Ubuntu Manpage: systemd.service - Service unit configuration

Provided by: systemd_204-5ubuntu20.31_amd64

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.

Unless DefaultDependencies= is set to false, service units will implicitly have
dependencies of type Requires= and 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.

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.

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)
and systemd.kill(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, forking,
oneshot, dbus, notify or idle.

If set to simple (the default value if BusName= is not specified) 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 daemon is started up (e.g.
sockets set up by systemd, via socket activation), as systemd will immediately proceed
starting follow-up units.

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 set up. The child continues to run as the
main daemon process. This is the behavior of traditional UNIX daemons. If this setting
is used, it is recommended to also use the PIDFile= option, so that systemd can
identify the main process of the daemon. systemd will proceed starting follow-up units
as soon as the parent process exits.

Behavior of oneshot is similar to simple, however it is expected that the process has
to exit before systemd starts follow-up units. RemainAfterExit= is particularly
useful for this type of service.

Behavior of dbus is similar to simple, however it is expected that the daemon acquires
a name on the D-Bus bus, as configured by BusName=. systemd will proceed 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 simple, however it is expected that the daemon sends
a notification message via sd_notify(3) or an equivalent call when it finished
starting up. systemd will proceed 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 not
set, it will be implicitly set to main.

Behavior of idle is very similar to simple, however actual execution of the service
binary is delayed until all jobs are dispatched. This may be used to avoid
interleaving of output of shell services with the status output on the console.

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 file name pointing to the PID file of this daemon. Use of this
option is recommended for services where Type= is set to forking. systemd will read
the PID of the main process of the daemon after start-up of the service. systemd will
not write to the file configured here.

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, but its use is otherwise recommended as well
if the process takes a name on the D-Bus bus.

ExecStart=
Commands with their arguments that are executed when this service is started. The
first argument must be an absolute path name.

When Type is not oneshot, only one command may be given. When Type=oneshot is used,
more than one command may be specified. Multiple command lines may be concatenated in
a single directive, by separating them with semicolons (these semicolons must be
passed as separate words). Alternatively, this directive may be specified more than
once with the same effect. However, the latter syntax is not recommended for
compatibility with parsers suitable for XDG .desktop files. Lone semicolons may be
escaped as '\;'. 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 more than one command is specified, the commands are invoked one by one
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.

The command line accepts '%' specifiers as described in systemd.unit(5). Note that the
first argument of the command line (i.e. the program to execute) may not include
specifiers.

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 up at whitespace,
resulting in zero or more arguments. Note that the first argument (i.e. the program to
execute) may not be a variable, since it must be a literal and absolute path name.

Optionally, if the absolute file name is prefixed with '@', the second token will be
passed as argv[0] to the executed process, followed by the further arguments
specified. If the absolute file name 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 both '-' and '@' are used they can
appear in either order.

Note that this setting does not directly support shell command lines. If shell command
lines are to be used they need to be passed explicitly to a shell implementation of
some kind. Example:

ExecStart=/bin/sh -c 'dmesg | tac'

For services run by a user instance of systemd the special environment variable
$MANAGERPID is set to the PID of the systemd instance.

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.

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 variables 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

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. All processes remaining for a service after the
commands configured in this option are run are terminated according to the KillMode=
setting (see systemd.kill(5)). If this option is not specified the process is
terminated right-away when service stop is requested. Specifier and environment
variable substitution is supported (including $MAINPID, see above).

ExecStopPost=
Additional commands that are executed after the service was stopped. This includes
cases where the commands configured in ExecStop= were used, where the service doesn't
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.

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 be
shut down again. Takes a unit-less value in seconds, or a time span value such as
"5min 20s". Pass 0 to disable the timeout logic. Defaults to 90s, except when
Type=oneshot is used in which case the timeout is disabled by default.

TimeoutStopSec=
Configures the time to wait for stop. If a service is asked to stop but does not
terminate in the specified time, it will be terminated forcibly via SIGTERM, and after
another delay of this time with SIGKILL (See KillMode= in systemd.kill(5)). Takes a
unit-less value in seconds, or a time span value such as "5min 20s". Pass 0 to disable
the timeout logic. Defaults to 90s.

TimeoutSec=
A shorthand for configuring both TimeoutStartSec= and TimeoutStopSec= to the specified
value.

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 failure state. By setting Restart= to
on-failure 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.

