Platforms

A spec declares one or more platforms, and each is a kind plus an image, optionally with its own install script and startup command.

The list order is scheduler priority, not a statement about which operating system we prefer.

The policy

The goal is that every game is deployable on either kind of node, and that a native build always wins.

1. Bias toward the native build for the node's OS. A Windows node runs the native Windows build; a Linux node runs the native Linux build. The spec does not push a server onto one OS. The node it lands on picks.
2. Most games ship a native Windows server. When a native Linux server also exists, declare both. Then the game loads on either Agent.
3. When no Linux build exists, add a linux-wine entry, so Linux nodes can still host it. Wine is the fallback, never the preference, so put the native kinds first in the list.

Dragonwilds is the case where one appid ships both depots: the same id sits under linux and windows in steam_app_ids, SteamCMD picks the depot for the platform it runs on, and the Panel injects {{APP_ID}} from the entry matching the placement's OS family.

Per-platform overrides

A platforms[] entry may override install_script, startup_command and skip_update_on_start. The spec-level install.script and startup.command are the fallback for every kind that does not override them.

config_files, stop, ports and backup have no per-platform variant. That is a deliberate constraint rather than an omission, and it produces three rules worth knowing before you write a dual-platform spec:

Config paths always use the logical /data root. The Agent maps it to C:\data on a Windows node and leaves it alone on Linux. A literal C:\data\… in a spec breaks on a Linux or Wine node, where it resolves to a C: subdirectory.

Platform-named config folders get one entry each. Unreal reads Saved/Config/LinuxServer/ on the Linux build and Saved/Config/WindowsServer/ on the Windows build. Declare both config_files entries with the same template. Every save writes both; each build reads its own and ignores the other.

Declare the Linux stop signal. stop: { type: signal, value: SIGINT }. A Windows daemon ignores custom stop signals and sends its own shutdown event, and a Linux Agent ignores a Windows-only name such as CTRL_SHUTDOWN_EVENT and falls back to SIGTERM. Either name is safe on both, but the Linux signal is the only one either Agent can actually honour, which makes it the convention.

Backup globs are data-directory-relative and OS-neutral, so check that the Windows build actually writes its saves under the data directory. An Unreal build marked "installed" defaults to %LOCALAPPDATA%\<Project>; pin it with -UserDir=C:\data\<Project> in the Windows startup command.

Wine, specifically

The kraken-steam-wine image is a Linux image with WineHQ and a headless X server. A linux-wine install pulls the Windows depot with the Linux SteamCMD by forcing the platform type:

steamcmd +@sSteamCmdForcePlatformType windows +force_install_dir /data \
  +login anonymous +app_update {{APP_ID}} validate +quit

Two things about launching under it, both of which the image encodes so specs do not have to rediscover them:

Use wine64, not wine. They are not interchangeable in this image.

Use wine-headless, not xvfb-run. xvfb-run waits for Xvfb's SIGUSR1 readiness signal, and when a spec's startup command execs it as container PID 1 that signal is ignored, because PID 1 default-ignores signals with no handler. The container then sits there having started nothing. wine-headless starts Xvfb and polls for its socket instead, and it is on PATH in the image:

wine-headless /data/<Game>/Binaries/Win64/<Server>-Win64-Shipping.exe -log

For a UE5 server whose launcher respawns itself in ways Wine dislikes, launch the Win64-Shipping binary directly rather than the wrapper.

Wine placements are validated per game, not in general. Enshrouded's linux-wine entry is live-validated to its ready line under Wine 10; Abiotic Factor's carries the direct-binary note above. If you add a linux-wine entry, boot it once and watch the console before you call it supported.