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NAME | SYNOPSIS | DESCRIPTION | SERVICE TEMPLATES | AUTOMATIC DEPENDENCIES | OPTIONS | COMMAND LINES | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD.SERVICE(5) systemd.service SYSTEMD.SERVICE(5)
systemd.service - Service unit configuration
service.service
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 SysV init compat is enabled, systemd automatically creates
service units that wrap SysV init scripts (the service name is the
same as the name of the script, with a ".service" suffix added);
see systemd-sysv-generator(8).
The systemd-run(1) command allows creating .service and .scope
units dynamically and transiently from the command line.
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.
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).
Service unit files may include [Unit] and [Install] sections,
which are described in systemd.unit(5).
Service unit 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 mechanism via which the service notifies the
manager that the service start-up has finished. One of simple,
exec, forking, oneshot, dbus, notify, notify-reload, or idle:
• If set to simple (the default if ExecStart= is specified
but neither Type= nor BusName= are, and credentials are
not used), the service manager will consider the unit
started immediately after the main service process has
been forked off (i.e. immediately after fork(), and before
various process attributes have been configured and in
particular before the new process has called execve() to
invoke the actual service binary). Typically, Type=exec is
the better choice, see below.
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= does not 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= does not exist, or the
service binary is missing). This type is implied if
credentials are used (refer to LoadCredential= in
systemd.exec(5) for details).
• If set to forking, the manager will consider the unit
started immediately after the binary that forked off by
the manager exits. The use of this type is discouraged,
use notify, notify-reload, or dbus instead.
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. The manager will
proceed with starting follow-up units after the parent
process exits.
• Behavior of oneshot is similar to simple; however, the
service manager will consider the unit up after the main
process exits. It will then start follow-up units.
RemainAfterExit= is particularly useful for this type of
service. Type=oneshot is the implied default if neither
Type= nor ExecStart= are specified. Note that if this
option is used without RemainAfterExit= the service will
never enter "active" unit state, but will directly
transition from "activating" to "deactivating" or "dead",
since no process is configured that shall run
continuously. In particular this means that after a
service of this type ran (and which has RemainAfterExit=
not set) it will not show up as started afterwards, but as
dead.
• Behavior of dbus is similar to simple; however, units of
this type must have the BusName= specified and the service
manager will consider the unit up when the specified bus
name has been acquired. This type is the default if
BusName= is specified.
Service units with this option configured implicitly gain
dependencies on the dbus.socket unit. A service unit of
this type is considered to be in the activating state
until the specified bus name is acquired. It is considered
activated while the bus name is taken. Once the bus name
is released the service is considered being no longer
functional which has the effect that the service manager
attempts to terminate any remaining processes belonging to
the service. Services that drop their bus name as part of
their shutdown logic thus should be prepared to receive a
SIGTERM (or whichever signal is configured in KillSignal=)
as result.
• Behavior of notify is similar to exec; however, it is
expected that the service sends a "READY=1" 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.
If the service supports reloading, and uses a signal to
start the reload, using notify-reload instead is
recommended.
• Behavior of notify-reload is similar to notify, with one
difference: the SIGHUP UNIX process signal is sent to the
service's main process when the service is asked to reload
and the manager will wait for a notification about the
reload being finished.
When initiating the reload process the service is expected
to reply with a notification message via sd_notify(3) that
contains the "RELOADING=1" field in combination with
"MONOTONIC_USEC=" set to the current monotonic time (i.e.
CLOCK_MONOTONIC in clock_gettime(2)) in μs, formatted as
decimal string. Once reloading is complete another
notification message must be sent, containing "READY=1".
Using this service type and implementing this reload
protocol is an efficient alternative to providing an
ExecReload= command for reloading of the service's
configuration.
The signal to send can be tweaked via ReloadSignal=, see
below.
• 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 recommended to use Type=exec for long-running services,
as it ensures that process setup errors (e.g. errors such as a
missing service executable, or missing user) are properly
tracked. However, as this service type will not propagate the
failures in the service's own startup code (as opposed to
failures in the preparatory steps the service manager executes
before execve()) and does not allow ordering of other units
against completion of initialization of the service code
itself (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, notify-reload, 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/notify-reload service
types require 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 is not supported,
then forking is an alternative: it supports the traditional
heavy-weight UNIX service start-up protocol. Note that using
any type other than simple possibly delays the boot process,
as the service manager needs to wait for at least some service
initialization to complete. (Also note it is generally not
recommended to use idle or oneshot for long-running services.)
