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 a service is requested under a certain name but no unit
configuration file is found, systemd looks for a SysV init script
by the same name (with the .service suffix
removed) and dynamically creates a service unit from that script.
This is useful for compatibility with SysV. Note that this
compatibility is quite comprehensive but not 100%. For details
about the incompatibilities, see the Incompatibilities
with SysV document.
It is possible for systemd services to take a single argument via the
"service@argument.serviceargument 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.
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).
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 files must include a "[Service]"
section, which carries information about the service and the
process it supervises. A number of options that may be used in
this section are shared with other unit types. These options are
documented in
systemd.exec(5),
systemd.kill(5)
and
systemd.resource-control(5).
The options specific to the "[Service]" section
of service units are the following:
Type=¶Configures the process start-up type for this service unit. One of simple,
exec, forking, oneshot, dbus,
notify or idle:
If set to simple (the default if ExecStart= is
specified but neither Type= nor BusName= are), the service manager
will consider the unit started immediately after the main service process has been forked off. It is
expected that the process configured with ExecStart= is the main process of the
service. In this mode, if the process offers functionality to other processes on the system, its
communication channels should be installed before the service is started up (e.g. sockets set up by
systemd, via socket activation), as the service manager will immediately proceed starting follow-up units,
right after creating the main service process, and before executing the service's binary. Note that this
means systemctl start command lines for simple services will report
success even if the service's binary cannot be invoked successfully (for example because the selected
User= doesn't exist, or the service binary is missing).
The exec type is similar to simple, but the service
manager will consider the unit started immediately after the main service binary has been executed. The service
manager will delay starting of follow-up units until that point. (Or in other words:
simple proceeds with further jobs right after fork() returns, while
exec will not proceed before both fork() and
execve() in the service process succeeded.) Note that this means systemctl
start command lines for exec services will report failure when the service's
binary cannot be invoked successfully (for example because the selected User= doesn't
exist, or the service binary is missing).
If set to forking, it is expected that the process configured with
ExecStart= will call fork() as part of its start-up. The parent
process is expected to exit when start-up is complete and all communication channels are set up. The child
continues to run as the main service process, and the service manager will consider the unit started when
the parent process exits. This is the behavior of traditional UNIX services. If this setting is used, it is
recommended to also use the PIDFile= option, so that systemd can reliably identify the
main process of the service. systemd will proceed with starting follow-up units as soon as the parent
process exits.
Behavior of oneshot is similar to simple; however, the
service manager will consider the unit started after the main process exits. It will then start follow-up
units. RemainAfterExit= is particularly useful for this type of
service. Type=oneshot is the implied default if neither
Type= nor ExecStart= are specified.
Behavior of dbus is similar to simple; however, it is
expected that the service acquires a name on the D-Bus bus, as configured by
BusName=. systemd will proceed with starting follow-up units after the D-Bus bus name
has been acquired. Service units with this option configured implicitly gain dependencies on the
dbus.socket unit. This type is the default if BusName= is
specified.
Behavior of notify is similar to exec; however, it is
expected that the service sends a notification message via
sd_notify(3) or an
equivalent call when it has finished starting up. systemd will proceed with starting follow-up units after
this notification message has been sent. If this option is used, NotifyAccess= (see
below) should be set to open access to the notification socket provided by systemd. If
NotifyAccess= is missing or set to none, it will be forcibly set to
main. Note that currently Type=notify will not work if
used in combination with PrivateNetwork=yes.
Behavior of idle is very similar to simple; however,
actual execution of the service program is delayed until all active jobs are dispatched. This may be used
to avoid interleaving of output of shell services with the status output on the console. Note that this
type is useful only to improve console output, it is not useful as a general unit ordering tool, and the
effect of this service type is subject to a 5s time-out, after which the service program is invoked
anyway.
