http://smarden.sunsite.dk/runit/runsv.8.html

> Two arguments are given to ./finish. The first one is ./run’s exit code, or -1
> if ./run didn’t exit normally. The second one is the least significant byte of
> the exit status as determined by waitpid(2); for instance it is 0 if ./run
> exited normally, and the signal number if ./run was terminated by a signal. If
> runsv cannot start ./run for some reason, the exit code is 111 and the
> status is 0.