Note that various service settings (e.g. User=, Group=
through libc NSS) might result in "hidden" blocking IPC calls
to other services when used. Sometimes it might be advisable
to use the simple service type to ensure that the service
manager's transaction logic is not affected by such
potentially slow operations and hidden dependencies, as this
is the only service type where the service manager will not
wait for such service execution setup operations to complete
before proceeding.
ExitType=
Specifies when the manager should consider the service to be
finished. One of main or cgroup:
• If set to main (the default), the service manager will
consider the unit stopped when the main process, which is
determined according to the Type=, exits. Consequently, it
cannot be used with Type=oneshot.
• If set to cgroup, the service will be considered running
as long as at least one process in the cgroup has not
exited.
It is generally recommended to use ExitType=main when a
service has a known forking model and a main process can
reliably be determined. ExitType= cgroup is meant for
applications whose forking model is not known ahead of time
and which might not have a specific main process. It is well
suited for transient or automatically generated services, such
as graphical applications inside of a desktop environment.
Added in version 250.
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.
Note that PID files should be avoided in modern projects. Use
Type=notify, Type=notify-reload or Type=simple where possible,
which does not require use of PID files to determine the main
process of a service and avoids needless forking.
BusName=
Takes a D-Bus destination name that this service shall use.
This option is mandatory for services where Type= is set to
dbus. It is recommended to always set this property if known
to make it easy to map the service name to the D-Bus
destination. In particular, systemctl
service-log-level/service-log-target verbs make use of this.
ExecStart=
Commands that are executed when this service is started.
Unless Type= is oneshot, exactly one command must be given.
When Type=oneshot is used, this setting may be used multiple
times to define multiple commands to execute. 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.)
If more than one command is configured, 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=. Multiple command lines are allowed, regardless of
the service type (i.e. Type=), 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/Type=notify-reload, or the BusName= has been taken
for Type=dbus).
Note that ExecStartPre= may not be used to start long-running
processes. All processes forked off by processes invoked via
ExecStartPre= will be killed before the next service process
is run.
Note that if any of the commands specified in ExecStartPre=,
ExecStart=, or ExecStartPost= fail (and are not prefixed with
"-", see above) or time out before the service is fully up,
execution continues with commands specified in ExecStopPost=,
the commands in ExecStop= are skipped.
Note that the execution of ExecStartPost= is taken into
account for the purpose of Before=/After= ordering
constraints.
ExecCondition=
Optional commands that are executed before the commands in
ExecStartPre=. Syntax is the same as for ExecStart=. Multiple
command lines are allowed, regardless of the service type
(i.e. Type=), and the commands are executed one after the
other, serially.
The behavior is like an ExecStartPre= and condition check
hybrid: when an ExecCondition= command exits with exit code 1
through 254 (inclusive), the remaining commands are skipped
and the unit is not marked as failed. However, if an
ExecCondition= command exits with 255 or abnormally (e.g.
timeout, killed by a signal, etc.), the unit will be
considered failed (and remaining commands will be skipped).
Exit code of 0 or those matching SuccessExitStatus= will
continue execution to the next commands.
The same recommendations about not running long-running
processes in ExecStartPre= also applies to ExecCondition=.
ExecCondition= will also run the commands in ExecStopPost=, as
part of stopping the service, in the case of any non-zero or
abnormal exits, like the ones described above.
Added in version 243.
ExecReload=
Commands to execute to trigger a configuration reload in the
service. This argument takes multiple command lines, following
the same scheme as described for ExecStart= above. Use of this
setting is optional. Specifier and environment variable
substitution is supported here following the same scheme as
for ExecStart=.
One additional, special environment variable is set: if known,
$MAINPID is set to the main process of the daemon, and may be
used for command lines like the following:
ExecReload=kill -HUP $MAINPID
Note however that reloading a daemon by enqueuing a signal (as
with the example line above) is usually not a good choice,
because this is an asynchronous operation and hence not
suitable when ordering reloads of multiple services against
each other. It is thus strongly recommended to either use
Type=notify-reload in place of ExecReload=, or to set
ExecReload= to a command that not only triggers a
configuration reload of the daemon, but also synchronously
waits for it to complete. For example, dbus-broker(1) uses the
following:
ExecReload=busctl call org.freedesktop.DBus \
/org/freedesktop/DBus org.freedesktop.DBus \
ReloadConfig
ExecStop=
Commands to execute to stop the service started via
ExecStart=. This argument takes multiple command lines,
following the same scheme as described for ExecStart= above.
Use of this setting is optional. After the commands configured
in this option are run, it is implied that the service is
stopped, and any processes remaining for it are terminated
according to the KillMode= setting (see systemd.kill(5)). If
this option is not specified, the process is terminated by
sending the signal specified in KillSignal= or
RestartKillSignal= when service stop is requested. Specifier
and environment variable substitution is supported (including
$MAINPID, see above).
