MySQL trouble shooting -- Can't start server : Bind on unix socket: Permission denied

如果遇到 MySQL 無法啟動, 怎麼設定也找不出問題時, 有可能就是 Apparmor 在背後搞鬼, 看看這兩篇

http://askubuntu.com/questions/234668/cant-start-mysql-server-if-the-sock-file-is-changed-in-etc-mysql-my-cnf
http://serverfault.com/questions/362595/mysql-bind-on-unix-socket-permission-denied