Service files must include a [Service] section, which carries
information about the service and the process it supervises. A
number of options that may be used in this section are shared
with other unit types. These options are documented in
systemd.exec(5), systemd.kill(5) and systemd.resource-control(5).
The options specific to the [Service] section of service units
are the following:
Type=
Configures the process start-up type for this service unit.
One of simple, exec, forking, oneshot, dbus, notify or idle:
• If set to simple (the default if ExecStart= is specified
but neither Type= nor BusName= are), the service manager
will consider the unit started immediately after the main
service process has been forked off. It is expected that
the process configured with ExecStart= is the main
process of the service. In this mode, if the process
offers functionality to other processes on the system,
its communication channels should be installed before the
service is started up (e.g. sockets set up by systemd,
via socket activation), as the service manager will
immediately proceed starting follow-up units, right after
creating the main service process, and before executing
the service's binary. Note that this means systemctl
start command lines for simple services will report
success even if the service's binary cannot be invoked
successfully (for example because the selected User=
doesn't exist, or the service binary is missing).
• The exec type is similar to simple, but the service
manager will consider the unit started immediately after
the main service binary has been executed. The service
manager will delay starting of follow-up units until that
point. (Or in other words: simple proceeds with further
jobs right after fork() returns, while exec will not
proceed before both fork() and execve() in the service
process succeeded.) Note that this means systemctl start
command lines for exec services will report failure when
the service's binary cannot be invoked successfully (for
example because the selected User= doesn't exist, or the
service binary is missing).
• If set to forking, it is expected that the process
configured with ExecStart= will call fork() as part of
its start-up. The parent process is expected to exit when
start-up is complete and all communication channels are
set up. The child continues to run as the main service
process, and the service manager will consider the unit
started when the parent process exits. This is the
behavior of traditional UNIX services. If this setting is
used, it is recommended to also use the PIDFile= option,
so that systemd can reliably identify the main process of
the service. systemd will proceed with starting follow-up
units as soon as the parent process exits.
• Behavior of oneshot is similar to simple; however, the
service manager will consider the unit up after the main
process exits. It will then start follow-up units.
RemainAfterExit= is particularly useful for this type of
service. Type=oneshot is the implied default if neither
Type= nor ExecStart= are specified. Note that if this
option is used without RemainAfterExit= the service will
never enter "active" unit state, but directly transition
from "activating" to "deactivating" or "dead" since no
process is configured that shall run continuously. In
particular this means that after a service of this type
ran (and which has RemainAfterExit= not set) it will not
show up as started afterwards, but as dead.
• Behavior of dbus is similar to simple; however, it is
expected that the service acquires a name on the D-Bus
bus, as configured by BusName=. systemd will proceed with
starting follow-up units after the D-Bus bus name has
been acquired. Service units with this option configured
implicitly gain dependencies on the dbus.socket unit.
This type is the default if BusName= is specified. A
service unit of this type is considered to be in the
activating state until the specified bus name is
acquired. It is considered activated while the bus name
is taken. Once the bus name is released the service is
considered being no longer functional which has the
effect that the service manager attempts to terminate any
remaining processes belonging to the service. Services
that drop their bus name as part of their shutdown logic
thus should be prepared to receive a SIGTERM (or
whichever signal is configured in KillSignal=) as result.
• Behavior of notify is similar to exec; however, it is
expected that the service sends a notification message
via sd_notify(3) or an equivalent call when it has
finished starting up. systemd will proceed with starting
follow-up units after this notification message has been
sent. If this option is used, NotifyAccess= (see below)
should be set to open access to the notification socket
provided by systemd. If NotifyAccess= is missing or set
to none, it will be forcibly set to main.
• Behavior of idle is very similar to simple; however,
actual execution of the service program is delayed until
all active jobs are dispatched. This may be used to avoid
interleaving of output of shell services with the status
output on the console. Note that this type is useful only
to improve console output, it is not useful as a general
unit ordering tool, and the effect of this service type
is subject to a 5s timeout, after which the service
program is invoked anyway.