Note that it is usually not sufficient to specify a command
for this setting that only asks the service to terminate (for
example, by sending some form of termination signal to it),
but does not wait for it to do so. Since the remaining
processes of the services are killed according to KillMode=
and KillSignal= or RestartKillSignal= as described above
immediately after the command exited, this may not result in a
clean stop. The specified command should hence be a
synchronous operation, not an asynchronous one.
Note that the commands specified in ExecStop= are only
executed when the service started successfully first. They are
not invoked if the service was never started at all, or in
case its start-up failed, for example because any of the
commands specified in ExecStart=, ExecStartPre= or
ExecStartPost= failed (and were not prefixed with "-", see
above) or timed out. Use ExecStopPost= to invoke commands when
a service failed to start up correctly and is shut down again.
Also note that the stop operation is always performed if the
service started successfully, even if the processes in the
service terminated on their own or were killed. The stop
commands must be prepared to deal with that case. $MAINPID
will be unset if systemd knows that the main process exited by
the time the stop commands are called.
Service restart requests are implemented as stop operations
followed by start operations. This means that ExecStop= and
ExecStopPost= are executed during a service restart operation.
It is recommended to use this setting for commands that
communicate with the service requesting clean termination. For
post-mortem clean-up steps use ExecStopPost= instead.
ExecStopPost=
Additional commands that are executed after the service is
stopped. This includes cases where the commands configured in
ExecStop= were used, where the service does not have any
ExecStop= defined, or where the service exited unexpectedly.
This argument takes multiple command lines, following the same
scheme as described for ExecStart=. Use of these settings is
optional. Specifier and environment variable substitution is
supported. Note that – unlike ExecStop= – commands specified
with this setting are invoked when a service failed to start
up correctly and is shut down again.
It is recommended to use this setting for clean-up operations
that shall be executed even when the service failed to start
up correctly. Commands configured with this setting need to be
able to operate even if the service failed starting up
half-way and left incompletely initialized data around. As the
service's processes have likely exited already when the
commands specified with this setting are executed they should
not attempt to communicate with them.
Note that all commands that are configured with this setting
are invoked with the result code of the service, as well as
the main process' exit code and status, set in the
$SERVICE_RESULT, $EXIT_CODE and $EXIT_STATUS environment
variables, see systemd.exec(5) for details.
Note that the execution of ExecStopPost= is taken into account
for the purpose of Before=/After= ordering constraints.
RestartSec=
Configures the time to sleep before restarting a service (as
configured with Restart=). Takes a unit-less value in seconds,
or a time span value such as "5min 20s". Defaults to 100ms.
RestartSteps=
Configures the number of steps to take to increase the
interval of auto-restarts from RestartSec= to
RestartMaxDelaySec=. Takes a positive integer or 0 to disable
it. Defaults to 0.
This setting is effective only if RestartMaxDelaySec= is also
set.
Added in version 254.
RestartMaxDelaySec=
Configures the longest time to sleep before restarting a
service as the interval goes up with RestartSteps=. Takes a
value in the same format as RestartSec=, or "infinity" to
disable the setting. Defaults to "infinity".
This setting is effective only if RestartSteps= is also set.
Added in version 254.
TimeoutStartSec=
Configures the time to wait for start-up. If a daemon service
does not signal start-up completion within the configured
time, the service will be considered failed and will be shut
down again. The precise action depends on the
TimeoutStartFailureMode= option. Takes a unit-less value in
seconds, or a time span value such as "5min 20s". Pass
"infinity" to disable the timeout logic. Defaults to
DefaultTimeoutStartSec= set in the manager, 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/Type=notify-reload sends
"EXTEND_TIMEOUT_USEC=...", this may cause the start time to be
extended beyond TimeoutStartSec=. The first receipt of this
message must occur before TimeoutStartSec= is exceeded, and
once the start time has extended beyond TimeoutStartSec=, the
service manager will allow the service to continue to start,
provided the service repeats "EXTEND_TIMEOUT_USEC=..." within
the interval specified until the service startup status is
finished by "READY=1". (see sd_notify(3)).
Note that the start timeout is also applied to service
reloads, regardless of whether implemented through ExecReload=
or via the reload logic enabled via Type=notify-reload. If the
reload does not complete within the configured time, the
reload will be considered failed and the service will continue
running with the old configuration. This will not affect the
running service, but will be logged and will cause e.g.
systemctl reload to fail.
Added in version 188.
