I'm not a computer guy, so I thought I would pass this along as a reference post for other noob's too.
I built a 3 GPU rig last month using Ubuntu 16.04 server as the OS. I also installed LXDE, which is a light GUI to make some tasks a little less formidable. I was using RX470 cards and AMDGPU-Pro and Genoil's miner.
I could not get the rig to run properly for more than two days, sometimes 12 hours, before it stopped mining. The CPU, PSU and GPU fans would all run, but the cards where stone cold. I spent considerable time testing risers, GPU, re-installing and compiling the software to no avail.
I thought in the end I might be having a CPU issue, so I used the "TOP" command to display CPU information. I discovered that my memory was slowly being consumed, SWAP space was also being consumed (shouldn't be). The biggest memory user was the GUI (LXDE).
I was manually starting my miner, through either Xterm or root term in LXDE. I came to the conclusion that when starting operations through the GUI, the software must be temporarily storing all the "hashing" information. Consuming all the HD memory over a period of hours or days. Anyway, I changed the run level (no GUI) and started my miner operation through SSH and screen. This was the solution and the rig has been running with no problems. Memory usage is where it should be.
I'm not sure if this is common knowledge. So if your new to mining and using Ubuntu, don't start your miner op's through a GUI terminal window. Use SSH and screen