SYSTEMD.SERVICE(5) systemd.service SYSTEMD.SERVICE(5)
NAME
systemd.service - Service unit configuration
SYNOPSIS
service.service
DESCRIPTION
A unit configuration file whose name ends in ".service" encodes
information about a process controlled and supervised by systemd.
This man page lists the configuration options specific to this unit
type. See systemd.unit(5) for the common options of all unit
configuration files. The common configuration items are configured in
the generic "[Unit]" and "[Install]" sections. The service specific
configuration options are configured in the "[Service]" section.
Additional options are listed in systemd.exec(5), which define the
execution environment the commands are executed in, and in
systemd.kill(5), which define the way the processes of the service are
terminated, and in systemd.resource-control(5), which configure
resource control settings for the processes of the service.
If a service is requested under a certain name but no unit
configuration file is found, systemd looks for a SysV init script by
the same name (with the .service suffix removed) and dynamically
creates a service unit from that script. This is useful for
compatibility with SysV. Note that this compatibility is quite
comprehensive but not 100%. For details about the incompatibilities,
see the Incompatibilities with SysV[1] document.
SERVICE TEMPLATES
It is possible for systemd services to take a single argument via the
"service AT argument.service" syntax. Such services are called
"instantiated" services, while the unit definition without the argument
parameter is called a "template". An example could be a dhcpcd@.service
service template which takes a network interface as a parameter to form
an instantiated service. Within the service file, this parameter or
"instance name" can be accessed with %-specifiers. See systemd.unit(5)
for details.
AUTOMATIC DEPENDENCIES
Implicit Dependencies
The following dependencies are implicitly added:
o Services with Type=dbus set automatically acquire dependencies of
type Requires= and After= on dbus.socket.
o 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:
o 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.
o Instanced service units (i.e. service units with an "@" in their
name) are assigned by default a per-template slice unit (see
systemd.slice(5)), named after the template unit, containing all
instances of the specific template. This slice is normally stopped
at shutdown, together with all template instances. If that is not
desired, set DefaultDependencies=no in the template unit, and
either define your own per-template slice unit file that also sets
DefaultDependencies=no, or set Slice=system.slice (or another
suitable slice) in the template unit. Also see systemd.resource-
control(5).
OPTIONS
Service files must include a "[Service]" section, which carries
information about the service and the process it supervises. A number
of options that may be used in this section are shared with other unit
types. These options are documented in systemd.exec(5), systemd.kill(5)
and systemd.resource-control(5). The options specific to the
"[Service]" section of service units are the following:
Type=
Configures the process start-up type for this service unit. One of
simple, exec, forking, oneshot, dbus, notify or idle:
o 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).
o 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).
o 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.
o 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.
o 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.
o 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.
o 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:
o exit code of 0;
o for types other than Type=oneshot, one of the signals SIGHUP,
SIGINT, SIGTERM, or SIGPIPE;
o exit statuses and signals specified in SuccessExitStatus=.
If set to on-failure, the service will be restarted when the
process exits with a non-zero exit code, is terminated by a signal
(including on core dump, but excluding the aforementioned four
signals), when an operation (such as service reload) times out, and
when the configured watchdog timeout is triggered. If set to
on-abnormal, the service will be restarted when the process is
terminated by a signal (including on core dump, excluding the
aforementioned four signals), when an operation times out, or when
the watchdog timeout is triggered. If set to on-abort, the service
will be restarted only if the service process exits due to an
uncaught signal not specified as a clean exit status. If set to
on-watchdog, the service will be restarted only if the watchdog
timeout for the service expires. If set to always, the service will
be restarted regardless of whether it exited cleanly or not, got
terminated abnormally by a signal, or hit a timeout.
Table 2. Exit causes and the effect of the Restart= settings on
them
+--------------+----+--------+------------+------------+-------------+----------+-------------+
|Restart | no | always | on-success | on-failure | on-abnormal | on-abort | on-watchdog |
|settings/Exit | | | | | | | |
|causes | | | | | | | |
+--------------+----+--------+------------+------------+-------------+----------+-------------+
|Clean exit | | X | X | | | | |
|code or | | | | | | | |
|signal | | | | | | | |
+--------------+----+--------+------------+------------+-------------+----------+-------------+
|Unclean exit | | X | | X | | | |
|code | | | | | | | |
+--------------+----+--------+------------+------------+-------------+----------+-------------+
|Unclean | | X | | X | X | X | |
|signal | | | | | | | |
+--------------+----+--------+------------+------------+-------------+----------+-------------+
|Timeout | | X | | X | X | | |
+--------------+----+--------+------------+------------+-------------+----------+-------------+
|Watchdog | | X | | X | X | | X |
+--------------+----+--------+------------+------------+-------------+----------+-------------+
As exceptions to the setting above, the service will not be
restarted if the exit code or signal is specified in
RestartPreventExitStatus= (see below) or the service is stopped
with systemctl stop or an equivalent operation. Also, the services
will always be restarted if the exit code or signal is specified in
RestartForceExitStatus= (see below).
