Flake structure: inputs and outputs

Basic Flake structure#

A typical flake.nix is an attribute set in which outputs is a function that takes inputs and returns an output attribute set.

{
  description = "我的 NixOS 配置";

  inputs = {
    # 这里定义依赖
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    home-manager.url = "github:nix-community/home-manager";
  };

  outputs = { self, nixpkgs, ... }@inputs: {
    # 这里定义产出（系统配置、软件包、Shell 环境等）
    nixosConfigurations.my-host = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [ ./configuration.nix ];
    };
  };
}

1. Inputs#

inputs contains the external resources you want to reference.

• nixpkgs: the entire package repository.

• home-manager: a user-level configuration tool.

• flake-utils: a commonly used helper library.

• The follows keyword: very important! It makes a specified nested input follow the top-level nixpkgs, reducing duplicate nixpkgs sources in the dependency graph. Multiple package versions may still exist, and sharing an input does not guarantee compatibility across all external projects.

  EXCERPTCopy code

  home-manager.inputs.nixpkgs.follows = "nixpkgs";

2. Outputs#

outputs contains what your Flake produces.

• nixosConfigurations: used by nixos-rebuild; your system is at its core.
• homeConfigurations: used by home-manager.
• devShells: development environments used by nix develop.
• packages: software you package yourself.

What are self and @inputs here?#

• self: represents the current Flake itself. You can use it to reference files defined within it.
• @inputs: syntactic sugar that captures all input arguments together.

Practical tip: understand the outputs hierarchy#

Running nix flake show displays the outputs as a tree. Those levels must match exactly in your code for nixos-rebuild to find your configuration.