TimeoutStopSec=
This option serves two purposes. First, it configures the time
to wait for each ExecStop= command. If any of them times out,
subsequent ExecStop= commands are skipped and the service will
be terminated by SIGTERM. If no ExecStop= commands are
specified, the service gets the SIGTERM immediately. This
default behavior can be changed by the TimeoutStopFailureMode=
option. Second, it configures the time to wait for the service
itself to stop. If it does not 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/Type=notify-reload sends
"EXTEND_TIMEOUT_USEC=...", this may cause the stop time to be
extended beyond TimeoutStopSec=. The first receipt of this
message must occur before TimeoutStopSec= is exceeded, and
once the stop time has extended beyond TimeoutStopSec=, the
service manager will allow the service to continue to stop,
provided the service repeats "EXTEND_TIMEOUT_USEC=..." within
the interval specified, or terminates itself (see
sd_notify(3)).
Added in version 188.
TimeoutAbortSec=
This option configures the time to wait for the service to
terminate when it was aborted due to a watchdog timeout (see
WatchdogSec=). If the service has a short TimeoutStopSec= this
option can be used to give the system more time to write a
core dump of the service. Upon expiration the service will be
forcibly terminated by SIGKILL (see KillMode= in
systemd.kill(5)). The core file will be truncated in this
case. Use TimeoutAbortSec= to set a sensible timeout for the
core dumping per service that is large enough to write all
expected data while also being short enough to handle the
service failure in due time.
Takes a unit-less value in seconds, or a time span value such
as "5min 20s". Pass an empty value to skip the dedicated
watchdog abort timeout handling and fall back TimeoutStopSec=.
Pass "infinity" to disable the timeout logic. Defaults to
DefaultTimeoutAbortSec= from the manager configuration file
(see systemd-system.conf(5)).
If a service of Type=notify/Type=notify-reload handles SIGABRT
itself (instead of relying on the kernel to write a core dump)
it can send "EXTEND_TIMEOUT_USEC=..." to extended the abort
time beyond TimeoutAbortSec=. The first receipt of this
message must occur before TimeoutAbortSec= is exceeded, and
once the abort time has extended beyond TimeoutAbortSec=, the
service manager will allow the service to continue to abort,
provided the service repeats "EXTEND_TIMEOUT_USEC=..." within
the interval specified, or terminates itself (see
sd_notify(3)).
Added in version 243.
TimeoutSec=
A shorthand for configuring both TimeoutStartSec= and
TimeoutStopSec= to the specified value.
TimeoutStartFailureMode=, TimeoutStopFailureMode=
These options configure the action that is taken in case a
daemon service does not signal start-up within its configured
TimeoutStartSec=, respectively if it does not stop within
TimeoutStopSec=. Takes one of terminate, abort and kill. Both
options default to terminate.
If terminate is set the service will be gracefully terminated
by sending the signal specified in KillSignal= (defaults to
SIGTERM, see systemd.kill(5)). If the service does not
terminate the FinalKillSignal= is sent after TimeoutStopSec=.
If abort is set, WatchdogSignal= is sent instead and
TimeoutAbortSec= applies before sending FinalKillSignal=. This
setting may be used to analyze services that fail to start-up
or shut-down intermittently. By using kill the service is
immediately terminated by sending FinalKillSignal= without any
further timeout. This setting can be used to expedite the
shutdown of failing services.
Added in version 246.
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 (use TimeoutStartSec= to limit their
activation). Pass "infinity" (the default) to configure no
runtime limit.
If a service of Type=notify/Type=notify-reload sends
"EXTEND_TIMEOUT_USEC=...", this may cause the runtime to be
extended beyond RuntimeMaxSec=. The first receipt of this
message must occur before RuntimeMaxSec= is exceeded, and once
the runtime has extended beyond RuntimeMaxSec=, the service
manager will allow the service to continue to run, provided
the service repeats "EXTEND_TIMEOUT_USEC=..." within the
interval specified until the service shutdown is achieved by
"STOPPING=1" (or termination). (see sd_notify(3)).
Added in version 229.
RuntimeRandomizedExtraSec=
This option modifies RuntimeMaxSec= by increasing the maximum
runtime by an evenly distributed duration between 0 and the
specified value (in seconds). If RuntimeMaxSec= is
unspecified, then this feature will be disabled.
Added in version 250.
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 any of the following:
• exit code of 0;
• for types other than Type=oneshot, one of the signals
SIGHUP, SIGINT, SIGTERM, or SIGPIPE;
• 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. Note that Type=oneshot services will never be
restarted on a clean exit status, i.e. always and on-success
are rejected for them.
Table 1. Exit causes and the effect of the Restart= settings
┌───────────────┬────┬────────┬────────────┬────────────┬─────────────┬──────────┬─────────────┐
│ 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.
