code: func LookupUser(username string) (user.User, error) {
  	// first try a local system files lookup using existing capabilities
  	usr, err := user.LookupUser(username)
  	if err == nil {
  		return usr, nil
  	}
  	// local files lookup failed; attempt to call `getent` to query configured passwd dbs
  	usr, err = getentUser(fmt.Sprintf("%s %s", "passwd", username))
  	if err != nil {
  		return user.User{}, err
  	}
  	return usr, nil
  }
docs: // LookupUser uses traditional local system files lookup (from libcontainer/user) on a username,
  // followed by a call to `getent` for supporting host configured non-files passwd and group dbs