README.md

Valheim Server Flake

A Nix flake for the Valheim dedicated server, providing both an overlay and a NixOS module.

Usage

(Your NixOS system configuration must already be a flake.)

Add this flake as an input, and add the NixOS module. Your config should look something like this.

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-22.11";
    valheim-server = {
      url = "github:aidalgol/valheim-server-flake";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };
  outputs = {
    self,
    nixpkgs,
    valheim-server,
  }: let
    system = "x86_64-linux";
    pkgs = import nixpkgs {inherit system;};
  in {
    nixosConfigurations.my-server= nixpkgs.lib.nixosSystem {
      inherit system;
      modules = [
        ./configuration.nix
        valheim-server.nixosModules.default
      ];
    };
  };
}

Then in your configuration.nix,

{
  config,
  pkgs,
  ...  
}: {
  # ...
  nixpkgs.config.allowUnfreePredicate = pkg:
    builtins.elem (lib.getName pkg) [
      "valheim-server"
      "steamworks-sdk-redist"
    ];
  # ...
  services.valheim = {
    enable = true;
    serverName = "Some cozy server";
    worldName = "Midgard";
    openFirewall = true;
    password = "sekkritpasswd";
    # If you want to use BepInEx mods.
    bepinexMods = [
      # This does NOT fetch mod dependencies.  You need to add those manually,
      # if there are any (besides BepInEx).
      (pkgs.fetchValheimThunderstoreMod {
        owner = "Somebody";
        name = "SomeMod";
        version = "x.y.z";
        hash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
      })
      # ...
    ];
    bepinexConfigs = [
      ./some_mod.cfg
      # ...
    ];
  };
  # ...
}

Managing the server

The NixOS module in this flake runs Valheim server as a systemd service, which you can manage this service using systemctl and journalctl.

# Start, stop, or restart the server (requires superuser).
$ systemctl <start|stop|restart> valheim

# Show the runtime status with most recent log data. 
$ systemctl status valheim

Note that nixos-rebuild switch automatically restarts the service if any attributes under services.valheim are changed. Also be aware that stopping a service does not disable it, and the service will be started again on next boot, nixos-rebuild switch, etc.

# Show live log from the service.
$ journalctl -u valheim -f

Notes on using mods

Because BepInEx (the mod framework used by just about every Valheim mod) must both be installed in-tree with Valheim, and to be able to write to various files in the directory tree, we cannot run the modded Valheim server from the Nix store. To work around this without completely giving up on immutability, we copy the files out of the Nix store to a directory under /var/lib/valheim and run from there, but wipe and rebuild this directory on each launch.