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.
RestartMode=
Takes a string value that specifies how a service should
restart:
• If set to normal (the default), the service restarts by
going through a failed/inactive state.
Added in version 254.
• If set to direct, the service transitions to the
activating state directly during auto-restart, skipping
failed/inactive state. ExecStopPost= is still invoked.
OnSuccess= and OnFailure= are skipped.
This option is useful in cases where a dependency can fail
temporarily but we do not want these temporary failures to
make the dependent units fail. Dependent units are not
notified of these temporary failures.
Added in version 254.
• If set to debug, the service manager will log messages
that are related to this unit at debug level while
automated restarts are attempted, until either the service
hits the rate limit or it succeeds, and the
$DEBUG_INVOCATION=1 environment variable will be set for
the unit. This is useful to be able to get additional
information when a service fails to start, without needing
to proactively or permanently enable debug level logging
in systemd, which is very verbose. This is otherwise
equivalent to normal mode.
Added in version 257.
Added in version 254.
SuccessExitStatus=
Takes a list of exit status definitions that, when returned by
the main service process, will be considered successful
termination, in addition to the normal successful exit status
0 and, except for Type=oneshot, the signals SIGHUP, SIGINT,
SIGTERM, and SIGPIPE. Exit status definitions can be numeric
termination statuses, termination status names, or termination
signal names, separated by spaces. See the Process Exit Codes
section in systemd.exec(5) for a list of termination status
names (for this setting only the part without the "EXIT_" or
"EX_" prefix should be used). See signal(7) for a list of
signal names.
Note that this setting does not change the mapping between
numeric exit statuses and their names, i.e. regardless how
this setting is used 0 will still be mapped to "SUCCESS" (and
thus typically shown as "0/SUCCESS" in tool outputs) and 1 to
"FAILURE" (and thus typically shown as "1/FAILURE"), and so
on. It only controls what happens as effect of these exit
statuses, and how it propagates to the state of the service as
a whole.
This option may appear more than once, in which case the list
of successful exit statuses is merged. If the empty string is
assigned to this option, the list is reset, all prior
assignments of this option will have no effect.
Example 1. A service with the SuccessExitStatus= setting
SuccessExitStatus=TEMPFAIL 250 SIGKILL
Exit status 75 (TEMPFAIL), 250, and the termination signal
SIGKILL are considered clean service terminations.
Note: systemd-analyze exit-status may be used to list exit
statuses and translate between numerical status values and
names.
Added in version 189.
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 be numeric termination
statuses, termination status names, or termination signal
names, separated by spaces. Defaults to the empty list, so
that, by default, no exit status is excluded from the
configured restart logic.
This option may appear more than once, in which case the list
of restart-preventing statuses is merged. If the empty string
is assigned to this option, the list is reset and all prior
assignments of this option will have no effect.
Note that this setting has no effect on processes configured
via ExecStartPre=, ExecStartPost=, ExecStop=, ExecStopPost= or
ExecReload=, but only on the main service process, i.e. either
the one invoked by ExecStart= or (depending on Type=,
PIDFile=, ...) the otherwise configured main process.
Added in version 189.
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=.
Note that for Type=oneshot services, a success exit status
will prevent them from auto-restarting, no matter whether the
corresponding exit statuses are listed in this option or not.
Added in version 215.
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.
Note that if the same socket unit is configured to be passed
to multiple service units (via the Sockets= setting, see
below), and these services have different NonBlocking=
configurations, the precise state of O_NONBLOCK depends on the
order in which these services are invoked, and will possibly
change after service code already took possession of the
socket file descriptor, simply because the O_NONBLOCK state of
a socket is shared by all file descriptors referencing it.
Hence it is essential that all services sharing the same
socket use the same NonBlocking= configuration, and do not
change the flag in service code either.
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/Type=notify-reload or WatchdogSec= (see above). If
those options are used but NotifyAccess= is not configured, it
will be implicitly set to main.
Note that sd_notify() notifications may be attributed to units
correctly only if either the sending process is still around
at the time PID 1 processes the message, or if the sending
process is explicitly runtime-tracked by the service manager.
The latter is the case if the service manager originally
forked off the process, i.e. on all processes that match main
or exec. Conversely, if an auxiliary process of the unit sends
an sd_notify() message and immediately exits, the service
manager might not be able to properly attribute the message to
the unit, and thus will ignore it, even if NotifyAccess=all is
set for it.
Hence, to eliminate all race conditions involving lookup of
the client's unit and attribution of notifications to units
correctly, sd_notify_barrier() may be used. This call acts as
a synchronization point and ensures all notifications sent
before this call have been picked up by the service manager
when it returns successfully. Use of sd_notify_barrier() is
needed for clients which are not invoked by the service
manager, otherwise this synchronization mechanism is
unnecessary for attribution of notifications to the unit.