It is generally recommended to use Type=simple for
long-running services whenever possible, as it is the
simplest and fastest option. However, as this service type
won't propagate service start-up failures and doesn't allow
ordering of other units against completion of initialization
of the service (which for example is useful if clients need
to connect to the service through some form of IPC, and the
IPC channel is only established by the service itself — in
contrast to doing this ahead of time through socket or bus
activation or similar), it might not be sufficient for many
cases. If so, notify or dbus (the latter only in case the
service provides a D-Bus interface) are the preferred options
as they allow service program code to precisely schedule when
to consider the service started up successfully and when to
proceed with follow-up units. The notify service type
requires explicit support in the service codebase (as
sd_notify() or an equivalent API needs to be invoked by the
service at the appropriate time) — if it's not supported,
then forking is an alternative: it supports the traditional
UNIX service start-up protocol. Finally, exec might be an
option for cases where it is enough to ensure the service
binary is invoked, and where the service binary itself
executes no or little initialization on its own (and its
initialization is unlikely to fail). Note that using any type
other than simple possibly delays the boot process, as the
service manager needs to wait for service initialization to
complete. It is hence recommended not to needlessly use any
types other than simple. (Also note it is generally not
recommended to use idle or oneshot for long-running
services.)
RemainAfterExit=
Takes a boolean value that specifies whether the service
shall be considered active even when all its processes
exited. Defaults to no.
GuessMainPID=
Takes a boolean value that specifies whether systemd should
try to guess the main PID of a service if it cannot be
determined reliably. This option is ignored unless
Type=forking is set and PIDFile= is unset because for the
other types or with an explicitly configured PID file, the
main PID is always known. The guessing algorithm might come
to incorrect conclusions if a daemon consists of more than
one process. If the main PID cannot be determined, failure
detection and automatic restarting of a service will not work
reliably. Defaults to yes.
PIDFile=
Takes a path referring to the PID file of the service. Usage
of this option is recommended for services where Type= is set
to forking. The path specified typically points to a file
below /run/. If a relative path is specified it is hence
prefixed with /run/. The service manager will read the PID of
the main process of the service from this file after start-up
of the service. The service manager will not write to the
file configured here, although it will remove the file after
the service has shut down if it still exists. The PID file
does not need to be owned by a privileged user, but if it is
owned by an unprivileged user additional safety restrictions
are enforced: the file may not be a symlink to a file owned
by a different user (neither directly nor indirectly), and
the PID file must refer to a process already belonging to the
service.
Note that PID files should be avoided in modern projects. Use
Type=notify or Type=simple where possible, which does not
require use of PID files to determine the main process of a
service and avoids needless forking.
BusName=
Takes a D-Bus destination name that this service shall use.
This option is mandatory for services where Type= is set to
dbus. It is recommended to always set this property if known
to make it easy to map the service name to the D-Bus
destination. In particular, systemctl
service-log-level/service-log-target verbs make use of this.
ExecStart=
Commands with their arguments that are executed when this
service is started. The value is split into zero or more
command lines according to the rules described below (see
section "Command Lines" below).
Unless Type= is oneshot, exactly one command must be given.
When Type=oneshot is used, zero or more commands may be
specified. Commands may be specified by providing multiple
command lines in the same directive, or alternatively, this
directive may be specified more than once with the same
effect. If the empty string is assigned to this option, the
list of commands to start is reset, prior assignments of this
option will have no effect. If no ExecStart= is specified,
then the service must have RemainAfterExit=yes and at least
one ExecStop= line set. (Services lacking both ExecStart= and
ExecStop= are not valid.)
