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SYSTEMD.SERVICE(5) | systemd.service | SYSTEMD.SERVICE(5) |
NAME¶
systemd.service - Service unit configurationSYNOPSIS¶
service.serviceDESCRIPTION¶
A unit configuration file whose name ends in .service encodes information about a process controlled and supervised by systemd. This man page lists the configuration options specific to this unit type. See systemd.unit(5) for the common options of all unit configuration files. The common configuration items are configured in the generic "[Unit]" and "[Install]" sections. The service specific configuration options are configured in the "[Service]" section. Additional options are listed in systemd.exec(5), which define the execution environment the commands are executed in, and in systemd.kill(5), which define the way the processes of the service are terminated, and in systemd.resource-control(5), which configure resource control settings for the processes of the service. 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 if neither Type= nor
BusName=, but ExecStart= are 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 are 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 with 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. This
is the implied default if neither Type= or ExecStart= are
specified.
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 with starting follow-up units after the
D-Bus bus name has been acquired. Service units with this option configured
implicitly gain dependencies on the dbus.socket unit. This type is the default
if BusName= is specified.
Behavior of notify is similar to simple; however, it is expected
that the daemon 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 not set, it will be implicitly set to main. Note that currently
Type= notify will not work if used in combination with
PrivateNetwork= yes.
Behavior of idle is very similar to simple; however, actual
execution of the service 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 if the process takes a name
on the D-Bus bus.
ExecStart=
Commands with their arguments that are executed when this
service is started. For each of the specified commands, the first argument
must be an absolute and literal path to an executable.
When Type is not oneshot, only one command may and must be given.
When Type=oneshot is used, none or 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. 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 no ExecStart=
is specified, then the service must have RemainAfterExit=yes set.
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, in which case
everything until the next matching quote becomes part of the same argument.
Quotes themselves are removed after parsing. In addition, a trailing backslash
("\") may be used to merge lines. This syntax is intended to be very
similar to shell syntax, but only the meta-characters and expansions described
in the following paragraphs are understood. Specifically, redirection using
"<", "<<", ">", and
">>", pipes using "|", and running programs in the
background using "&" and other elements of shell syntax are
not supported.
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.
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 at whitespace, resulting in zero
or more arguments. 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).
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 filename 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:
Example:
This will execute /bin/echo two times, each time with one argument:
"one" and "two two", respectively. Because two commands
are specified, Type=oneshot must be used.
Example:
This will execute /bin/echo with five arguments: "/",
">/dev/null", "&", ";", and
"/bin/ls".
Example:
This will execute /bin/echo with four arguments: "one",
"two", "two", and "two two".
ExecStartPre=, ExecStartPost=
ExecStart=/bin/sh -c 'dmesg | tac'
ExecStart=/bin/echo one ; /bin/echo "two two"
ExecStart=/bin/echo / >/dev/null & \; \ /bin/ls
Environment="ONE=one" 'TWO=two two' ExecStart=/bin/echo $ONE $TWO ${TWO}
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 variable is set: if known, $MAINPID
is set to the main process of the daemon, and may be used for command lines
like the following:
Note however that reloading a daemon by sending a signal (as with the example
line above) is usually not a good choice, because this is an asynchronous
operation and hence not suitable to order reloads of multiple services against
each other. It is strongly recommended to set ExecReload= to a command
that not only triggers a configuration reload of the daemon, but also
synchronously waits for it to complete.
ExecStop=
/bin/kill -HUP $MAINPID
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, all processes
remaining for a service are terminated according to the KillMode=
setting (see systemd.kill(5)). If this option is not specified, the
process is terminated immediately 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 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.
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 "0" to disable the timeout logic. Defaults to
TimeoutStartSec= from the manager configuration file, 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 timeout of equal
duration 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
TimeoutStartSec= from the manager configuration file.
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 failed 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 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 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 a non-zero exit code, is terminated by a
signal (including on core dump, but excluding the aforementiond 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 1. Exit causes and the effect of the Restart=
settings on them
As exceptions to the setting above the service will not be restarted if the exit
code or signal is specified in
RestartPreventExitStatus= (see below). Also, the services will always be
restarted if the exit code or signal is specified in
RestartForceExitStatus= (see below).
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=
Restart settings/Exit causes | no | always | on-success | on-failure | on-abnormal | on-abort | on-watchdog |
Clean exit code or signal | X | X | |||||
Unclean exit code | X | X | |||||
Unclean signal | X | X | X | X | |||
Timeout | X | X | X | ||||
Watchdog | X | X | X | X |
Takes a list of exit status definitions that when
returned by the main service process will be considered successful
termination, in addition to the normal successful exit 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. For example:
ensures that exit codes 1, 2, 8 and the termination signal SIGKILL are
considered clean service terminations.
Note that if a process has a signal handler installed and exits by calling
_exit(2) in response to a signal, the information about the signal is
lost. Programs should instead perform cleanup and kill themselves with the
same signal instead. See Proper handling of SIGINT/SIGQUIT — How to
be a proper program[2].
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=
SuccessExitStatus=1 2 8 SIGKILL
Takes a list of exit status definitions that when
returned by the main service process will prevent automatic service restarts,
regardless of the restart setting configured with Restart=. Exit status
definitions can either be numeric exit codes or termination signal names, and
are separated by spaces. Defaults to the empty list, so that, by default, no
exit status is excluded from the configured restart logic. For example:
ensures that exit codes 1 and 6 and the termination signal SIGABRT will
not result in automatic service restarting. This option may appear more than
once, in which case the list of restart-preventing statuses is merged. If the
empty string is assigned to this option, the list is reset and all prior
assignments of this option will have no effect.
RestartForceExitStatus=
RestartPreventExitStatus=1 6 SIGABRT
Takes a list of exit status definitions that when
returned by the main service process will force automatic service restarts,
regardless of the restart setting configured with Restart=. The
argument format is similar to RestartPreventExitStatus=.
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, and 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= is 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
that which inherits the sockets. 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.
StartLimitInterval=, StartLimitBurst=
Configure service start rate limiting. By default,
services which are started more than 5 times within 10 seconds are not
permitted to start any more times until the 10 second interval ends. With
these two options, this rate limiting may be modified. Use
StartLimitInterval= to configure the checking interval (defaults to
DefaultStartLimitInterval= in manager configuration file, set to 0 to
disable any kind of rate limiting). Use StartLimitBurst= to configure
how many starts per interval are allowed (defaults to
DefaultStartLimitBurst= in manager configuration file). These
configuration options are particularly useful in conjunction with
Restart=; however, they 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 a 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.
RebootArgument=
Configure the optional argument for the reboot(2)
system call if StartLimitAction= is a reboot action. This works just
like the optional argument to systemctl reboot command.
FailureAction=
Configure the action to take when the service enters a
failed state. Takes the same values as StartLimitAction= and executes
the same actions. 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 a temporary compatibility option and should 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.
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
- 2.
- Proper handling of SIGINT/SIGQUIT — How to be a proper program
systemd 215 |