feat(services): add valheim server module and preset

docs/CHANGELOG.md

@@ -50,6 +50,21 @@
 
 ## 2026-09-29
 
+- **Added Valheim dedicated server package, service, and preset**:
+  - Added `steam-fetcher` (`github:nix-community/steam-fetcher`) flake input with `inputs.nixpkgs.follows = "nixpkgs"`.
+  - Added `inputs.steam-fetcher.overlay` to system overlays in `lib/default.nix`.
+  - Added `pkgs/valheim-server/package.nix` wrapping the Valheim dedicated server with modern `buildFHSEnv`, updated to latest release 1.0.16 (Steam depot `896661`, manifest `1285123405092214913`), with graceful fallback for non-x86_64-linux platforms.
+  - Added `overlays/valheim.nix` exposing `valheim-server`, `valheim-server-unwrapped`, and `fetchValheimThunderstoreMod` for compatibility.
+  - Added NixOS service module `platforms/nixos/modules/services/valheim.nix` defining `services.valheim`:
+    - Manages dedicated user/group `valheim` and systemd service `valheim.service`.
+    - Supports runtime decryption/loading of server password via `passwordFile` (avoiding plaintext secrets in the Nix store) as well as fallback `password` string option.
+    - Configures firewall rules for Valheim UDP ports (`port`, `port + 1`, `port + 2`).
+    - Configures admin, permitted, and banned Steam ID list files.
+  - Added preset module `platforms/nixos/modules/nmasur/presets/services/valheim/valheim.nix` with options for `nmasur.presets.services.valheim.enable`:
+    - Wires up `secrets.valheim-password` with encrypted secret file `valheim-password.age` and sets `systemd.services.valheim-password-secret` dependency before `valheim.service`.
+    - Adds `valheim = "valheim.masu.rs"` hostname to `flake.nix` and configures `nmasur.presets.services.cloudflare.noProxyDomains = [ hostnames.valheim ]` for DNS-only UDP routing.
+    - Adds `valheim.enable = lib.mkDefault false;` under `services` in `platforms/nixos/modules/nmasur/profiles/communications.nix`.
+
 - **Separated Restic backup repositories per host**:
   - Updated `services.restic.backups.default.repository` in `platforms/nixos/modules/nmasur/presets/services/restic/restic.nix` to append `/${config.networking.hostName}`, isolating backups by host in S3 (e.g., `.../restic/flame` and `.../restic/swan`).
   - Enabled `services.restic.backups.default.initialize = true` to automatically initialize the repository in S3 if it does not already exist.

flake.lock

@@ -547,6 +547,7 @@
         "nixpkgs-stable": "nixpkgs-stable",
         "nur": "nur",
         "rust-overlay": "rust-overlay",
+        "steam-fetcher": "steam-fetcher",
         "wsl": "wsl",
         "zellij-switch": "zellij-switch",
         "zenyd-mpv-scripts": "zenyd-mpv-scripts"
@@ -570,6 +571,26 @@
         "type": "github"
       }
     },
+    "steam-fetcher": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1758622040,
+        "narHash": "sha256-BRUZZoQDCD1qByJjHm4YKipQlB2PburWLG9Iaggr8XQ=",
+        "owner": "nix-community",
+        "repo": "steam-fetcher",
+        "rev": "ab5e3a0828b4b179feb548c57be584ce812956a8",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "steam-fetcher",
+        "type": "github"
+      }
+    },
     "systems": {
       "locked": {
         "lastModified": 1681028828,

flake.nix

@@ -92,6 +92,12 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
 
+    # Steam depot fetcher
+    steam-fetcher = {
+      url = "github:nix-community/steam-fetcher";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
     # # Text editor
     # helix = {
     #   url = "github:helix-editor/helix";
@@ -166,6 +172,7 @@
           status = "status.${baseName}";
           stream = "stream.${baseName}";
           transmission = "transmission.${baseName}";
+          valheim = "valheim.${baseName}";
         };
 
       lib = import ./lib inputs;

lib/default.nix

@@ -67,6 +67,7 @@ lib
     inputs.nur.overlays.default
     inputs.nix2vim.overlay
     inputs.api.overlays.default
+    inputs.steam-fetcher.overlay
     (final: prev: {
       zellij-switch = inputs.zellij-switch.packages.${prev.stdenv.hostPlatform.system}.default;
     })

