[Guide] Valheim, Valheim+ and other mods on Debian (PopOS Release)

I'm writing this guide as I had some issues setting up my linux distribution to work with Valheim mods. With an out of the box PopOS (latest nVidia release) installation I had no issues installing Steam, downloading Valheim, and running it straight. I didn't have to install any vulkan drivers, mesa drivers, nothing.

The issue I had was getting the mods to load, particularly, Valheim+, so I can join my brethren on our server which I was currently playing mostly via my Windows installation. I spent many hours trying to figure out why it didn't work. The issue I faced was after installing the mod per the instructions the game simply wouldn't launch. Adding the launch options to Steam would show that it was trying to open the application but it never did, however, removing the launch options let it start normally. This means that something with the script wasn't working right.

Hopefully this helps some of you trying to run Valheim+ and other mods on your Linux distribution. Assuming the game starts normally on your machine you can probably follow this guide to get it to work.

What you'll need:

Fresh install of Valheim on Linux
BepInEx 5.4.8 Valheim Pack found here: https://valheim.thunderstore.io/package/denikson/BepInExPack_Valheim/
Valheim+: Download the Unix release to match your server from: https://www.nexusmods.com/valheim/mods/4?tab=description&BH=0

1) Unpack the BepInEx 5.4.8 files to a directory of your choosing. In my case I put it under ~/BepInExPack (My home folder)

2) In your BepInEx folder open 'start_game_bepinex.sh' with vi, or vim. Whatever you prefer. (nano?)

3) Here's where I made my changes. Line 16 has the following:
a="/$0"; a=${a%/*}; a=${a#/}; a=${a:-.}; BASEDIR=$(cd "$a"; pwd -P)

I added the full path of my Valheim installation on my system which was
/home/youruser/.steam/debian-installation/steamapps/common/Valheim

It should look like this
a="/$0"; a=${a%/*}; a=${a#/}; a=${a:-.}; BASEDIR=/home/youruser/.steam/debian-installation/steamapps/common/Valheim

Change this, line 18: exec="$BASEDIR/valheim.x86_64"
to
exec="/home/youruser/.steam/debian-installation/steamapps/common/Valheim/valheim.x86_64"

4) Now I replaced the working directories for the dlls since they're not in my Valheim folder. I did it this way so I didn't alter anything in my steam Valheim folder.

Line 21: export DOORSTOP_INVOKE_DLL_PATH="/home/youruser/BepInExPack/BepInEx/core/BepInEx.Preloader.dll"
Line 22: export DOORSTOP_CORLIB_OVERRIDE_PATH="/home/youruser/BepInExPack/unstripped_corlib"
Line 66: export LD_LIBRARY_PATH="/home/youruser/BepInExPack/doorstop_libs:$LD_LIBRARY_PATH"

5) Save the file. Now we want to modify the Valheim launch properties in Steam.
a) Open Steam
b) Navigate to Valheim, right-click on it, and select Properties
c) For launch properties you're going to point it to the directory of your .sh file
i.e. /home/youruser/BepInExPack/start_game_bepinex.sh %command%

6) Test out launching the game. Unlike Windows you won't see a console Window open up. Also, when I launch my game I get a pop up after the first splash screens saying if I want to Force Quit or Wait. Click on Wait and it'll continue to load. (Not sure why this happens. It always does for me). If it's successful you will see on the top left corner the plugin information for BepInEx and how many plugins are loaded.

7) After you've tested it works now we can move the Valheim+ plugin files. Don't copy everything from the downloaded .zip file. You want to now copy the valheim_plus.cfg found in the BepinEx/Config folder of the zip to your config folder, and the ValheimPlus.dll found in the BepinEx/plugins folder to your plugins folder. PS. The Windows VaheimPlus.dll and cfg files work fine if you have them. I ended up just copying mine over from my Windows installation.

8) Launch Valheim again. If it loads correctly you will see on the top left that BepInEx has loaded additional plugins, and you'll see the Valheim Plus logo. From here on out I copied over the rest of my mod files from the plugin folder and so far they worked for me. I use EquipmentAndQuickSlots and ModernMP on top of Valheim+.

PS: If you're using Steam Cloud and you have the EquipmentandQuickSlots mod you will see your character is naked when you launch Valheim IF you didn't have the mod installed prior to launching. This is because those slots don't exist without the mod and those items won't show up. After I enabled the mod I deleted my character files and let Steam Cloud sync them up again. Once I reloaded Valheim everything was normal.

Please be aware if you log into a game and save and quit you may lose those items (maybe not? I'm not 100% sure) because it will overwrite your character file and then sync up to the cloud. (again, I could be wrong here)

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I hope this helps those of you who've had some issues launching Valheim+ on Linux. Please leave a comment and I will try my best to answer and help you guys out. I will refine my config and guide a bit as time permits.