Unity games and BepInEx

Many games made with the Unity engine, including Valheim, Lethal Company, Risk of Rain 2, R.E.P.O. and Content Warning, are modded through BepInEx. BepInEx is a mod loader: a small program you add to the game once, which then loads all the other mods.

Who does what

  • You install BepInEx into the game, once, and set one launch option in Steam (below).
  • lmm installs, updates and removes the mods that run on top of it.

lmm deliberately leaves BepInEx itself to you. It’s part of the game’s setup, it has to stay put whichever profile you use, and every game and Linux setup needs it done slightly differently.

Step 1: install BepInEx

Follow the instructions for your game on the game’s modding community or Thunderstore page. That usually means downloading the BepInEx pack and unpacking it into the game’s own folder, so a BepInEx folder sits next to the game’s program.

Step 2: tell Steam to load it

Most Windows games run on Linux through Proton, and Proton needs telling to load BepInEx. lmm works out the exact launch option your game needs. To see it, open ⚙ Setup → Games and click the pencil next to the game, or run:

lmm game show lethal-company

In Steam, right-click the game, choose Properties, and paste that text into Launch Options.

Step 3: add the game to lmm

The games above are recognised automatically, so adding them through Steam detection sets up everything, BepInEx included. For any other BepInEx game, add it by hand (see Adding a game by hand) and tell lmm it uses BepInEx: in the browser it’s in the game’s editor, and in the terminal it’s --loader bepinex:

lmm game add --name "My Unity Game" --source thunderstore --id my-unity-game --path ~/Games/MyUnityGame --loader bepinex

Then install mods as normal

From here it’s the same as any other game. lmm puts each mod where BepInEx expects it, however the mod’s author packed it.

Checking it all works

lmm can check that BepInEx is installed and set up the way your game needs:

lmm game show lethal-company
lmm verify

Many Thunderstore mods list “BepInExPack” as something they need. That’s BepInEx itself, so lmm doesn’t install it as a mod. If BepInEx isn’t set up yet, lmm stops before downloading anything and tells you the steps above.