It is generally recommended to use Type=simple for long-running
services whenever possible, as it is the simplest and fastest option. However, as this service type won't
propagate service start-up failures and doesn't allow ordering of other units against completion of
initialization of the service (which for example is useful if clients need to connect to the service through
some form of IPC, and the IPC channel is only established by the service itself — in contrast to doing this
ahead of time through socket or bus activation or similar), it might not be sufficient for many cases. If so,
notify or dbus (the latter only in case the service provides a D-Bus
interface) are the preferred options as they allow service program code to precisely schedule when to
consider the service started up successfully and when to proceed with follow-up units. The
notify service type requires explicit support in the service codebase (as
sd_notify() or an equivalent API needs to be invoked by the service at the appropriate
time) — if it's not supported, then forking is an alternative: it supports the traditional
UNIX service start-up protocol. Finally, exec might be an option for cases where it is
enough to ensure the service binary is invoked, and where the service binary itself executes no or little
initialization on its own (and its initialization is unlikely to fail). Note that using any type other than
simple possibly delays the boot process, as the service manager needs to wait for service
initialization to complete. It is hence recommended not to needlessly use any types other than
simple. (Also note it is generally not recommended to use idle or
oneshot for long-running services.)
RemainAfterExit=¶Takes a boolean value that specifies whether
the service shall be considered active even when all its
processes exited. Defaults to no.
GuessMainPID=¶Takes a boolean value that specifies whether
systemd should try to guess the main PID of a service if it
cannot be determined reliably. This option is ignored unless
Type=forking is set and
PIDFile= is unset because for the other types
or with an explicitly configured PID file, the main PID is
always known. The guessing algorithm might come to incorrect
conclusions if a daemon consists of more than one process. If
the main PID cannot be determined, failure detection and
automatic restarting of a service will not work reliably.
Defaults to yes.
PIDFile=¶Takes an absolute path referring to the PID file of the service. Usage of this option is
recommended for services where Type= is set to forking. The service manager
will read the PID of the main process of the service from this file after start-up of the service. The service
manager will not write to the file configured here, although it will remove the file after the service has shut
down if it still exists. The PID file does not need to be owned by a privileged user, but if it is owned by an
unprivileged user additional safety restrictions are enforced: the file may not be a symlink to a file owned by
a different user (neither directly nor indirectly), and the PID file must refer to a process already belonging
to the service.
BusName=¶Takes a D-Bus bus name that this service is
reachable as. This option is mandatory for services where
Type= is set to
dbus.
ExecStart=¶Commands with their arguments that are executed when this service is started. The value is split into zero or more command lines according to the rules described below (see section "Command Lines" below).
Unless Type= is oneshot, exactly one command must be given. When
Type=oneshot is used, zero or more commands may be specified. Commands may be specified by
providing multiple command lines in the same directive, or alternatively, this directive may be specified more
than once with the same effect. If the empty string is assigned to this option, the list of commands to start
is reset, prior assignments of this option will have no effect. If no ExecStart= is
specified, then the service must have RemainAfterExit=yes and at least one
ExecStop= line set. (Services lacking both ExecStart= and
ExecStop= are not valid.)
For each of the specified commands, the first argument must be either an absolute path to an executable or a simple file name without any slashes. Optionally, this filename may be prefixed with a number of special characters:
Table 1. Special executable prefixes
| Prefix | Effect |
|---|---|
"@" | If the executable path is prefixed with "@", the second specified token will be passed as "argv[0]" to the executed process (instead of the actual filename), followed by the further arguments specified. |
"-" | If the executable path is prefixed with "-", an exit code of the command normally considered a failure (i.e. non-zero exit status or abnormal exit due to signal) is ignored and considered success. |
"+" | If the executable path is prefixed with "+" then the process is executed with full privileges. In this mode privilege restrictions configured with User=, Group=, CapabilityBoundingSet= or the various file system namespacing options (such as PrivateDevices=, PrivateTmp=) are not applied to the invoked command line (but still affect any other ExecStart=, ExecStop=, … lines). |
"!" | Similar to the "+" character discussed above this permits invoking command lines with elevated privileges. However, unlike "+" the "!" character exclusively alters the effect of User=, Group= and SupplementaryGroups=, i.e. only the stanzas that affect user and group credentials. Note that this setting may be combined with DynamicUser=, in which case a dynamic user/group pair is allocated before the command is invoked, but credential changing is left to the executed process itself. |
"!!" | This prefix is very similar to "!", however it only has an effect on systems lacking support for ambient process capabilities, i.e. without support for AmbientCapabilities=. It's intended to be used for unit files that take benefit of ambient capabilities to run processes with minimal privileges wherever possible while remaining compatible with systems that lack ambient capabilities support. Note that when "!!" is used, and a system lacking ambient capability support is detected any configured SystemCallFilter= and CapabilityBoundingSet= stanzas are implicitly modified, in order to permit spawned processes to drop credentials and capabilities themselves, even if this is configured to not be allowed. Moreover, if this prefix is used and a system lacking ambient capability support is detected AmbientCapabilities= will be skipped and not be applied. On systems supporting ambient capabilities, "!!" has no effect and is redundant. |
"@", "-", and one of
"+"/"!"/"!!" may be used together and they can appear in any
order. However, only one of "+", "!", "!!" may be used at a
time. Note that these prefixes are also supported for the other command line settings,
i.e. ExecStartPre=, ExecStartPost=, ExecReload=,
ExecStop= and ExecStopPost=.
