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267 lines
10 KiB
Markdown
267 lines
10 KiB
Markdown
# Enabling NixOS with Flakes
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## Enabling Flakes Support
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Flakes provide improved reproducibility and a more organized package structure, making it easier to maintain NixOS configurations compared to the traditional approach. Therefore, it is recommended to manage NixOS using Flakes.
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However, as Flakes is still an experimental feature, it is not enabled by default. To enable Flakes, you need to modify the `/etc/nixos/configuration.nix` file as follows:
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```nix{15,18-19}
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# Edit this configuration file to define what should be installed on
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# your system. Help is available in the configuration.nix(5) man page
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# and in the NixOS manual (accessible by running 'nixos-help').
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{ config, pkgs, ... }:
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{
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imports =
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[ # Include the results of the hardware scan.
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./hardware-configuration.nix
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];
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# Omit the previous configuration...
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# Enable Flakes and the new command-line tool
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nix.settings.experimental-features = [ "nix-command" "flakes" ];
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environment.systemPackages = with pkgs; [
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# Flakes use Git to pull dependencies from data sources, so Git must be installed first
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git
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vim
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wget
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curl
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];
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# Omit the rest of the configuration...
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}
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```
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To apply the changes, run `sudo nixos-rebuild switch`. After that, you can start writing the configuration for NixOS using Flakes.
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## Switching to `flake.nix` for System Configuration
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After enabling `flakes`, whenever you run `sudo nixos-rebuild switch`, it will first attempt to read the `/etc/nixos/flake.nix` file. If the file is not found, it will fallback to `/etc/nixos/configuration.nix`.
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To learn how to write a Flakes configuration, you can refer to the official Flakes templates provided by Nix. To check the available templates, run the following command:
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```bash
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nix flake show templates
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```
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The `templates#full` template contains examples covering various use cases. Let's take a look at them:
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```bash
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nix flake init -t templates#full
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cat flake.nix
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```
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After reviewing the example, create a file named `/etc/nixos/flake.nix` and copy the content of the example into it. From now on, all system modifications will be managed by Flakes using `/etc/nixos/flake.nix`.
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Note that the copied template cannot be used directly. You need to modify it to make it work. Here's an example of `/etc/nixos/flake.nix`:
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```nix
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{
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description = "Ryan's NixOS Flake";
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# This is the standard format for flake.nix.
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# `inputs` are the dependencies of the flake,
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# and `outputs` function will return all the build results of the flake.
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# Each item in `inputs` will be passed as a parameter to
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# the `outputs` function after being pulled and built.
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inputs = {
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# There are many ways to reference flake inputs.
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# The most widely used is `github:owner/name/reference`,
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# which represents the GitHub repository URL + branch/commit-id/tag.
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# Official NixOS package source, using nixos-unstable branch here
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nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
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# home-manager, used for managing user configuration
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home-manager = {
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url = "github:nix-community/home-manager/release-23.05";
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# The `follows` keyword in inputs is used for inheritance.
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# Here, `inputs.nixpkgs` of home-manager is kept consistent with
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# the `inputs.nixpkgs` of the current flake,
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# to avoid problems caused by different versions of nixpkgs.
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inputs.nixpkgs.follows = "nixpkgs";
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};
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};
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# `outputs` are all the build result of the flake.
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# A flake can have many use cases and different types of outputs.
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# parameters in `outputs` are defined in `inputs` and
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# can be referenced by their names. However, `self` is an exception,
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# this special parameter points to the `outputs` itself(self-reference)
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# The `@` syntax here is used to alias the attribute set of the
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# inputs's parameter, making it convenient to use inside the function.
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outputs = { self, nixpkgs, ... }@inputs: {
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nixosConfigurations = {
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# By default, NixOS will try to refer the nixosConfiguration with
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# its hostname, so the system named `nixos-test` will use this one.
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# However, the configuration name can also be specified using:
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# sudo nixos-rebuild switch --flake /path/to/flakes/directory#<name>
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#
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# The `nixpkgs.lib.nixosSystem` function is used to build this
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# configuration, the following attribute set is its parameter.
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#
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# Run the following command in the flake's directory to
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# deploy this configuration on any NixOS system:
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# sudo nixos-rebuild switch --flake .#nixos-test
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"nixos-test" = nixpkgs.lib.nixosSystem {
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system = "x86_64-linux";
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# The Nix module system can modularize configuration,
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# improving the maintainability of configuration.
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#
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# Each parameter in the `modules` is a Nix Module, and
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# there is a partial introduction to it in the nixpkgs manual:
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# <https://nixos.org/manual/nixpkgs/unstable/#module-system-introduction>
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# It is said to be partial because the documentation is not
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# complete, only some simple introductions.
