Man page
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.

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

       Socket activated service are automatically ordered after their
       activated .socket units via an automatic After= dependency.

       Unless DefaultDependencies= in the "[Unit]" is set to false, service
       units will implicitly 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).

       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).

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) and
       systemd.kill(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, forking, oneshot, dbus, notify or idle.

           If set to simple (the default if neither Type= nor BusName=, but
           ExecStart= are specified), 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 daemon is started up (e.g. sockets set up by systemd,
           via socket activation), as systemd will immediately proceed
           starting follow-up units.

           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 daemon process. This is the behavior of traditional UNIX
           daemons. If this setting is used, it is recommended to also use the
           PIDFile= option, so that systemd can identify the main process of
           the daemon. systemd will proceed with starting follow-up units as
           soon as the parent process exits.

           Behavior of oneshot is similar to simple; however, it is expected
           that the process has to exit before systemd starts follow-up units.
           RemainAfterExit= is particularly useful for this type of service.
           This is the implied default if neither Type= or ExecStart= are
           specified.

           Behavior of dbus is similar to simple; however, it is expected that
           the daemon 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 simple; however, it is expected
           that the daemon 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. Note that currently Type=notify will
           not work if used in combination with PrivateNetwork=yes.

           Behavior of idle is very similar to simple; however, actual
           execution of the service binary is delayed until all jobs are
           dispatched. This may be used to avoid interleaving of output of
           shell services with the status output on the console.

       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 an absolute file name pointing to the PID file of this
           daemon. Use of this option is recommended for services where Type=
           is set to forking. systemd will read the PID of the main process of
           the daemon after start-up of the service. systemd will not write to
           the file configured here, although it will remove the file after
           the service has shut down if it still exists.

       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).

           When Type= is not oneshot, only one command may and must be given.
           When Type=oneshot is used, zero or more commands may be specified.
           This can 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 set.

           For each of the specified commands, the first argument must be an
           absolute path to an executable. Optionally, if this file name is
           prefixed with "@", the second token will be passed as "argv[0]" to
           the executed process, followed by the further arguments specified.
           If the absolute filename 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 ignored and considered success. If
           the absolute path is prefixed with "+" then it is executed with
           full privileges.  "-", "@", and "+" may be used together and they
           can appear in any order.

           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 service has started
           successfully, as determined by Type= (i.e. the process has been
           started for Type=simple or Type=idle, the process exits
           successfully for Type=oneshot, the initial process exits
           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.

       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:

               /bin/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.

       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, all
           processes remaining for a service 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= 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 queuing some form of termination signal for it), but does not
           wait for it to do so. Since the remaining processes of the services
           are killed using SIGKILL immediately after the command exited, this
           would 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.

           It is recommended to use this setting for commands that communicate
           with the service requesting clean termination. When the commands
           specified with this option are executed it should be assumed that
           the service is still fully up and is able to react correctly to all
           commands. 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.

       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.
           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)).

       TimeoutStopSec=
           Configures the time to wait for stop. If a service is asked to
           stop, but does not terminate in the specified time, it will be
           terminated forcibly via SIGTERM, and after another timeout of equal
           duration with 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)).

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

       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.

       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. 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 1. 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). Also, the services will
           always be restarted if the exit code or signal is specified in
           RestartForceExitStatus= (see below).

           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 code 0 and the signals
           SIGHUP, SIGINT, SIGTERM, and SIGPIPE. Exit status definitions can
           either be numeric exit codes or termination signal names, separated
           by spaces. For example:

               SuccessExitStatus=1 2 8 SIGKILL

           ensures that exit codes 1, 2, 8 and the termination signal SIGKILL
           are considered clean service terminations.

           Note that if a process has a signal handler installed and exits by
           calling _exit(2) in response to a signal, the information about the
           signal is lost. Programs should instead perform cleanup and kill
           themselves with the same signal instead. See Proper handling of
           SIGINT/SIGQUIT -- How to be a proper program[2].

           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.

       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.

       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=.

       PermissionsStartOnly=
           Takes a boolean argument. If true, the permission-related execution
           options, as configured with User= and similar options (see
           systemd.exec(5) for more information), are 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.

       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, and stderr) will have the O_NONBLOCK flag
           set and hence are in non-blocking mode. This option is only useful
           in conjunction with a socket unit, as described in
           systemd.socket(5). 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 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 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.

       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. If the empty string is assigned to this
           option, the list of sockets is reset, and all prior uses of this
           setting will have no effect.

       FailureAction=
           Configure the action to take when the service enters a failed
           state. Takes the same values as the unit setting StartLimitAction=
           and executes the same actions (see systemd.unit(5)). Defaults to
           none.

       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 service
           restart schemes where the state is serialized to /run and the file
           descriptors passed to the service manager, to allow restarts
           without losing state. Defaults to 0, i.e. no file descriptors may
           be stored in the service manager by default. 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 queued or being executed for it.

       USBFunctionDescriptors=
           Configure the location of a file containing USB FunctionFS[3]
           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.

       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, in which
       case everything until the next matching quote becomes part of the same
       argument. C-style escapes are also supported. The table below contains
       the list of allowed escape patterns. Only patterns which match the
       syntax in the table are allowed; others will result in an error, and
       must be escaped by doubling the backslash. Quotes themselves are
       removed after parsing and escape sequences substituted. In addition, a
       trailing backslash ("\") may be used to merge lines.

       This syntax is intended to be very similar to shell syntax, but only
       the meta-characters and expansions described in the following
       paragraphs are understood. 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 must be an absolute path name. It may contain
       spaces, but control characters are not allowed.

       The command line accepts "%" specifiers as described in
       systemd.unit(5). Note that the first argument of the command line (i.e.
       the program to execute) may not include specifiers.

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

       Example:

           Environment="ONE=one" 'TWO=two two'
           ExecStart=/bin/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 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=/bin/sh -c 'dmesg | tac'

       Example:

           ExecStart=/bin/echo one ; /bin/echo "two two"

       This will execute /bin/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=/bin/echo / >/dev/null & \; \
           /bin/ls

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

       Table 2. 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 1. 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 2. 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. They will be executed in order until either they
       are all successful or one of them fails.

       Example 3. 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 4. 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 5. 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 6. 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.unit(5), systemd.exec(5),
       systemd.resource-control(5), systemd.kill(5), systemd.directives(7)

NOTES
        1. Incompatibilities with SysV
           http://www.freedesktop.org/wiki/Software/systemd/Incompatibilities

        2. Proper handling of SIGINT/SIGQUIT -- How to be a proper program
           http://www.cons.org/cracauer/sigint.html

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

systemd 231                                                 SYSTEMD.SERVICE(5)



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