If more than one command is specified, the commands are
invoked sequentially in the order they appear in the unit
file. If one of the commands fails (and is not prefixed with
"-"), other lines are not executed, and the
unit is considered failed.
Unless Type=forking is set, the
process started via this command line will be considered the
main process of the daemon.
ExecStartPre=, ExecStartPost=¶Additional commands that are executed before
or after the command in ExecStart=,
respectively. Syntax is the same as for
ExecStart=, except that multiple command
lines are allowed and the commands are executed one after the
other, serially.
If any of those commands (not prefixed with
"-") fail, the rest are not executed and the
unit is considered failed.
ExecStart= commands are only run after
all ExecStartPre= commands that were not prefixed
with a "-" exit successfully.
ExecStartPost= commands are only run after the commands specified in
ExecStart= have been invoked successfully, as determined by Type=
(i.e. the process has been started for Type=simple or Type=idle, the last
ExecStart= process exited successfully for Type=oneshot, the initial
process exited successfully for Type=forking, "READY=1" is sent for
Type=notify, or the BusName= has been taken for
Type=dbus).
Note that ExecStartPre= may not be
used to start long-running processes. All processes forked
off by processes invoked via ExecStartPre= will
be killed before the next service process is run.
Note that if any of the commands specified in ExecStartPre=,
ExecStart=, or ExecStartPost= fail (and are not prefixed with
"-", see above) or time out before the service is fully up, execution continues with commands
specified in ExecStopPost=, the commands in ExecStop= are skipped.
ExecCondition=¶Optional commands that are executed before the command(s) 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 command(s).
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:
/bin/kill -HUP $MAINPID
Note however that reloading a daemon by sending a signal
(as with the example line above) is usually not a good choice,
because this is an asynchronous operation and hence not
suitable to order reloads of multiple services against each
other. It is strongly recommended to set
ExecReload= to a command that not only
triggers a configuration reload of the daemon, but also
synchronously waits for it to complete.
ExecStop=¶Commands to execute to stop the service
started via ExecStart=. This argument takes
multiple command lines, following the same scheme as described
for ExecStart= above. Use of this setting
is optional. After the commands configured in this option are
run, it is implied that the service is stopped, and any processes
remaining for it are terminated
according to the KillMode= setting (see
systemd.kill(5)).
If this option is not specified, the process is terminated by
sending the signal specified in KillSignal=
when service stop is requested. Specifier and environment
variable substitution is supported (including
$MAINPID, see above).
Note that it is usually not sufficient to specify a command for this setting that only asks the service
to terminate (for example, by queuing some form of termination signal for it), but does not wait for it to do
so. Since the remaining processes of the services are killed according to KillMode= and
KillSignal= as described above immediately after the command exited, this may not result in
a clean stop. The specified command should hence be a synchronous operation, not an asynchronous one.
Note that the commands specified in ExecStop= are only executed when the service
started successfully first. They are not invoked if the service was never started at all, or in case its
start-up failed, for example because any of the commands specified in ExecStart=,
ExecStartPre= or ExecStartPost= failed (and weren't prefixed with
"-", see above) or timed out. Use ExecStopPost= to invoke commands when a
service failed to start up correctly and is shut down again. Also note that, service restart requests are
implemented as stop operations followed by start operations. This means that ExecStop= and
ExecStopPost= are executed during a service restart operation.
It is recommended to use this setting for commands that communicate with the service requesting clean
termination. When the commands specified with this option are executed it should be assumed that the service is
still fully up and is able to react correctly to all commands. For post-mortem clean-up steps use
ExecStopPost= instead.
ExecStopPost=¶Additional commands that are executed after the service is stopped. This includes cases where
the commands configured in ExecStop= were used, where the service does not have any
ExecStop= defined, or where the service exited unexpectedly. This argument takes multiple
command lines, following the same scheme as described for ExecStart=. Use of these settings
is optional. Specifier and environment variable substitution is supported. Note that – unlike
ExecStop= – commands specified with this setting are invoked when a service failed to start
up correctly and is shut down again.
