NixOS modules: Difference between revisions
imported>Malteneuss m Add imports vs import note which trips ups beginners often |
imported>Malteneuss m Improve structure and reuse formulations |
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'''Modules''' | NixOS produces a full system configuration by combining smaller, more isolated and reusable components: '''Modules'''. A module is a file containing a Nix expression with a specific structure. It ''declares'' options for other modules to ''define'' (give a value). It processes them and defines options declared in other modules.<ref>{{manual:nixos|sec=#sec-writing-modules|chapter=Chapter 42. Writing NixOS Modules}}</ref> | ||
For example, {{ic|/etc/nixos/configuration.nix}} is a module. Most other modules are in {{Nixpkgs Link|nixos/modules}}. | For example, {{ic|/etc/nixos/configuration.nix}} is a module. Most other modules are in {{Nixpkgs Link|nixos/modules}}. | ||
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== Example == | == Example == | ||
put | To see how modules are setup and reuse other modules in practice put <code>hello.nix</code> in the same folder as your <code>configuration.nix</code>: | ||
<syntaxhighlight lang="nix"> | <syntaxhighlight lang="nix"> | ||
{ lib, pkgs, config, ... }: | { lib, pkgs, config, ... }: | ||
with lib; | with lib; | ||
let | let | ||
# Shorter name to access final settings a | |||
# user of hello.nix module HAS ACTUALLY SET. | |||
# cfg is a typical convention. | |||
cfg = config.services.hello; | cfg = config.services.hello; | ||
in { | in { | ||
# Declare what settings a user of this "hello.nix" module CAN SET. | |||
options.services.hello = { | options.services.hello = { | ||
enable = mkEnableOption "hello service"; | enable = mkEnableOption "hello service"; | ||
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}; | }; | ||
# Define what other settings, services and resources should be active IF | |||
# a user of this "hello.nix" module ENABLED this module | |||
# by setting "services.hello.enable = true;". | |||
config = mkIf cfg.enable { | config = mkIf cfg.enable { | ||
systemd.services.hello = { | systemd.services.hello = { | ||
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</syntaxhighlight> | </syntaxhighlight> | ||
The other <code>configuration.nix</code> module can then import this <code>hello.nix</code> module | |||
and decide to enable it (and optionally set other allowed settings) as follows: | |||
<syntaxhighlight lang=nix> | <syntaxhighlight lang=nix> | ||
{ | { | ||