwards removed.

       Example:

           Environment="ONE=one" 'TWO=two two'
           ExecStart=echo $ONE $TWO ${TWO}

       This will execute /bin/echo with four arguments: "one", "two",
       "two", and "two two".

       Example:

           Environment=ONE='one' "TWO='two two' too" THREE=
           ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
           ExecStart=/bin/echo $ONE $TWO $THREE

       This results in /bin/echo being called twice, the first time with
       arguments "'one'", "'two two' too", "", and the second time with
       arguments "one", "two two", "too".

       To pass a literal dollar sign, use "$$". Variables whose value is
       not known at expansion time are treated as empty strings. Note
       that the first argument (i.e. the program to execute) may not be
       a variable.

       Variables to be used in this fashion may be defined through
       Environment= and EnvironmentFile=. In addition, variables listed
       in the section "Environment variables in spawned processes" in
       systemd.exec(5), which are considered "static configuration", may
       be used (this includes e.g.  $USER, but not $TERM).

       Note that shell command lines are not directly supported. If
       shell command lines are to be used, they need to be passed
       explicitly to a shell implementation of some kind. Example:

           ExecStart=sh -c 'dmesg | tac'

       Example:

           ExecStart=echo one ; echo "two two"

       This will execute echo two times, each time with one argument:
       "one" and "two two", respectively. Because two commands are
       specified, Type=oneshot must be used.

       Example:

           Type=oneshot
           ExecStart=:echo $USER ; -false ; +:@true $TEST

       This will execute /usr/bin/echo with the literal argument "$USER"
       (":" suppresses variable expansion), and then /usr/bin/false (the
       return value will be ignored because "-" suppresses checking of
       the return value), and /usr/bin/true (with elevated privileges,
       with "$TEST" as argv[0]).

       Example:

           ExecStart=echo / >/dev/null & \; \
           ls

       This will execute echo with five arguments: "/", ">/dev/null",
       "&", ";", and "ls".

EXAMPLES         top

       Example 2. Simple service

       The following unit file creates a service that will execute
       /usr/sbin/foo-daemon. Since no Type= is specified, the default
       Type=simple will be assumed. systemd will assume the unit to be
       started immediately after the program has begun executing.

           [Unit]
           Description=Foo

           [Service]
           ExecStart=/usr/sbin/foo-daemon

           [Install]
           WantedBy=multi-user.target

       Note that systemd assumes here that the process started by
       systemd will continue running until the service terminates. If
       the program daemonizes itself (i.e. forks), please use
       Type=forking instead.

       Since no ExecStop= was specified, systemd will send SIGTERM to
       all processes started from this service, and after a timeout also
       SIGKILL. This behavior can be modified, see systemd.kill(5) for
       details.

       Note that this unit type does not include any type of
       notification when a service has completed initialization. For
       this, you should use other unit types, such as
       Type=notify/Type=notify-reload if the service understands
       systemd's notification protocol, Type=forking if the service can
       background itself or Type=dbus if the unit acquires a DBus name
       once initialization is complete. See below.

       Example 3. Oneshot service

       Sometimes, units should just execute an action without keeping
       active processes, such as a filesystem check or a cleanup action
       on boot. For this, Type=oneshot exists. Units of this type will
       wait until the process specified terminates and then fall back to
       being inactive. The following unit will perform a cleanup action:

           [Unit]
           Description=Cleanup old Foo data

           [Service]
           Type=oneshot
           ExecStart=/usr/sbin/foo-cleanup

           [Install]
           WantedBy=multi-user.target

       Note that systemd will consider the unit to be in the state
       "starting" until the program has terminated, so ordered
       dependencies will wait for the program to finish before starting
       themselves. The unit will revert to the "inactive" state after
       the execution is done, never reaching the "active" state. That
       means another request to start the unit will perform the action
       again.

       Type=oneshot are the only service units that may have more than
       one ExecStart= specified. For units with multiple commands
       (Type=oneshot), all commands will be run again.

       For Type=oneshot, Restart=always and Restart=on-success are not
       allowed.

       Example 4. Stoppable oneshot service

       Similarly to the oneshot services, there are sometimes units that
       need to execute a program to set up something and then execute
       another to shut it down, but no process remains active while they
       are considered "started". Network configuration can sometimes
       fall into this category. Another use case is if a oneshot service
       shall not be executed each time when they are pulled in as a
       dependency, but only the first time.

