BeaconServer

BeaconServer is the open-source host supervisor for Beacon multiplayer in Subnautica 2. It starts and watches the hosted game process, takes and restores save snapshots, exposes an admin HTTP API, answers Source A2S query, and runs Source RCON.

Players join with the Beacon launcher. A playable host also needs Beacon's in-game runtime (a ue4ss\ folder with Beacon's server mods, plus the native Beacon.dll) next to the BeaconServer\ folder — the release zip bundles this runtime, so a downloaded server is complete. Building from this source yourself produces the supervisor only; see Installation.

Features

🖥 Host supervision

Starts Subnautica 2 with the Beacon runtime, monitors the game process, tracks the plugin heartbeat, and coordinates restarts.

💾 Save snapshots

Snapshots the world automatically on every game auto-save (when SnapshotsEnabled is on) and on admin trigger. Restore swaps the save directory atomically so a failed restore does not leave a half-written world, and a pre-restore snapshot is taken first so the operation is reversible.

📡 Source query

Answers standard Source A2S query on the configured query port so monitoring tools can read server name, map, player count, and the player list.

🛠 Source RCON

Runs a Source-compatible RCON listener with help, status, players, ping, save snapshot, save list, say, announce, and motd, plus slash commands registered by server mods.

🔐 Admin HTTP API

Exposes snapshot list/upload/download/restore, save import, health, player list, mod manifest, chat, and live-map endpoints. Admin routes are HMAC-signed with a key derived from the RCON password.

🧩 Mod surface

Loads UE4SS Lua and C++ mods through the Beacon runtime layout, and publishes the server's mod manifest at GET /api/v1/manifest for the launcher to install on join.

Requirements

• Windows 10/11 or Windows Server x64
• Subnautica 2 game files installed on the host machine (BeaconServer launches them; it does not ship the game)
• Open/forwarded ports for gameplay, query, RCON, and admin HTTP as needed

Release builds are self-contained; a separate .NET install is not required for normal use.

Installation

Managed hosting

SurvivalServers.com Subnautica 2 hosting ships the complete Beacon server runtime already installed and handles ports, updates, and panel integration.

Self-host

1. Download Beacon-Server-Windows-x64-v<version>.zip from the latest release. It is self-contained: BeaconServer\ (the supervisor + appsettings.json), ue4ss\ and Beacon.dll (the in-game runtime), and tools\ (the injector).
2. Extract it to a stable folder, such as C:\Beacon\.
3. Install the Subnautica 2 game files under the folder set as SnInstallRoot (default C:\Beacon\game) — copy your steamapps\common\Subnautica2 folder there, or install with SteamCMD (app 1962700). The server runs headless; no GPU is required.
4. Edit BeaconServer\appsettings.json (see below).
5. Open/forward the ports listed below.
6. Run BeaconServer\BeaconServer.exe.

Players connect with the Beacon launcher to <host>:<GameplayPort>.

Note: the release zip above is complete — it bundles the in-game runtime (the ue4ss\ folder with UE4SS + Beacon's server mods, plus the native Beacon.dll) alongside the MIT-licensed supervisor. If you instead build BeaconServer from this source, you get the supervisor only; the runtime must then sit next to the BeaconServer\ folder, or BeaconServer logs an error and the game runs as a plain Subnautica 2 listen server (no password gate, chat, roster, or live map). Managed hosting includes the runtime.

Use the latest release. A run of older release pages carried a zip that held only the supervisor, with no ue4ss\ folder and no Beacon.dll. Extracting one of those gives a host that players connect to and bounce straight back to the main menu from. A complete bundle is around 110 MB and contains ue4ss\Mods\; anything near 50 MB is the broken artifact. Affected pages are marked at the top of their release notes.

Server Settings

BeaconServer reads appsettings.json (next to BeaconServer.exe) under the Beacon section.

