Reusing a Steam Library drive on Linux? Game won’t start? It’s your prefix…

TL;DR: Steam for Linux puts your wine prefixes and stuff into a folder on your drive named compatdata, and it has stuff in it specific to your distro. If your game fails to launch it’s becuause you can’t reuse those. Either rename the folder specific to the game failing to launch, or just move compatdata to compatdata-backup and restart Steam. Warning! For games that save locally and don’t sync to the cloud, this ALSO moves the save files. This is why you rename, not delete! Recovering your save files is left as an exercise for the reader.

I’ve been using Ubuntu as my daily driver for over a year, but finally took the plunge into trying out Bazzite. I don’t like dual booting and I do like diving in face first, so I made a second partition and installed Bazzite (Nvidia, KDE).

Now, I had a year’s worth of games installed on my dedicated game drive, so instead of downloading all of those again, I just pointed the Bazzite installation of Steam to my drive, and wow! It found all my games. Amazing.

My friend has been hooked on Palia, and I’ve been playing it a bit, so I got the itch and decided to try playing it under Bazzite… and it failed. Button said starting, said running, then failed. No window, no crash, no error message.

I tried a different game, EVE Online, same thing.

I tried a different different game, Here Comes Niko! and… it launched.

So, it’s specific to specific games, right?

The internet had no help for me.

In the past, games failing to launch had to do with a dirty Proton setup, so I tried forcing a different Proton version, I tried deleting shaders… I could NOT get the game to start.

Despite being a Linux user for decades, I sometimes forget basic debug steps. So, I was reminded by the Internet to run Steam on the command line so I could see output.

That’s when I saw it. Amongst a sea of errors about some 32 bit .so file, I saw it:

wine: failed to open "c:\\windows\\system32\\steam.exe": c0000135

But wait, I thought, I changed Proton versions, doesn’t that do winey things in the background? A quick talk with the Internet told me about a directory in your Steam library I’ve never played with before: compatdata.

compatdata is where Steam puts your Wine prefixes and various compatbility files in… and sometimes it does things that are installation or distro specific. What things? I don’t know… but things that can cause steam.exe to fail to launch!

Because my drive was a Ubuntu-mounted drive and is now a Bazzite-mounted drive, I wondered if there was Ubuntu debris in the prefix.

In true Windows debugging fashion, I decided to reinstall Windows. First, I found the Steam app ID for Palia by going to ProtonDB: https://www.protondb.com/app/2707930?device=pc (it’s right there in the URL), then I went into compatdata and…

mv 2707930 2707930-backup

I restarted Steam, and then pressed “Play”. Steam scrolled a ton of messages in the terminal about installing a wine prefix and… after a couple of minutes…!

Palia, on Bazzite Linux!

That’s when it occurred to me: I’d played a lot of Palia and EVE Online on Ubuntu, but had never launched Here Comes Niko! so there was no prefix for Niko.

Just to be sure…

cd /var/mnt/fastgames/SteamLibrary/steamapps
mv compatdata compatdata-backup
mkdir compatdata

Restart Steam… now everything is fresh. And every game I test launches clean!

A warning!

Game on Linux Steam run inside a wine prefix. That’s an entire “installation” of wine that emulates a C:/ drive, and that includes a Windows version of Steam. It’s horribly inefficient on drive space, but it’s amazing because it makes your Windows only games run on Linux.

This is important because games store their save files inside the prefix; the game thinks it’s the only application installed on Windows and can do whatever it wants with that drive.

When you move (you moved it, right?) the prefix directory, a brand new Windows install is made for your game…

…and any game caches or saves are gone!

Now, Steam has Steam Cloud, and a lot of games are online games, so you probably won’t notice. But an old game that doesn’t support Steam Cloud will appear to have lost all your saves!

This is why you moved the directory instead of deleting it, right?

You can go into the old prefix, like…

cd /path/to/SteamLibrary/steamapps/compatdata-backup/2707930/pfx/drive_c/

And you are now looking at the root directory of the Windows “installation” your game runs in. Locate the files you need (saves, caches, whatever) and copy them into the appropriate location of the new compatdata directory.

Exactly what and how you copy… you figure it out. It’s different for every game.