Mysqld can`t start after I changed the socket path
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