Linux Standalone player can not find GPU

I am trying to run a Unity game through the command line on a Ubuntu 14.04 server.
I build the game as headless as I’ve read that it is used to run a game without displaying anything, but still being able to render texture and such. See What does the headless build option do? - Questions & Answers - Unity Discussions

When inspecting the Player.log file, it says “Forcing GfxDevice: Null”, but I have two dedicated GPUs installed (2x Titan X). How can i get the game to detect one or both of these GPUs?

I use the game to train a neural network using the pixel data as pixels, which is why I don’t need the see anything, but I do need to be able to project the camera onto a render texture to grab the pixel data.

bump.

Did you find the answer?
I am struggling with the exact same thing.