NAME
systemd.service - Service unit configurationSYNOPSIS
service.serviceDESCRIPTION
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.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 [email protected] 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 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 process start-up type for this
service unit. One of simple, exec, forking,
oneshot, dbus, notify or idle:
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.)
ExitType=
•If set to simple (the default
if ExecStart= is specified but neither Type= nor BusName=
are), the service manager will consider the unit started immediately after the
main service process has been forked off. It is expected that the process
configured with ExecStart= is the main process of the service. In this
mode, if the process offers functionality to other processes on the system,
its communication channels should be installed before the service is started
up (e.g. sockets set up by systemd, via socket activation), as the service
manager will immediately proceed starting follow-up units, right after
creating the main service process, and before executing the service's binary.
Note that this means systemctl start command lines for simple
services will report success even if the service's binary cannot be invoked
successfully (for example because the selected User= doesn't exist, or
the service binary is missing).
•The exec type is similar to
simple, but the service manager will consider the unit started
immediately after the main service binary has been executed. The service
manager will delay starting of follow-up units until that point. (Or in other
words: simple proceeds with further jobs right after fork()
returns, while exec will not proceed before both fork() and
execve() in the service process succeeded.) Note that this means
systemctl start command lines for exec services will report
failure when the service's binary cannot be invoked successfully (for example
because the selected User= doesn't exist, or the service binary is
missing).
•If set to forking, it is
expected that the process configured with ExecStart= will call
fork() as part of its start-up. The parent process is expected to exit
when start-up is complete and all communication channels are set up. The child
continues to run as the main service process, and the service manager will
consider the unit started when the parent process exits. This is the behavior
of traditional UNIX services. If this setting is used, it is recommended to
also use the PIDFile= option, so that systemd can reliably identify the
main process of the service. systemd will proceed with starting follow-up
units as soon as the parent process exits.
•Behavior of oneshot is similar
to simple; however, the service manager will consider the unit up after
the main process exits. It will then start follow-up units.
RemainAfterExit= is particularly useful for this type of service.
Type= oneshot is the implied default if neither Type= nor
ExecStart= are specified. Note that if this option is used without
RemainAfterExit= the service will never enter "active" unit
state, but directly transition from "activating" to
"deactivating" or "dead" since no process is configured
that shall run continuously. In particular this means that after a service of
this type ran (and which has RemainAfterExit= not set) it will not show
up as started afterwards, but as dead.
•Behavior of dbus is similar to
simple; however, it is expected that the service acquires a name on the
D-Bus bus, as configured by BusName=. systemd will proceed with
starting follow-up units after the D-Bus bus name has been acquired. Service
units with this option configured implicitly gain dependencies on the
dbus.socket unit. This type is the default if BusName= is specified. 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 notification
message via sd_notify(3) or an equivalent call when it has finished
starting up. systemd will proceed with starting follow-up units after this
notification message has been sent. If this option is used,
NotifyAccess= (see below) should be set to open access to the
notification socket provided by systemd. If NotifyAccess= is missing or
set to none, it will be forcibly set to main.
•Behavior of idle is very
similar to simple; however, actual execution of the service program is
delayed until all active jobs are dispatched. This may be used to avoid
interleaving of output of shell services with the status output on the
console. Note that this type is useful only to improve console output, it is
not useful as a general unit ordering tool, and the effect of this service
type is subject to a 5s timeout, after which the service program is invoked
anyway.
Specifies when the manager should consider the
service to be finished. One of main or cgroup:
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.
RemainAfterExit=
•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.
