code: func LookupGID(gid int) (user.Group, error) {
  	// first try a local system files lookup using existing capabilities
  	group, err := user.LookupGid(gid)
  	if err == nil {
  		return group, nil
  	}
  	// local files lookup failed; attempt to call `getent` to query configured group dbs
  	return getentGroup(fmt.Sprintf("%s %d", "group", gid))
  }
docs: // LookupGID uses traditional local system files lookup (from libcontainer/user) on a group ID,
  // followed by a call to `getent` for supporting host configured non-files passwd and group dbs