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# such is the current state of Nix documentation...
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#
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# A Nix Module can be an attribute set, or a function that
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# returns an attribute set. By default, if a Nix Module is a
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# function, this function can only have the following parameters:
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#
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# lib: the nixpkgs function library, which provides many
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# useful functions for operating Nix expressions:
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# https://nixos.org/manual/nixpkgs/stable/#id-1.4
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# config: all config options of the current flake
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# options: all options defined in all NixOS Modules
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# in the current flake
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# pkgs: a collection of all packages defined in nixpkgs.
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# you can assume its default value is
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# `nixpkgs.legacyPackages."${system}"` for now.
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# can be customed by `nixpkgs.pkgs` option
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# modulesPath: the default path of nixpkgs's modules folder,
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# used to import some extra modules from nixpkgs.
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# this parameter is rarely used,
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# you can ignore it for now.
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#
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# Only these parameters can be passed by default.
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# If you need to pass other parameters,
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# you must use `specialArgs` by uncomment the following line:
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#
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# specialArgs = {...} # pass custom arguments into all sub module.
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modules = [
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# Import the configuration.nix here, so that the
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# old configuration file can still take effect.
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# Note: configuration.nix itself is also a Nix Module,
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./configuration.nix
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];
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};
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};
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};
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}
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```
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We defined a NixOS system called `nixos-test` with a configuration file at `./configuration.nix`, which is the classic configuration we modified before. Therefore, we can still make use of it.
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To apply the configuration to a system with hostname `nixos-test`, run `sudo nixos-rebuild switch`. No changes will be made to the system because we imported the old configuration file in `/etc/nixos/flake.nix`, so the actual state we declared remains unchanged.
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## Managing System Packages with Flakes
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After the switch, we can manage the system using Flakes. One common requirement is installing packages. We have previously seen how to install packages using `environment.systemPackages` from the official `nixpkgs` repository.
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Now let's learn how to install packages from other sources using Flakes. This provides greater flexibility, particularly when it comes to specifying software versions. Let's use [Helix](https://github.com/helix-editor/helix) editor as an example.
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First, we need to add Helix as an input in `flake.nix`:
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```nix{10,20}
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{
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description = "NixOS configuration of Ryan Yin";
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# ...
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inputs = {
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# ...
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# Helix editor, using version 23.05
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helix.url = "github:helix-editor/helix/23.05";
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};
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outputs = inputs@{ self, nixpkgs, ... }: {
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nixosConfigurations = {
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nixos-test = nixpkgs.lib.nixosSystem {
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system = "x86_64-linux";
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# Set all input parameters as specialArgs of all sub-modules
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# so that we can use the `helix` input in sub-modules
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specialArgs = inputs;
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modules = [
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./configuration.nix
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];
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};
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};
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};
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}
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```
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Next, update `configuration.nix` to install `helix` from the `helix` input:
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```nix{3,14-15}
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# Nix will automatically inject `helix` from specialArgs
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# into the third parameter of this function through name matching
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{ config, pkgs, helix, ... }:
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{
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# Omit other configurations...
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environment.systemPackages = with pkgs; [
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git
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vim
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wget
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curl
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# Install Helix from the `helix` input
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helix.packages."${pkgs.system}".helix
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];
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# Omit other configurations...
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}
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```
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To deploy the changes, run `sudo nixos-rebuild switch`. After that, you can start the Helix editor by running the `hx` command.
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## Adding Custom Cache Mirrors
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> If you don't need to customize the cache mirror, you can safely skip this section.
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To accelerate package building, Nix provides <https://cache.nixos.org> to cache build results and avoid rebuilding packages locally.
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With the classic configuration method in NixOS, additional cache sources can be added using `nix-channel`. However, Nix Flakes strives to avoid using any system-level configurations or environment variables as much as possible, ensuring that its build results are not affected by the environment. Therefore, after switching to Flakes, the `nix-channel` command becomes ineffective.
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To customize the cache source, we must add the related configuration in `flake.nix` using the `nixConfig` parameter. Here's an example:
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```nix{4-19}
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{
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description = "NixOS configuration of Ryan Yin";
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nixConfig = {
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experimental-features = [ "nix-command" "flakes" ];
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substituters = [
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# Replace the official cache with a mirror located in China
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"https://mirrors.bfsu.edu.cn/nix-channels/store"
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"https://cache.nixos.org/"
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];
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extra-substituters = [
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# Nix community's cache server
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"https://nix-community.cachix.org"
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];
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extra-trusted-public-keys = [
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"nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
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];
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};
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inputs = {
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# Omit some configurations...
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};
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outputs = {
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# Omit some configurations...
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};
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}
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```
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After making the modifications, run `sudo nixos-rebuild switch` to apply the updates.
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