code: func ReadOrMakeHostUUID(dataDir string) (string, error) {
  	id, err := ReadHostUUID(dataDir)
  	if err == nil {
  		return id, nil
  	}
  	if !trace.IsNotFound(err) {
  		return "", trace.Wrap(err)
  	}
  	id = uuid.New()
  	if err = WriteHostUUID(dataDir, id); err != nil {
  		return "", trace.Wrap(err)
  	}
  	return id, nil
  }
docs: // ReadOrMakeHostUUID looks for a hostid file in the data dir. If present,
  // returns the UUID from it, otherwise generates one