Sockets=
Specifies the name of the socket units this service shall
inherit socket file descriptors from when the service is
started. Normally, it should not be necessary to use this
setting, as all socket file descriptors whose unit shares the
same name as the service (subject to the different unit name
suffix of course) are passed to the spawned process.
Note that the same socket file descriptors may be passed to
multiple processes simultaneously. Also note that a different
service may be activated on incoming socket traffic than the
one which is ultimately configured to inherit the socket file
descriptors. Or, in other words: the Service= setting of
.socket units does not have to match the inverse of the
Sockets= setting of the .service it refers to.
This option may appear more than once, in which case the list
of socket units is merged. Note that once set, clearing the
list of sockets again (for example, by assigning the empty
string to this option) is not supported.
FileDescriptorStoreMax=
Configure how many file descriptors may be stored in the
service manager for the service using
sd_pid_notify_with_fds(3)'s "FDSTORE=1" messages. This is
useful for implementing services that can restart after an
explicit request or a crash without losing state. Any open
sockets and other file descriptors which should not be closed
during the restart may be stored this way. Application state
can either be serialized to a file in RuntimeDirectory=, or
stored in a memfd_create(2) memory file descriptor. Defaults
to 0, i.e. no file descriptors may be stored in the service
manager. All file descriptors passed to the service manager
from a specific service are passed back to the service's main
process on the next service restart (see sd_listen_fds(3) for
details about the precise protocol used and the order in which
the file descriptors are passed). Any file descriptors passed
to the service manager are automatically closed when POLLHUP
or POLLERR is seen on them, or when the service is fully
stopped and no job is queued or being executed for it (the
latter can be tweaked with FileDescriptorStorePreserve=, see
below). 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.
The fdstore command of systemd-analyze(1) may be used to list
the current contents of a service's file descriptor store.
Note that the service manager will only pass file descriptors
contained in the file descriptor store to the service's own
processes, never to other clients via IPC or similar. However,
it does allow unprivileged clients to query the list of
currently open file descriptors of a service. Sensitive data
may hence be safely placed inside the referenced files, but
should not be attached to the metadata (e.g. included in
filenames) of the stored file descriptors.
If this option is set to a non-zero value the $FDSTORE
environment variable will be set for processes invoked for
this service. See systemd.exec(5) for details.
For further information on the file descriptor store see the
File Descriptor Store[1] overview.
Added in version 219.
FileDescriptorStorePreserve=
Takes one of no, yes, restart and controls when to release the
service's file descriptor store (i.e. when to close the
contained file descriptors, if any). If set to no the file
descriptor store is automatically released when the service is
stopped; if restart (the default) it is kept around as long as
the unit is neither inactive nor failed, or a job is queued
for the service, or the service is expected to be restarted.
If yes the file descriptor store is kept around until the unit
is removed from memory (i.e. is not referenced anymore and
inactive). The latter is useful to keep entries in the file
descriptor store pinned until the service manager exits.
Use systemctl clean --what=fdstore ... to release the file
descriptor store explicitly.
Added in version 254.
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.
Added in version 227.
USBFunctionStrings=
Configure the location of a file containing USB FunctionFS
strings. Behavior is similar to USBFunctionDescriptors= above.
Added in version 227.
OOMPolicy=
Configure the out-of-memory (OOM) killing policy for the
kernel and the userspace OOM killer systemd-oomd.service(8).
On Linux, when memory becomes scarce to the point that the
kernel has trouble allocating memory for itself, it might
decide to kill a running process in order to free up memory
and reduce memory pressure. Note that systemd-oomd.service is
a more flexible solution that aims to prevent out-of-memory
situations for the userspace too, not just the kernel, by
attempting to terminate services earlier, before the kernel
would have to act.
This setting takes one of continue, stop or kill. If set to
continue and a process in the unit is killed by the OOM
killer, this is logged but the unit continues running. If set
to stop the event is logged but the unit is terminated cleanly
by the service manager. If set to kill and one of the unit's
processes is killed by the OOM killer the kernel is instructed
to kill all remaining processes of the unit too, by setting
the memory.oom.group attribute to 1; also see kernel page
Control Group v2[3].
Defaults to the setting DefaultOOMPolicy= in
systemd-system.conf(5) is set to, except for units where
Delegate= is turned on, where it defaults to continue.
Use the OOMScoreAdjust= setting to configure whether processes
of the unit shall be considered preferred or less preferred
candidates for process termination by the Linux OOM killer
logic. See systemd.exec(5) for details.