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
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 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
"@",
"-", ":", 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=
Prefix | Effect |
"@" | If the executable path is prefixed with "@", the second specified token will be passed as "argv[0]" to the executed process (instead of the actual filename), followed by the further arguments specified. |
"-" | If the executable path is prefixed with "-", an exit code of the command normally considered a failure (i.e. non-zero exit status or abnormal exit due to signal) is recorded, but has no further effect and is considered equivalent to success. |
":" | If the executable path is prefixed with ":", environment variable substitution (as described by the "Command Lines" section below) is not applied. |
"+" | If the executable path is prefixed with "+" then the process is executed with full privileges. In this mode privilege restrictions configured with User=, Group=, CapabilityBoundingSet= or the various file system namespacing options (such as PrivateDevices=, PrivateTmp=) are not applied to the invoked command line (but still affect any other ExecStart=, ExecStop=, ... lines). |
"!" | Similar to the "+" character discussed above this permits invoking command lines with elevated privileges. However, unlike "+" the "!" character exclusively alters the effect of User=, Group= and SupplementaryGroups=, i.e. only the stanzas that affect user and group credentials. Note that this setting may be combined with DynamicUser=, in which case a dynamic user/group pair is allocated before the command is invoked, but credential changing is left to the executed process itself. |
"!!" | This prefix is very similar to "!", however it only has an effect on systems lacking support for ambient process capabilities, i.e. without support for AmbientCapabilities=. It's intended to be used for unit files that take benefit of ambient capabilities to run processes with minimal privileges wherever possible while remaining compatible with systems that lack ambient capabilities support. Note that when "!!" is used, and a system lacking ambient capability support is detected any configured SystemCallFilter= and CapabilityBoundingSet= stanzas are implicitly modified, in order to permit spawned processes to drop credentials and capabilities themselves, even if this is configured to not be allowed. Moreover, if this prefix is used and a system lacking ambient capability support is detected AmbientCapabilities= will be skipped and not be applied. On systems supporting ambient capabilities, "!!" has no effect and is redundant. |
Additional commands that are executed before
or after the command in ExecStart=, respectively. Syntax is the same as
for ExecStart=, except that multiple command lines are allowed and the
commands are executed one after the other, serially.
If any of those commands (not prefixed with "-") fail, the rest are
not executed and the unit is considered failed.
ExecStart= commands are only run after all ExecStartPre= commands
that were not prefixed with a "-" exit successfully.
ExecStartPost= commands are only run after the commands specified in
ExecStart= have been invoked successfully, as determined by
Type= (i.e. the process has been started for Type=simple or
Type=idle, the last ExecStart= process exited successfully for
Type=oneshot, the initial process exited successfully for
Type=forking, "READY=1" is sent for Type=notify, or
the BusName= has been taken for Type=dbus).
Note that ExecStartPre= may not be used to start long-running processes.
All processes forked off by processes invoked via ExecStartPre= will be
killed before the next service process is run.
Note that if any of the commands specified in ExecStartPre=,
ExecStart=, or ExecStartPost= fail (and are not prefixed with
"-", see above) or time out before the service is fully up,
execution continues with commands specified in ExecStopPost=, the
commands in ExecStop= are skipped.
Note that the execution of ExecStartPost= is taken into account for the
purpose of Before=/After= ordering constraints.
ExecCondition=
Optional commands that are executed before the
commands in ExecStartPre=. Syntax is the same as for ExecStart=,
except that multiple command lines are allowed and the commands are executed
one after the other, serially.
The behavior is like an ExecStartPre= and condition check hybrid: when an
ExecCondition= command exits with exit code 1 through 254 (inclusive),
the remaining commands are skipped and the unit is not marked as
failed. However, if an ExecCondition= command exits with 255 or
abnormally (e.g. timeout, killed by a signal, etc.), the unit will be
considered failed (and remaining commands will be skipped). Exit code of 0 or
those matching SuccessExitStatus= will continue execution to the next
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.