It is recommended to use this setting for clean-up operations that shall be executed even when the service failed to start up correctly. Commands configured with this setting need to be able to operate even if the service failed starting up half-way and left incompletely initialized data around. As the service's processes have been terminated already when the commands specified with this setting are executed they should not attempt to communicate with them.
Note that all commands that are configured with this setting are invoked with the result code of the
service, as well as the main process' exit code and status, set in the $SERVICE_RESULT,
$EXIT_CODE and $EXIT_STATUS environment variables, see
systemd.exec(5) for
details.
RestartSec=¶Configures the time to sleep before restarting
a service (as configured with Restart=).
Takes a unit-less value in seconds, or a time span value such
as "5min 20s". Defaults to 100ms.
TimeoutStartSec=¶Configures the time to wait for start-up. If a
daemon service does not signal start-up completion within the
configured time, the service will be considered failed and
will be shut down again. Takes a unit-less value in seconds,
or a time span value such as "5min 20s". Pass
"infinity" to disable the timeout logic. Defaults to
DefaultTimeoutStartSec= from the manager
configuration file, except when
Type=oneshot is used, in which case the
timeout is disabled by default (see
systemd-system.conf(5)).
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=…", this may cause
the start time to be extended beyond TimeoutStartSec=. The first receipt of this message
must occur before TimeoutStartSec= is exceeded, and once the start time has exended beyond
TimeoutStartSec=, the service manager will allow the service to continue to start, provided
the service repeats "EXTEND_TIMEOUT_USEC=…" within the interval specified until the service
startup status is finished by "READY=1". (see
sd_notify(3)).
TimeoutStopSec=¶This option serves two purposes. First, it configures the time to wait for each
ExecStop= command. If any of them times out, subsequent ExecStop= commands
are skipped and the service will be terminated by SIGTERM. If no ExecStop=
commands are specified, the service gets the SIGTERM immediately. Second, it configures the time
to wait for the service itself to stop. If it doesn't terminate in the specified time, it will be forcibly terminated
by SIGKILL (see KillMode= in
systemd.kill(5)).
Takes a unit-less value in seconds, or a time span value such
as "5min 20s". Pass "infinity" to disable the
timeout logic. Defaults to
DefaultTimeoutStopSec= from the manager
configuration file (see
systemd-system.conf(5)).
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=…", this may cause
the stop time to be extended beyond TimeoutStopSec=. The first receipt of this message
must occur before TimeoutStopSec= is exceeded, and once the stop time has exended beyond
TimeoutStopSec=, the service manager will allow the service to continue to stop, provided
the service repeats "EXTEND_TIMEOUT_USEC=…" within the interval specified, or terminates itself
(see sd_notify(3)).
TimeoutSec=¶A shorthand for configuring both
TimeoutStartSec= and
TimeoutStopSec= to the specified value.
RuntimeMaxSec=¶Configures a maximum time for the service to run. If this is used and the service has been
active for longer than the specified time it is terminated and put into a failure state. Note that this setting
does not have any effect on Type=oneshot services, as they terminate immediately after
activation completed. Pass "infinity" (the default) to configure no runtime
limit.
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=…", this may cause
the runtime to be extended beyond RuntimeMaxSec=. The first receipt of this message
must occur before RuntimeMaxSec= is exceeded, and once the runtime has exended beyond
RuntimeMaxSec=, the service manager will allow the service to continue to run, provided
the service repeats "EXTEND_TIMEOUT_USEC=…" within the interval specified until the service
shutdown is achieved by "STOPPING=1" (or termination). (see
sd_notify(3)).
WatchdogSec=¶Configures the watchdog timeout for a service.
The watchdog is activated when the start-up is completed. The
service must call
sd_notify(3)
regularly with "WATCHDOG=1" (i.e. the
"keep-alive ping"). If the time between two such calls is
larger than the configured time, then the service is placed in
a failed state and it will be terminated with
SIGABRT. 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:
Type=oneshot, one of the signals
SIGHUP,
SIGINT,
SIGTERM, or
SIGPIPE;SuccessExitStatus=.
