# File lib/headless/cli_util.rb, line 17
    def self.read_pid(pid_filename)
      pid = (File.read(pid_filename) rescue "").strip.to_i
      pid = nil if pid.zero?

      if pid
        begin
          Process.kill(0, pid)
          pid
        rescue Errno::ESRCH
          nil
        end
      else
        nil
      end
    end