For each of the specified commands, the first argument must
be either an absolute path to an executable or a simple file
name without any slashes. Optionally, this filename may be
prefixed with a number of special characters:
Table 1. Special executable prefixes
┌───────┬──────────────────────────┐
│Prefix │ Effect │
├───────┼──────────────────────────┤
│"@" │ If the executable path │
│ │ is prefixed with "@", │
│ │ the second specified │
│ │ token will be passed as │
│ │ "argv[0]" to the │
│ │ executed process │
│ │ (instead of the actual │
│ │ filename), followed by │
│ │ the further arguments │
│ │ specified. │
├───────┼──────────────────────────┤
│"-" │ If the executable path │
│ │ is prefixed with "-", an │
│ │ exit code of the command │
│ │ normally considered a │
│ │ failure (i.e. non-zero │
│ │ exit status or abnormal │
│ │ exit due to signal) is │
│ │ recorded, but has no │
│ │ further effect and is │
│ │ considered equivalent to │
│ │ success. │
├───────┼──────────────────────────┤
│":" │ If the executable path │
│ │ is prefixed with ":", │
│ │ environment variable │
│ │ substitution (as │
│ │ described by the │
│ │ "Command Lines" section │
│ │ below) is not applied. │
├───────┼──────────────────────────┤
│"+" │ If the executable path │
│ │ is prefixed with "+" │
│ │ then the process is │
│ │ executed with full │
│ │ privileges. In this mode │
│ │ privilege restrictions │
│ │ configured with User=, │
│ │ Group=, │
│ │ CapabilityBoundingSet= │
│ │ or the various file │
│ │ system namespacing │
│ │ options (such as │
│ │ PrivateDevices=, │
│ │ PrivateTmp=) are not │
│ │ applied to the invoked │
│ │ command line (but still │
│ │ affect any other │
│ │ ExecStart=, ExecStop=, │
│ │ ... lines). │
├───────┼──────────────────────────┤
│"!" │ Similar to the "+" │
│ │ character discussed │
│ │ above this permits │
│ │ invoking command lines │
│ │ with elevated │
│ │ privileges. However, │
│ │ unlike "+" the "!" │
│ │ character exclusively │
│ │ alters the effect of │
│ │ User=, Group= and │
│ │ SupplementaryGroups=, │
│ │ i.e. only the stanzas │
│ │ that affect user and │
│ │ group credentials. Note │
│ │ that this setting may be │
│ │ combined with │
│ │ DynamicUser=, in which │
│ │ case a dynamic │
│ │ user/group pair is │
│ │ allocated before the │
│ │ command is invoked, but │
│ │ credential changing is │
│ │ left to the executed │
│ │ process itself. │
├───────┼──────────────────────────┤
│"!!" │ This prefix is very │
│ │ similar to "!", however │
│ │ it only has an effect on │
│ │ systems lacking support │
│ │ for ambient process │
│ │ capabilities, i.e. │
│ │ without support for │
│ │ AmbientCapabilities=. │
│ │ It's intended to be used │
│ │ for unit files that take │
│ │ benefit of ambient │
│ │ capabilities to run │
│ │ processes with minimal │
│ │ privileges wherever │
│ │ possible while remaining │
│ │ compatible with systems │
│ │ that lack ambient │
│ │ capabilities support. │
│ │ Note that when "!!" is │
│ │ used, and a system │
│ │ lacking ambient │
│ │ capability support is │
│ │ detected any configured │
│ │ SystemCallFilter= and │
│ │ CapabilityBoundingSet= │
│ │ stanzas are implicitly │
│ │ modified, in order to │
│ │ permit spawned processes │
│ │ to drop credentials and │
│ │ capabilities themselves, │
│ │ even if this is │
│ │ configured to not be │
│ │ allowed. Moreover, if │
│ │ this prefix is used and │
│ │ a system lacking ambient │
│ │ capability support is │
│ │ detected │
│ │ AmbientCapabilities= │
│ │ will be skipped and not │
│ │ be applied. On systems │
│ │ supporting ambient │
│ │ capabilities, "!!" has │
│ │ no effect and is │
│ │ redundant. │
└───────┴──────────────────────────┘
"@", "-", ":", and one of "+"/"!"/"!!" may be used together
and they can appear in any order. However, only one of "+",
"!", "!!" may be used at a time. Note that these prefixes
are also supported for the other command line settings, i.e.
ExecStartPre=, ExecStartPost=, ExecReload=, ExecStop= and
ExecStopPost=.
If more than one command is specified, the commands are
invoked sequentially in the order they appear in the unit
file. If one of the commands fails (and is not prefixed with
"-"), other lines are not executed, and the unit is
considered failed.
Unless Type=forking is set, the process started via this
command line will be considered the main process of the
daemon.
ExecStartPre=, ExecStartPost=
Additional commands that are executed before or after the
command in ExecStart=, respectively. Syntax is the same as
for ExecStart=, except that multiple command lines are
allowed and the commands are executed one after the other,
serially.
If any of those commands (not prefixed with "-") fail, the
rest are not executed and the unit is considered failed.
ExecStart= commands are only run after all ExecStartPre=
commands that were not prefixed with a "-" exit successfully.
