I'm using Pop!_OS 17.10 (based on Ubuntu 17.10) on a Dell XPS 15 9560 and Blender 2.79b. CUDA is installed, the Nvidia GPU (GeForce GTX 1050) activated and Blender is recognising both:
But when I hit render, it's rendering on the CPU:
This is my second Pop!_OS installation because I messed up the previous one. But before, Blender was rendering on the GPU as expected. Am I missing something here? How can I make this work again?