How to update only miner T_Rex?
Do it manually by replacing the old T_Rex binary. Otherwise, if you run nvOC upgrade and this installs some other miner you don't like or do not work well on your rig, you can specifically select the older version from 1bash replacing default "recommended" with the exact miner version number.
There is no errors at all.
I have this report in approx 10sec.
What version of ubuntu 16 image are you running?