openrc/supervise-daemon-guide.md

Using supervise-daemon

Beginning with OpenRC-0.21 we have our own daemon supervisor, supervise-daemon., which can start a daemon and restart it if it terminates unexpectedly.

The following is a brief guide on using this capability.

• Use Default start, stop and status functions If you write your own start, stop and status functions in your service script, none of this will work. You must allow OpenRC to use the default functions.

• Daemons must not fork Any deamon that you would like to have monitored by supervise-daemon must not fork. Instead, it must stay in the foreground. If the daemon forks, the supervisor will be unable to monitor it.

  If the daemon can be configured to not fork, this should be done in the daemon's configuration file, or by adding a command line option that instructs it not to fork to the command_args_foreground variable shown below.

Variable Settings

The most important setting is the supervisor variable. At the top of your service script, you should set this variable as follows:

supervisor=supervise-daemon

Several other variables affect the way services behave under supervise-daemon. They are documented on the openrc-run man page, but I will list them here for convenience:

pidfile=/pid/of/supervisor.pid

If you are using start-stop-daemon to monitor your scripts, the pidfile is the path to the pidfile the daemon creates. If, on the other hand, you are using supervise-daemon, this is the path to the pidfile the supervisor creates.

command_args_foreground="arguments"

This should be used if the daemon you want to monitor forks and goes to the background by default. This should be set to the command line option that instructs the daemon to stay in the foreground.

respawn_delay

This is the number of seconds to delay before attempting to respawn a supervised process after it dies unexpectedly. The default is to respawn immediately.

respawn_max=x

This is the maximum number of times to respawn a supervised process during the given respawn period. The default is unlimited.

respawn_period=seconds

This works in conjunction with respawn_max and respawn_delay above to decide if a process should not be respawned for some reason.

For example, if respawn_period is 60, respawn_max is 2 and respawn_delay is 3 and a process dies more than 4 times, the process will not be respawned and the supervisor will terminate.