       For this, systemd knows the setting RemainAfterExit=yes, which
       causes systemd to consider the unit to be active if the start
       action exited successfully. This directive can be used with all
       types, but is most useful with Type=oneshot and Type=simple. With
       Type=oneshot, systemd waits until the start action has completed
       before it considers the unit to be active, so dependencies start
       only after the start action has succeeded. With Type=simple,
       dependencies will start immediately after the start action has
       been dispatched. The following unit provides an example for a
       simple static firewall.

           [Unit]
           Description=Simple firewall

           [Service]
           Type=oneshot
           RemainAfterExit=yes
           ExecStart=/usr/local/sbin/simple-firewall-start
           ExecStop=/usr/local/sbin/simple-firewall-stop

           [Install]
           WantedBy=multi-user.target

       Since the unit is considered to be running after the start action
       has exited, invoking systemctl start on that unit again will
       cause no action to be taken.

       Example 5. Traditional forking services

       Many traditional daemons/services background (i.e. fork,
       daemonize) themselves when starting. Set Type=forking in the
       service's unit file to support this mode of operation. systemd
       will consider the service to be in the process of initialization
       while the original program is still running. Once it exits
       successfully and at least a process remains (and
       RemainAfterExit=no), the service is considered started.

       Often, a traditional daemon only consists of one process.
       Therefore, if only one process is left after the original process
       terminates, systemd will consider that process the main process
       of the service. In that case, the $MAINPID variable will be
       available in ExecReload=, ExecStop=, etc.

       In case more than one process remains, systemd will be unable to
       determine the main process, so it will not assume there is one.
       In that case, $MAINPID will not expand to anything. However, if
       the process decides to write a traditional PID file, systemd will
       be able to read the main PID from there. Please set PIDFile=
       accordingly. Note that the daemon should write that file before
       finishing with its initialization. Otherwise, systemd might try
       to read the file before it exists.

       The following example shows a simple daemon that forks and just
       starts one process in the background:

           [Unit]
           Description=Some simple daemon

           [Service]
           Type=forking
           ExecStart=/usr/sbin/my-simple-daemon -d

           [Install]
           WantedBy=multi-user.target

       Please see systemd.kill(5) for details on how you can influence
       the way systemd terminates the service.

       Example 6. DBus services

       For services that acquire a name on the DBus system bus, use
       Type=dbus and set BusName= accordingly. The service should not
       fork (daemonize). systemd will consider the service to be
       initialized once the name has been acquired on the system bus.
       The following example shows a typical DBus service:

           [Unit]
           Description=Simple DBus service

           [Service]
           Type=dbus
           BusName=org.example.simple-dbus-service
           ExecStart=/usr/sbin/simple-dbus-service

           [Install]
           WantedBy=multi-user.target

       For bus-activatable services, do not include a [Install] section
       in the systemd service file, but use the SystemdService= option
       in the corresponding DBus service file, for example
       (/usr/share/dbus-1/system-services/org.example.simple-dbus-service.service):

           [D-BUS Service]
           Name=org.example.simple-dbus-service
           Exec=/usr/sbin/simple-dbus-service
           User=root
           SystemdService=simple-dbus-service.service

       Please see systemd.kill(5) for details on how you can influence
       the way systemd terminates the service.

       Example 7. Services that notify systemd about their
       initialization

       Type=simple services are really easy to write, but have the major
       disadvantage of systemd not being able to tell when
       initialization of the given service is complete. For this reason,
       systemd supports a simple notification protocol that allows
       daemons to make systemd aware that they are done initializing.
       Use Type=notify or Type=notify-reload for this. A typical service
       file for such a daemon would look like this:

           [Unit]
           Description=Simple notifying service

           [Service]
           Type=notify
           ExecStart=/usr/sbin/simple-notifying-service

           [Install]
           WantedBy=multi-user.target

       Note that the daemon has to support systemd's notification
       protocol, else systemd will think the service has not started yet
       and kill it after a timeout. For an example of how to update
       daemons to support this protocol transparently, take a look at
       sd_notify(3). systemd will consider the unit to be in the
       'starting' state until a readiness notification has arrived.

       Please see systemd.kill(5) for details on how you can influence
       the way systemd terminates the service.

SEE ALSO         top

       systemd(1), systemctl(1), systemd-system.conf(5),
       systemd.unit(5), systemd.exec(5), systemd.resource-control(5),
       systemd.kill(5), systemd.directives(7), systemd-run(1)

NOTES         top

        1. File Descriptor Store
           https://systemd.io/FILE_DESCRIPTOR_STORE

        2. USB FunctionFS
           https://docs.kernel.org/usb/functionfs.html

        3. Control Group v2
           https://docs.kernel.org/admin-guide/cgroup-v2.html

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 255                                           SYSTEMD.SERVICE(5)

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