Nix Flake for Motor Town Server

This flake is for running a dedicated "Motor Town: Behind the Wheel" dedicated server.

Usage

Use this flake as an input for your flake.

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    motortown-server.url = "github:ASEAN-Motor-Club/motortown-server-flake";
  };
  outputs =
    { self, nixpkgs, motortown-server, ... }@inputs: {
    # Your flake outputs here
  }
}

Include nixosModules.default as a module in your NixOS configuration.

{
  ### in configuration.nix, or as a module passed into nixpkgs.lib.nixosSystem
  services.motortown-server = {
    enable = true;
    enableMods = false;
    user = "steam";
    openFirewall = true;
    credentialsFile = /path/to/dotenv/file;
    dedicatedServerConfig =  {
      ServerName = "Test Server";
      ServerMessage = "Welcome";
      Password = "";
      MaxPlayers = 10;
      MaxVehiclePerPlayer = 10;
      bAllowPlayerToJoinWithCompanyVehicles = true;
      bAllowCompanyAIDriver = true;
      MaxHousingPlotRentalPerPlayer = 1;
      MaxHousingPlotRentalDays = 7;
      HousingPlotRentalPriceRatio = 0.1;
      bAllowModdedVehicle = false;
      NPCVehicleDensity = 0.2;
      NPCPoliceDensity = 0.1;
      bEnableHostWebAPIServer = true;
      HostWebAPIServerPassword = "hackme";
      HostWebAPIServerPort = 8080;
      Admins = [
        {
          UniqueNetId = "12345";
          Nickname = "Admin1";
        }
        {
          UniqueNetId = "54321";
          Nickname = "Admin2";
        }
      ];
    };
  };
}

Bootstraping

Before you can run this service successfully, you have to run steam at least once under the user you provided, in order for the dedicated server to launch successfully.

Updating the Dedicated Server

A dedicated motortown-server-update systemd service handles game updates. It stops the server, runs steamcmd to update, then restarts — all in one shot.

Via trigger file (recommended)

The backend writes a trigger file watched by a host systemd .path unit. This is the same pattern used for restarts:

# From the host or backend (inside the container):
systemctl start motortown-server-update.service

Or via the trigger file:

echo "update requested at $(date)" > /var/lib/motortown-update-trigger/trigger

The host's motortown-update-triggered.service clears the trigger and starts the update. The update service stops the server, runs steamcmd, then starts the server again.

Via backend

Set the UPDATE_MOTORTOWN_SCRIPT environment variable on the amc-backend service. The backend can call this script to trigger an update cycle.

First boot

The initial game download still happens automatically via preStart when DedicatedServerConfig.json does not exist (first boot). Subsequent updates should use the update service.

Mod Development Workflow

Mods are stored in the MotorTownMods submodule. We use a branch-based versioning system where each release has its own branch (e.g., release/v19).

Local Development

1. Set services.motortown-server.modVersion = "dev"; in your NixOS configuration.
2. Make changes to the Lua scripts in ./MotorTownMods/Scripts.
3. If you have a new compiled DLL, place it in ./MotorTownMods/dlls/main.dll.
4. Important: Because this is a Flake, you must stage your changes for Nix to see them:

   git add MotorTownMods

5. Deploy as usual. Nix will bundle your local ./MotorTownMods folder.

Creating a New Release

1. Make sure your changes on the master branch in the MotorTownMods submodule are ready.
2. Create and push a new release branch:

   cd MotorTownMods
   git checkout -b release/v20
   git push -u origin release/v20

3. GitHub Actions will automatically trigger, compile the project on Windows, and commit the resulting main.dll back to the release/v20 branch.
4. Get the commit hash of the new release:

   git rev-parse HEAD

5. Update mods.nix in the parent repository:
   • Add the version to ue4ssVersionMap.
   • Add the version and its commit hash to revMap.

Updating an Existing Release

If you need to push a fix to an existing release branch (e.g., release/v19):

1. Push the changes to the branch in the submodule.
2. Wait for the CI to finish and commit the new DLL.
3. Update the commit hash in mods.nix's revMap. This is required to keep the build "locked" and pure-compatible.

