Drivers: Restrict Nvidia GPU access to certain users

I have a box with multiple GPUs running ubuntu 16.04. The box will have several users running different experiments and I should restrict access to GPUs so that only certain users have access to certain GPUs. As suggested in Restricting user access to GPUs, I tried to change the group and the permission of / dev / nvidia * However, when a new session is opened, the files return to their original configuration. I have also created /etc/modprode.d/nvidia.conf containing nvidia options NVreg_DeviceFileGID = 120 But this does not work either. I'm placing nvidia.conf in the wrong place or is the syntax wrong? Any other suggestions would be much appreciated!