add-system-service

name	add-system-service
description	This skill should be used when the user asks to "add a service", "install docker", "enable a system service", "add podman", "enable virtualization", or wants to add any system-level service to NixOS. Provides patterns for creating service modules and integrating them with hosts.

Adding System Services to NixOS

This skill covers adding system-level services (Docker, databases, etc.) to the NixOS configuration.

Service Module Location

system/services/<service-name>.nix

Standard Service Pattern

# system/services/<service-name>.nix
{ config, pkgs, user, ... }: {
  # Enable the service
  services.<service-name>.enable = true;

  # Add user to service group if needed
  users.users.${user}.extraGroups = [ "<service-group>" ];

  # Install related tools
  environment.systemPackages = with pkgs; [
    <related-package>
  ];
}

Docker Example

# system/services/docker.nix
{ pkgs, user, ... }: {
  virtualisation.docker = {
    enable = true;
    enableOnBoot = true;
  };
  users.users.${user}.extraGroups = [ "docker" ];
  environment.systemPackages = [ pkgs.docker-compose ];
}

PostgreSQL Example

# system/services/postgresql.nix
{ pkgs, ... }: {
  services.postgresql = {
    enable = true;
    package = pkgs.postgresql_15;
    enableTCPIP = true;
    authentication = ''
      local all all trust
      host all all 127.0.0.1/32 trust
    '';
  };
}

Integration Steps

1. Create the service module in system/services/

2. Import in host config:

# hosts/<hostname>/default.nix
imports = [
  ./hardware.nix
  ../../system/profiles/desktop.nix
  ../../system/services/<service-name>.nix  # Add this
];

3. Rebuild and switch:

sudo nixos-rebuild switch --flake .#<hostname>

4. For VM development, use dev-sync:

./scripts/dev-sync rebuild

Common Services

Service	NixOS Option	Group
Docker	virtualisation.docker	docker
Podman	virtualisation.podman	-
PostgreSQL	services.postgresql	-
MySQL	services.mysql	-
Redis	services.redis	-
nginx	services.nginx	-

Verification

After rebuild, verify service is running:

systemctl status <service-name>

# For Docker
docker run hello-world

Important Notes

• The user variable comes from flake.nix extraSpecialArgs
• Services in system/services/ are opt-in per host
• Don't add services directly to system/base/ (those apply to all hosts)