Problem with Ubuntu 16.04 and RX480 ref 8Gb

Normally i mine on windows but i wanted to try ubuntu.
I got it run more or less.

I installed the amd drivers and managed to get the claymore miner running.

But the miner shows only 7xxxMB ram and only 14 compute units.
Whats wrong?

Can someone please explain me step by step what to do?
How can i set the Fan rpm?
Does the config file work like on windows?

Thanks a lot