overlays/valheim.nix

@@ -0,0 +1,25 @@
+_inputs: final: prev:
+
+{
+  fetchValheimThunderstoreMod =
+    {
+      owner,
+      name,
+      version,
+      hash,
+    }:
+    let
+      depString = "${owner}-${name}";
+    in
+    prev.fetchzip {
+      inherit version hash;
+      name = "valheim-thunderstore-${depString}";
+      url = "https://thunderstore.io/package/download/${owner}/${name}/${version}/";
+      extension = "zip";
+      stripRoot = false;
+    };
+}
+// prev.lib.optionalAttrs (prev.stdenv.hostPlatform.isLinux && prev.stdenv.hostPlatform.isx86_64) {
+  valheim-server = final.nmasur.valheim-server;
+  valheim-server-unwrapped = final.nmasur.valheim-server.unwrapped;
+}

pkgs/valheim-server/package.nix

@@ -0,0 +1,82 @@
+{
+  lib,
+  stdenv,
+  fetchSteam,
+  buildFHSEnv,
+  writeScript,
+  steamworks-sdk-redist,
+  zlib,
+  pulseaudio,
+}:
+
+if !stdenv.hostPlatform.isLinux || !stdenv.hostPlatform.isx86_64 then
+  null
+else
+  let
+    valheim-server-unwrapped = stdenv.mkDerivation (finalAttrs: {
+      pname = "valheim-server-unwrapped";
+      version = "1.0.16";
+
+      src = fetchSteam {
+        name = "valheim-server";
+        appId = "896660";
+        depotId = "896661";
+        manifestId = "1285123405092214913";
+        hash = "sha256-AH9yU0YW0RpgkD9VSGFLj+qIXk3UlvrAgIu9fy/D+N8=";
+      };
+
+      dontBuild = true;
+      dontConfigure = true;
+      dontFixup = true;
+
+      installPhase = ''
+        runHook preInstall
+
+        mkdir -p $out
+        shopt -s nullglob
+        cp -r *.so *.debug valheim_server.x86_64 valheim_server_Data $out
+        chmod +x $out/valheim_server.x86_64
+
+        runHook postInstall
+      '';
+
+      meta = with lib; {
+        description = "Valheim dedicated server (unwrapped)";
+        homepage = "https://steamdb.info/app/896660/";
+        changelog = "https://store.steampowered.com/news/app/892970?updates=true";
+        sourceProvenance = with sourceTypes; [
+          binaryBytecode
+          binaryNativeCode
+        ];
+        license = licenses.unfree;
+        platforms = [ "x86_64-linux" ];
+      };
+    });
+  in
+  buildFHSEnv {
+    name = "valheim-server";
+    pname = "valheim-server";
+    version = valheim-server-unwrapped.version;
+
+    runScript = writeScript "valheim-server-wrapper" ''
+      export LD_LIBRARY_PATH=${steamworks-sdk-redist}/lib:$LD_LIBRARY_PATH
+      export SteamAppId=892970
+      exec ${valheim-server-unwrapped}/valheim_server.x86_64 "$@"
+    '';
+
+    targetPkgs = pkgs: [
+      valheim-server-unwrapped
+      steamworks-sdk-redist
+      zlib
+      pulseaudio
+    ];
+
+    passthru = {
+      unwrapped = valheim-server-unwrapped;
+    };
+
+    meta = valheim-server-unwrapped.meta // {
+      description = "Valheim dedicated server";
+      mainProgram = "valheim-server";
+    };
+  }

platforms/nixos/modules/nmasur/presets/services/valheim/valheim-password.age

@@ -0,0 +1,16 @@
+-----BEGIN AGE ENCRYPTED FILE-----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==
+-----END AGE ENCRYPTED FILE-----