This setting also applies to systemd-oomd.service(8).
Similarly to the kernel OOM kills performed by the kernel,
this setting determines the state of the unit after
systemd-oomd kills a cgroup associated with it.
Added in version 243.
OpenFile=
Takes an argument of the form "path[:fd-name:options]", where:
• "path" is a path to a file or an AF_UNIX socket in the
file system;
• "fd-name" is a name that will be associated with the file
descriptor; the name may contain any ASCII character, but
must exclude control characters and ":", and must be at
most 255 characters in length; it is optional and, if not
provided, defaults to the file name;
• "options" is a comma-separated list of access options;
possible values are "read-only", "append", "truncate",
"graceful"; if not specified, files will be opened in rw
mode; if "graceful" is specified, errors during
file/socket opening are ignored. Specifying the same
option several times is treated as an error.
The file or socket is opened by the service manager and the
file descriptor is passed to the service. If the path is a
socket, we call connect() on it. See sd_listen_fds(3) for more
details on how to retrieve these file descriptors.
This setting is useful to allow services to access
files/sockets that they cannot access themselves (due to
running in a separate mount namespace, not having privileges,
...).
This setting can be specified multiple times, in which case
all the specified paths are opened and the file descriptors
passed to the service. If the empty string is assigned, the
entire list of open files defined prior to this is reset.
Added in version 253.
ReloadSignal=
Configures the UNIX process signal to send to the service's
main process when asked to reload the service's configuration.
Defaults to SIGHUP. This option has no effect unless
Type=notify-reload is used, see above.
Added in version 253.
Check systemd.unit(5), systemd.exec(5), and systemd.kill(5) for
more settings.
This section describes command line parsing and variable and
specifier substitutions for ExecStart=, ExecStartPre=,
ExecStartPost=, ExecReload=, ExecStop=, ExecStopPost=, and
ExecCondition= options.
Multiple command lines may be specified by using the relevant
setting multiple times.
Each command line is unquoted using the rules described in
"Quoting" section in systemd.syntax(7). The first item becomes the
command to execute, and the subsequent items the arguments.
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.
Each command may be prefixed with a number of special characters:
Table 2. Special executable prefixes
┌────────┬─────────────────────────────┐
│ Prefix │ Effect │
├────────┼─────────────────────────────┤
│ "@" │ If the executable path │
│ │ is prefixed with "@", │
│ │ the second specified │
│ │ token will be passed as │
│ │ argv[0] to the executed │
│ │ process (instead of the │
│ │ actual filename), │
│ │ followed by the further │
│ │ arguments specified. │
├────────┼─────────────────────────────┤
│ "-" │ If the executable path │
│ │ is prefixed with "-", an │
│ │ exit code of the command │
│ │ normally considered a │
│ │ failure (i.e. non-zero │
│ │ exit status or abnormal │
│ │ exit due to signal) is │
│ │ recorded, but has no │
│ │ further effect and is │
│ │ considered equivalent to │
│ │ success. │
├────────┼─────────────────────────────┤
│ ":" │ If the executable path │
│ │ is prefixed with ":", │
│ │ environment variable │
│ │ substitution (as │
│ │ described below this │
│ │ table) is not applied. │
├────────┼─────────────────────────────┤
│ "+" │ If the executable path │
│ │ is prefixed with "+" │
│ │ then the process is │
│ │ executed with full │
│ │ privileges. In this mode │
│ │ privilege restrictions │
│ │ configured with User=, │
│ │ Group=, │
│ │ CapabilityBoundingSet= │
│ │ or the various file │
│ │ system namespacing │
│ │ options (such as │
│ │ PrivateDevices=, │
│ │ PrivateTmp=) are not │
│ │ applied to the invoked │
│ │ command line (but still │
│ │ affect any other │
│ │ ExecStart=, ExecStop=, │
│ │ ... lines). However, │
│ │ note that this will not │
│ │ bypass options that │
│ │ apply to the whole │
│ │ control group, such as │
│ │ DevicePolicy=, see │
│ │ systemd.resource-control(5) │
│ │ for the full list. │
├────────┼─────────────────────────────┤
│ "!" │ 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. │
└────────┴─────────────────────────────┘
"@", "-", ":", and one of "+"/"!"/"!!" may be used together and
they can appear in any order. However, only one of "+", "!", "!!"
may be used at a time.
For each command, the first argument must be either an absolute
path to an executable or a simple file name without any slashes.
If the command is not a full (absolute) path, it will be resolved
to a full path using a fixed search path determined at compilation
time. Searched directories include /usr/local/bin/, /usr/bin/, and
their sbin/ counterparts (only 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. Hint: this search path
may be queried using systemd-path search-binaries-default.
