Empty pid file bug

[mjk-old]

When the pid file is empty pid and read_pid_file methods return 0, because en empty string is converted to zero by to_i. And since process with pid 0 always exists in the system the daemon can't be started or restarted. That also happens for other non-integer content of the pid file

Empty pid file can occur when there's no space left on device. Additionally, number of bytes could be checked to distinguish this case (and maybe delete the pid file?).