Solving MySQL Error "The server quit without updating PID file (/usr/local/var/mysql/XXXX.pid)"

Today I ran out through this problem when trying to start mysql service. It took an hour to solve, and the problem wasn't really with MySQL.
If you look at the log it creates inside the mysql data folder you'll see several of permission denied warning, and that's really it.

Simply change the permission of every folder inside mysql recursively to, say, 777.
* So, run terminal.app;
* Go the mysql folder;
* Type "sudo chmod -R 777 ./*" (don't you dare to type the quotes);

Done. Try to start the server again, and it should work like a charm.

I'm using OSX 10.9, but I think it works for every linux/unix systems.
See u.