code: func GetFSGroupLinux(pathname string) (int64, error) {
  	info, err := os.Stat(pathname)
  	if err != nil {
  		return 0, err
  	}
  	return int64(info.Sys().(*syscall.Stat_t).Gid), nil
  }
docs: // GetFSGroupLinux is shared between Linux and NsEnterMounter
  // pathname must already be evaluated for symlinks