Confusing PDO-only problem : Can't connect through socket/Access denied/Can't connect to server (shared host)

Question

So the problem changed from what it was, i\'ll leave the original question below to prevent bad reviews on answers like I had after someone editing his question I answered :

Answer 1

Using the connection which works, run the query:

show variables like 'socket';

(this behaves just like a select statement)...and you'll get the path of the running socket.

Then check the file permissions.