1 files changed, 64 insertions, 0 deletions
diff --git a/nixos/doc/manual/development/replace-modules.section.md b/nixos/doc/manual/development/replace-modules.section.md
new file mode 100644
index 00000000000..0700a82004c
--- /dev/null
+++ b/nixos/doc/manual/development/replace-modules.section.md
@@ -0,0 +1,64 @@
+# 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 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.
+
+```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 it\'s implementation details.
+
+```nix
+{ 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." ];
+  };
+}
+```