Note that service restart is subject to unit start rate limiting
configured with StartLimitIntervalSec= and StartLimitBurst=, see
systemd.unit(5) for details. A restarted service enters the failed
state only after the start limits are reached.
Setting this to on-failure is the recommended choice for
long-running services, in order to increase reliability by
attempting automatic recovery from errors. For services that shall
be able to terminate on their own choice (and avoid immediate
restarting), on-abnormal is an alternative choice.
SuccessExitStatus=
Takes a list of exit status definitions that, when returned by the
main service process, will be considered successful termination, in
addition to the normal successful exit code 0 and, 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[2]
descriptors, for implementation of USB gadget functions. This is
used only in conjunction with a socket unit with ListenUSBFunction=
configured. The contents of this file are written to the ep0 file
after it is opened.
USBFunctionStrings=
Configure the location of a file containing USB FunctionFS strings.
Behavior is similar to USBFunctionDescriptors= above.
Check systemd.exec(5) and systemd.kill(5) for more settings.
COMMAND LINES
This section describes command line parsing and variable and specifier
substitutions for ExecStart=, ExecStartPre=, ExecStartPost=,
ExecReload=, ExecStop=, and ExecStopPost= options.
Multiple command lines may be concatenated in a single directive by
separating them with semicolons (these semicolons must be passed as
separate words). Lone semicolons may be escaped as "\;".
Each command line is split on whitespace, with the first item being the
command to execute, and the subsequent items being the arguments.
Double quotes ("...") and single quotes ('...') may be used to wrap a
whole item (the opening quote may appear only at the beginning or after
whitespace that is not quoted, and the closing quote must be followed
by whitespace or the end of line), in which case everything until the
next matching quote becomes part of the same argument. Quotes
themselves are removed. C-style escapes are also supported. The table
below contains the list of known escape patterns. Only escape patterns
which match the syntax in the table are allowed; other patterns may be
added in the future and unknown patterns will result in a warning. In
particular, any backslashes should be doubled. Finally, a trailing
backslash ("\") may be used to merge lines.
This syntax is inspired by shell syntax, but only the meta-characters
and expansions described in the following paragraphs are understood,
and the expansion of variables is different. Specifically, redirection
using "<", "<<", ">", and ">>", pipes using "|", running programs in
the background using "&", and other elements of shell syntax are not
supported.
The command to execute may contain spaces, but control characters are
not allowed.
The command line accepts "%" specifiers as described in
systemd.unit(5).
Basic environment variable substitution is supported. Use "${FOO}" as
part of a word, or as a word of its own, on the command line, in which
case it will be replaced by the value of the environment variable
including all whitespace it contains, resulting in a single argument.
Use "$FOO" as a separate word on the command line, in which case it
will be replaced by the value of the environment variable split at
whitespace, resulting in zero or more arguments. For this type of
expansion, quotes are respected when splitting into words, and
afterwards removed.
If the command is not a full (absolute) path, it will be resolved to a
full path using a fixed search path determinted at compilation time.
Searched directories include /usr/local/bin/, /usr/bin/, /bin/ on
systems using split /usr/bin/ and /bin/ directories, and their sbin/
counterparts on systems using split bin/ and sbin/. It is thus safe to
use just the executable name in case of executables located in any of
the "standard" directories, and an absolute path must be used in other
cases. Using an absolute path is recommended to avoid ambiguity. Hint:
this search path may be queried using systemd-path
search-binaries-default.
Example:
Environment="ONE=one" 'TWO=two two'
ExecStart=echo $ONE $TWO ${TWO}
This will execute /bin/echo with four arguments: "one", "two", "two",
and "two two".