ExecStartPost= commands are only run after the commands
specified in ExecStart= have been invoked successfully, as
determined by Type= (i.e. the process has been started for
Type=simple or Type=idle, the last ExecStart= process exited
successfully for Type=oneshot, the initial process exited
successfully for Type=forking, "READY=1" is sent for
Type=notify, or the BusName= has been taken for Type=dbus).
Note that ExecStartPre= may not be used to start long-running
processes. All processes forked off by processes invoked via
ExecStartPre= will be killed before the next service process
is run.
Note that if any of the commands specified in ExecStartPre=,
ExecStart=, or ExecStartPost= fail (and are not prefixed with
"-", see above) or time out before the service is fully up,
execution continues with commands specified in ExecStopPost=,
the commands in ExecStop= are skipped.
Note that the execution of ExecStartPost= is taken into
account for the purpose of Before=/After= ordering
constraints.
ExecCondition=
Optional commands that are executed before the command(s) in
ExecStartPre=. Syntax is the same as for ExecStart=, except
that multiple command lines are allowed and the commands are
executed one after the other, serially.
The behavior is like an ExecStartPre= and condition check
hybrid: when an ExecCondition= command exits with exit code 1
through 254 (inclusive), the remaining commands are skipped
and the unit is not marked as failed. However, if an
ExecCondition= command exits with 255 or abnormally (e.g.
timeout, killed by a signal, etc.), the unit will be
considered failed (and remaining commands will be skipped).
Exit code of 0 or those matching SuccessExitStatus= will
continue execution to the next command(s).
The same recommendations about not running long-running
processes in ExecStartPre= also applies to ExecCondition=.
ExecCondition= will also run the commands in ExecStopPost=,
as part of stopping the service, in the case of any non-zero
or abnormal exits, like the ones described above.
ExecReload=
Commands to execute to trigger a configuration reload in the
service. This argument takes multiple command lines,
following the same scheme as described for ExecStart= above.
Use of this setting is optional. Specifier and environment
variable substitution is supported here following the same
scheme as for ExecStart=.
One additional, special environment variable is set: if
known, $MAINPID is set to the main process of the daemon, and
may be used for command lines like the following:
ExecReload=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. For
example, dbus-broker(1) uses the following:
ExecReload=busctl call org.freedesktop.DBus \
/org/freedesktop/DBus org.freedesktop.DBus \
ReloadConfig
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= or RestartKillSignal= 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 sending some form of termination signal to it),
but does not wait for it to do so. Since the remaining
processes of the services are killed according to KillMode=
and KillSignal= or RestartKillSignal= as described above
immediately after the command exited, this may not result in
a clean stop. The specified command should hence be a
synchronous operation, not an asynchronous one.
Note that the commands specified in ExecStop= are only
executed when the service started successfully first. They
are not invoked if the service was never started at all, or
in case its start-up failed, for example because any of the
commands specified in ExecStart=, ExecStartPre= or
ExecStartPost= failed (and weren't prefixed with "-", see
above) or timed out. Use ExecStopPost= to invoke commands
when a service failed to start up correctly and is shut down
again. Also note that the stop operation is always performed
if the service started successfully, even if the processes in
the service terminated on their own or were killed. The stop
commands must be prepared to deal with that case. $MAINPID
will be unset if systemd knows that the main process exited
by the time the stop commands are called.
Service restart requests are implemented as stop operations
followed by start operations. This means that ExecStop= and
ExecStopPost= are executed during a service restart
operation.
It is recommended to use this setting for commands that
communicate with the service requesting clean termination.
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.
Note that the execution of ExecStopPost= is taken into
account for the purpose of Before=/After= ordering
constraints.
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. The precise action depends on the
TimeoutStartFailureMode= option. Takes a unit-less value in
seconds, or a time span value such as "5min 20s". Pass
"infinity" to disable the timeout logic. Defaults to
DefaultTimeoutStartSec= from the manager configuration file,
except when Type=oneshot is used, in which case the timeout
is disabled by default (see systemd-system.conf(5)).
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=...",
this may cause the start time to be extended beyond
TimeoutStartSec=. The first receipt of this message must
occur before TimeoutStartSec= is exceeded, and once the start
time has extended beyond TimeoutStartSec=, the service
manager will allow the service to continue to start, provided
the service repeats "EXTEND_TIMEOUT_USEC=..." within the
interval specified until the service startup status is
finished by "READY=1". (see sd_notify(3)).
