systemd.service

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



NAME
       systemd.service - Service unit configuration

SYNOPSIS
       service.service

DESCRIPTION
       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
       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
   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
       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 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.

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

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



systemd 246                                                   SYSTEMD.SERVICE(5)