From BlenderWiki

Solving GPU issues with Cycles

This is more like a placeholder page to write and refine instructions before they go into the official manual.

Unknown CUDA error -999

On quite recent Linux distros it's possible that Cycles wouldn't be able to use CUDA even tho all drivers and toolkits are installed.

Symptom of this problem is that there's an unknown error with cod -999 is printed into the console when doing cuInit().

Reasons why it happens is because NVidia changed the memory model in their drivers introducing so called unified memory model. It requires having special device file which isn't being prepared by the kernel in certain distros.

In order to solve this it's possible to create a special udev rule which will take care of creating such a device. For this simple create new udev rule, say /etc/udev/rules.d/90-nvidia_uvm.rules and put the following line into that file:

 KERNEL=="nvidia_uvm", RUN+="/bin/bash -c '/bin/mknod -m 664 /dev/nvidia-uvm c $(grep nvidia-uvm /proc/devices | cut -d \  -f 1) 0; /bin/chgrp video /dev/nvidia-uvm'"

After reboot the file should exist and Cycles should totally be able to use CUDA.