NixOS modules: Difference between revisions

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# Option declarations.

# Declare what settings a user of this module module can set.

# Usually this includes an "enable" option to ~~let a user of this module choose~~.

# Usually this includes a global "enable" option which defaults to false.

};

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# Option definitions.

# Define what other settings, services and resources should be active.

# Usually these ~~are~~ depend on whether a user of this module chose to "enable" it

# Usually these depend on whether a user of this module chose to "enable" it

# using the "option" above.

# ~~You also set options here~~ for modules ~~that you~~ imported in "imports".

# Options for modules imported in "imports" can be set here.

};

}

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];

# ~~Option~~ definitions.

# Config definitions.

services.othermodule.enable = true;

# ...

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<dt><code>options</code></dt>

<dd>All option declarations refined with all definition and declaration references.</dd>

<dd>An instance of the nixpkgs "standard library", providing what usually is in <code>pkgs.lib</code>.</dd>

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</dl>

==== Passing custom values to modules ====

The [[NixOS:config_argument|<code>config</code>]], <code>options</code>, <code>lib</code>, <code>pkgs</code>, and <code>modulesPath</code> arguments are passed automatically to modules, when the module is imported.

For example, in the following Nix flake, the `./configuration.nix` file will be provided with the default set of arguments listed above, plus `extraArg`, which was set in the `specialArgs` argument to the `nixosGenerate` function.<syntaxhighlight lang="nix">

{

inputs = {

nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.11";

nixos-generators = {

url = "github:nix-community/nixos-generators";

inputs.nixpkgs.follows = "nixpkgs";

};

xc = {

url = "github:joerdav/xc";

inputs.nixpkgs.follows = "nixpkgs";

};

outputs = { nixpkgs, nixos-generators, xc, ... }:

let

pkgsForSystem = system: import nixpkgs {

inherit system;

overlays = [

(final: prev: { xc = xc.packages.${system}.xc; })

];

};

allVMs = [ "x86_64-linux" "aarch64-linux" ];

forAllVMs = f: nixpkgs.lib.genAttrs allVMs (system: f {

inherit system;

pkgs = pkgsForSystem system;

});

in

{

packages = forAllVMs ({ system, pkgs }: {

vm = nixos-generators.nixosGenerate {

system = system;

specialArgs = {

extraArg = "foobar";

};

modules = [

./configuration.nix

];

format = "raw";

};

});

};

}

</syntaxhighlight>

==== modulesPath ====

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</syntaxhighlight>

They are created with {{ic|mkOption}}, a function accepting a set with following attributes:<ref>{{Nixpkgs Link|lib/options.nix#~~L51~~-~~L84~~}}</ref><ref>{{manual:nixos|sec=#sec-option-declarations|chapter=42.1. Option Declarations}}</ref>

They are created with {{ic|mkOption}}, a function accepting a set with following attributes:<ref>{{Nixpkgs Link|lib/options.nix#L66-L88}}</ref><ref>{{manual:nixos|sec=#sec-option-declarations|chapter=42.1. Option Declarations}}</ref>

<dl>

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</syntaxhighlight>

If you're developing on top of master, this will potentially cause the compilation of lots of packages, since changes on master might not cached on cache.nixos.org yet. To avoid that, you can develop your module on top of the <code>nixos-unstable</code> [[~~Channels~~|channel]], tracked by the eponymous branch in https://github.com/NixOS/nixpkgs:

If you're developing on top of master, this will potentially cause the compilation of lots of packages, since changes on master might not cached on cache.nixos.org yet. To avoid that, you can develop your module on top of the <code>nixos-unstable</code> [[Channel branches|channel branch]], tracked by the eponymous branch in https://github.com/NixOS/nixpkgs:

git checkout -b mymodule upstream/nixos-unstable

</syntaxhighlight>

=== With Flakes ===

If you're developing a module from nixpkgs, you can try and follow the directions here: https://github.com/Misterio77/nix-starter-configs/issues/28.

If you want to develop a module from a git repo, you can use `--override-input`. For example, if you have an input in your flake called {{ic|jovian}},, you can use

nixos-rebuild switch --override-input jovian <path-to-url>` --flake <uri>

</syntaxhighlight>

Of course, it doesn't have to be {{|c|nixos-rebuild}} in particular.

== References ==