Gathering an exact percentage of sales for Linux turned out to be a bit complicated. Purchases made in our store gets all three platforms, which is the only place to get the Linux version. The total amount of sold units in our own store is about 5000. Since we can connect some of these sales with steam activations and similar, we can make a conservative estimate of 2500 Windows users, leaving 2500 left for Mac and Linux. And since this this is the only store for Linux users, we assume 70% of these are Linux. This means 1750 sold Linux units, or 5% of the total sales.
There’s additional discussion about overall sales with respect to their expectations, and implications for future projects. Speaking for myself, I think it’s commendable that with all the risks and uncertainties that are inherent to independent game development and publishing, Frictional Games, and all others who support Linux, spent the human-hours to port the code, test the builds, and release the game for our platform.