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:
Note however that reloading a daemon by sending a signal (as with the example
line above) is usually not a good choice, because this is an asynchronous
operation and hence not suitable to order reloads of multiple services against
each other. It is strongly recommended to set ExecReload= to a command
that not only triggers a configuration reload of the daemon, but also
synchronously waits for it to complete. For example, dbus-broker(1)
uses the following:
ExecStop=
ExecReload=kill -HUP $MAINPID
ExecReload=busctl call org.freedesktop.DBus \ /org/freedesktop/DBus org.freedesktop.DBus \ ReloadConfig
Commands to execute to stop the service
started via ExecStart=. This argument takes multiple command lines,
following the same scheme as described for ExecStart= above. Use of
this setting is optional. After the commands configured in this option are
run, it is implied that the service is stopped, and any processes remaining
for it are terminated according to the KillMode= setting (see
systemd.kill(5)). If this option is not specified, the process is
terminated by sending the signal specified in KillSignal= or
RestartKillSignal= when service stop is requested. Specifier and
environment variable substitution is supported (including $MAINPID, see
above).
Note that it is usually not sufficient to specify a command for this setting
that only asks the service to terminate (for example, by sending some form of
termination signal to it), but does not wait for it to do so. Since the
remaining processes of the services are killed according to KillMode=
and KillSignal= or RestartKillSignal= as described above
immediately after the command exited, this may not result in a clean stop. The
specified command should hence be a synchronous operation, not an asynchronous
one.
Note that the commands specified in ExecStop= are only executed when the
service started successfully first. They are not invoked if the service was
never started at all, or in case its start-up failed, for example because any
of the commands specified in ExecStart=, ExecStartPre= or
ExecStartPost= failed (and weren't prefixed with "-", see
above) or timed out. Use ExecStopPost= to invoke commands when a
service failed to start up correctly and is shut down again. Also note that
the stop operation is always performed if the service started successfully,
even if the processes in the service terminated on their own or were killed.
The stop commands must be prepared to deal with that case. $MAINPID
will be unset if systemd knows that the main process exited by the time the
stop commands are called.
Service restart requests are implemented as stop operations followed by start
operations. This means that ExecStop= and ExecStopPost= are
executed during a service restart operation.
It is recommended to use this setting for commands that communicate with the
service requesting clean termination. For post-mortem clean-up steps use
ExecStopPost= instead.
ExecStopPost=
Additional commands that are executed after
the service is stopped. This includes cases where the commands configured in
ExecStop= were used, where the service does not have any
ExecStop= defined, or where the service exited unexpectedly. This
argument takes multiple command lines, following the same scheme as described
for ExecStart=. Use of these settings is optional. Specifier and
environment variable substitution is supported. Note that – unlike
ExecStop= – commands specified with this setting are invoked
when a service failed to start up correctly and is shut down again.
It is recommended to use this setting for clean-up operations that shall be
executed even when the service failed to start up correctly. Commands
configured with this setting need to be able to operate even if the service
failed starting up half-way and left incompletely initialized data around. As
the service's processes have been terminated already when the commands
specified with this setting are executed they should not attempt to
communicate with them.
Note that all commands that are configured with this setting are invoked with
the result code of the service, as well as the main process' exit code and
status, set in the $SERVICE_RESULT, $EXIT_CODE and
$EXIT_STATUS environment variables, see systemd.exec(5) for
details.
Note that the execution of ExecStopPost= is taken into account for the
purpose of Before=/After= ordering constraints.
RestartSec=
Configures the time to sleep before restarting
a service (as configured with Restart=). Takes a unit-less value in
seconds, or a time span value such as "5min 20s". Defaults to
100ms.
TimeoutStartSec=
Configures the time to wait for start-up. If a
daemon service does not signal start-up completion within the configured time,
the service will be considered failed and will be shut down again. The precise
action depends on the TimeoutStartFailureMode= option. Takes a
unit-less value in seconds, or a time span value such as "5min 20s".
Pass "infinity" to disable the timeout logic. Defaults to
DefaultTimeoutStartSec= from the manager configuration file, except
when Type=oneshot is used, in which case the timeout is disabled by
default (see systemd-system.conf(5)).
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=...",
this may cause the start time to be extended beyond TimeoutStartSec=.
The first receipt of this message must occur before TimeoutStartSec= is
exceeded, and once the start time has extended beyond TimeoutStartSec=,
the service manager will allow the service to continue to start, provided the
service repeats "EXTEND_TIMEOUT_USEC=..." within the interval
specified until the service startup status is finished by "READY=1".