If set to
on-failure, the service will be restarted
when the process exits with a non-zero exit code, is
terminated by a signal (including on core dump, but excluding
the aforementioned four signals), when an operation (such as
service reload) times out, and when the configured watchdog
timeout is triggered. If set to on-abnormal,
the service will be restarted when the process is terminated
by a signal (including on core dump, excluding the
aforementioned four signals), when an operation times out, or
when the watchdog timeout is triggered. If set to
on-abort, the service will be restarted only
if the service process exits due to an uncaught signal not
specified as a clean exit status. If set to
on-watchdog, the service will be restarted
only if the watchdog timeout for the service expires. If set
to always, the service will be restarted
regardless of whether it exited cleanly or not, got terminated
abnormally by a signal, or hit a timeout.
Table 2. Exit causes and the effect of the Restart= settings on them
| Restart 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 |
As exceptions to the setting above, the service will not
be restarted if the exit code or signal is specified in
RestartPreventExitStatus= (see below) or
the service is stopped with systemctl stop
or an equivalent operation. Also, the services will always be
restarted if the exit code or signal is specified in
RestartForceExitStatus= (see below).
Note that service restart is subject to unit start rate
limiting configured with StartLimitIntervalSec=
and StartLimitBurst=, see
systemd.unit(5)
for details. A restarted service enters the failed state only
after the start limits are reached.
Setting this to on-failure is the
recommended choice for long-running services, in order to
increase reliability by attempting automatic recovery from
errors. For services that shall be able to terminate on their
own choice (and avoid immediate restarting),
on-abnormal is an alternative choice.
SuccessExitStatus=¶Takes a list of exit status definitions that,
when returned by the main service process, will be considered
successful termination, in addition to the normal successful
exit code 0 and, except for Type=oneshot,
the signals SIGHUP,
SIGINT, SIGTERM, and
SIGPIPE. Exit status definitions can
either be numeric exit codes or termination signal names,
separated by spaces. For example:
SuccessExitStatus=1 2 8 SIGKILL
ensures that exit codes 1, 2, 8 and
the termination signal SIGKILL are
considered clean service terminations.
This option may appear more than once, in which case the list of successful exit statuses is merged. If the empty string is assigned to this option, the list is reset, all prior assignments of this option will have no effect.
RestartPreventExitStatus=¶Takes a list of exit status definitions that,
when returned by the main service process, will prevent
automatic service restarts, regardless of the restart setting
configured with Restart=. Exit status
definitions can either be numeric exit codes or termination
signal names, and are separated by spaces. Defaults to the
empty list, so that, by default, no exit status is excluded
from the configured restart logic. For example:
RestartPreventExitStatus=1 6 SIGABRT
ensures that exit codes 1 and 6 and the termination signal
SIGABRT will not result in automatic
service restarting. This option may appear more than once, in
which case the list of restart-preventing statuses is
merged. If the empty string is assigned to this option, the
list is reset and all prior assignments of this option will
have no effect.
RestartForceExitStatus=¶Takes a list of exit status definitions that,
when returned by the main service process, will force automatic
service restarts, regardless of the restart setting configured
with Restart=. The argument format is
similar to
RestartPreventExitStatus=.
PermissionsStartOnly=¶Takes a boolean argument. If true, the
permission-related execution options, as configured with
User= and similar options (see
systemd.exec(5)
for more information), are only applied to the process started
with
ExecStart=, and not to the various other
ExecStartPre=,
ExecStartPost=,
ExecReload=,
ExecStop=, and
ExecStopPost=
commands. If false, the setting is applied to all configured
commands the same way. Defaults to false.
RootDirectoryStartOnly=¶Takes a boolean argument. If true, the root
directory, as configured with the
RootDirectory= option (see
systemd.exec(5)
for more information), is only applied to the process started
with ExecStart=, and not to the various
other ExecStartPre=,
ExecStartPost=,
ExecReload=, ExecStop=,
and ExecStopPost= commands. If false, the
setting is applied to all configured commands the same way.
Defaults to false.
NonBlocking=¶Set the O_NONBLOCK flag for all file descriptors passed via socket-based
activation. If true, all file descriptors >= 3 (i.e. all except stdin, stdout, stderr), excluding those passed
in via the file descriptor storage logic (see FileDescriptorStoreMax= for details), will
have the O_NONBLOCK flag set and hence are in non-blocking mode. This option is only
useful in conjunction with a socket unit, as described in
systemd.socket(5) and has no
effect on file descriptors which were previously saved in the file-descriptor store for example. Defaults to
false.
