elden-ring-ersc.md

Elden Ring Seamless Coop / ERSC

This page documents the working launch shape for ERSC when it needs Steam running and Spacewar/AppID 480 available.

This is a proof-of-concept capture from the RipperMoonKit Elden Ring profile. It shows the game running through Apple Game Porting Toolkit 3 with the HUD visible.

Tested Content Layout

This ERSC workflow was tested with a copy of an installed Windows game folder placed in the target Games directory.

Use the installed game folder from a Windows PC:

$GPTK_EXTERNAL_ROOT/Games/EldenRing/Game/
    eldenring.exe
    ersc_launcher.exe
    SeamlessCoop/

Run from the installed game folder rather than from game installer files. In this GPTK build, the installer path is fragile; the reliable path was copying the installed Game folder and launching from there.

This repository does not include game files, saves, Steam data, Wine prefixes, or runtime blobs.

Example Launcher Profile

The GUI profile keeps the Elden Ring folder, Steam prefix, runner, and launch options in one place so the setup is easier to repeat.

Gameplay Capture

This second capture is included to show the setup during active gameplay. It is not a promise of exact performance on every Mac.

Path Variables

Set these for your machine:

export ER_GAME_DIR="$GPTK_EXTERNAL_ROOT/Games/EldenRing/Game"
export ER_LOG="$GPTK_HOME/logs/ERSC-steam-prefix.log"

If you use the Golden Pot lobby fix, point GPTK_WINE_HOME at the patched GPTK runner:

export GPTK_WINE_HOME="$HOME/GPTK/runners/gptk-dsound-nocap-20260513"

That runner is a stock GPTK runner with only Wine DirectSound capture disabled. It prevents Steam Voice from locking the process when ERSC opens the world to wanderers. See steam-voice-capture-fix-2026-05-13.md.

Launch Sequence

Run the Spacewar/AppID 480 setup once from the Steam profile before co-op testing. Steam uses AppID 480 as the public Steamworks test app, and some co-op paths rely on that local Steam state even when the game folder itself is copied locally.

From the GUI:

1. Open the Steam profile.
2. Click Install Spacewar.
3. Wait for Steam to finish installing Spacewar and any first-run redistributables.
4. Close Spacewar.
5. Launch Elden Ring ERSC or ModEngine from the Elden Ring profile.

From Terminal:

gptk-steam --log --install-spacewar

Then start Steam normally:

gptk-steam --log

The raw Steam argument form is equivalent to the one-time Spacewar setup:

gptk-steam --log -applaunch 480

Then launch ERSC from the game folder using the same Steam prefix:

cd "$ER_GAME_DIR"
WINEDLLOVERRIDES='winmm=n,b;steam_api64=n,b' \
  gptk-launch --prefix Steam --set-winver win10 --no-dxr --log-file "$ER_LOG" -- ./ersc_launcher.exe

ModEngine And Randomizer Launch

For the Item and Enemy Randomizer workflow, the final launcher is not ersc_launcher.exe. The final launcher is ModEngine 2:

Game/ModEngine2/launchmod_eldenring.bat

The randomizer GUI imports a .randomizeopt file and generates randomized files under:

Game/ModEngine2/randomizer/

ModEngine then launches eldenring.exe, loads Seamless Coop as an external DLL, and mounts the randomizer folder:

external_dlls = [
    "../SeamlessCoop/ersc.dll"
]

mods = [
    { enabled = true, name = "default", path = "mod" },
    { enabled = true, name = "randomizer", path = "randomizer" }
]

RipperMoonKit's Mod Manager panel can write the current-machine config_eldenring.toml and launchmod_eldenring.bat. It intentionally does not copy Windows drive letters from another PC. A copied Windows example such as G:\Games\ELDEN RING\Game\eldenring.exe becomes the current GPTK/Wine path, usually through Wine's default Z:\... mapping.

The panel can also run Install ModEngine + Randomizer. That action installs .NET 6 Desktop Runtime into the Elden Ring randomizer tools prefix, clones or updates the elden-randomizer-coop setup reference repo under $GPTK_HOME/tools, opens the download pages, scans its inputs/ folder, installs recognized ZIPs, and writes the local ModEngine config/launch files.

The panel also includes Backup Mod State and Import From Friend. Backup captures ModEngine2, SeamlessCoop, and the root helper executables into a rollback ZIP. Import From Friend accepts an exported co-op/randomizer packet, stages its bundled ZIP files, copies the shared .randomizeopt, and applies the shared Seamless password without printing it.

RipperMoonKit does this natively instead of running setup.bat, because the Windows setup path calls powershell.exe. A normal GPTK prefix does not include Windows PowerShell, and native macOS PowerShell is not required for this workflow.

The critical runtime is not PowerShell. It is Windows .NET 6 Desktop Runtime, because EldenRingRandomizer.exe is a .NET desktop application. RipperMoonKit installs that with:

gptk-dotnet6 --prefix EldenRingToolsStaging

The randomizer GUI is not launched through the live Steam/game prefix. If Wine Staging 11.8 is installed, RipperMoonKit uses it for the randomizer tools prefix to avoid the GPTK/Wine 7.7 WinForms UIAutomation crash. The actual Elden Ring and ERSC launches continue to use the configured GPTK game runner.

The ZIP installer recognizes ZIPs by their contents:

modengine2_launcher.exe      ModEngine 2
EldenRingRandomizer.exe      Item and Enemy Randomizer
ersc_launcher.exe            Seamless Coop
toggle_anti_cheat.exe        Anti Cheat Toggler

Existing Seamless settings are preserved, and an existing randomizer folder is moved to a timestamped backup before replacement.