The command line accepts "%" specifiers as described in
systemd.unit(5).
An argument solely consisting of ";" must be escaped, i.e.
specified as "\;".
Basic environment variable substitution is supported. Use "${FOO}"
as part of a word, or as a word of its own, on the command line,
in which case it will be erased and replaced by the exact value of
the environment variable (if any) including all whitespace it
contains, always resulting in exactly a single argument. Use
"$FOO" as a separate word on the command line, in which case it
will be replaced by the value of the environment variable split at
whitespace, resulting in zero or more arguments. For this type of
expansion, quotes are respected when splitting into words, and
afterwards removed.
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
ExecStart=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:
Type=oneshot
ExecStart=:echo $USER
ExecStart=-false
ExecStart=+:@true $TEST
This will execute /usr/bin/echo with the literal argument "$USER"
(":" suppresses variable expansion), and then /usr/bin/false (the
return value will be ignored because "-" suppresses checking of
the return value), and /usr/bin/true (with elevated privileges,
with "$TEST" as argv[0]).
Example:
ExecStart=echo / >/dev/null & \; \
ls
This will execute echo with five arguments: "/", ">/dev/null",
"&", ";", and "ls".
Example 3. 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/Type=notify-reload 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 4. Oneshot service
Sometimes, units should just execute an action without keeping
active processes, such as a filesystem check or a cleanup action
on boot. For this, Type=oneshot exists. Units of this type will
wait until the process specified terminates and then fall back to
being inactive. The following unit will perform a cleanup action:
[Unit]
Description=Cleanup old Foo data
[Service]
Type=oneshot
ExecStart=/usr/sbin/foo-cleanup
[Install]
WantedBy=multi-user.target
Note that systemd will consider the unit to be in the state
"starting" until the program has terminated, so ordered
dependencies will wait for the program to finish before starting
themselves. The unit will revert to the "inactive" state after the
execution is done, never reaching the "active" state. That means
another request to start the unit will perform the action again.
Type=oneshot are the only service units that may have more than
one ExecStart= specified. For units with multiple commands
(Type=oneshot), all commands will be run again.
For Type=oneshot, Restart=always and Restart=on-success are not
allowed.
Example 5. 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 6. 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 7. 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 8. 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 or Type=notify-reload for this. A typical service file
for such a daemon would look like this:
[Unit]
Description=Simple notifying service
[Service]
Type=notify-reload
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.
To avoid code duplication, it is preferable to use sd_notify(3)
when possible, especially when other APIs provided by
libsystemd(3) are also used, but note that the notification
protocol is very simple and guaranteed to be stable as per the
Interface Portability and Stability Promise[4], so it can be
reimplemented by services with no external dependencies. For a
self-contained example, see sd_notify(3).
systemd(1), systemctl(1), systemd-system.conf(5), systemd.unit(5),
systemd.exec(5), systemd.resource-control(5), systemd.kill(5),
systemd.directives(7), systemd-run(1)
1. File Descriptor Store
https://systemd.io/FILE_DESCRIPTOR_STORE
2. USB FunctionFS
https://docs.kernel.org/usb/functionfs.html
3. Control Group v2
https://docs.kernel.org/admin-guide/cgroup-v2.html
4. Interface Portability and Stability Promise
https://systemd.io/PORTABILITY_AND_STABILITY/
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-02-02. (At that
time, the date of the most recent commit that was found in the
repository was 2025-02-02.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~devel SYSTEMD.SERVICE(5)
Pages that refer to this page: systemctl(1), systemd(1), systemd-analyze(1), systemd-notify(1), systemd-run(1), systemd-socket-activate(1), sd-daemon(3), sd_event_set_watchdog(3), sd_is_fifo(3), sd_listen_fds(3), sd_notify(3), sd_watchdog_enabled(3), capsule@.service(5), environment.d(5), org.freedesktop.LogControl1(5), org.freedesktop.systemd1(5), systemd.exec(5), systemd.kill(5), systemd.mount(5), systemd.path(5), systemd.resource-control(5), systemd.scope(5), systemd.slice(5), systemd.socket(5), systemd-system.conf(5), systemd.timer(5), systemd.unit(5), user@.service(5), daemon(7), systemd.directives(7), systemd.index(7), systemd.special(7), systemd.syntax(7), pam_systemd(8), systemd-networkd-wait-online.service(8), systemd-oomd.service(8), systemd-run-generator(8), systemd-socket-proxyd(8), systemd-soft-reboot.service(8), systemd-sysv-generator(8), systemd-xdg-autostart-generator(8)
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