https://blog.toright.com/posts/4411/%e5%b0%8f%e7%8c%b4%e5%ad%90%e4%b9%9f%e6%9c%83%e7%9a%84-ubuntu-desktop-14-04-%e5%ae%89%e8%a3%9d%e6%95%99%e5%ad%b8