Example:
Environment=ONE='one' "TWO='two two' too" THREE=
ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
ExecStart=/bin/echo $ONE $TWO $THREE
This results in /bin/echo being called twice, the first time with
arguments "'one'", "'two two' too", "", and the second time with
arguments "one", "two two", "too".
To pass a literal dollar sign, use "$$". Variables whose value is not
known at expansion time are treated as empty strings. Note that the
first argument (i.e. the program to execute) may not be a variable.
Variables to be used in this fashion may be defined through
Environment= and EnvironmentFile=. In addition, variables listed in the
section "Environment variables in spawned processes" in
systemd.exec(5), which are considered "static configuration", may be
used (this includes e.g. $USER, but not $TERM).
Note that shell command lines are not directly supported. If shell
command lines are to be used, they need to be passed explicitly to a
shell implementation of some kind. Example:
ExecStart=sh -c 'dmesg | tac'
Example:
ExecStart=echo one ; echo "two two"
This will execute echo two times, each time with one argument: "one"
and "two two", respectively. Because two commands are specified,
Type=oneshot must be used.
Example:
ExecStart=echo / >/dev/null & \; \
ls
This will execute echo with five arguments: "/", ">/dev/null", "&",
";", and "ls".
Table 3. C escapes supported in command lines and environment variables
+--------+-------------------------+
|Literal | Actual value |
+--------+-------------------------+
|"\a" | bell |
+--------+-------------------------+
|"\b" | backspace |
+--------+-------------------------+
|"\f" | form feed |
+--------+-------------------------+
|"\n" | newline |
+--------+-------------------------+
|"\r" | carriage return |
+--------+-------------------------+
|"\t" | tab |
+--------+-------------------------+
|"\v" | vertical tab |
+--------+-------------------------+
|"\\" | backslash |
+--------+-------------------------+
|"\"" | double quotation mark |
+--------+-------------------------+
|"\'" | single quotation mark |
+--------+-------------------------+
|"\s" | space |
+--------+-------------------------+
|"\xxx" | character number xx in |
| | hexadecimal encoding |
+--------+-------------------------+
|"\nnn" | character number nnn in |
| | octal encoding |
+--------+-------------------------+
EXAMPLES
Example 1. Simple service
The following unit file creates a service that will execute
/usr/sbin/foo-daemon. Since no Type= is specified, the default
Type=simple will be assumed. systemd will assume the unit to be started
immediately after the program has begun executing.
[Unit]
Description=Foo
[Service]
ExecStart=/usr/sbin/foo-daemon
[Install]
WantedBy=multi-user.target
Note that systemd assumes here that the process started by systemd will
continue running until the service terminates. If the program
daemonizes itself (i.e. forks), please use Type=forking instead.
Since no ExecStop= was specified, systemd will send SIGTERM to all
processes started from this service, and after a timeout also SIGKILL.
This behavior can be modified, see systemd.kill(5) for details.
Note that this unit type does not include any type of notification when
a service has completed initialization. For this, you should use other
unit types, such as Type=notify if the service understands systemd's
notification protocol, Type=forking if the service can background
itself or Type=dbus if the unit acquires a DBus name once
initialization is complete. See below.
Example 2. Oneshot service
Sometimes, units should just execute an action without keeping active
processes, such as a filesystem check or a cleanup action on boot. For
this, Type=oneshot exists. Units of this type will wait until the
process specified terminates and then fall back to being inactive. The
following unit will perform a cleanup action:
[Unit]
Description=Cleanup old Foo data
[Service]
Type=oneshot
ExecStart=/usr/sbin/foo-cleanup
[Install]
WantedBy=multi-user.target
Note that systemd will consider the unit to be in the state "starting"
until the program has terminated, so ordered dependencies will wait for
the program to finish before starting themselves. The unit will revert
to the "inactive" state after the execution is done, never reaching the
"active" state. That means another request to start the unit will
perform the action again.
Type=oneshot are the only service units that may have more than one
ExecStart= specified. 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.
SEE ALSO
systemd(1), systemctl(1), systemd.unit(5), systemd.exec(5),
systemd.resource-control(5), systemd.kill(5), systemd.directives(7)
NOTES
1. Incompatibilities with SysV
https://www.freedesktop.org/wiki/Software/systemd/Incompatibilities
2. USB FunctionFS
https://www.kernel.org/doc/Documentation/usb/functionfs.txt
systemd 239 SYSTEMD.SERVICE(5)
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