finit/doc/service.md

Finit Services

Starting & Monitoring

Finit can start and monitor the following types of daemons:

• Forks to background, creates a PID file
• Runs in foreground:
  • creates a PID file
  • does not create a PID file -- Finit can create it for you (optional)

Finit can not start and monitor a daemon that:

• Forks to background and does not create a PID file

	Forking	Creates PID File	Finit creates PID File
✔	Yes	Yes	No
✔	No	Yes	No
✔	No	No	Yes, optionally
✘	Yes	No	No

Note: PID files is one mechanism used to assert conditions to synchronize the start and stop of other, dependent, services.

Forks to Background w/ PID File

service pid:!/run/serv.pid serv       -- Forking service

Runs in Foreground w/ PID File

service                    serv -n -p -- Foreground service w/ PID file

Runs in Foreground w/o PID File

Same as previous, but we tell Finit to create the PID file, because we need it to synchronize start/stop of a dependent service.

service pid:/run/serv.pid  serv -n    -- Foreground service w/o PID file

Runs in Foreground w/ Custom PID File

service pid:/run/servy.pid serv -n -p -P /run/servy.pid -- Foreground service w/ custom PID file

State Machine

A service is bound to a state machine that is in one of six (6) states. For runs and tasks there is an additional end state called DONE, not shown in the diagram for brevity. Services start in the HALTED state.

The current state depends on the two following conditions:

• E: Service enabled. In order for E to be satisfied, the service must be allowed to run in the current runlevel and not be stopped.

  A service may be stopped, or blocked, for several reasons:

  • The user has manually stopped the service using initctl stop NAME
  • The program exits immediately. I.e. keeps crashing (make sure to use the 'run this service in the foreground' command line option)
  • The binary is missing in the filesystem

• C: Service conditions are satisfied:

  • on (+): The condition is asserted.
  • off (-): The condition is deasserted.
  • flux (~): The condition state is unknown.

For a detailed description of conditions, and how to debug them, see the Finit Conditions document.