NotifyAccess=¶Controls access to the service status notification socket, as accessible via the
sd_notify(3) call. Takes one
of none (the default), main, exec or
all. If none, no daemon status updates are accepted from the service
processes, all status update messages are ignored. If main, only service updates sent from the
main process of the service are accepted. If exec, only service updates sent from any of the
main or control processes originating from one of the Exec*= commands are accepted. If
all, all services updates from all members of the service's control group are accepted. This
option should be set to open access to the notification socket when using Type=notify or
WatchdogSec= (see above). If those options are used but NotifyAccess= is
not configured, it will be implicitly set to main.
Note that sd_notify() notifications may be attributed to units correctly only if
either the sending process is still around at the time PID 1 processes the message, or if the sending process
is explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally
forked off the process, i.e. on all processes that match main or
exec. Conversely, if an auxiliary process of the unit sends an
sd_notify() message and immediately exits, the service manager might not be able to
properly attribute the message to the unit, and thus will ignore it, even if
NotifyAccess=all is set for it.
Sockets=¶Specifies the name of the socket units this service shall inherit socket file descriptors from when the service is started. Normally, it should not be necessary to use this setting, as all socket file descriptors whose unit shares the same name as the service (subject to the different unit name suffix of course) are passed to the spawned process.
Note that the same socket file descriptors may be passed
to multiple processes simultaneously. Also note that a
different service may be activated on incoming socket traffic
than the one which is ultimately configured to inherit the
socket file descriptors. Or, in other words: the
Service= setting of
.socket units does not have to match the
inverse of the Sockets= setting of the
.service it refers to.
This option may appear more than once, in which case the list of socket units is merged. If the empty string is assigned to this option, the list of sockets is reset, and all prior uses of this setting will have no effect.
FileDescriptorStoreMax=¶Configure how many file descriptors may be stored in the service manager for the service using
sd_pid_notify_with_fds(3)'s
"FDSTORE=1" messages. This is useful for implementing services that can restart after an
explicit request or a crash without losing state. Any open sockets and other file descriptors which should not
be closed during the restart may be stored this way. Application state can either be serialized to a file in
/run, or better, stored in a
memfd_create(2) memory file
descriptor. Defaults to 0, i.e. no file descriptors may be stored in the service manager. All file descriptors
passed to the service manager from a specific service are passed back to the service's main process on the next
service restart. Any file descriptors passed to the service manager are automatically closed when
POLLHUP or POLLERR is seen on them, or when the service is fully
stopped and no job is queued or being executed for it. 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 descriptors, for implementation of USB
gadget functions. This is used only in conjunction with a
socket unit with ListenUSBFunction=
configured. The contents of this file are written to the
ep0 file after it is
opened.
USBFunctionStrings=¶Configure the location of a file containing
USB FunctionFS strings. Behavior is similar to
USBFunctionDescriptors=
above.
Check systemd.exec(5) and systemd.kill(5) for more settings.
This section describes command line parsing and
variable and specifier substitutions for
ExecStart=,
ExecStartPre=,
ExecStartPost=,
ExecReload=,
ExecStop=, and
ExecStopPost= options.
Multiple command lines may be concatenated in a single
directive by separating them with semicolons (these semicolons
must be passed as separate words). Lone semicolons may be escaped
as "\;".
Each command line is split on whitespace, with the first item being the command to
execute, and the subsequent items being the arguments. Double quotes ("…") and single quotes
('…') may be used to wrap a whole item (the opening quote may appear only at the beginning or
after whitespace that is not quoted, and the closing quote must be followed by whitespace or the
end of line), in which case everything until the next matching quote becomes part of the same
argument. Quotes themselves are removed. C-style escapes are also supported. The table below
contains the list of known escape patterns. Only escape patterns which match the syntax in the
table are allowed; other patterns may be added in the future and unknown patterns will result in
a warning. In particular, any backslashes should be doubled. Finally, a trailing backslash
("\") may be used to merge lines.
This syntax is inspired by shell syntax, but only the meta-characters and expansions
described in the following paragraphs are understood, and the expansion of variables is
different. Specifically, redirection using
"<",
"<<",
">", and
">>", pipes using
"|", running programs in the background using
"&", and other elements of shell
syntax are not supported.
The command to execute may contain spaces, but control characters are not allowed.
The command line accepts "%" specifiers as described in
systemd.unit(5).
