Message: mkdir(): Permission denied

P.S.

You seem surprised by the fact that when YOU run some commands (chmod) via the command line, it works, as opposed to when you run the commands via PHP exec(), which dont work.

You realize the commands you run via shell are being ran as a totally different user, right?

Im just saying that because your "It worked!" statement seemed like you were surprised, but you shouldnt be.

Yes it seems like that, but in this case which is the correct one ??? What user and what permissions should have my uploads, my posts and my thumbnails folders to work properly ???