Service supervision
Once we have created service directories with run scripts under /etc/sv and ensured that BusyBox init starts runsvdir, BusyBox runit handles all the rest. That includes starting, stopping, monitoring, and restarting all the services under its control. The runsvdir utility starts a runsv process for each service directory and restarts a runsv process if it terminates. Because run scripts run their respective daemons in the foreground, runsv expects run to block so that when run exits, runsv will restart it automatically.
Service auto-restart is desirable during system startup because run scripts can crash. This is especially true under BusyBox runit where services start virtually simultaneously instead of one after the other. For instance, a service may fail to start when a dependent service or essential system resource (such as a GPIO or device driver) is not yet available. In the next section, I will show you how to express dependencies between services so that...