platforms/nixos/modules/nmasur/presets/services/valheim/valheim.nix

@@ -0,0 +1,90 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+
+let
+  inherit (config.nmasur.settings) hostnames;
+  cfg = config.nmasur.presets.services.valheim;
+in
+
+{
+
+  options.nmasur.presets.services.valheim = {
+    enable = lib.mkEnableOption "Valheim dedicated server";
+
+    serverName = lib.mkOption {
+      type = lib.types.str;
+      default = "Midgard";
+      description = "Server name in server browser.";
+    };
+
+    worldName = lib.mkOption {
+      type = lib.types.str;
+      default = "Midgard";
+      description = "World save name.";
+    };
+
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 2456;
+      description = "Server port.";
+    };
+
+    crossplay = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Enable cross-platform play.";
+    };
+
+    openFirewall = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = "Open UDP ports in firewall.";
+    };
+
+    passwordFile = lib.mkOption {
+      type = lib.types.path;
+      default = ./valheim-password.age;
+      description = "Age-encrypted secret file containing the server password.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+
+    allowUnfreePackages = [
+      "valheim-server"
+      "steamworks-sdk-redist"
+    ];
+
+    secrets.valheim-password = {
+      source = cfg.passwordFile;
+      dest = "${config.secretsDirectory}/valheim-password";
+      owner = "valheim";
+      group = "valheim";
+      permissions = "0400";
+    };
+
+    systemd.services.valheim-password-secret = {
+      requiredBy = [ "valheim.service" ];
+      before = [ "valheim.service" ];
+    };
+
+    services.valheim = {
+      enable = true;
+      serverName = cfg.serverName;
+      worldName = cfg.worldName;
+      port = cfg.port;
+      crossplay = cfg.crossplay;
+      openFirewall = cfg.openFirewall;
+      passwordFile = config.secrets.valheim-password.dest;
+    };
+
+    # Configure Cloudflare DNS (no proxy for UDP game traffic)
+    nmasur.presets.services.cloudflare.noProxyDomains = [ hostnames.valheim ];
+
+  };
+
+}

platforms/nixos/modules/nmasur/profiles/communications.nix

@@ -61,6 +61,7 @@ in
         stalwart.enable = lib.mkDefault true;
         thelounge.enable = lib.mkDefault true;
         uptime-kuma.enable = lib.mkDefault true;
+        valheim.enable = lib.mkDefault false;
         vaultwarden.enable = lib.mkDefault true;
         victoriametrics.enable = lib.mkDefault true;
       };

