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Manual page for systemd.service unit configurations. A unit configuration file whose name ends with ".service" is a systemd stores information about the process controlled and monitored by
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man systemd.serviceSYSTEMD.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.
SERVICE TEMPLATES
It is possible for systemd services to take a single argument via the "service@argument.service" syntax. Such services are
called "instantiated" services, while the unit definition without the argument parameter is called a "template". An example
could be a dhcpcd@.service service template which takes a network interface as a parameter to form an instantiated service.
Within the service file, this parameter or "instance name" can be accessed with %-specifiers. See systemd.unit(5) for
details.
AUTOMATIC DEPENDENCIES
Implicit Dependencies
The following dependencies are implicitly added:
• Services with Type=dbus set automatically acquire dependencies of type Requires= and After= on dbus.socket.
• Socket activated services are automatically ordered after their activating .socket units via an automatic After=
dependency. Services also pull in all .socket units listed in Sockets= via automatic Wants= and After= dependencies.
Additional implicit dependencies may be added as result of execution and resource control parameters as documented in
systemd.exec(5) and systemd.resource-control(5).
Default Dependencies
The following dependencies are added unless DefaultDependencies=no is set:
• Service units will have dependencies of type Requires= and After= on sysinit.target, a dependency of type After= on
basic.target as well as dependencies of type Conflicts= and Before= on shutdown.target. These ensure that normal service
units pull in basic system initialization, and are terminated cleanly prior to system shutdown. Only services involved
with early boot or late system shutdown should disable this option.
• Instanced service units (i.e. service units with an "@" in their name) are assigned by default a per-template slice unit
(see systemd.slice(5)), named after the template unit, containing all instances of the specific template. This slice is
normally stopped at shutdown, together with all template instances. If that is not desired, set DefaultDependencies=no
in the template unit, and either define your own per-template slice unit file that also sets DefaultDependencies=no, or
set Slice=system.slice (or another suitable slice) in the template unit. Also see systemd.resource-control(5).
OPTIONS
Service files must include a "[Service]" section, which carries information about the service and the process it supervises.
A number of options that may be used in this section are shared with other unit types. These options are documented in
systemd.exec(5), systemd.kill(5) and systemd.resource-control(5). The options specific to the "[Service]" section of service
units are the following:
Type=
Configures the process start-up type for this service unit. One of simple, exec, forking, oneshot, dbus, notify or idle:
• If set to simple (the default if ExecStart= is specified but neither Type= nor BusName= are), the service manager
will consider the unit started immediately after the main service process has been forked off. It is expected that
the process configured with ExecStart= is the main process of the service. In this mode, if the process offers
functionality to other processes on the system, its communication channels should be installed before the service is
started up (e.g. sockets set up by systemd, via socket activation), as the service manager will immediately proceed
starting follow-up units, right after creating the main service process, and before executing the service's binary.
Note that this means systemctl start command lines for simple services will report success even if the service's
binary cannot be invoked successfully (for example because the selected User= doesn't exist, or the service binary
is missing).
• The exec type is similar to simple, but the service manager will consider the unit started immediately after the
main service binary has been executed. The service manager will delay starting of follow-up units until that point.
(Or in other words: simple proceeds with further jobs right after fork() returns, while exec will not proceed before
both fork() and execve() in the service process succeeded.) Note that this means systemctl start command lines for
exec services will report failure when the service's binary cannot be invoked successfully (for example because the
selected User= doesn't exist, or the service binary is missing).
• If set to forking, it is expected that the process configured with ExecStart= will call fork() as part of its
start-up. The parent process is expected to exit when start-up is complete and all communication channels are set
up. The child continues to run as the main service process, and the service manager will consider the unit started
when the parent process exits. This is the behavior of traditional UNIX services. If this setting is used, it is
recommended to also use the PIDFile= option, so that systemd can reliably identify the main process of the service.
systemd will proceed with starting follow-up units as soon as the parent process exits.
• Behavior of oneshot is similar to simple; however, the service manager will consider the unit started after the main
process exits. It will then start follow-up units. RemainAfterExit= is particularly useful for this type of
service. Type=oneshot is the implied default if neither Type= nor ExecStart= are specified.
• Behavior of dbus is similar to simple; however, it is expected that the service acquires a name on the D-Bus bus, as
configured by BusName=. systemd will proceed with starting follow-up units after the D-Bus bus name has been
acquired. Service units with this option configured implicitly gain dependencies on the dbus.socket unit. This type
is the default if BusName= is specified.