Basic environment variable substitution is supported. Use
"${FOO}" as part of a word, or as a word of its
own, on the command line, in which case it will be replaced by the
value of the environment variable including all whitespace it
contains, resulting in a single argument. Use
"$FOO" as a separate word on the command line, in
which case it will be replaced by the value of the environment
variable split at whitespace, resulting in zero or more arguments.
For this type of expansion, quotes are respected when splitting
into words, and afterwards removed.
If the command is not a full (absolute) path, it will be resolved to a full path using a
fixed search path determinted at compilation time. Searched directories include
/usr/local/bin/, /usr/bin/, /bin/
on systems using split /usr/bin/ and /bin/
directories, and their sbin/ counterparts on systems using split
bin/ and sbin/. It is thus safe to use just the
executable name in case of executables located in any of the "standard" directories, and an
absolute path must be used in other cases. Using an absolute path is recommended to avoid
ambiguity. Hint: this search path may be queried using
systemd-path search-binaries-default.
Example:
Environment="ONE=one" 'TWO=two two'
ExecStart=echo $ONE $TWO ${TWO}This will execute /bin/echo with four
arguments: "one", "two",
"two", and "two two".
Example:
Environment=ONE='one' "TWO='two two' too" THREE=
ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
ExecStart=/bin/echo $ONE $TWO $THREEThis results in /bin/echo being
called twice, the first time with arguments
"'one'",
"'two two' too", "",
and the second time with arguments
"one", "two two",
"too".
To pass a literal dollar sign, use "$$".
Variables whose value is not known at expansion time are treated
as empty strings. Note that the first argument (i.e. the program
to execute) may not be a variable.
Variables to be used in this fashion may be defined through
Environment= and
EnvironmentFile=. In addition, variables listed
in the section "Environment variables in spawned processes" in
systemd.exec(5),
which are considered "static configuration", may be used (this
includes e.g. $USER, but not
$TERM).
Note that shell command lines are not directly supported. If shell command lines are to be used, they need to be passed explicitly to a shell implementation of some kind. Example:
ExecStart=sh -c 'dmesg | tac'
Example:
ExecStart=echo one ; echo "two two"
This will execute echo two times,
each time with one argument: "one" and
"two two", respectively. Because two commands are
specified, Type=oneshot must be used.
Example:
ExecStart=echo / >/dev/null & \; \ ls
This will execute echo
with five arguments: "/",
">/dev/null",
"&", ";", and
"ls".
Table 3. C escapes supported in command lines and environment variables
| Literal | Actual value |
|---|---|
"\a" | bell |
"\b" | backspace |
"\f" | form feed |
"\n" | newline |
"\r" | carriage return |
"\t" | tab |
"\v" | vertical tab |
"\\" | backslash |
"\"" | double quotation mark |
"\'" | single quotation mark |
"\s" | space |
"\x" | character number xx in hexadecimal encoding |
"\" | character number nnn in octal encoding |
Example 1. Simple service
The following unit file creates a service that will
execute /usr/sbin/foo-daemon. Since no
Type= is specified, the default
Type=simple will be assumed.
systemd will assume the unit to be started immediately after the
program has begun executing.
[Unit] Description=Foo [Service] ExecStart=/usr/sbin/foo-daemon [Install] WantedBy=multi-user.target
Note that systemd assumes here that the process started by
systemd will continue running until the service terminates. If
the program daemonizes itself (i.e. forks), please use
Type=forking instead.
Since no ExecStop= was specified,
systemd will send SIGTERM to all processes started from this
service, and after a timeout also SIGKILL. This behavior can be
modified, see
systemd.kill(5)
for details.
Note that this unit type does not include any type of
notification when a service has completed initialization. For
this, you should use other unit types, such as
Type=notify if the service
understands systemd's notification protocol,
Type=forking if the service
can background itself or
Type=dbus if the unit
acquires a DBus name once initialization is complete. See
below.
Example 2. Oneshot service
Sometimes, units should just execute an action without
keeping active processes, such as a filesystem check or a
cleanup action on boot. For this,
Type=oneshot exists. Units
of this type will wait until the process specified terminates
and then fall back to being inactive. The following unit will
perform a cleanup action:
[Unit] Description=Cleanup old Foo data [Service] Type=oneshot ExecStart=/usr/sbin/foo-cleanup [Install] WantedBy=multi-user.target
Note that systemd will consider the unit to be in the state "starting" until the program has terminated, so ordered dependencies will wait for the program to finish before starting themselves. The unit will revert to the "inactive" state after the execution is done, never reaching the "active" state. That means another request to start the unit will perform the action again.
