def stop(&block)
      block.call('stop') unless block.nil?
      pid = read_pid
      fail 'No valid PID file.' unless pid && pid > 0
      Process.kill('TERM', pid)
      delete_pid
      puts 'Process terminated.'
    end
def stop(&block)
      block.call('stop') unless block.nil?
      pid = read_pid
      fail 'No valid PID file.' unless pid && pid > 0
      Process.kill('TERM', pid)
      delete_pid
      puts 'Process terminated.'
    end
Stop the process.
 @param [Block] will execute prior to shutdown, if given.