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 also one of the processes specified with ExecStartPre=, ExecStartPost=,
ExecStopPre=, 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-abort, or always. If set to no (the
default) the service will not be restarted. If set to on-success it will be restarted
only when the service process exits cleanly. In this context, a clean exit means an
exit code of 0, or one of the signals SIGHUP, SIGINT, SIGTERM, or SIGPIPE, and
additionally, exit statuses and signals specified in SuccessExitStatus=. If set to
on-failure the service will be restarted when the process exits with an nonzero exit
code, is terminated by a signal (including on core dump), when an operation (such as
service reload) times out, and when the configured 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 always the service
will be restarted regardless whether it exited cleanly or not, got terminated
abnormally by a signal or hit a timeout.

In addition to the above settings, the service will not be restarted if the exit code
or signal is specified in RestartPreventExitStatus= (see below).

SuccessExitStatus=
Takes a list of exit status definitions that when returned by the main service process
will be considered successful termination, in addition to the normal successful exit
code 0 and the signals SIGHUP, SIGINT, SIGTERM and SIGPIPE. Exit status definitions
can either be numeric exit codes or termination signal names, separated by spaces.
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. 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, all prior
assignments of this option will have no effect.

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=, 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=, ExecStopPost= commands. If false, the setting
is applied to all configured commands the same way. Defaults to false.

NonBlocking=
Set 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) 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). 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 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 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= not configured it will be implicitly set to main.

Sockets=
Specifies the name of the socket units this service shall inherit the sockets from
when the service is started. Normally it should not be necessary to use this setting
as all sockets whose unit shares the same name as the service (ignoring the different
suffix of course) are passed to the spawned process.

Note that the same socket may be passed to multiple processes at the same time. Also
note that a different service may be activated on incoming traffic than inherits the
sockets. Or in other words: the Service= setting of .socket units doesn't 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,
all prior uses of this setting will have no effect.

StartLimitInterval=, StartLimitBurst=
Configure service start rate limiting. By default services which are started more
often than 5 times within 10s are not permitted to start any more times until the 10s
interval ends. With these two options this rate limiting may be modified. Use
StartLimitInterval= to configure the checking interval (defaults to 10s, set to 0 to
disable any kind of rate limiting). Use StartLimitBurst= to configure how many starts
per interval are allowed (defaults to 5). These configuration options are particularly
useful in conjunction with Restart=, however apply to all kinds of starts (including
manual), not just those triggered by the Restart= logic. Note that units which are
configured for Restart= and which reach the start limit are not attempted to be
restarted anymore, however they may still be restarted manually at a later point from
which point on the restart logic is again activated. Note that systemctl reset-failed
will cause the restart rate counter for a service to be flushed, which is useful if
the administrator wants to manually start a service and the start limit interferes
with that.

StartLimitAction=
Configure the action to take if the rate limit configured with StartLimitInterval= and
StartLimitBurst= is hit. Takes one of none, reboot, reboot-force or reboot-immediate.
If none is set, hitting the rate limit will trigger no action besides that the start
will not be permitted. reboot causes a reboot following the normal shutdown procedure
(i.e. equivalent to systemctl reboot), reboot-force causes an forced reboot which will
terminate all processes forcibly but should cause no dirty file systems on reboot
(i.e. equivalent to systemctl reboot -f) and reboot-immediate causes immediate
execution of the reboot(2) system call, which might result in data loss. Defaults to
none.

Check systemd.exec(5) and systemd.kill(5) for more settings.

COMPATIBILITY OPTIONS

The following options are also available in the [Service] section, but exist purely for
compatibility reasons and should not be used in newly written service files.

SysVStartPriority=
Set the SysV start priority to use to order this service in relation to SysV services
lacking LSB headers. This option is only necessary to fix ordering in relation to
legacy SysV services, that have no ordering information encoded in the script headers.
As such it should only be used as temporary compatibility option, and not be used in
new unit files. Almost always it is a better choice to add explicit ordering
directives via After= or Before=, instead. For more details see systemd.unit(5). If
used, pass an integer value in the range 0-99.

FsckPassNo=
Set the fsck passno priority to use to order this service in relation to other file
system checking services. This option is only necessary to fix ordering in relation to
fsck jobs automatically created for all /etc/fstab entries with a value in the
fs_passno column > 0. As such it should only be used as option for fsck services.
Almost always it is a better choice to add explicit ordering directives via After= or
Before=, instead. For more details see systemd.unit(5). If used, pass an integer value
in the same range as /etc/fstab's fs_passno column. See fstab(5) for details.

NOTES