Type=oneshot are the
only service units that may have more than one
ExecStart= specified. 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 3. Stoppable oneshot service
Similarly to the oneshot services, there are sometimes units that need to execute a program to set up something and then execute another to shut it down, but no process remains active while they are considered "started". Network configuration can sometimes fall into this category. Another use case is if a oneshot service shall not be executed each time when they are pulled in as a dependency, but only the first time.
For this, systemd knows the setting
RemainAfterExit=yes, which
causes systemd to consider the unit to be active if the start
action exited successfully. This directive can be used with all
types, but is most useful with
Type=oneshot and
Type=simple. With
Type=oneshot, systemd waits
until the start action has completed before it considers the
unit to be active, so dependencies start only after the start
action has succeeded. With
Type=simple, dependencies
will start immediately after the start action has been
dispatched. The following unit provides an example for a simple
static firewall.
[Unit] Description=Simple firewall [Service] Type=oneshot RemainAfterExit=yes ExecStart=/usr/local/sbin/simple-firewall-start ExecStop=/usr/local/sbin/simple-firewall-stop [Install] WantedBy=multi-user.target
Since the unit is considered to be running after the start action has exited, invoking systemctl start on that unit again will cause no action to be taken.
Example 4. Traditional forking services
Many traditional daemons/services background (i.e. fork,
daemonize) themselves when starting. Set
Type=forking in the
service's unit file to support this mode of operation. systemd
will consider the service to be in the process of initialization
while the original program is still running. Once it exits
successfully and at least a process remains (and
RemainAfterExit=no), the
service is considered started.
Often, a traditional daemon only consists of one process.
Therefore, if only one process is left after the original
process terminates, systemd will consider that process the main
process of the service. In that case, the
$MAINPID variable will be available in
ExecReload=, ExecStop=,
etc.
In case more than one process remains, systemd will be
unable to determine the main process, so it will not assume
there is one. In that case, $MAINPID will not
expand to anything. However, if the process decides to write a
traditional PID file, systemd will be able to read the main PID
from there. Please set PIDFile= accordingly.
Note that the daemon should write that file before finishing
with its initialization. Otherwise, systemd might try to read the
file before it exists.
The following example shows a simple daemon that forks and just starts one process in the background:
[Unit] Description=Some simple daemon [Service] Type=forking ExecStart=/usr/sbin/my-simple-daemon -d [Install] WantedBy=multi-user.target
Please see systemd.kill(5) for details on how you can influence the way systemd terminates the service.
Example 5. DBus services
For services that acquire a name on the DBus system bus,
use Type=dbus and set
BusName= accordingly. The service should not
fork (daemonize). systemd will consider the service to be
initialized once the name has been acquired on the system bus.
The following example shows a typical DBus service:
[Unit] Description=Simple DBus service [Service] Type=dbus BusName=org.example.simple-dbus-service ExecStart=/usr/sbin/simple-dbus-service [Install] WantedBy=multi-user.target
For bus-activatable services, do not
include a "[Install]" section in the systemd
service file, but use the SystemdService=
option in the corresponding DBus service file, for example
(/usr/share/dbus-1/system-services/org.example.simple-dbus-service.service):
[D-BUS Service] Name=org.example.simple-dbus-service Exec=/usr/sbin/simple-dbus-service User=root SystemdService=simple-dbus-service.service
Please see systemd.kill(5) for details on how you can influence the way systemd terminates the service.
Example 6. Services that notify systemd about their initialization
Type=simple services
are really easy to write, but have the major disadvantage of
systemd not being able to tell when initialization of the given
service is complete. For this reason, systemd supports a simple
notification protocol that allows daemons to make systemd aware
that they are done initializing. Use
Type=notify for this. A
typical service file for such a daemon would look like
this:
[Unit] Description=Simple notifying service [Service] Type=notify ExecStart=/usr/sbin/simple-notifying-service [Install] WantedBy=multi-user.target
Note that the daemon has to support systemd's notification protocol, else systemd will think the service has not started yet and kill it after a timeout. For an example of how to update daemons to support this protocol transparently, take a look at sd_notify(3). systemd will consider the unit to be in the 'starting' state until a readiness notification has arrived.
Please see systemd.kill(5) for details on how you can influence the way systemd terminates the service.