TimeoutStopSec=
This option serves two purposes. First, it configures the
time to wait for each ExecStop= command. If any of them times
out, subsequent ExecStop= commands are skipped and the
service will be terminated by SIGTERM. If no ExecStop=
commands are specified, the service gets the SIGTERM
immediately. This default behavior can be changed by the
TimeoutStopFailureMode= option. Second, it configures the
time to wait for the service itself to stop. If it doesn't
terminate in the specified time, it will be forcibly
terminated by SIGKILL (see KillMode= in systemd.kill(5)).
Takes a unit-less value in seconds, or a time span value such
as "5min 20s". Pass "infinity" to disable the timeout logic.
Defaults to DefaultTimeoutStopSec= from the manager
configuration file (see systemd-system.conf(5)).
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=...",
this may cause the stop time to be extended beyond
TimeoutStopSec=. The first receipt of this message must occur
before TimeoutStopSec= is exceeded, and once the stop time
has extended beyond TimeoutStopSec=, the service manager will
allow the service to continue to stop, provided the service
repeats "EXTEND_TIMEOUT_USEC=..." within the interval
specified, or terminates itself (see sd_notify(3)).
TimeoutAbortSec=
This option configures the time to wait for the service to
terminate when it was aborted due to a watchdog timeout (see
WatchdogSec=). If the service has a short TimeoutStopSec=
this option can be used to give the system more time to write
a core dump of the service. Upon expiration the service will
be forcibly terminated by SIGKILL (see KillMode= in
systemd.kill(5)). The core file will be truncated in this
case. Use TimeoutAbortSec= to set a sensible timeout for the
core dumping per service that is large enough to write all
expected data while also being short enough to handle the
service failure in due time.
Takes a unit-less value in seconds, or a time span value such
as "5min 20s". Pass an empty value to skip the dedicated
watchdog abort timeout handling and fall back
TimeoutStopSec=. Pass "infinity" to disable the timeout
logic. Defaults to DefaultTimeoutAbortSec= from the manager
configuration file (see systemd-system.conf(5)).
If a service of Type=notify handles SIGABRT itself (instead
of relying on the kernel to write a core dump) it can send
"EXTEND_TIMEOUT_USEC=..." to extended the abort time beyond
TimeoutAbortSec=. The first receipt of this message must
occur before TimeoutAbortSec= is exceeded, and once the abort
time has extended beyond TimeoutAbortSec=, the service
manager will allow the service to continue to abort, provided
the service repeats "EXTEND_TIMEOUT_USEC=..." within the
interval specified, or terminates itself (see sd_notify(3)).
TimeoutSec=
A shorthand for configuring both TimeoutStartSec= and
TimeoutStopSec= to the specified value.
TimeoutStartFailureMode=, TimeoutStopFailureMode=
These options configure the action that is taken in case a
daemon service does not signal start-up within its configured
TimeoutStartSec=, respectively if it does not stop within
TimeoutStopSec=. Takes one of terminate, abort and kill. Both
options default to terminate.
If terminate is set the service will be gracefully terminated
by sending the signal specified in KillSignal= (defaults to
SIGTERM, see systemd.kill(5)). If the service does not
terminate the FinalKillSignal= is sent after TimeoutStopSec=.
If abort is set, WatchdogSignal= is sent instead and
TimeoutAbortSec= applies before sending FinalKillSignal=.
This setting may be used to analyze services that fail to
start-up or shut-down intermittently. By using kill the
service is immediately terminated by sending FinalKillSignal=
without any further timeout. This setting can be used to
expedite the shutdown of failing services.
RuntimeMaxSec=
Configures a maximum time for the service to run. If this is
used and the service has been active for longer than the
specified time it is terminated and put into a failure state.
Note that this setting does not have any effect on
Type=oneshot services, as they terminate immediately after
activation completed. Pass "infinity" (the default) to
configure no runtime limit.
If a service of Type=notify sends "EXTEND_TIMEOUT_USEC=...",
this may cause the runtime to be extended beyond
RuntimeMaxSec=. The first receipt of this message must occur
before RuntimeMaxSec= is exceeded, and once the runtime has
extended beyond RuntimeMaxSec=, the service manager will
allow the service to continue to run, provided the service
repeats "EXTEND_TIMEOUT_USEC=..." within the interval
specified until the service shutdown is achieved by
"STOPPING=1" (or termination). (see sd_notify(3)).
