Overclocking Nvidia on Ubuntu

Question

I'm trying to overclock a multi-GPU system running under Ubuntu but somehow it doesn't work.

I have a 10 GPU system based on Nvidia GTX 1060.

Here is what I have done so far:

1. Fresh Ubuntu install 16.04

2. Install Nvidia drivers like this:

   sudo add-apt-repository ppa:graphics-drivers/ppa 
   sudo apt-get update 
   ubuntu-drivers devices  
   sudo apt-get install nvidia-381
   

3. Install CUDA drivers by downloading .deb file from Nvidia (https://developer.nvidia.com/cuda-downloads)

   sudo dpkg -i cuda-repo-ubuntu1604_8.0.61-1_amd64.deb
   sudo apt-get update
   sudo apt-get install cuda
   

4. enable overclock with coolbits

   sudo nvidia-xconfig -a --cool-bits=28 --allow-empty-initial-configuration
   

So far, everything is ok, I see that the xorg.conf has been updated properly but when I reboot, my xorg.conf goes back to a previous version without the overclocking.

I have seen some people experiencing the same issue, some solutions here: gpu-manager overwrites xorg.conf I tried this but ended up with a login loop and being obliged to purge all Nvidia drivers.

When I tried with only one GPU I could overclock the card without any issue but since I added other cards, it doesn't work anymore. The problem seems to come from xorg.conf where my configuration is systematically overwritten.

Any idea of how I could solve this?