NixOS Core Skill

Validation Flow

1. •Edit file -> nix-instantiate --parse
2. •Before commit -> nix flake check
3. •Before switch -> nixos-rebuild build
4. •Apply -> nixos-rebuild switch

Module Structure

Always use:

{ config, lib, pkgs, ... }:
let cfg = config.modules.X; in
{
  options.modules.X = { enable = lib.mkEnableOption "X"; };
  config = lib.mkIf cfg.enable { ... };
}

Common lib Functions

• •lib.mkIf - Conditional config
• •lib.mkEnableOption - Boolean enable option
• •lib.mkOption - Custom option
• •lib.mkDefault - Default with low priority
• •lib.mkForce - Override with high priority
• •lib.mkMerge - Merge multiple configs
• •lib.optionals - Conditional list items
• •lib.optionalString - Conditional string
• •lib.recursiveUpdate - Deep merge attribute sets

Build Commands

# Syntax check single file
nix-instantiate --parse <file.nix>

# Check all files
find /etc/nixos -name "*.nix" -not -path "*/.git/*" -exec nix-instantiate --parse {} \;

# Flake check
nix flake check

# Dry build
sudo nixos-rebuild dry-build --flake /etc/nixos#hanibal

# Build without activating
sudo nixos-rebuild build --flake /etc/nixos#hanibal

# Apply changes
sudo nixos-rebuild switch --flake /etc/nixos#hanibal

# Test without making permanent
sudo nixos-rebuild test --flake /etc/nixos#hanibal

Anti-Patterns

• •Hardcoded paths (use pkgs.X or options)
• •with pkgs; at module level (pollutes scope)
• •Missing lib.mkIf for conditional config
• •Circular imports
• •Modifying hardware-configuration.nix
• •Using rec { } instead of let ... in
• •Top-level with statements
• •Using <nixpkgs> lookup paths

Essential Arguments

Always include in module arguments:

{ config, lib, pkgs, ... }:  # ... is critical!

Priority System