WatchdogSec=
Configures the watchdog timeout for a service. The watchdog
is activated when the start-up is completed. The service must
call sd_notify(3) regularly with "WATCHDOG=1" (i.e. the
"keep-alive ping"). If the time between two such calls is
larger than the configured time, then the service is placed
in a failed state and it will be terminated with SIGABRT (or
the signal specified by WatchdogSignal=). By setting Restart=
to on-failure, on-watchdog, on-abnormal or always, the
service will be automatically restarted. The time configured
here will be passed to the executed service process in the
WATCHDOG_USEC= environment variable. This allows daemons to
automatically enable the keep-alive pinging logic if watchdog
support is enabled for the service. If this option is used,
NotifyAccess= (see below) should be set to open access to the
notification socket provided by systemd. If NotifyAccess= is
not set, it will be implicitly set to main. Defaults to 0,
which disables this feature. The service can check whether
the service manager expects watchdog keep-alive
notifications. See sd_watchdog_enabled(3) for details.
sd_event_set_watchdog(3) may be used to enable automatic
watchdog notification support.
Restart=
Configures whether the service shall be restarted when the
service process exits, is killed, or a timeout is reached.
The service process may be the main service process, but it
may also be one of the processes specified with
ExecStartPre=, ExecStartPost=, ExecStop=, ExecStopPost=, or
ExecReload=. When the death of the process is a result of
systemd operation (e.g. service stop or restart), the service
will not be restarted. Timeouts include missing the watchdog
"keep-alive ping" deadline and a service start, reload, and
stop operation timeouts.
Takes one of no, on-success, on-failure, on-abnormal,
on-watchdog, on-abort, or always. If set to no (the default),
the service will not be restarted. If set to on-success, it
will be restarted only when the service process exits
cleanly. In this context, a clean exit means any of the
following:
• exit code of 0;
• for types other than Type=oneshot, one of the signals
SIGHUP, SIGINT, SIGTERM, or SIGPIPE;
• exit statuses and signals specified in
SuccessExitStatus=.
If set to on-failure, the service will be restarted when the
process exits with a non-zero exit code, is terminated by a
signal (including on core dump, but excluding the
aforementioned four signals), when an operation (such as
service reload) times out, and when the configured watchdog
timeout is triggered. If set to on-abnormal, the service will
be restarted when the process is terminated by a signal
(including on core dump, excluding the aforementioned four
signals), when an operation times out, or when the watchdog
timeout is triggered. If set to on-abort, the service will be
restarted only if the service process exits due to an
uncaught signal not specified as a clean exit status. If set
to on-watchdog, the service will be restarted only if the
watchdog timeout for the service expires. If set to always,
the service will be restarted regardless of whether it exited
cleanly or not, got terminated abnormally by a signal, or hit
a timeout.
Table 2. Exit causes and the effect of the Restart= settings
┌──────────────┬────┬────────┬────────────┬────────────┬─────────────┬──────────┬─────────────┐
│Restart │ no │ always │ on-success │ on-failure │ on-abnormal │ on-abort │ on-watchdog │
│settings/Exit │ │ │ │ │ │ │ │
│causes │ │ │ │ │ │ │ │
├──────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Clean exit │ │ X │ X │ │ │ │ │
│code or │ │ │ │ │ │ │ │
│signal │ │ │ │ │ │ │ │
├──────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Unclean exit │ │ X │ │ X │ │ │ │
│code │ │ │ │ │ │ │ │
├──────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Unclean │ │ X │ │ X │ X │ X │ │
│signal │ │ │ │ │ │ │ │
├──────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Timeout │ │ X │ │ X │ X │ │ │
├──────────────┼────┼────────┼────────────┼────────────┼─────────────┼──────────┼─────────────┤
│Watchdog │ │ X │ │ X │ X │ │ X │
└──────────────┴────┴────────┴────────────┴────────────┴─────────────┴──────────┴─────────────┘
As exceptions to the setting above, the service will not be
restarted if the exit code or signal is specified in
RestartPreventExitStatus= (see below) or the service is
stopped with systemctl stop or an equivalent operation. Also,
the services will always be restarted if the exit code or
signal is specified in RestartForceExitStatus= (see below).
