[NTSYNC] [SteamOS] Helldivers 2 does not launch

[Txordi00]

Compatibility Report

• Name of the game with compatibility issues: HELLDIVERS 2
• Steam AppID of the game: 553850

System Information

• GPU: Steam Deck OLED APU
• Video driver version: Mesa 25.2
• Kernel version: 6.15.9
• Link to full system information report as Gist: https://gist.github.com/Txordi00/6a1ad6a95ba320e45de43e8875fa54f5
• Proton version: proton-cachyos-10.0-20250807-slr-ntsync-x86_64_v3

I confirm:

• that I haven't found an existing compatibility report for this game.
• that I have checked whether there are updates for my system available.
• that I have verified the issue is present when using Proton-CachyOS-SLR from this repository.
• that I haven't encountered the issue using an official Proton, such as Proton, Proton Experimental or Proton Bleeding Edge.

steam-553850.log

Symptoms

Using the NTSYNC version with PROTON_USE_NTSYNC=1 fails to launch Helldivers 2 in the Steam Deck. Without NTSYNC with the exact same proton version it runs alright. It works as well with PROTON-GE+NTSYNC.

Reproduction

1. Launch game with proton-cachyos-10.0-20250807-slr-ntsync-x86_64_v3 and PROTON_USE_NTSYNC=1.
2. It never passes the anticheat check screen, but it does not complain either. It just gets stuck.

[loathingKernel]

SteamDeck doesn't have the ntsync module, are you using a custom OS?

[Txordi00]

It does now, in the "Main" SteamOS branch. It ships the 6.15.9 kernel at the time of writing. See: https://steamdeck-packages.steamos.cloud/archlinux-mirror/sources/jupiter-main/?C=M&O=D. You just need to load the module manually as in many linux distros.

[loathingKernel]

Huh, I was not aware of this. I do not have a SteamDeck to debug this myself. What other steps have you taken to ensure that ntsync is available for proton to use? Have you made sure that device is user accessible for example? Have you verified with lsof /dev/ntsync that it is indeed used? This could be something simple such as not falling back gracefully or something more complicated.

Also, have you tried on another OS/system? Does it work there?

[Txordi00]

Other games work with ntsync in the deck, btw. With this same proton version, the outer wilds for example works fine. Helldivers 2 works with ge-proton+ntsync.

[Txordi00]

Huh, I was not aware of this. I do not have a SteamDeck to debug this myself. What other steps have you taken to ensure that ntsync is available for proton to use? Have you made sure that device is user accessible for example? Have you verified with lsof /dev/ntsync that it is indeed used? This could be something simple such as not falling back gracefully or something more complicated.

I did not check lsof /dev/ntsync this time, but other times I did and it was displaying stuff. I did however check on the proton log and the line about fsync is not there. The same happens with the outer wilds (and it works)

[Txordi00]

Yep, it is engaged (this is with Helldivers 2).

[loathingKernel]

Hmm, I see, this so far looks like a valid issue. I will have to have someone test on desktop, see if it works there. I expect someone would have reported it by now if it didn't, but can never be too sure.

[Txordi00]

Ty for the answers by the way!