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 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 .service suffix removed) and dynamically
       creates a service unit from that script. This is useful for
       compatibility with SysV. Note that this compatibility is quite
       comprehensive but not 100%. For details about the incompatibilities,
       see the Incompatibilities with SysV[1] document.

       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 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 process start-up type for this service unit. One
           of simple, exec, forking, oneshot, dbus, notify 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. 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, 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. systemd will
               proceed with starting follow-up units as soon as 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 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, it is
               expected that the service acquires a name on the D-Bus bus,
               as configured by BusName=. systemd will proceed with starting
               follow-up units after the D-Bus bus name has been acquired.
               Service units with this option configured implicitly gain
               dependencies on the dbus.socket unit. This type is the
               default if BusName= is specified.

           ·   Behavior of notify is similar to exec; however, it is
               expected that the service sends a 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
           .

           ·   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 generally recommended to use Type=simple for long-running
           services whenever possible, as it is the simplest and fastest
           option. However, as this service type won't propagate service
           start-up failures and doesn't allow ordering of other units
           against completion of initialization of the service (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 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 service type requires
           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 UNIX service start-up
           protocol. Finally, exec might be an option for cases where it is
           enough to ensure the service binary is invoked, and where the
           service binary itself executes no or little initialization on its
           own (and its initialization is unlikely to fail). Note that using
           any type other than simple possibly delays the boot process, as
           the service manager needs to wait for service initialization to
           complete. It is hence recommended not to needlessly use any types
           other than simple. (Also note it is generally not recommended to
           use idle or oneshot for long-running services.)

       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.

       BusName=
           Takes a D-Bus bus name that this service is reachable as. This
           option is mandatory for services where Type= is set to dbus.

       ExecStart=
           Commands with their arguments that are executed when this service
           is started. The value is split into zero or more command lines
           according to the rules described below (see 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.)

           For each of the specified commands, the first argument must be
           either an absolute path to an executable or a simple file name
           without any slashes. Optionally, this filename may be prefixed
           with a number of special characters:

           Table 1. 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).               │
           ├───────┼───────────────────────────┤
           │"!"    │ 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. Note that these prefixes are also
           supported for the other command line settings, i.e.
           ExecStartPre=, ExecStartPost=, ExecReload=, ExecStop= and
           ExecStopPost=.

           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, 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 command(s) 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 command(s).

           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.

       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 sending a signal (as with
           the example line above) is usually not a good choice, because
           this is an asynchronous operation and hence not suitable to order
           reloads of multiple services against each other. It is strongly
           recommended 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.

       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= from the manager
           configuration file, 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 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)).

       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 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)).

       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 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)).

       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.

       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 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)).

       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 an exit code of 0, or one of the
           signals SIGHUP, SIGINT, SIGTERM or SIGPIPE, and additionally,
           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 2. Exit causes and the effect of the Restart= settings on
           them
           ┌──────────────┬────┬────────┬────────────┬────────────┬─────────────┬──────────┬─────────────┐
           │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. A restarted service enters the
           failed state only after the start limits are reached.

           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.

       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 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 SIGUSR1

           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.

       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.

       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=.

       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.

       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 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 /run, or
           better, 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. 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. 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.

       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.

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

       OOMPolicy=
           Configure the Out-Of-Memory (OOM) killer policy. On Linux, when
           memory becomes scarce the kernel might decide to kill a running
           process in order to free up memory and reduce memory pressure.
           This setting takes one of continue, stop or kill. If set to
           continue and a process of the service is killed by the kernel's
           OOM killer this is logged but the service continues running. If
           set to stop the event is logged but the service is terminated
           cleanly by the service manager. If set to kill and one of the
           service's processes is killed by the OOM killer the kernel is
           instructed to kill all remaining processes of the service, too.
           Defaults to the setting DefaultOOMPolicy= in
           systemd-system.conf(5) is set to, except for services 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.

       Check 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 split on whitespace, with the first item being
       the command to execute, and the subsequent items being the arguments.
       Double quotes ("...") and single quotes ('...') may be used to wrap a
       whole item (the opening quote may appear only at the beginning or
       after whitespace that is not quoted, and the closing quote must be
       followed by whitespace or the end of line), in which case everything
       until the next matching quote becomes part of the same argument.
       Quotes themselves are removed. C-style escapes are also supported.
       The table below contains the list of known escape patterns. Only
       escape patterns which match the syntax in the table are allowed;
       other patterns may be added in the future and unknown patterns will
       result in a warning. In particular, any backslashes should be
       doubled. Finally, a trailing backslash ("\") may be used to merge
       lines.

       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.

       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.

       If the command is not a full (absolute) path, it will be resolved to
       a full path using a fixed search path determinted 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. Using an absolute path is recommended to avoid
       ambiguity. Hint: this search path may be queried using systemd-path
       search-binaries-default.

       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:

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

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

       Table 3. C escapes supported in command lines and environment
       variables
       ┌────────┬─────────────────────────┐
       │Literal Actual value            │
       ├────────┼─────────────────────────┤
       │"\a"    │ bell                    │
       ├────────┼─────────────────────────┤
       │"\b"    │ backspace               │
       ├────────┼─────────────────────────┤
       │"\f"    │ form feed               │
       ├────────┼─────────────────────────┤
       │"\n"    │ newline                 │
       ├────────┼─────────────────────────┤
       │"\r"    │ carriage return         │
       ├────────┼─────────────────────────┤
       │"\t"    │ tab                     │
       ├────────┼─────────────────────────┤
       │"\v"    │ vertical tab            │
       ├────────┼─────────────────────────┤
       │"\\"    │ backslash               │
       ├────────┼─────────────────────────┤
       │"\""    │ double quotation mark   │
       ├────────┼─────────────────────────┤
       │"\'"    │ single quotation mark   │
       ├────────┼─────────────────────────┤
       │"\s"    │ space                   │
       ├────────┼─────────────────────────┤
       │"\xxx"  │ character number xx in  │
       │        │ hexadecimal encoding    │
       ├────────┼─────────────────────────┤
       │"\nnn"  │ character number nnn in │
       │        │ octal encoding          │
       └────────┴─────────────────────────┘

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 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 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. Incompatibilities with SysV
           https://www.freedesktop.org/wiki/Software/systemd/Incompatibilities

        2. USB FunctionFS
           https://www.kernel.org/doc/Documentation/usb/functionfs.txt

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 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-07-14.)  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 246                                               SYSTEMD.SERVICE(5)

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