Note that service restart is subject to unit start rate
limiting configured with StartLimitIntervalSec= and
StartLimitBurst=, see systemd.unit(5) for details. A
restarted service enters the failed state only after the
start limits are reached.
Setting this to on-failure is the recommended choice for
long-running services, in order to increase reliability by
attempting automatic recovery from errors. For services that
shall be able to terminate on their own choice (and avoid
immediate restarting), on-abnormal is an alternative choice.
SuccessExitStatus=
Takes a list of exit status definitions that, when returned
by the main service process, will be considered successful
termination, in addition to the normal successful exit status
0 and, except for Type=oneshot, the signals SIGHUP, SIGINT,
SIGTERM, and SIGPIPE. Exit status definitions can be numeric
termination statuses, termination status names, or
termination signal names, separated by spaces. See the
Process Exit Codes section in systemd.exec(5) for a list of
termination status names (for this setting only the part
without the "EXIT_" or "EX_" prefix should be used). See
signal(7) for a list of signal names.
Note that this setting does not change the mapping between
numeric exit statuses and their names, i.e. regardless how
this setting is used 0 will still be mapped to "SUCCESS" (and
thus typically shown as "0/SUCCESS" in tool outputs) and 1 to
"FAILURE" (and thus typically shown as "1/FAILURE"), and so
on. It only controls what happens as effect of these exit
statuses, and how it propagates to the state of the service
as a whole.
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.
Example 1. A service with the SuccessExitStatus= setting
SuccessExitStatus=TEMPFAIL 250 SIGKILL
Exit status 75 (TEMPFAIL), 250, and the termination signal
SIGKILL are considered clean service terminations.
Note: systemd-analyze exit-status may be used to list exit
statuses and translate between numerical status values and
names.
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.
Note that this setting has no effect on processes configured
via ExecStartPre=, ExecStartPost=, ExecStop=, ExecStopPost=
or ExecReload=, but only on the main service process, i.e.
either the one invoked by ExecStart= or (depending on Type=,
PIDFile=, ...) the otherwise configured main process.
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=.
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.
Hence, to eliminate all race conditions involving lookup of
the client's unit and attribution of notifications to units
correctly, sd_notify_barrier() may be used. This call acts as
a synchronization point and ensures all notifications sent
before this call have been picked up by the service manager
when it returns successfully. Use of sd_notify_barrier() is
needed for clients which are not invoked by the service
manager, otherwise this synchronization mechanism is
unnecessary for attribution of notifications to the unit.
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. Note that once set, clearing the
list of sockets again (for example, by assigning the empty
string to this option) is not supported.
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 (see sd_listen_fds(3) for
details about the precise protocol used and the order in
which the file descriptors are passed). Any file descriptors
passed to the service manager are automatically closed when
POLLHUP or POLLERR is seen on them, or when the service is
fully stopped and no job is queued or being executed for it.
If this option is used, NotifyAccess= (see above) should be
set to open access to the notification socket provided by
systemd. If NotifyAccess= is not set, it will be implicitly
set to main.
USBFunctionDescriptors=
Configure the location of a file containing USB FunctionFS
USBFunctionStrings=
Configure the location of a file containing USB FunctionFS
strings. Behavior is similar to USBFunctionDescriptors=
above.
OOMPolicy=
Configure the Out-Of-Memory (OOM) killer policy. On Linux,
when memory becomes scarce the kernel might decide to kill a
running process in order to free up memory and reduce memory
pressure. This setting takes one of continue, stop or kill.
If set to continue and a process of the service is killed by
the kernel's OOM killer this is logged but the service
continues running. If set to stop the event is logged but the
service is terminated cleanly by the service manager. If set
to kill and one of the service's processes is killed by the
OOM killer the kernel is instructed to kill all remaining
processes of the service, too. Defaults to the setting
DefaultOOMPolicy= in systemd-system.conf(5) is set to, except
for services where Delegate= is turned on, where it defaults
to continue.
Use the OOMScoreAdjust= setting to configure whether
processes of the unit shall be considered preferred or less
preferred candidates for process termination by the Linux OOM
killer logic. See systemd.exec(5) for details.
Check systemd.exec(5) and systemd.kill(5) for more settings.
