Provided by: systemd_237-3ubuntu10.57_amd64 
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.
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, 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= nor
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
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 time-out,
after which the service program is invoked anyway.
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 path referring to the PID file of the service. Usage of this option
is recommended for services where Type= is set to forking. 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 an absolute path to an
executable. 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 ignored │
│ │ and considered success. │
├───────┼──────────────────────────────────┤
│"+" │ 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 the 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.
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,
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= 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 according to KillMode= and KillSignal= 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, 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. 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.
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.
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)).
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 exended 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=
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)).
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 exended 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)).
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.
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 exended 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 acheived 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. 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 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.
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, 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.
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.
FileDescriptorStoreMax=
Configure how many file descriptors may be stored in the service manager for the
service using sd_pid_notify_with_fds(3)'s "FDSTORE=1" messages. This is useful for
implementing services that can restart after an explicit request or a crash without
losing state. Any open sockets and other file descriptors which should not be closed
during the restart may be stored this way. Application state can either be serialized
to a file in /run, or better, stored in a memfd_create(2) memory file descriptor.
Defaults to 0, i.e. no file descriptors may be stored in the service manager. All file
descriptors passed to the service manager from a specific service are passed back to
the service's main process on the next service restart. Any file descriptors passed to
the service manager are automatically closed when POLLHUP or POLLERR is seen on them,
or when the service is fully stopped and no job is queued or being executed for it.
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.
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 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 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 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
https://www.freedesktop.org/wiki/Software/systemd/Incompatibilities
2. USB FunctionFS
https://www.kernel.org/doc/Documentation/usb/functionfs.txt