Having the same issues on my deck. My dad had done the same on his deck about a week ago, and everything works for him.

My launcher version: 2.27.0.14542 (broken)
His launcher version: 2.26.1.14494 (working)

We are both using Proton 8/Experimental. I tried using Proton GE as well to no avail

dang you blizzard!!

"Adding WINE_SIMULATE_WRITECOPY=1 as an environment variable fixes 14542."

"For anyone using Lutris, you just need to add the flag on Configure > System Options > [Scrolldown to “Game Execution”] > Environment Variables."

"If you're launching with steam, change launch options to WINE_SIMULATE_WRITECOPY=1 %command%"

I googled for nearly an hour, but cannot find any information on this env variable.
So what does WINE_SIMULATE_WRITECOPY do?

EDIT: I would't label this issue "unofficial". Isn't Diablo IV (app ID 2344520) launched through Battle.net?

EDIT: I would't label this issue "unofficial". Isn't Diablo IV (app ID 2344520) launched through Battle.net?

Nope, Bnet is not in the foodchain on Steam D4. Which is why I bought it there.

Is there a way to re-download the working version?
I forgot to make a backup and bnet deleted t on a recent launch, leaving me without a working version.

Is there a way to re-download the working version? I forgot to make a backup and bnet deleted t on a recent launch, leaving me without a working version.

How are you launching BNet? I am using proton experimental via steam and can play d4 and d2 with zero issue. Bnet version appears to be the latest (no updates pending) -- 2.28.0.14589

Battle.Net Agent start failing for me a few days ago.

So I found a solution that worked, usingo proton 10.0 beta, and it does work, but Steam MUST be open otherwise I got this message.

Will it be necessary to have steam open on the future?

@ruinedraziel Also - how are you installing/launching battle.net? Could you give some more detailed steps on the failing setup with steam not running and how to recreate it?

Sure thing, I'm at work, will compile the info when im home. It started when the agent would not work anymore on ge-proton 9.27, tried to reinstall it wont finishe stuck at 45%, using lutris installation. Has already spawn reports in other places (https://www.reddit.com/r/linux_gaming/comments/1kbu0ia/comment/mpxhs0p/).

And if you have installed already the agent wont start unless you are on proton 10, and if you are on proton 10 I get this message if steam is not opened, this is reproducible in my two main systems. both similar configs (desktop and laptop).

I'll also document a crude vm step to step to see if its reproducible that way also. @alasky17

edit: Right now, if I revert back to proton 9 battle net agent will not work. So im assuming some fix from the 10 beta will be necessary anyway.

@alasky17 Srry for the delay, I removed the battle.net app and tried to reinstall it, Im using Lutris.

When trying to install while using Proton 10.0 Beta I got this error without even seeing the installer:

After canceling this message a few times installation proceeds.

After installing, every launch of battle.net give me this message:

No matter the answer, ok or cancel, battle.net fails to start.

So I tried clean, new VM, Arch linux > steam > installed proton 10.0 > closed steam > installed lutris > installed wine > Picked proton 10 > installed battle.net
same error

but this time installation wont progress any further (probably VM related)

I can do this on a bare metal on the weekend and report back.

Here is system information, and lutris logs.

systemspec.txt
systeminfo.txt
lutrislog.txt

edit: fixed some typos

Srry, adding up PROTON_LOG=1 with both situations steam closed, and open, cant see a diference on them except for the number of lines.

steam-open.log
steam-closed.log

@kisak-valve Thx for the feedback, I will look where it's coming from and remove it, probably something on lutris, and redo the logs. Update when I'm home.

Is this non reproducible for you guys? I might have to make a bare bone clean install for testing then.

edit: fixed some typos...

@ruinedraziel It would be great if you could try an install without Lutris to remove that variable. It is possible to manually install battle.net as a non-steam game (I know because I've done it :). Also yes - VMs can create all sorts of chaos 😅

Edit: Also - when you say it works great with Steam open -- do you mean if Steam is running in the background but the steam window is closed, it doesn't work? Or do you mean it only fails if Steam processes are completely shut down (in which case, how do you launch battle.net?)?

@ruinedraziel It would be great if you could try an install without Lutris to remove that variable. It is possible to manually install battle.net as a non-steam game (I know because I've done it :). Also yes - VMs can create all sorts of chaos 😅

Edit: Also - when you say it works great with Steam open -- do you mean if Steam is running in the background but the steam window is closed, it doesn't work? Or do you mean it only fails if Steam processes are completely shut down (in which case, how do you launch battle.net?)?

Yes, steam must be running, it can be minized to tray, don't need to be visible on screen.

Im opening from lutris, I've always used it this way,

I agree that would probably be better off runing b.net from steam already, but if I run it as a non-steam game trough steam the problem probably will disapear, as steam will be running.

And I'm able to use it and play without issues as long as steam is running without changing how I currently use. :)

In Proton 10 we have reworked how our steam.exe shim works. This is not the full blown Steam having issues here but just our small helper source of which you can find in the Proton tree. It was rewritten to use the new PE split instead of the old .exe.so mechanism and apparently it's fatal for it when it's not run in the Steam environment. We'll look into that and try to fix it.

It does query some things via steamapi as well as populated Steam-related registry entries and creates .vdf files for the benefit of mod launchers and similar. Also some Steam games expect to be children of the steam.exe process.

In the meantime you can just make sure the build you are using outside of Steam doesn't use steam.exe:

diff --git a/proton b/proton
index 0cd637496bd1..509a36184a6f 100755
--- a/proton
+++ b/proton
@@ -1831,9 +1831,9 @@ class Session:
                     "311210",   # CoD: Black Ops 3
                     "1549250",  # Undecember
                 ]:
-            argv = [g_proton.wine_bin, "c:\\Program Files (x86)\\Steam\\steam.exe"]
+            argv = [g_proton.wine_bin]
         else:
-            argv = [g_proton.wine64_bin, "c:\\windows\\system32\\steam.exe"]
+            argv = [g_proton.wine64_bin]
 
         rc = self.run_proc(adverb + argv + sys.argv[2:] + self.cmdlineappend)
 

steam-17945278634453368832.log

https://gist.github.com/Az0na/29bfe7cf2e65f5069cfe4cac2ee61b3e

This enough?

seems nvidia drivers 595 does not have 32 libraries, I downgraded to 580 and working fine now. used 590 before that worked to so not sure why 595 does not has them. seems be ubuntu issue as I run Zorin OS 18.1 based on ubuntu and I read somewhere cashyos does not have this problem with the drivers. oh well. thanks for the assistance.

It should be noted that this https://github.com/ValveSoftware/Proton/issues/7302#issuecomment-4528696853
was not happening in Ubuntu 25.10. Battle.net started failing only after the 26.04 upgrade. If the steps to reproduce don't cause this behavior, maybe try installing ubuntu 25.10, then installing steam and adding battle.net to steam, and confirming it works fine, and then upgradeing ubuntu to 26.04.

I'm noticing a high CPU usage when using 'certain windows sizes' on battle.net launcher trough proton.

Wich I can solve it by resizing it just a little.
Screenshots

Small video

https://github.com/user-attachments/assets/9cc9d913-8ca4-4f3f-805a-b9c4d9c0f9d1

This is not reproducible in KDE Plasma, might be a Hyprland specific.

Hyprland 0.55.4 (Wayland)
CachyOS
Linux 7.1.1-2-cachyos
Mesa-Git 26.2.0-devel (git-05a6b192a5)