• Behavior of notify is similar to exec; however, it is expected that the service sends a notification message via
sd_notify(3) or an equivalent call when it has finished starting up. systemd will proceed with starting follow-up
units after this notification message has been sent. If this option is used, NotifyAccess= (see below) should be set
to open access to the notification socket provided by systemd. If NotifyAccess= is missing or set to none, it will
be forcibly set to main. 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 timeout, after which the service program
is invoked anyway.
It is generally recommended to use Type=simple for long-running services whenever possible, as it is the simplest and
fastest option. However, as this service type won't propagate service start-up failures and doesn't allow ordering of
other units against completion of initialization of the service (which for example is useful if clients need to connect
to the service through some form of IPC, and the IPC channel is only established by the service itself — in contrast to
doing this ahead of time through socket or bus activation or similar), it might not be sufficient for many cases. If so,
notify or dbus (the latter only in case the service provides a D-Bus interface) are the preferred options as they allow
service program code to precisely schedule when to consider the service started up successfully and when to proceed with
follow-up units. The notify service type requires explicit support in the service codebase (as sd_notify() or an
equivalent API needs to be invoked by the service at the appropriate time) — if it's not supported, then forking is an
alternative: it supports the traditional UNIX service start-up protocol. Finally, exec might be an option for cases
where it is enough to ensure the service binary is invoked, and where the service binary itself executes no or little
initialization on its own (and its initialization is unlikely to fail). Note that using any type other than simple
possibly delays the boot process, as the service manager needs to wait for service initialization to complete. It is
hence recommended not to needlessly use any types other than simple. (Also note it is generally not recommended to use
idle or oneshot for long-running services.)
RemainAfterExit=
Takes a boolean value that specifies whether the service shall be considered active even when all its processes exited.
Defaults to no.
GuessMainPID=
Takes a boolean value that specifies whether systemd should try to guess the main PID of a service if it cannot be
determined reliably. This option is ignored unless Type=forking is set and PIDFile= is unset because for the other types
or with an explicitly configured PID file, the main PID is always known. The guessing algorithm might come to incorrect
conclusions if a daemon consists of more than one process. If the main PID cannot be determined, failure detection and
automatic restarting of a service will not work reliably. Defaults to yes.
PIDFile=
Takes a path referring to the PID file of the service. Usage of this option is recommended for services where Type= is
set to forking. The path specified typically points to a file below /run/. If a relative path is specified it is hence
prefixed with /run/. The service manager will read the PID of the main process of the service from this file after
start-up of the service. The service manager will not write to the file configured here, although it will remove the
file after the service has shut down if it still exists. The PID file does not need to be owned by a privileged user,
but if it is owned by an unprivileged user additional safety restrictions are enforced: the file may not be a symlink to
a file owned by a different user (neither directly nor indirectly), and the PID file must refer to a process already
belonging to the service.
BusName=
Takes a D-Bus bus name that this service is reachable as. This option is mandatory for services where Type= is set to
dbus.
ExecStart=
Commands with their arguments that are executed when this service is started. The value is split into zero or more
command lines according to the rules described below (see section "Command Lines" below).
Unless Type= is oneshot, exactly one command must be given. When Type=oneshot is used, zero or more commands may be
specified. Commands may be specified by providing multiple command lines in the same directive, or alternatively, this
directive may be specified more than once with the same effect. If the empty string is assigned to this option, the list
of commands to start is reset, prior assignments of this option will have no effect. If no ExecStart= is specified, then
the service must have RemainAfterExit=yes and at least one ExecStop= line set. (Services lacking both ExecStart= and
ExecStop= are not valid.)