(see sd_notify(3)).
TimeoutStopSec=
This option serves two purposes. First, it
configures the time to wait for each ExecStop= command. If any of them
times out, subsequent ExecStop= commands are skipped and the service
will be terminated by SIGTERM. If no ExecStop= commands are
specified, the service gets the SIGTERM immediately. This default
behavior can be changed by the TimeoutStopFailureMode= option. Second,
it configures the time to wait for the service itself to stop. If it doesn't
terminate in the specified time, it will be forcibly terminated by
SIGKILL (see KillMode= in systemd.kill(5)). Takes a
unit-less value in seconds, or a time span value such as "5min 20s".
Pass "infinity" to disable the timeout logic. Defaults to
DefaultTimeoutStopSec= from the manager configuration file (see
systemd-system.conf(5)).
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=...",
this may cause the stop time to be extended beyond TimeoutStopSec=. The
first receipt of this message must occur before TimeoutStopSec= is
exceeded, and once the stop time has extended beyond TimeoutStopSec=,
the service manager will allow the service to continue to stop, provided the
service repeats "EXTEND_TIMEOUT_USEC=..." within the interval
specified, or terminates itself (see sd_notify(3)).
TimeoutAbortSec=
This option configures the time to wait for
the service to terminate when it was aborted due to a watchdog timeout (see
WatchdogSec=). If the service has a short TimeoutStopSec= this
option can be used to give the system more time to write a core dump of the
service. Upon expiration the service will be forcibly terminated by
SIGKILL (see KillMode= in systemd.kill(5)). The core file
will be truncated in this case. Use TimeoutAbortSec= to set a sensible
timeout for the core dumping per service that is large enough to write all
expected data while also being short enough to handle the service failure in
due time.
Takes a unit-less value in seconds, or a time span value such as "5min
20s". Pass an empty value to skip the dedicated watchdog abort timeout
handling and fall back TimeoutStopSec=. Pass "infinity" to
disable the timeout logic. Defaults to DefaultTimeoutAbortSec= from the
manager configuration file (see systemd-system.conf(5)).
If a service of Type=notify handles SIGABRT itself (instead of
relying on the kernel to write a core dump) it can send
"EXTEND_TIMEOUT_USEC=..." to extended the abort time beyond
TimeoutAbortSec=. The first receipt of this message must occur before
TimeoutAbortSec= is exceeded, and once the abort time has extended
beyond TimeoutAbortSec=, the service manager will allow the service to
continue to abort, provided the service repeats
"EXTEND_TIMEOUT_USEC=..." within the interval specified, or
terminates itself (see sd_notify(3)).
TimeoutSec=
A shorthand for configuring both
TimeoutStartSec= and TimeoutStopSec= to the specified
value.
TimeoutStartFailureMode=, TimeoutStopFailureMode=
These options configure the action that is
taken in case a daemon service does not signal start-up within its configured
TimeoutStartSec=, respectively if it does not stop within
TimeoutStopSec=. Takes one of terminate, abort and
kill. Both options default to terminate.
If terminate is set the service will be gracefully terminated by sending
the signal specified in KillSignal= (defaults to SIGTERM, see
systemd.kill(5)). If the service does not terminate the
FinalKillSignal= is sent after TimeoutStopSec=. If abort
is set, WatchdogSignal= is sent instead and TimeoutAbortSec=
applies before sending FinalKillSignal=. This setting may be used to
analyze services that fail to start-up or shut-down intermittently. By using
kill the service is immediately terminated by sending
FinalKillSignal= without any further timeout. This setting can be used
to expedite the shutdown of failing services.
RuntimeMaxSec=
Configures a maximum time for the service to
run. If this is used and the service has been active for longer than the
specified time it is terminated and put into a failure state. Note that this
setting does not have any effect on Type=oneshot services, as they
terminate immediately after activation completed. Pass "infinity"
(the default) to configure no runtime limit.