platforms/nixos/modules/services/valheim.nix

@@ -0,0 +1,249 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+
+let
+  cfg = config.services.valheim;
+
+  startScript = pkgs.writeShellScriptBin "valheim-server-start" ''
+    set -euo pipefail
+
+    CONFIG_DIR="${cfg.dataDir}/.config/unity3d/IronGate/Valheim"
+    mkdir -p "$CONFIG_DIR"
+
+    ${lib.optionalString (cfg.adminList != [ ]) ''
+      cat << 'EOF' > "$CONFIG_DIR/adminlist.txt"
+      // List of Steam IDs for adminlist ONE per line
+      ${lib.concatStringsSep "\n" cfg.adminList}
+      EOF
+    ''}
+
+    ${lib.optionalString (cfg.permittedList != [ ]) ''
+      cat << 'EOF' > "$CONFIG_DIR/permittedlist.txt"
+      // List of Steam IDs for permittedlist ONE per line
+      ${lib.concatStringsSep "\n" cfg.permittedList}
+      EOF
+    ''}
+
+    ${lib.optionalString (cfg.bannedList != [ ]) ''
+      cat << 'EOF' > "$CONFIG_DIR/bannedlist.txt"
+      // List of Steam IDs for bannedlist ONE per line
+      ${lib.concatStringsSep "\n" cfg.bannedList}
+      EOF
+    ''}
+
+    ${
+      if cfg.passwordFile != null then
+        ''
+          if [ ! -f "${cfg.passwordFile}" ]; then
+            echo "Valheim password file '${cfg.passwordFile}' not found!" >&2
+            exit 1
+          fi
+          PASS="$(tr -d '\r\n' < '${cfg.passwordFile}')"
+        ''
+      else
+        ''
+          PASS="${cfg.password}"
+        ''
+    }
+
+    if [ ''${#PASS} -lt 5 ]; then
+      echo "Valheim server password must be at least 5 characters long!" >&2
+      exit 1
+    fi
+
+    ARGS=(
+      "-name" "${cfg.serverName}"
+      "-port" "${toString cfg.port}"
+      "-world" "${cfg.worldName}"
+      "-password" "$PASS"
+      "-public" "${if cfg.public then "1" else "0"}"
+    )
+
+    ${lib.optionalString cfg.crossplay ''ARGS+=("-crossplay")''}
+    ${lib.optionalString (cfg.saveDir != null) ''ARGS+=("-savedir" "${cfg.saveDir}")''}
+    ${lib.concatMapStringsSep "\n" (arg: ''ARGS+=("${arg}")'') cfg.extraArgs}
+
+    exec ${cfg.package}/bin/valheim-server "''${ARGS[@]}"
+  '';
+
+in
+{
+
+  options.services.valheim = {
+    enable = lib.mkEnableOption "Valheim dedicated server";
+
+    package = lib.mkOption {
+      type = lib.types.package;
+      default = pkgs.valheim-server;
+      defaultText = lib.literalExpression "pkgs.valheim-server";
+      description = "The valheim-server package to use.";
+    };
+
+    serverName = lib.mkOption {
+      type = lib.types.str;
+      default = "Valheim Server";
+      example = "Some cozy server";
+      description = "The name listed in the server browser.";
+    };
+
+    worldName = lib.mkOption {
+      type = lib.types.str;
+      default = "Dedicated";
+      example = "Midgard";
+      description = ''
+        The name of the world file to use, without the extension.
+        If the world does not exist, the server will generate a world from a random seed.
+      '';
+    };
+
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 2456;
+      description = ''
+        The port on which to listen for incoming connections.
+        Ports (port + 1) and (port + 2) are used for Steam queries and routing.
+      '';
+    };
+
+    crossplay = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Whether to enable cross-platform play via PlayFab backend.";
+    };
+
+    public = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = "Whether to list the server in the public server browser.";
+    };
+
+    openFirewall = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Whether to open UDP ports in the firewall.";
+    };
+
+    password = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      description = ''
+        The server password in plain text.
+        Prefer `passwordFile` to avoid storing passwords in the world-readable Nix store.
+      '';
+    };
+
+    passwordFile = lib.mkOption {
+      type = lib.types.nullOr (lib.types.either lib.types.str lib.types.path);
+      default = null;
+      description = "Path to file containing the server password.";
+    };
+
+    dataDir = lib.mkOption {
+      type = lib.types.path;
+      default = "/var/lib/valheim";
+      description = "Directory for valheim server data and state.";
+    };
+
+    saveDir = lib.mkOption {
+      type = lib.types.nullOr lib.types.path;
+      default = null;
+      description = "Directory where world saves are placed (-savedir). Defaults to Unity config dir in dataDir.";
+    };
+
+    adminList = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      example = [ "72057602627862526" ];
+      description = "List of Steam IDs to add to adminlist.txt.";
+    };
+
+    permittedList = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      example = [ "72057602627862526" ];
+      description = "List of Steam IDs to add to permittedlist.txt.";
+    };
+
+    bannedList = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      example = [ "72057602627862526" ];
+      description = "List of Steam IDs to add to bannedlist.txt.";
+    };
+
+    bepinexMods = lib.mkOption {
+      type = lib.types.listOf lib.types.package;
+      default = [ ];
+      description = "BepInEx mods to install.";
+    };
+
+    bepinexConfigs = lib.mkOption {
+      type = lib.types.listOf lib.types.path;
+      default = [ ];
+      description = "Config files for BepInEx mods.";
+    };
+
+    extraArgs = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      description = "Extra command line arguments to pass to valheim-server.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+
+    users.users.valheim = {
+      isSystemUser = true;
+      group = "valheim";
+      home = cfg.dataDir;
+      createHome = true;
+    };
+    users.groups.valheim = { };
+
+    systemd.services.valheim = {
+      description = "Valheim dedicated server";
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+      path = with pkgs; [ coreutils ];
+      serviceConfig = {
+        Type = "exec";
+        User = "valheim";
+        Group = "valheim";
+        StateDirectory = "valheim";
+        WorkingDirectory = cfg.dataDir;
+        Restart = "on-failure";
+        RestartSec = "10s";
+        ExecStart = "${startScript}/bin/valheim-server-start";
+      };
+    };
+
+    networking.firewall = lib.mkIf cfg.openFirewall {
+      allowedUDPPorts = [
+        cfg.port
+        (cfg.port + 1)
+        (cfg.port + 2)
+      ];
+    };
+
+    assertions = [
+      {
+        assertion = cfg.serverName != "";
+        message = "services.valheim.serverName must not be empty.";
+      }
+      {
+        assertion = cfg.worldName != "";
+        message = "services.valheim.worldName must not be empty.";
+      }
+      {
+        assertion = (cfg.password != null && cfg.password != "") || cfg.passwordFile != null;
+        message = "services.valheim requires either services.valheim.password or services.valheim.passwordFile to be set.";
+      }
+    ];
+
+  };
+
+}