For each of the specified commands, the first argument must be either an absolute path to an executable or a simple file
name without any slashes. Optionally, this filename may be prefixed with a number of special characters:
Table 1. Special executable prefixes
┌───────┬──────────────────────────────────────────────┐
│Prefix │ Effect │
├───────┼──────────────────────────────────────────────┤
│"@" │ If the executable path is prefixed with "@", │
│ │ the second specified token will be passed as │
│ │ "argv[0]" to the executed process (instead │
│ │ of the actual filename), followed by the │
│ │ further arguments specified. │
├───────┼──────────────────────────────────────────────┤
│"-" │ If the executable path is prefixed with "-", │
│ │ an exit code of the command normally │
│ │ considered a failure (i.e. non-zero exit │
│ │ status or abnormal exit due to signal) is │
│ │ recorded, but has no further effect and is │
│ │ considered equivalent to success. │
├───────┼──────────────────────────────────────────────┤
│"+" │ If the executable path is prefixed with "+" │
│ │ then the process is executed with full │
│ │ privileges. In this mode privilege │
│ │ restrictions configured with User=, Group=, │
│ │ CapabilityBoundingSet= or the various file │
│ │ system namespacing options (such as │
│ │ PrivateDevices=, PrivateTmp=) are not │
│ │ applied to the invoked command line (but │
│ │ still affect any other ExecStart=, │
│ │ ExecStop=, ... lines). │
├───────┼──────────────────────────────────────────────┤
│"!" │ Similar to the "+" character discussed above │
│ │ this permits invoking command lines with │
│ │ elevated privileges. However, unlike "+" the │
│ │ "!" character exclusively alters the effect │
│ │ of User=, Group= and SupplementaryGroups=, │
│ │ i.e. only the stanzas that affect user and │
│ │ group credentials. Note that this setting │
│ │ may be combined with DynamicUser=, in which │
│ │ case a dynamic user/group pair is allocated │
│ │ before the command is invoked, but │
│ │ credential changing is left to the executed │
│ │ process itself. │
├───────┼──────────────────────────────────────────────┤
│"!!" │ This prefix is very similar to "!", however │
│ │ it only has an effect on systems lacking │
│ │ support for ambient process capabilities, │
│ │ i.e. without support for │
│ │ AmbientCapabilities=. It's intended to be │
│ │ used for unit files that take benefit of │
│ │ ambient capabilities to run processes with │
│ │ minimal privileges wherever possible while │
│ │ remaining compatible with systems that lack │
│ │ ambient capabilities support. Note that when │
│ │ "!!" is used, and a system lacking ambient │
│ │ capability support is detected any │
│ │ configured SystemCallFilter= and │
│ │ CapabilityBoundingSet= stanzas are │
│ │ implicitly modified, in order to permit │
│ │ spawned processes to drop credentials and │
│ │ capabilities themselves, even if this is │
│ │ configured to not be allowed. Moreover, if │
│ │ this prefix is used and a system lacking │
│ │ ambient capability support is detected │
│ │ AmbientCapabilities= will be skipped and not │
│ │ be applied. On systems supporting ambient │
│ │ capabilities, "!!" has no effect and is │
│ │ redundant. │
└───────┴──────────────────────────────────────────────┘
"@", "-", and one of "+"/"!"/"!!" may be used together and they can appear in any order. However, only one of "+", "!",
"!!" may be used at a time. Note that these prefixes are also supported for the other command line settings, i.e.
ExecStartPre=, ExecStartPost=, ExecReload=, ExecStop= and ExecStopPost=.
If more than one command is specified, the commands are invoked sequentially in the order they appear in the unit file.
If one of the commands fails (and is not prefixed with "-"), other lines are not executed, and the unit is considered
failed.
Unless Type=forking is set, the process started via this command line will be considered the main process of the daemon.
ExecStartPre=, ExecStartPost=
Additional commands that are executed before or after the command in ExecStart=, respectively. Syntax is the same as for
ExecStart=, except that multiple command lines are allowed and the commands are executed one after the other, serially.
If any of those commands (not prefixed with "-") fail, the rest are not executed and the unit is considered failed.
ExecStart= commands are only run after all ExecStartPre= commands that were not prefixed with a "-" exit successfully.
ExecStartPost= commands are only run after the commands specified in ExecStart= have been invoked successfully, as
determined by Type= (i.e. the process has been started for Type=simple or Type=idle, the last ExecStart= process exited
successfully for Type=oneshot, the initial process exited successfully for Type=forking, "READY=1" is sent for
Type=notify, or the BusName= has been taken for Type=dbus).
Note that ExecStartPre= may not be used to start long-running processes. All processes forked off by processes invoked
via ExecStartPre= will be killed before the next service process is run.
Note that if any of the commands specified in ExecStartPre=, ExecStart=, or ExecStartPost= fail (and are not prefixed
with "-", see above) or time out before the service is fully up, execution continues with commands specified in
ExecStopPost=, the commands in ExecStop= are skipped.
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=
This option serves two purposes. First, it configures the time to wait for each ExecStop= command. If any of them times
out, subsequent ExecStop= commands are skipped and the service will be terminated by SIGTERM. If no ExecStop= commands
are specified, the service gets the SIGTERM immediately. Second, it configures the time to wait for the service itself
to stop. If it doesn't terminate in the specified time, it will be forcibly terminated by SIGKILL (see KillMode= in
systemd.kill(5)). Takes a unit-less value in seconds, or a time span value such as "5min 20s". Pass "infinity" to
disable the timeout logic. Defaults to DefaultTimeoutStopSec= from the manager configuration file (see systemd-
system.conf(5)).
