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