GetPidLocation finds the location to store our pid file and fallback to /var/run if none found.

GetRemoteProcPid gets the pid as it appears in the pid file (maybe not ours).

KillParent sends a signal to make the parent exit gracefully with SIGQUIT.

Recover from a seamless binary upgrade and use an already existing listener to take over the connections.

Relaunch launches {self} as a child process passing listener details to provide a seamless binary upgrade.

RemovePidFile removes the current pid file.

WritePidFile writes the current pid file to disk.

ErrInvalidfd is returned when the given file descriptor is invalid.