systemd.service

If set to simple (the default value if BusName= is not specified) it is expected that the process configured with ExecStart= is the main process of the service. In this mode, if the process offers functionality to other processes on the system its communication channels should be installed before the daemon is started up (e.g. sockets set up by systemd, via socket activation), as systemd will immediately proceed starting follow-up units.

If set to forking it is expected that the process configured with ExecStart= will call fork() as part of its start-up. The parent process is expected to exit when start-up is complete and all communication channels set up. The child continues to run as the main daemon process. This is the behavior of traditional UNIX daemons. If this setting is used, it is recommended to also use the PIDFile= option, so that systemd can identify the main process of the daemon. systemd will proceed starting follow-up units as soon as the parent process exits.

Behavior of oneshot is similar to simple, however it is expected that the process has to exit before systemd starts follow-up units. RemainAfterExit= is particularly useful for this type of service.

Behavior of dbus is similar to simple, however it is expected that the daemon acquires a name on the D-Bus bus, as configured by BusName=. systemd will proceed starting follow-up units after the D-Bus bus name has been acquired. Service units with this option configured implicitly gain dependencies on the dbus.socket unit. This type is the default if BusName= is specified.

Behavior of notify is similar to simple, however it is expected that the daemon sends a notification message via sd_notify(3) or an equivalent call when it finished starting up. systemd will proceed starting follow-up units after this notification message has been sent. If this option is used NotifyAccess= (see below) should be set to open access to the notification socket provided by systemd. If NotifyAccess= is not set, it will be implicitly set to main.

Behavior of idle is very similar to simple, however actual execution of the service binary is delayed until all jobs are dispatched. This may be used to avoid interleaving of output of shell services with the status output on the console.

When Type is not oneshot, only one command may be given. When Type=oneshot is used, more than one command may be specified. Multiple command lines may be concatenated in a single directive, by separating them with semicolons (these semicolons must be passed as separate words). Alternatively, this directive may be specified more than once with the same effect. However, the latter syntax is not recommended for compatibility with parsers suitable for XDG .desktop files. Lone semicolons may be escaped as '\;'. If the empty string is assigned to this option the list of commands to start is reset, prior assignments of this option will have no effect.

If more than one command is specified, the commands are invoked one by one sequentially in the order they appear in the unit file. If one of the commands fails (and is not prefixed with '-'), other lines are not executed and the unit is considered failed.

Unless Type=forking is set, the process started via this command line will be considered the main process of the daemon.

The command line accepts '%' specifiers as described in systemd.unit(5). Note that the first argument of the command line (i.e. the program to execute) may not include specifiers.

Basic environment variable substitution is supported. Use ${FOO} as part of a word, or as a word of its own on the command line, in which case it will be replaced by the value of the environment variable including all whitespace it contains, resulting in a single argument. Use $FOO as a separate word on the command line, in which case it will be replaced by the value of the environment variable split up at whitespace, resulting in zero or more arguments. Note that the first argument (i.e. the program to execute) may not be a variable, since it must be a literal and absolute path name.

Optionally, if the absolute file name is prefixed with '@', the second token will be passed as argv[0] to the executed process, followed by the further arguments specified. If the absolute file name is prefixed with '-' an exit code of the command normally considered a failure (i.e. non-zero exit status or abnormal exit due to signal) is ignored and considered success. If both '-' and '@' are used they can appear in either order.

Note that this setting does not directly support shell command lines. If shell command lines are to be used they need to be passed explicitly to a shell implementation of some kind. Example:

ExecStart=/bin/sh -c 'dmesg | tac'
                                

For services run by a user instance of systemd the special environment variable $MANAGERPID is set to the PID of the systemd instance.

If any of those commands (not prefixed with '-') fail, the rest are not executed and the unit is considered failed.

One additional special environment variables is set: if known $MAINPID is set to the main process of the daemon, and may be used for command lines like the following:

/bin/kill -HUP $MAINPID

Takes one of no, on-success, on-failure, on-abort, or always. If set to no (the default) the service will not be restarted. If set to on-success it will be restarted only when the service process exits cleanly. In this context, a clean exit means an exit code of 0, or one of the signals SIGHUP, SIGINT, SIGTERM, or SIGPIPE, and additionally, exit statuses and signals specified in SuccessExitStatus=. If set to on-failure the service will be restarted when the process exits with an nonzero exit code, is terminated by a signal (including on core dump), when an operation (such as service reload) times out, and when the configured watchdog timeout is triggered. If set to on-abort the service will be restarted only if the service process exits due to an uncaught signal not specified as a clean exit status. If set to always the service will be restarted regardless whether it exited cleanly or not, got terminated abnormally by a signal or hit a timeout.

In addition to the above settings, the service will not be restarted if the exit code or signal is specified in RestartPreventExitStatus= (see below).

Note that the same socket may be passed to multiple processes at the same time. Also note that a different service may be activated on incoming traffic than inherits the sockets. Or in other words: the Service= setting of .socket units doesn't have to match the inverse of the Sockets= setting of the .service it refers to.

This option may appear more than once, in which case the list of socket units is merged. If the empty string is assigned to this option the list of sockets is reset, all prior uses of this setting will have no effect.