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=...", this may cause the stop time to be extended beyond
TimeoutStopSec=. The first receipt of this message must occur before TimeoutStopSec= is exceeded, and once the stop time
has 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 achieved by "STOPPING=1"
(or termination). (see sd_notify(3)).
WatchdogSec=
Configures the watchdog timeout for a service. The watchdog is activated when the start-up is completed. The service
must call sd_notify(3) regularly with "WATCHDOG=1" (i.e. the "keep-alive ping"). If the time between two such calls is
larger than the configured time, then the service is placed in a failed state and it will be terminated with SIGABRT (or
the signal specified by WatchdogSignal=). By setting Restart= to on-failure, on-watchdog, on-abnormal or always, the
service will be automatically restarted. The time configured here will be passed to the executed service process in the
WATCHDOG_USEC= environment variable. This allows daemons to automatically enable the keep-alive pinging logic if
watchdog support is enabled for the service. If this option is used, NotifyAccess= (see below) should be set to open
access to the notification socket provided by systemd. If NotifyAccess= is not set, it will be implicitly set to main.
Defaults to 0, which disables this feature. The service can check whether the service manager expects watchdog
keep-alive notifications. See sd_watchdog_enabled(3) for details. sd_event_set_watchdog(3) may be used to enable
automatic watchdog notification support.
Restart=
Configures whether the service shall be restarted when the service process exits, is killed, or a timeout is reached.
The service process may be the main service process, but it may also be one of the processes specified with
ExecStartPre=, ExecStartPost=, ExecStop=, ExecStopPost=, or ExecReload=. When the death of the process is a result of
systemd operation (e.g. service stop or restart), the service will not be restarted. Timeouts include missing the
watchdog "keep-alive ping" deadline and a service start, reload, and stop operation timeouts.
Takes one of no, on-success, on-failure, on-abnormal, on-watchdog, on-abort, or always. If set to no (the default), the
service will not be restarted. If set to on-success, it will be restarted only when the service process exits cleanly.
In this context, a clean exit means an exit code of 0, or one of the signals SIGHUP, SIGINT, SIGTERM or SIGPIPE, and
additionally, exit statuses and signals specified in SuccessExitStatus=. If set to on-failure, the service will be
restarted when the process exits with a non-zero exit code, is terminated by a signal (including on core dump, but
excluding the aforementioned four signals), when an operation (such as service reload) times out, and when the
configured watchdog timeout is triggered. If set to on-abnormal, the service will be restarted when the process is
terminated by a signal (including on core dump, excluding the aforementioned four signals), when an operation times out,
or when the watchdog timeout is triggered. If set to on-abort, the service will be restarted only if the service process
exits due to an uncaught signal not specified as a clean exit status. If set to on-watchdog, the service will be
restarted only if the watchdog timeout for the service expires. If set to always, the service will be restarted
regardless of whether it exited cleanly or not, got terminated abnormally by a signal, or hit a timeout.
Table 2. Exit causes and the effect of the Restart= settings on them
┌────────────────┬────┬────────┬────────────┬────────────┬─────────────┬──────────┬─────────────┐
│Restart │ no │ always │ on-success │ on-failure │ on-abnormal │ on-abort │ on-watchdog │
│settings/Exit │ │ │ │ │ │ │ │
│causes │ │ │ │ │ │ │ │
├────────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Clean exit code │ │ X │ X │ │ │ │ │
│or signal │ │ │ │ │ │ │ │
├────────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Unclean exit │ │ X │ │ X │ │ │ │
│code │ │ │ │ │ │ │ │
├────────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Unclean signal │ │ X │ │ X │ X │ X │ │
├────────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│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=.
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. If this option is used, NotifyAccess= (see above) should be set to open access to the notification socket provided
by systemd. If NotifyAccess= is not set, it will be implicitly set to main.
USBFunctionDescriptors=
Configure the location of a file containing USB FunctionFS[2] descriptors, for implementation of USB gadget functions.
This is used only in conjunction with a socket unit with ListenUSBFunction= configured. The contents of this file are
written to the ep0 file after it is opened.
USBFunctionStrings=
Configure the location of a file containing USB FunctionFS strings. Behavior is similar to USBFunctionDescriptors=
above.
Check systemd.exec(5) and systemd.kill(5) for more settings.
COMMAND LINES
This section describes command line parsing and variable and specifier substitutions for ExecStart=, ExecStartPre=,
ExecStartPost=, ExecReload=, ExecStop=, and ExecStopPost= options.
Multiple command lines may be concatenated in a single directive by separating them with semicolons (these semicolons must
be passed as separate words). Lone semicolons may be escaped as "\;".
