Mysqld can`t start after I changed the socket path here is the log

131229 14:55:27 [ERROR] Can't start server : Bind on unix socket: Permission denied
131229 14:55:27 [ERROR] Do you already have another mysqld server running on socket: /tmp/mysql.sock ?


and what i had down is this in my.cnf:

[mysqld]
socket =/tmp/mysql.sock


what to put the sock file in here and tmp

drwxrwxrwt.  15 root root  4096 Dec 29 14:55 tmp


But I can start it anymore, if I remove that /tmp/mysql.sock. every think is ok.
why?
why tmp got a 777 permission but it still got this error?
thinks in advance.
When everything you can think of to check seems right, you have to think of the things you can't think of. :)

Like possibly "apparmor."

https://askubuntu.com/questions/234668/cant-start-mysql-server-if-the-sock-file-is-changed-in-etc-mysql-my-cnf

https://wiki.ubuntu.com/AppArmor

http://en.wikipedia.org/wiki/AppArmor