[Bug]: Incorrect Proton Prefix used on Linux

[Hordini]

What happened?

I have two drives, one for my Home and another for games. Both have their own Steam library:

Drive 1: /home/hordini/.local/share/Steam/steamapps/... <-- Proton Prefix used by me3
Drive 2: /mnt/860 EVO/Steam Games/steamapps/ <-- Elden Ring Installation

Elden Ring is installed on the secondary drive, along with it's proton prefix and save data, while the script provided in Releases installs me3 and related files to the Home drive.

Upon launching the game with me3 today, I noticed that my save file was not being loaded correctly and I found that another proton prefix had been generated in Drive 1's compatdata directory that was being used by me3 instead despite the game remaining on Drive 2. Prior to v0.12.x, the correct proton prefix path was used.

This problem only occurs when launching Elden Ring with me3. Launching the game from Steam uses the correct proton prefix path and save files. My me3 profile does not specify a save-file location.

Version

v0.12.1

What operating system are you seeing this problem on?

Linux

Relevant log output

INFO me3: version="0.12.1" commit_id="6d7697b49e2e4067b68394c0d22fbba8c98065a2"
 INFO launch: me3::commands::launch: resolved game game=Game(EldenRing) game_options=GameOptions { boot_boost: None, skip_logos: None, skip_steam_init: None, exe: None } profile_options=ProfileOptions { start_online: None, disable_arxan: None, no_mem_patch: None, heap_size: None, debug_properties: [] }
 INFO launch: me3::commands::launch::strategy::compat_tool: found compat tool path="/usr/share/steam/compatibilitytools.d/proton-cachyos-slr/."
 INFO launch: me3::commands::launch::strategy::compat_tool: using Proton launch verb launch_verb=waitforexitandrun
DEBUG launch: me3::commands::launch::strategy::compat_tool: Configuring tool CompatToolManifest {
    version: 2,
    commandline: "/proton %verb%",
    require_tool_appid: Some(
        4183110,
    ),
    use_sessions: Some(
        true,
    ),
    compatmanager_layer_name: "proton",
}
DEBUG launch: me3::commands::launch::strategy::compat_tool: Configuring tool CompatToolManifest {
    version: 2,
    commandline: "/_v2-entry-point --verb=%verb% --",
    require_tool_appid: None,
    use_sessions: None,
    compatmanager_layer_name: "container-runtime",
}
DEBUG launch: me3::commands::launch::strategy::compat_tool: mounting additional filesystems for SLR: "/home:"
 INFO launch: me3::commands::launch: wrote attach config attach_config_file=NamedTempFile("/home/hordini/.cache/me3/.tmpggUOJ5") attach_config=AttachConfig { game: EldenRing, natives: [Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/SeamlessCoop/ersc.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }, Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/AdjustTheFov.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }, Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/IncreaseAnimationDistance.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }, Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/RemoveChromaticAberration.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }, Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/RemoveVignette.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }, Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/SkipTheIntro.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }, Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/UltrawideFix.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }, Native { path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/UnlockTheFps.dll"), optional: false, enabled: true, load_before: [], load_after: [], initializer: None, finalizer: None, load_early: false }], early_natives: [], packages: [Package { id: None, enabled: true, path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/Ultrawide_UI_Fixes/"), load_after: [], load_before: [] }, Package { id: None, enabled: true, path: ModFile("/home/hordini/.config/me3/profiles/eldenring-mods/PS5_DualSense_UI/"), load_after: [], load_before: [] }], savefile: None, cache_path: Some("/home/hordini/.cache/me3"), suspend: false, boot_boost: true, skip_logos: true, start_online: false, disable_arxan: false, mem_patch: true, mem_patch_heap_size: None, skip_steam_init: false, property_overrides: {} }
 INFO launch: me3::commands::launch: monitor pipe created path="/tmp/.tmp15B0tQ"
 INFO launch: me3::commands::launch: created log file log_file_path="/home/hordini/.local/share/me3/logs/eldenring-custom/2026-07-20_01-14-05.log"
