Nix Flakes

Modern Nix project management with hermeticity and reproducibility through flake.lock.

Core Commands

Project Management

Initialize a new flake in the current directory

nix flake init

Create a new flake from template

nix flake new hello -t templates#hello

Update flake.lock (updates all inputs)

nix flake update

Update specific input only

nix flake update nixpkgs

Lock without updating (create missing entries)

nix flake lock

Check flake for syntax and common errors

nix flake check

Show flake outputs

nix flake show

Show flake metadata (inputs, revisions)

nix flake metadata path:. nix flake info path:. # Alias for metadata

Prefetch flake and inputs into store

nix flake prefetch github:NixOS/nixpkgs nix flake prefetch-inputs path:.

Clone flake repository

nix flake clone nixpkgs --dest ./nixpkgs

Running and Building

Always prefix local flake paths with path: (e.g., path:. ) to ensure Nix uses all files in the directory without requiring them to be staged in Git.

Build the default package

nix build path:.

Build a specific output

nix build path:.#packageName

Run the default app

nix run path:.

Run a specific app from a flake

nix run path:.#appName

Run an app from a remote flake

nix run github:numtide/treefmt

Development Environments

In a headless environment, use nix develop with --command to run tasks within the environment.

Run a command inside the devShell

nix develop path:. --command make build

Check if current environment matches devShell

nix develop path:. --command env

Flake Structure (flake.nix )

A basic flake.nix pattern:

{ description = "A basic flake";

inputs = { nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable"; };

outputs = { self, nixpkgs }: let system = "x86_64-linux"; pkgs = nixpkgs.legacyPackages.${system}; in { packages.${system}.default = pkgs.hello;

  devShells.${system}.default = pkgs.mkShell {
    buildInputs = [ pkgs.git pkgs.vim ];
  };
};

}

Best Practices

• Locking: Manage the flake.lock file to ensure reproducibility.

• Purity: Flakes are "pure" by default. They cannot access files outside the flake directory unless they are tracked (e.g. in the git tree if using git).

• Non-Interactive: When using nix develop , always use the --command flag to ensure scripts remain non-interactive.

Debugging Flakes

Inspect inputs

nix flake metadata path:.

Evaluate a specific output

nix eval path:.#packages.x86_64-linux.default.name

Related Skills

• nix: Run applications without installation and create development environments using Nix.

• nh: Manage NixOS and Home Manager operations with improved output using nh.

Related Tools

• search-nix-packages: Search for packages available in the NixOS package repository when working with flakes.

• search-nix-options: Find configuration options available in NixOS for flake configurations.

• search-home-manager-options: Find configuration options for Home Manager in flake setups.