Manual launch shape:

cd "$ER_GAME_DIR/ModEngine2"
WINEDLLOVERRIDES='winmm=n,b;steam_api64=n,b' \
  gptk-launch --prefix Steam --set-winver win10 --no-dxr \
    --log-file "$GPTK_HOME/logs/elden-ring-modengine.log" \
    -- ./modengine2_launcher.exe \
       -t er \
       -c ./config_eldenring.toml \
       --game-path "Z:\\path\\to\\Game\\eldenring.exe"

Use the ERSC-only launcher first if you still need to create the Seamless save. Use the ModEngine launcher after the randomizer has generated its files.

Confirmed behavior: when the same game folder is launched without ModEngine, the randomized changes are not active. That is expected. Randomizer output is mounted through ModEngine, so the modded and non-modded launch paths stay separate.

Tool Credits

RipperMoonKit coordinates local launches and setup files, but the Elden Ring mod workflow depends on community tools downloaded by the user:

• ModEngine 2 provides modengine2_launcher.exe and the TOML-driven mod loading path.
• Elden Ring Seamless Co-op / ERSC provides ersc_launcher.exe, ersc.dll, and the co-op save/online flow.
• MoonTheRipper/elden-randomizer-coop provided the Windows setup reference used to design the native macOS helper.
• Elden Ring Item and Enemy Randomizer provides the randomizer GUI and generated randomizer files.

Full Placeholder Commands

These commands use literal placeholders for GitHub readers. Replace USERNAME with your macOS user name and replace EXE PATH with the folder that contains ersc_launcher.exe and eldenring.exe.

Start Windows Steam with the tested DirectSound no-capture runner:

env GPTK_WINE_HOME="/Users/USERNAME/GPTK/runners/gptk-dsound-nocap-20260513" \
  /Users/USERNAME/bin/gptk-steam --no-log

Launch ERSC from the copied game folder:

cd "EXE PATH"
env GPTK_WINE_HOME="/Users/USERNAME/GPTK/runners/gptk-dsound-nocap-20260513" \
  WINEDLLOVERRIDES='winmm=n,b;steam_api64=n,b' \
  /Users/USERNAME/bin/gptk-launch \
    --prefix Steam \
    --set-winver win10 \
    --no-dxr \
    --log-file "/Users/USERNAME/GPTK/logs/ERSC-dsound-nocap.log" \
    -- ./ersc_launcher.exe

Stop Steam and the Steam-prefix game processes:

/Users/USERNAME/bin/gptk-steam --kill

Optional Spacewar/AppID 480 launch when a setup needs it initialized explicitly:

env GPTK_WINE_HOME="/Users/USERNAME/GPTK/runners/gptk-dsound-nocap-20260513" \
  /Users/USERNAME/bin/gptk-steam --no-log --install-spacewar

Why Same Prefix Matters

Steam API calls depend on the running Steam client's IPC state. If Steam is running in one prefix and ERSC launches from another prefix, the game may not see the same named pipes and process environment.

The working model is:

Steam prefix:
  steam.exe
  steamwebhelper.exe
  ersc_launcher.exe
  eldenring.exe

Esync Rule

The current ERSC profile starts both Steam and ERSC with esync disabled. This avoids the repeated pipe: Too many open files / eventfd: Too many open files failure seen when Steam, Spacewar/AppID 480, and ERSC keep opening sockets through Wine esync.

This was confirmed on 2026-05-16: after disabling esync for the ERSC profile, the Golden Pot lobby stopped hanging.

If Steam's Wine server is already running with esync enabled, stop Steam before launching the ERSC profile again:

gptk-steam --kill

Then launch Steam and ERSC through the same RipperMoonKit profile so both processes use the same esync setting.

An esync mismatch looks like:

Server is running with WINEESYNC but this process is not

Do not mix esync settings between Steam and ERSC inside the same Wine prefix.

Steam Runner Rule

Steam must also be started with the same Wine runner expected by the Elden Ring profile. For the Golden Pot and ModEngine path, that is the DirectSound no-capture runner plus no-esync. If Steam was started from the standalone Steam tile or from a manual terminal command using the stock GPTK runner, the game can freeze when joining or opening a world.

The matching failure usually repeats these lines in the logs:

getsockname failed in BGetBoundAddr with error: 10022
CSteamEngine::BMainLoop appears to have stalled
DirectSoundCaptureDevice.lock wait timed out

RipperMoonKit records how it started Steam for a game profile and blocks Steam-dependent launches when an already-running Steam process does not match the profile runner/no-esync state. Close Steam, press the Elden Ring profile's Start Steam button, then use Launch Modded.

The main Launch button and the library banner power button also run this sequence. They start Steam with the Elden Ring profile when needed, wait until Steam's UI helper is present, then launch either ERSC or ModEngine based on the profile's Launch through ModEngine setting.

Useful Checks

Process check:

pgrep -af 'steam.exe|steamwebhelper|ersc_launcher|eldenring.exe|wineserver'

Latest logs:

ls -lt "$GPTK_HOME/logs" | head
tail -n 120 "$ER_LOG"

Crash dumps:

ls -lt "$ER_GAME_DIR/SeamlessCoop/crashdumps/reports" | head

Layout check:

examples/check-ersc-layout.zsh.example

No-capture launch example:

examples/ersc-launch-dsound-nocap.zsh.example