 INFO run: me3_launcher: Launcher started
 INFO run: me3_launcher: Parsed launcher args args=LauncherVars { argv: [], exe: "/mnt/860 EVO/Steam Games/steamapps/common/ELDEN RING/Game/eldenring.exe", host_dll: "/home/hordini/.local/share/me3/windows-bin/me3_mod_host.dll", host_config_path: "/home/hordini/.cache/me3/.tmpggUOJ5" }
 INFO run: me3_launcher: Starting game at "/mnt/860 EVO/Steam Games/steamapps/common/ELDEN RING/Game/eldenring.exe" with DLL "/home/hordini/.local/share/me3/windows-bin/me3_mod_host.dll"
 INFO run:launch: me3_launcher::game: trace_id=Some("10090dd78a219a097b78df3017d50862-45e4cf8f2f89dfeb-0")
 INFO run:attach: me3_launcher::game: attaching to process pid=344
 INFO me3_mod_host: Beginning host attach
 INFO me3_mod_host: Attaching to ELDEN RING™ 1.16.2.0 Worldwide
DEBUG skip_logos:defer_init:hook_steam_init:steam_init_fn: me3_mod_host::deferred: return=Ok(0x6ffffaf56c60)
 INFO filesystem:create_file: me3_mod_host::filesystem: applied filesystem hook
 INFO filesystem:create_directory: me3_mod_host::filesystem: applied filesystem hook
 INFO filesystem:delete_file: me3_mod_host::filesystem: applied filesystem hook
 INFO me3_mod_host: Host successfully attached
DEBUG defer_init:schedule_after_arxan: dearxan::disabler::game: game path: "S:\\steamapps\\common\\ELDEN RING\\Game\\eldenring.exe"
DEBUG defer_init:schedule_after_arxan: dearxan::disabler::game: preferred base address: 140000000
DEBUG defer_init:schedule_after_arxan: dearxan::disabler::steamstub: SteamStub not detected, running callback immediately
 INFO defer_init:schedule_after_arxan: dearxan::disabler: arxan detected: true
DEBUG defer_init:schedule_after_arxan: dearxan::disabler: detouring entry point via __security_init_cookie call hook
 INFO me3_mod_host: Deferred me3 attach
 INFO run:attach: me3_launcher::game: Successfully attached
DEBUG dearxan::disabler: removing __security_init_cookie entry point hook
 INFO run: me3_launcher: attached to game successfully
DEBUG dearxan::disabler: calling __security_init_cookie (will run Arxan initialization routines)
DEBUG dearxan::disabler: flushing callback functions
 INFO hook_system_allocator: me3_mod_host::alloc_hooks: hooking system allocator
 INFO skip_logos: me3_mod_host::skip_logos: applied hook
DEBUG attach_override: me3_mod_host::host::game_properties: set_game_prop_addr=0x140dce6c0
DEBUG attach_override:defer_init:hook_prop_init:find_prop_hook_addr: me3_mod_host::deferred: Game.Debug.NearOnlyDraw lea RVA: 4fc2812
DEBUG attach_override:defer_init:hook_prop_init: me3_mod_host::deferred: Game property map init hook installed
 INFO hook_heap_allocators: me3_mod_host::alloc_hooks: hooking heap allocators
 INFO oversized_regulation_fix: me3_mod_host::savefile: applied hooks
 INFO me3_mod_host::host: loaded native with me2 compatibility shim path="/home/hordini/.config/me3/profiles/eldenring-mods/SeamlessCoop/ersc.dll"
DEBUG assets:file_step: me3_mod_host::asset_hooks: FileStep::STEP_Init=0x1401f8310
 INFO assets:wwise: me3_mod_host::asset_hooks: applied asset override hook
DEBUG attach_override: me3_mod_host::host::game_properties: applying game property overrides (user has priority): PropertyOverrides {
    user: {},
    internal: {
        "Menu.IsEnableOnlineMode": "false",
    },
}
 INFO assets:file_step:hook:device_manager: me3_mod_host::asset_hooks: applied asset override hook
DEBUG assets:file_step:hook:mount_ebl: me3_mod_host::asset_hooks: mount_ebl=0x142427260
 INFO assets:file_step:hook:mount_ebl: me3_mod_host::asset_hooks: applied asset override hook
DEBUG assets:file_step:hook:ebl: me3_mod_host::asset_hooks: make_ebl_object=0x142427760
 INFO assets:file_step:hook:ebl: me3_mod_host::asset_hooks: applied asset override hook

[redacted for length]

[garyttierney]

DEBUG launch: me3::commands::launch::strategy::compat_tool: mounting additional filesystems for SLR: "/home:"

Hm, this should've included the mount point the game is on and that might be why Steam isn't seeing it. Can you share the full path to the proper prefix? I assume it's under /mnt/860 EVO/Steam Games/steamapps but I don't have a second steam library setup atm to check.

[Hordini]

Sure, here is the prefix path for both drives:

Drive 1: /home/hordini/.steam/steam/steamapps/compatdata/1245620/
Drive 2: /mnt/860 EVO/Steam Games/steamapps/compatdata/1245620/

Drive 2 is where Elden Ring is installed, and the prefix it should be using.