code: func supportsAufs() error {
  	// We can try to modprobe aufs first before looking at
  	// proc/filesystems for when aufs is supported
  	exec.Command("modprobe", "aufs").Run()
  
  	if rsystem.RunningInUserNS() {
  		return ErrAufsNested
  	}
  
  	f, err := os.Open("/proc/filesystems")
  	if err != nil {
  		return err
  	}
  	defer f.Close()
  
  	s := bufio.NewScanner(f)
  	for s.Scan() {
  		if strings.Contains(s.Text(), "aufs") {
  			return nil
  		}
  	}
  	return ErrAufsNotSupported
  }
docs: // Return a nil error if the kernel supports aufs
  // We cannot modprobe because inside dind modprobe fails
  // to run