Fallout 76 Proton GE 9-3

Are you someone who plays games on a Linux desktop computer with mods and wants to bring over your entire Proton prefix with all of your included mods to your Steam Deck? Well, with the newest Proton GE update, we can now do just that! A new option was added to the community-driven layer, which adds the option COPYPREFIX. By putting "COPYPREFIX=1 %command%" into your launch options and using Proton GE 9-3, you will be able to copy your prefix from your desktop and bring it over to use on your Steam Deck.

So, the option will check to see if Steam has launched with the argument -steamdeck appended to it, which happens when Steam is launched from Game Mode, and if it has, it will look for an existing prefix on your game partition or hard drive and replace the default steamdeck prefix with it. If you launch Steam without the -steamdeck argument, it will try to replace the current one on your game partition and replace it with the steamdeck one.

For a more in-depth explanation, here is how Proton GE's developer described it:

By default steam stores the wine prefixes in the steam library where the game is installed under SteamLibrary/steamapps/compatdata/ as well as shader cache files in shadercache/. When 'Steam Deck' session aka gamescope session is used, the -steamdeck option is appended to steam. This causes the default path for prefix compatdata and shadercache to change to the default steam install location ~/.steam/steam/steamapps/compatdata (or shadercache). This can be problematic if you are say for example switching from normal desktop steam to steamdeck. Or for example if you have a portable hard drive or SD card you keep your games on to use between the two. If you did something like say install mods for a game or played a game that doesnt work with cloud saves on the desktop, the prefix would not get used when you move the drive over from the desktop to steamdeck. Instead steamdeck would try to make a new one. The same goes in reverse for if you play games on the steam deck and try to move the game drive or sd card to a desktop.

What COPYPREFIX=1 DOES is if -steamdeck is applied it will check if a prefix exists on the game partition/drive. If it does, it will then WIPE the steamdeck prefix, and replace it with the one from the game partition/drive. . It does this with shader cache as well. This way steam will pick up your mods/saves that you had on your desktop or other PC you used the drive on before.

Alternatively, if -steamdeck is NOT applied -- it works in reverse. It will try to wipe the prefix on the game partition, and replace it with the one in steamdeck's default location. It does this with shader cache as well. A good use case for the reverse of the desktop -- say you've put in a ton of hours on a game with saves that don't work with steam cloud saving -- or have a bunch of mods you've applied on a game on your steam deck -- then you want to migrate to your desktop. In this case, put steam in desktop mode. Close steam then re-open it from the terminal using the steam command so that -steamdeck is NOT applied, then you can use COPYPREFIX to copy the steamdeck prefix to your game's partition/drive.

GloriousEggroll - Proton GE Developer

On top of that, we have updates to the components of the layer, like wine, dxvk, and vkd3d-proton, new fixes for Space Engineers and Fallout 76, and the ability to run winetricks within Proton easily. Overall, this is a hefty update, and I couldn't be happier to see it!

Proton GE 9-3 Changelog:

  • COPYPREFIX=1 option added. What this does:
  • wine updated to latest bleeding edge
  • dxvk updated to latest git
  • vkd3d-proton updated to latest git
  • imported upstream proton changes
  • imported upstream steamclient changes



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Noah Kupetsky
A lover of gaming since 4, Noah has grown up with a love and passion for the industry. From there, he started to travel a lot and develop a joy for handheld and PC gaming. When the Steam Deck released, it just all clicked.
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