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=...",
this may cause the runtime to be extended beyond RuntimeMaxSec=. The
first receipt of this message must occur before RuntimeMaxSec= is
exceeded, and once the runtime has extended beyond RuntimeMaxSec=, the
service manager will allow the service to continue to run, provided the
service repeats "EXTEND_TIMEOUT_USEC=..." within the interval
specified until the service shutdown is achieved by "STOPPING=1" (or
termination). (see sd_notify(3)).
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.
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:
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 2. Exit causes and the effect of the Restart=
settings
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.
SuccessExitStatus=
•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=.
Restart settings/Exit causes | no | always | on-success | on-failure | on-abnormal | on-abort | on-watchdog |
Clean exit code or signal | X | X | |||||
Unclean exit code | X | X | |||||
Unclean signal | X | X | X | X | |||
Timeout | X | X | X | ||||
Watchdog | X | X | X | X |
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
Exit status 75 ( TEMPFAIL), 250, and the termination signal
SIGKILL are considered clean service terminations.
Note: systemd-analyze exit-status may be used to list exit statuses and
translate between numerical status values and names.
RestartPreventExitStatus=
SuccessExitStatus=TEMPFAIL 250 SIGKILL
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:
ensures that exit codes 1 and 6 and the termination signal SIGABRT will
not result in automatic service restarting. This option may appear more than
once, in which case the list of restart-preventing statuses is merged. If the
empty string is assigned to this option, the list is reset and all prior
assignments of this option will have no effect.
Note that this setting has no effect on processes configured via
ExecStartPre=, ExecStartPost=, ExecStop=,
ExecStopPost= or ExecReload=, but only on the main service
process, i.e. either the one invoked by ExecStart= or (depending on
Type=, PIDFile=, ...) the otherwise configured main
process.
RestartForceExitStatus=
RestartPreventExitStatus=1 6 SIGABRT
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.
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 or WatchdogSec= (see above). If those options are
used but NotifyAccess= is not configured, it will be implicitly set to
main.
Note that sd_notify() notifications may be attributed to units correctly
only if either the sending process is still around at the time PID 1 processes
the message, or if the sending process is explicitly runtime-tracked by the
service manager. The latter is the case if the service manager originally
forked off the process, i.e. on all processes that match main or
exec. Conversely, if an auxiliary process of the unit sends an
sd_notify() message and immediately exits, the service manager might
not be able to properly attribute the message to the unit, and thus will
ignore it, even if NotifyAccess=all is set for it.
Hence, to eliminate all race conditions involving lookup of the client's unit
and attribution of notifications to units correctly,
sd_notify_barrier() may be used. This call acts as a synchronization
point and ensures all notifications sent before this call have been picked up
by the service manager when it returns successfully. Use of
sd_notify_barrier() is needed for clients which are not invoked by the
service manager, otherwise this synchronization mechanism is unnecessary for
attribution of notifications to the unit.
Sockets=
Specifies the name of the socket units this
service shall inherit socket file descriptors from when the service is
started. Normally, it should not be necessary to use this setting, as all
socket file descriptors whose unit shares the same name as the service
(subject to the different unit name suffix of course) are passed to the
spawned process.
Note that the same socket file descriptors may be passed to multiple processes
simultaneously. Also note that a different service may be activated on
incoming socket traffic than the one which is ultimately configured to inherit
the socket file descriptors. Or, in other words: the Service= setting
of .socket units does not have to match the inverse of the Sockets=
setting of the .service it refers to.
This option may appear more than once, in which case the list of socket units is
merged. Note that once set, clearing the list of sockets again (for example,
by assigning the empty string to this option) is not supported.
FileDescriptorStoreMax=
Configure how many file descriptors may be
stored in the service manager for the service using
sd_pid_notify_with_fds(3)'s "FDSTORE=1" messages. This is
useful for implementing services that can restart after an explicit request or
a crash without losing state. Any open sockets and other file descriptors
which should not be closed during the restart may be stored this way.