Each command line is split on whitespace, with the first item being the command to execute, and the subsequent items being
the arguments. Double quotes ("...") and single quotes ('...') may be used to wrap a whole item (the opening quote may
appear only at the beginning or after whitespace that is not quoted, and the closing quote must be followed by whitespace or
the end of line), in which case everything until the next matching quote becomes part of the same argument. Quotes
themselves are removed. C-style escapes are also supported. The table below contains the list of known escape patterns. Only
escape patterns which match the syntax in the table are allowed; other patterns may be added in the future and unknown
patterns will result in a warning. In particular, any backslashes should be doubled. Finally, a trailing backslash ("\") may
be used to merge lines.
This syntax is inspired by shell syntax, but only the meta-characters and expansions described in the following paragraphs
are understood, and the expansion of variables is different. Specifically, redirection using "<", "<<", ">", and ">>", pipes
using "|", running programs in the background using "&", and other elements of shell syntax are not supported.
The command to execute may contain spaces, but control characters are not allowed.
The command line accepts "%" specifiers as described in systemd.unit(5).
Basic environment variable substitution is supported. Use "${FOO}" as part of a word, or as a word of its own, on the
command line, in which case it will be 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.
If the command is not a full (absolute) path, it will be resolved to a full path using a fixed search path determinted at
compilation time. Searched directories include /usr/local/bin/, /usr/bin/, /bin/ on systems using split /usr/bin/ and /bin/
directories, and their sbin/ counterparts on systems using split bin/ and sbin/. It is thus safe to use just the executable
name in case of executables located in any of the "standard" directories, and an absolute path must be used in other cases.
Using an absolute path is recommended to avoid ambiguity. Hint: this search path may be queried using systemd-path
search-binaries-default.
Example:
Environment="ONE=one" 'TWO=two two'
ExecStart=echo $ONE $TWO ${TWO}
This will execute /bin/echo with four arguments: "one", "two", "two", and "two two".
Example:
Environment=ONE='one' "TWO='two two' too" THREE=
ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
ExecStart=/bin/echo $ONE $TWO $THREE
This results in /bin/echo being called twice, the first time with arguments "'one'", "'two two' too", "", and the second
time with arguments "one", "two two", "too".
To pass a literal dollar sign, use "$$". Variables whose value is not known at expansion time are treated as empty strings.
Note that the first argument (i.e. the program to execute) may not be a variable.
Variables to be used in this fashion may be defined through Environment= and EnvironmentFile=. In addition, variables listed
in the section "Environment variables in spawned processes" in systemd.exec(5), which are considered "static configuration",
may be used (this includes e.g. $USER, but not $TERM).
Note that shell command lines are not directly supported. If shell command lines are to be used, they need to be passed
explicitly to a shell implementation of some kind. Example:
ExecStart=sh -c 'dmesg | tac'
Example:
ExecStart=echo one ; echo "two two"
This will execute echo two times, each time with one argument: "one" and "two two", respectively. Because two commands are
specified, Type=oneshot must be used.
Example:
ExecStart=echo / >/dev/null & \; \
ls
This will execute echo with five arguments: "/", ">/dev/null", "&", ";", and "ls".
Table 3. C escapes supported in command lines and environment variables
┌────────┬─────────────────────────────────────────────┐
│Literal │ Actual value │
├────────┼─────────────────────────────────────────────┤
│"\a" │ bell │
├────────┼─────────────────────────────────────────────┤
│"\b" │ backspace │
├────────┼─────────────────────────────────────────────┤
│"\f" │ form feed │
├────────┼─────────────────────────────────────────────┤
│"\n" │ newline │
├────────┼─────────────────────────────────────────────┤
│"\r" │ carriage return │
├────────┼─────────────────────────────────────────────┤
│"\t" │ tab │
├────────┼─────────────────────────────────────────────┤
│"\v" │ vertical tab │
├────────┼─────────────────────────────────────────────┤
│"\\" │ backslash │
├────────┼─────────────────────────────────────────────┤
│"\"" │ double quotation mark │
├────────┼─────────────────────────────────────────────┤
│"\'" │ single quotation mark │
├────────┼─────────────────────────────────────────────┤
│"\s" │ space │
├────────┼─────────────────────────────────────────────┤
│"\xxx" │ character number xx in hexadecimal encoding │
├────────┼─────────────────────────────────────────────┤
│"\nnn" │ character number nnn in octal encoding │
└────────┴─────────────────────────────────────────────┘
EXAMPLES
Example 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-system.conf(5), 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
systemd 241 SYSTEMD.SERVICE(5)
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