Development Deployment Workflow

For rapid development iteration, use the scripts/deploy-dev-mod.sh script to deploy UE4SS mods (like MTDediMod) directly to a remote NixOS server without going through the full release process.

Script Overview

The deployment script (scripts/deploy-dev-mod.sh) automates:

• Building the mod package using Nix
• Syncing mod files and shared DLLs to the server
• Fixing permissions for container users
• Optionally restarting containers or reloading mods via API

Prerequisites

1. SSH Access: You need SSH access to the target server (e.g., root@asean-mt-server)
2. MTDediMod Source: The mod source should be in ./MTDediMod or a custom path
3. Shared DLLs: Windows DLLs (luasocket, cjson, ssl, etc.) should be in ../shared relative to the script or set via SHARED_PATH
4. Nix Package Command: The mod must have a nix run .#package command that builds to ./package/

Basic Usage

Deploy to a server (builds automatically if needed):

./scripts/deploy-dev-mod.sh root@asean-mt-server

The script will:

1. Build the mod package (unless package/ already exists)
2. Rsync files to /var/lib/mtdedimod-dev/ue4ss/ on the server
3. Copy shared DLLs to /var/lib/mtdedimod-dev/ue4ss/Mods/shared/
4. Fix permissions (steam:modders)

Common Options

Deploy and restart the container:

./scripts/deploy-dev-mod.sh root@asean-mt-server --restart

Deploy and restart a custom container:

./scripts/deploy-dev-mod.sh root@asean-mt-server --restart motortown-server-dev

Deploy and hot-reload mods via API (no container restart):

./scripts/deploy-dev-mod.sh root@asean-mt-server --reload

Skip building (use existing package):

./scripts/deploy-dev-mod.sh root@asean-mt-server --no-build

Custom mod path:

./scripts/deploy-dev-mod.sh root@asean-mt-server --path /custom/path/to/MTDediMod
# Or use environment variable
MTDEDIMOD_PATH=/custom/path ./scripts/deploy-dev-mod.sh root@asean-mt-server

Deployment Modes

Mode	Command	Use Case
Basic	./scripts/deploy-dev-mod.sh <target>	Deploy changes without server restart
Restart	--restart	Apply changes requiring full container restart
Hot Reload	--reload	Reload Lua scripts without downtime (via API)
Quick Sync	--no-build	Skip build, sync existing package only

Rapid Development Iteration

Typical workflow for script changes:

1. Make changes to your Lua scripts in MTDediMod/
2. Deploy with hot-reload:

   ./scripts/deploy-dev-mod.sh root@asean-mt-server --reload

3. Test your changes immediately (server stops briefly, then reloads mods)

For compiled mod changes (C++ DLLs):

1. Make changes to your C++ code
2. Force rebuild and restart:

   rm -rf MTDediMod/package
   ./scripts/deploy-dev-mod.sh root@asean-mt-server --restart

Quick sync without rebuild:

If you've already built locally and just want to sync files:

./scripts/deploy-dev-mod.sh root@asean-mt-server --no-build --restart

Advanced Configuration

Custom shared DLLs path:

SHARED_PATH=/path/to/shared ./scripts/deploy-dev-mod.sh root@server

Environment variables:

export MTDEDIMOD_PATH=/custom/mtdedimod
export SHARED_PATH=/custom/shared
./scripts/deploy-dev-mod.sh root@asean-mt-server

Troubleshooting

Package builds with root ownership:

If files in package/ are owned by root, remove the package and rebuild:

sudo rm -rf MTDediMod/package
./scripts/deploy-dev-mod.sh root@asean-mt-server

Permission errors on the server:

The script automatically fixes permissions, but if issues persist:

ssh root@asean-mt-server "chown -R steam:modders /var/lib/mtdedimod-dev/ue4ss/ && chmod -R u+w /var/lib/mtdedimod-dev/ue4ss/"

Reload API not responding:

Ensure the server has the web API enabled and the correct port (55000/55001):

bEnableHostWebAPIServer = true;
HostWebAPIServerPort = 8080;  # Or your custom port

Build not detecting changes:

Since this is a Nix flake, stage your changes:

cd MTDediMod
git add .
cd ..