ubuntu 把一个磁盘下的东西移动到另一个磁盘的一个 trick (.cache)
https://askubuntu.com/questions/87314/how-to-move-the-user-cache-directory-cache-out-of-the-home-directory-to-an
https://askubuntu.com/questions/87314/how-to-move-the-user-cache-directory-cache-out-of-the-home-directory-to-an