# Replace Modules

Modules that are imported can also be disabled. The option declarations, config implementation and the imports of a disabled module will be ignored, allowing another to take it's place. This can be used to import a set of modules from another channel while keeping the rest of the system on a stable release.

`disabledModules` is a top level attribute like `imports`, `options` and `config`. It contains a list of modules that will be disabled. This can either be the full path to the module or a string with the filename relative to the modules path (eg. <nixpkgs/nixos/modules> for nixos).

This example will replace the existing postgresql module with the version defined in the nixos-unstable channel while keeping the rest of the modules and packages from the original nixos channel. This only overrides the module definition, this won't use postgresql from nixos-unstable unless explicitly configured to do so.

    { config, lib, pkgs, ... }:

    {
      disabledModules = [ "services/databases/postgresql.nix" ];

      imports =
        [ # Use postgresql service from nixos-unstable channel.
          # sudo nix-channel --add https://nixos.org/channels/nixos-unstable nixos-unstable
          <nixos-unstable/nixos/modules/services/databases/postgresql.nix>
        ];

      services.postgresql.enable = true;
    }

This example shows how to define a custom module as a replacement for an existing module. Importing this module will disable the original module without having to know it's implementation details.

    { config, lib, pkgs, ... }:

    with lib;

    let
      cfg = config.programs.man;
    in

    {
      disabledModules = [ "services/programs/man.nix" ];

      options = {
        programs.man.enable = mkOption {
          type = types.bool;
          default = true;
          description = "Whether to enable manual pages.";
        };
      };

      config = mkIf cfg.enabled {
        warnings = [ "disabled manpages for production deployments." ];
      };
    }