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Nix Best Practices
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Comprehensive Nix best practices for flakes, NixOS, home-manager, nix-darwin, devshells, package management, and system configuration. Use this skill when working with Nix flakes, NixOS configuration, home-manager dotfiles, nix-darwin macOS setup, development shells (nix develop/nix-shell), package searching, testing, overlays, or any Nix-related tasks including debugging derivations and garbage collection.
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Showing SKILL.md
| name | nix |
| description | Nix Best Practices |
Comprehensive guide for working with Nix, including flakes, NixOS, home-manager, nix-darwin, and development environments.
Always prefer flakes over channels for new projects. Flakes provide:
flake.lock# In configuration.nix or nix.conf
nix.settings.experimental-features = [ "nix-command" "flakes" ];
nixos-config/
├── flake.nix # Entry point
├── flake.lock # Pinned dependencies
├── systems/ # Per-machine configs
│ ├── x86_64-linux/
│ │ └── hostname/default.nix
│ └── aarch64-darwin/
│ └── hostname/default.nix
├── modules/
│ ├── nixos/ # NixOS-specific modules
│ ├── darwin/ # macOS-specific modules
│ └── home/ # Home-manager (cross-platform)
├── homes/ # Per-user home-manager configs
├── packages/ # Custom packages
└── secrets/ # Encrypted secrets (sops-nix)
Configurations build up in layers, each can override the previous:
# BAD: Implicit scope with `with`
environment.systemPackages = with pkgs; [ git vim wget ];
# GOOD: Explicit references
environment.systemPackages = [ pkgs.git pkgs.vim pkgs.wget ];
# Or use a let binding
environment.systemPackages = let p = pkgs; in [ p.git p.vim p.wget ];
# Build and switch NixOS configuration
sudo nixos-rebuild switch --flake .#hostname
# Build and switch nix-darwin
darwin-rebuild switch --flake .#hostname
# Build home-manager standalone
home-manager switch --flake .#user@hostname
# Update all flake inputs
nix flake update
# Update specific input
nix flake update nixpkgs
# Search packages
nix search nixpkgs packagename
# Enter development shell
nix develop
# Garbage collection (with generation cleanup)
sudo nix-collect-garbage -d --delete-older-than 7d
# Show flake outputs
nix flake show
# Check flake for errors
nix flake check
{
description = "NixOS configuration";
inputs = {
nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
home-manager = {
url = "github:nix-community/home-manager";
inputs.nixpkgs.follows = "nixpkgs"; # Avoid duplicate nixpkgs
};
};
outputs = { self, nixpkgs, home-manager, ... }@inputs: {
nixosConfigurations.hostname = nixpkgs.lib.nixosSystem {
system = "x86_64-linux";
specialArgs = { inherit inputs; }; # Pass inputs to modules
modules = [
./configuration.nix
home-manager.nixosModules.home-manager
{
home-manager.useGlobalPkgs = true;
home-manager.useUserPackages = true;
home-manager.users.username = import ./home.nix;
}
];
};
};
}
# modules/home/git/default.nix
{ config, lib, pkgs, ... }:
let
cfg = config.custom.git;
in {
options.custom.git = {
enable = lib.mkEnableOption "Git configuration";
userName = lib.mkOption {
type = lib.types.str;
description = "Git user name";
};
userEmail = lib.mkOption {
type = lib.types.str;
description = "Git user email";
};
};
config = lib.mkIf cfg.enable {
programs.git = {
enable = true;
userName = cfg.userName;
userEmail = cfg.userEmail;
extraConfig = {
init.defaultBranch = "main";
pull.rebase = true;
};
};
};
}
# In flake.nix inputs
sops-nix.url = "github:Mic92/sops-nix";
# In configuration
sops = {
defaultSopsFile = ./secrets/secrets.yaml;
age.keyFile = "/var/lib/sops-nix/key.txt";
secrets.my-secret = {};
};
| Library | Purpose |
|---|---|
| Snowfall Lib | Standardized config structure |
| sops-nix | Encrypted secrets in git |
| home-manager | User environment management |
| nix-darwin | macOS declarative config |
| flake-utils | Multi-system helpers |
| devenv | Simplified dev environments |
follows to avoid duplicate nixpkgs in inputswith pkgslib.mkIf for conditional configurationnixos-rebuild build first