Application state can either be serialized to a file in /run/, or better,
stored in a memfd_create(2) memory file descriptor. Defaults to 0, i.e.
no file descriptors may be stored in the service manager. All file descriptors
passed to the service manager from a specific service are passed back to the
service's main process on the next service restart (see
sd_listen_fds(3) for details about the precise protocol used and the
order in which the file descriptors are passed). Any file descriptors passed
to the service manager are automatically closed when POLLHUP or
POLLERR is seen on them, or when the service is fully stopped and no
job is queued or being executed for it. If this option is used,
NotifyAccess= (see above) should be set to open access to the
notification socket provided by systemd. If NotifyAccess= is not set,
it will be implicitly set to main.
USBFunctionDescriptors=
Configure the location of a file containing
USB FunctionFS[1] descriptors, for implementation of USB gadget
functions. This is used only in conjunction with a socket unit with
ListenUSBFunction= configured. The contents of this file are written to
the ep0 file after it is opened.
USBFunctionStrings=
Configure the location of a file containing
USB FunctionFS strings. Behavior is similar to USBFunctionDescriptors=
above.
OOMPolicy=
Configure the out-of-memory (OOM) kernel
killer policy. Note that the userspace OOM killer
systemd-oomd.service(8) is a more flexible solution that aims to
prevent out-of-memory situations for the userspace, not just the kernel.
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. This setting takes one of
continue, stop or kill. If set to continue and a
process of the service 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 documentation[2].
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. Similarly to the kernel OOM
kills, this setting determines the state of the unit after systemd-oomd
kills a cgroup associated with it.
Check systemd.unit(5), 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 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. The command line accepts "%" specifiers as described in systemd.unit(5). Basic environment variable substitution is supported. Use "${FOO}" as part of a word, or as a word of its own, on the command line, in which case it will be erased and replaced by the exact value of the environment variable (if any) including all whitespace it contains, always resulting in exactly a single argument. Use "$FOO" as a separate word on the command line, in which case it will be replaced by the value of the environment variable split at whitespace, resulting in zero or more arguments. For this type of expansion, quotes are respected when splitting into words, and afterwards removed. If the command is not a full (absolute) path, it will be resolved to a full path using a fixed search path determined 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}
Environment=ONE='one' "TWO='two two' too" THREE= ExecStart=/bin/echo ${ONE} ${TWO} ${THREE} ExecStart=/bin/echo $ONE $TWO $THREE
ExecStart=sh -c 'dmesg | tac'
ExecStart=echo one ; echo "two two"
ExecStart=echo / >/dev/null & \; \ ls
EXAMPLES
Example 2. Simple service The following unit file creates a service that will execute /usr/sbin/foo-daemon. Since no Type= is specified, the default Type= simple will be assumed. systemd will assume the unit to be started immediately after the program has begun executing.[Unit] Description=Foo [Service] ExecStart=/usr/sbin/foo-daemon [Install] WantedBy=multi-user.target
[Unit] Description=Cleanup old Foo data [Service] Type=oneshot ExecStart=/usr/sbin/foo-cleanup [Install] WantedBy=multi-user.target
[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
[Unit] Description=Some simple daemon [Service] Type=forking ExecStart=/usr/sbin/my-simple-daemon -d [Install] WantedBy=multi-user.target
[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
[D-BUS Service] Name=org.example.simple-dbus-service Exec=/usr/sbin/simple-dbus-service User=root SystemdService=simple-dbus-service.service
[Unit] Description=Simple notifying service [Service] Type=notify ExecStart=/usr/sbin/simple-notifying-service [Install] WantedBy=multi-user.target
SEE ALSO
systemd(1), systemctl(1), systemd-system.conf(5), systemd.unit(5), systemd.exec(5), systemd.resource-control(5), systemd.kill(5), systemd.directives(7), systemd-run(1)NOTES
- 1.
- USB FunctionFS
- 2.
- kernel documentation
systemd 252 |