|
NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | OPTIONS | COMMAND LINES | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
|
SYSTEMD.SERVICE(5) systemd.service SYSTEMD.SERVICE(5)
systemd.service - Service unit configuration
service.service
A unit configuration file whose name ends in .service encodes
information about a process controlled and supervised by systemd.
This man page lists the configuration options specific to this unit
type. See systemd.unit(5) for the common options of all unit
configuration files. The common configuration items are configured in
the generic "[Unit]" and "[Install]" sections. The service specific
configuration options are configured in the "[Service]" section.
Additional options are listed in systemd.exec(5), which define the
execution environment the commands are executed in, and in
systemd.kill(5), which define the way the processes of the service
are terminated, and in systemd.resource-control(5), which configure
resource control settings for the processes of the service.
If a service is requested under a certain name but no unit
configuration file is found, systemd looks for a SysV init script by
the same name (with the .service suffix removed) and dynamically
creates a service unit from that script. This is useful for
compatibility with SysV. Note that this compatibility is quite
comprehensive but not 100%. For details about the incompatibilities,
see the Incompatibilities with SysV[1] document.
Services with Type=dbus set automatically acquire dependencies of
type Requires= and After= on dbus.socket.
Socket activated services are automatically ordered after their
activating .socket units via an automatic After= dependency. Services
also pull in all .socket units listed in Sockets= via automatic
Wants= and After= dependencies.
Unless DefaultDependencies= in the "[Unit]" is set to false, service
units will implicitly have dependencies of type Requires= and After=
on sysinit.target, a dependency of type After= on basic.target as
well as dependencies of type Conflicts= and Before= on
shutdown.target. These ensure that normal service units pull in basic
system initialization, and are terminated cleanly prior to system
shutdown. Only services involved with early boot or late system
shutdown should disable this option.
Instanced service units (i.e. service units with an "@" in their
name) are assigned by default a per-template slice unit (see
systemd.slice(5)), named after the template unit, containing all
instances of the specific template. This slice is normally stopped at
shutdown, together with all template instances. If that is not
desired, set DefaultDependencies=no in the template unit, and either
define your own per-template slice unit file that also sets
DefaultDependencies=no, or set Slice=system.slice (or another
suitable slice) in the template unit. Also see
systemd.resource-control(5).
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).
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, 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= nor
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 missing or set to none,
it will be forcibly set to main. Note that currently Type=notify
will not work if used in combination with PrivateNetwork=yes.
Behavior of idle is very similar to simple; however, actual
execution of the service binary 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 binary is invoked anyway.
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, although it will remove
the file after the service has shut down if it still exists.
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 an
absolute path to an executable. Optionally, if this 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 the absolute path is prefixed with "+"
then it is executed with full privileges. "@", "-", and "+" may
be used together and they can appear in any order.
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.
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.
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)).
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 "infinity" to disable the timeout logic.
Defaults to DefaultTimeoutStopSec= from the manager configuration
file (see systemd-system.conf(5)).
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.
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 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 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 1. 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.
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
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.
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=
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.
FailureAction=
Configure the action to take when the service enters a failed
state. Takes the same values as the unit setting
StartLimitAction= and executes the same actions (see
systemd.unit(5)). Defaults to none.
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.
USBFunctionDescriptors=
Configure the location of a file containing USB FunctionFS[3]
descriptors, for implementation of USB gadget functions. This is
used only in conjunction with a socket unit with
ListenUSBFunction= configured. The contents of this file are
written to the ep0 file after it is opened.
USBFunctionStrings=
Configure the location of a file containing USB FunctionFS
strings. Behavior is similar to USBFunctionDescriptors= above.
Check systemd.exec(5) and systemd.kill(5) for more settings.
This section describes command line parsing and variable and
specifier substitutions for ExecStart=, ExecStartPre=,
ExecStartPost=, ExecReload=, ExecStop=, and ExecStopPost= options.
Multiple command lines may be concatenated in a single directive by
separating them with semicolons (these semicolons must be passed as
separate words). Lone semicolons may be escaped as "\;".
Each command line is split on whitespace, with the first item being
the command to execute, and the subsequent items being the arguments.
Double quotes ("...") and single quotes ('...') may be used to wrap a
whole item (the opening quote may appear only at the beginning or
after whitespace that is not quoted, and the closing quote must be
followed by whitespace or the end of line), in which case everything
until the next matching quote becomes part of the same argument.
Quotes themselves are removed. C-style escapes are also supported.
The table below contains the list of known escape patterns. Only
escape patterns which match the syntax in the table are allowed;
other patterns may be added in the future and unknown patterns will
result in a warning. In particular, any backslashes should be
doubled. Finally, a trailing backslash ("\") may be used to merge
lines.
This syntax is inspired by shell syntax, but only the meta-characters
and expansions described in the following paragraphs are understood,
and the expansion of variables is different. Specifically,
redirection using "<", "<<", ">", and ">>", pipes using "|", running
programs in the background using "&", and other elements of shell
syntax are not supported.
The command to execute must be an absolute path name. It may contain
spaces, but control characters are not allowed.
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. For this
type of expansion, quotes are respected when splitting into words,
and afterwards removed.
Example:
Environment="ONE=one" 'TWO=two two'
ExecStart=/bin/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 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=/bin/sh -c 'dmesg | tac'
Example:
ExecStart=/bin/echo one ; /bin/echo "two two"
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:
ExecStart=/bin/echo / >/dev/null & \; \
/bin/ls
This will execute /bin/echo with five arguments: "/", ">/dev/null",
"&", ";", and "/bin/ls".
Table 2. 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 │
└────────┴─────────────────────────┘
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. They will be executed in order until either
they are all successful or one of them fails.
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.
systemd(1), systemctl(1), systemd.unit(5), systemd.exec(5),
systemd.resource-control(5), systemd.kill(5), systemd.directives(7)
1. Incompatibilities with SysV
https://www.freedesktop.org/wiki/Software/systemd/Incompatibilities
2. Proper handling of SIGINT/SIGQUIT — How to be a proper program
http://www.cons.org/cracauer/sigint.html
3. USB FunctionFS
https://www.kernel.org/doc/Documentation/usb/functionfs.txt
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2018-02-02. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2018-02-02.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
systemd 234 SYSTEMD.SERVICE(5)
Pages that refer to this page: systemctl(1), systemd(1), systemd-run(1), systemd-socket-activate(1), sd-daemon(3), sd_event_set_watchdog(3), sd_is_fifo(3), sd_listen_fds(3), sd_notify(3), sd_watchdog_enabled(3), systemd.exec(5), systemd.kill(5), systemd.mount(5), systemd.path(5), systemd.resource-control(5), systemd.scope(5), systemd.slice(5), systemd.socket(5), systemd-system.conf(5), systemd.timer(5), systemd.unit(5), daemon(7), systemd.directives(7), systemd.index(7), systemd.special(7), pam_systemd(8), systemd-activate(8), systemd-socket-proxyd(8), systemd-sysv-generator(8)
|
HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
|
|