command ~lock_file ~name main creates a command group for starting,
stopping, restarting, and checking the status of a daemon (the code
for which lives in the argument main). This family of commands
uses a lock_file to ensure that two instances of the daemon don't
run concurrently on the same machine. The name parameter is used
to name the daemon in the command help and various error messages.
lock_file should be on the local file system (for example in /var/tmp)
since file locking doesn't work over NFS.