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# Replace Modules {#sec-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 its 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),
- or an attribute set containing a specific `key` attribute.
The latter allows some modules to be disabled, despite them being distributed
via attributes instead of file paths. The `key` should be globally unique, so
it is recommended to include a file path in it, or rely on a framework to do it
for you.
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.
```nix
{ 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 its implementation details.
```nix
{ config, lib, pkgs, ... }:
let
inherit (lib) mkIf mkOption types;
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." ];
};
}
```
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