code: func AddSystemUser(name, homeDir string, gid int) (uid int, err error) {
  	s := NewShadow(name)
  	if err = s.Add(nil); err != nil {
  		return
  	}
  
  	return NewSystemUser(name, homeDir, gid).Add()
  }
docs: // AddSystemUser adds a system user to both user and shadow files.