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 m[blue]Incompatibilities with SysVm[][1] document.
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=
If set to simple (the default value if neither Type= nor BusName= 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.
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=
GuessMainPID=
PIDFile=
BusName=
ExecStart=
When Type is not oneshot, only one command may be given. When Type=oneshot is used, more than one command may be specified. Multiple command lines may be concatenated in a single directive by separating them with semicolons (these semicolons must be passed as separate words). Alternatively, this directive may be specified more than once with the same effect. 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.
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:
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".
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".
ExecStartPre=, ExecStartPost=
If any of those commands (not prefixed with "-") fail, the rest are not executed and the unit is considered failed.
ExecReload=
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=
ExecStopPost=
RestartSec=
TimeoutStartSec=
TimeoutStopSec=
TimeoutSec=
WatchdogSec=
Restart=
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
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
|
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=
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 m[blue]Proper handling of SIGINT/SIGQUIT --- How to be a proper programm[][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=
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=
PermissionsStartOnly=
RootDirectoryStartOnly=
NonBlocking=
NotifyAccess=
Sockets=
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=
StartLimitAction=
RebootArgument=
FailureAction=
Check systemd.exec(5) and systemd.kill(5) for more settings.
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=
systemd(1), systemctl(1), systemd.unit(5), systemd.exec(5), systemd.resource-control(5), systemd.kill(5), systemd.directives(7)