code: func isExitSignal(s os.Signal) (bool, bool) {
  	switch s {
  	case syscall.SIGTERM,
  		syscall.SIGHUP,
  		syscall.SIGINT,
  		syscall.SIGQUIT:
  		return true, true
  	default:
  		return false, false
  	}
  }
docs: // isExitSignal returns a flag indicating whether a signal SIGHUP,
  // SIGINT, SIGTERM, or SIGQUIT. The second return value is whether it is a
  // graceful exit. This flag is true for SIGTERM, SIGHUP, SIGINT, and SIGQUIT.