Setting	Default	Purpose
InstanceId	default	Stable instance name used in logs, query rules, and API responses.
ServerName	empty	Public name shown in the launcher and Source query. Empty falls back to the instance id.
SnInstallRoot	C:\Beacon\game	Subnautica 2 install folder. Beacon auto-detects Steam/Epic Win64 and Xbox WinGDK layouts under this root.
SnExecutablePath	empty	Optional direct path to the Subnautica 2 executable, for example an Xbox install's Subnautica2-WinGDK-Shipping.exe.
SnUserDir	C:\Beacon\userdir	User directory used by the hosted game process; the live save lives under Saved\SaveGames.
SaveDir	C:\Beacon\saves	Snapshot zips and archived saves.
GameplayPort	27015	UDP port players join through Beacon.
BeaconControlPort	27016	Reserved (the gameplay+1 slot of the per-instance port block).
QueryPort	27017	UDP Source A2S query port.
RconPort	27018	TCP Source RCON port. RCON is disabled when RconPassword is empty.
HttpPort	27019	TCP admin HTTP API port. Set to 0 to disable. Also requires RconPassword to be set.
RconPassword	empty	Admin password for RCON; the HTTP API signing key is derived from it. Set this before exposing RCON or HTTP.
ServerPassword	empty	Legacy — ignored since v0.3.55. Do not set; use BeaconAuthPassword.
BeaconAuthPassword	empty	Join password enforced server-side for remote players. Empty means an open server. Also sets the password flag in Source query.
Admins	[]	Identities (SteamID64, Beacon user id, or display name) treated as admin when running mod slash commands from in-game chat. RCON callers are always admin.
MaxPlayers	4	Slot count reported to the launcher and query clients.
SnapshotsEnabled	true	Auto-snapshot on every game auto-save. When false, only admin-triggered snapshots run.
MaxUploadBytes	2 GB	Size cap for snapshot uploads and save imports over the HTTP API.
PluginHeartbeatTimeoutSeconds	30	Seconds before BeaconServer treats the game runtime as unresponsive.
Chat:Enabled	true	In-game chat. When false, the chat overlay is dropped from the published mod manifest.
Mods	empty	Mod manifest published at GET /api/v1/manifest: Required, Recommended, and Blocked lists. Re-read on edit; no restart needed.
Map:Enabled	true	Live web map served at /map/ on the admin HTTP port.
Map:Public	false	When true, /api/v1/map/state is readable without auth, so the browser map shows live players to anyone with the URL.

Keep the ports unique for each server instance. The standard layout is:

Port	Protocol	Purpose
GameplayPort	UDP	Subnautica 2 gameplay
GameplayPort + 2	UDP	Source A2S query
GameplayPort + 3	TCP	Source RCON
GameplayPort + 4	TCP	Admin HTTP API

The launcher derives the RCON and admin HTTP ports as gameplay+3 and gameplay+4, so keep those offsets if you want the launcher's Console and world tools to work against your server. The query port is editable per-server in the launcher.

Source Query Example

BeaconServer answers standard Source A2S queries on QueryPort.

py -m pip install python-a2s
@'
import a2s

address = ("127.0.0.1", 27017)
info = a2s.info(address)
players = a2s.players(address)

print(f"{info.server_name} - {info.player_count}/{info.max_players} on {info.map_name}")
for player in players:
    print(f"{player.name} {player.duration:.0f}s")
'@ | py -

The same port works with tools such as GameDig, LGSM monitors, and Discord status bots that support Source query.

RCON

Connect to RconPort with the configured RconPassword (RCON is disabled while the password is empty).

help
status
players
ping
save snapshot
save list
say <message>
announce <message>
motd [message]

Mod-registered slash commands also run over RCON, with or without the leading /. Restoring a snapshot is not an RCON command — use the launcher's World backups dialog or the HTTP API.

See docs/ADMIN.md for exact command output, the HTTP API signing recipe, and the endpoint list.

Build From Source

git clone https://github.com/HumanGenome/BeaconServer.git
cd BeaconServer
dotnet build BeaconServer.sln -c Release
dotnet test BeaconServer.sln -c Release --no-build
dotnet publish src/server/BeaconServer/BeaconServer.csproj -c Release -r win-x64 --self-contained true

Published output lands under src/server/BeaconServer/bin/Release/net8.0/win-x64/publish/.

Known Issues

"The game was not started via the platform launcher and will be closed."

Subnautica 2 asks the Steam client to confirm the copy of the game it is running. On a headless host that answer often does not come back, and the game closes itself with exit code 0, which leaves BeaconServer relaunching it in a loop.

Three things have to be true on the server machine:

• The Steam client is running and signed in to an account that owns Subnautica 2. Offline mode is fine.
• Steam is signed in as the same Windows user, in the same session, as the one running BeaconServer. A Steam client in another session is not visible to the game.
• steam_appid.txt containing the single line 1962700 sits next to Subnautica2-Win64-Shipping.exe.

From v0.3.125 BeaconServer writes steam_appid.txt itself on every launch and passes the same id to the game through the environment, so the part left to you is the Steam client. If the game still closes itself, BeaconServer now says so in its log and stops relaunching instead of looping.

Tracked at HumanGenome/Beacon#8.

Game build must match between client and server

After a Subnautica 2 update, a client on a newer build joining an older server hangs at the main menu with no error. Update the server's game files whenever the game updates.

Community Note

Beacon is a community project and is not affiliated with or endorsed by the developers of Subnautica 2.

Contributing

Issues and pull requests for BeaconServer are welcome. For bug reports, include the BeaconServer version, Subnautica 2 build, and relevant logs from logs\beacon-*.log (one JSON object per line, rolled daily).

License

MIT. See LICENSE.

Credits

• UE4SS — Unreal Engine scripting and modding framework