Proton is a compatibility layer for Windows games to run on Linux. Running a Windows games is mostly just hitting the Play button within Steam. It’s that good that many games now run faster on Linux than on native Windows. That’s what makes the Steam Deck the best gaming handheld of the moment.

But a compatibility layer is still a layer, so you may encounter … incompatibilities. Ember Knights is a lovely game with fun co-op multiplayer support. It runs perfectly on the (Linux-based) Steam Deck, but on my Ubuntu laptop I encountered long loading times (startup was 5 minutes and loading between worlds was slow). But once the game was loaded it ran fine.

Debugging the game reveled that there were lost of EAGAIN errors while the game was trying to access the system clock. Changing the numer of allowed open files fixed the problem for me.

Add this to end end of the following files:

• in /etc/security/limits.conf:

* hard nofile 1048576

• in /etc/systemd/system.conf and /etc/systemd/user.conf:

DefaultLimitNOFILE=1048576 

Reboot.