Customizing modules is a little more complicated than customizing packages.

Development is very active on nixpgs main repository so trying to rebuild the configuration on it can trigger massive source building.

To avoid that, it is possible to use a nixpkgs version that is at the same state as nix channels to use the binary cache.

The first thing to do is to clone the `nixpgs-channel repository:

# git clone [email protected]:NixOS/nixpkgs-channels.git

Then, checkout the branch corresponding to the system channel.

To know the system channel, as root run:

# nix-channel --list

sample output:

nixos https://nixos.org/channels/nixos-unstable

The last part of the url, in this case nixos-unstable is the system channel.

To checkout the branch the you can run the following command from the folder where nixpkgs-channels has been cloned.

# git checkout nixos-unstable

or

# git checkout nixos-15.09

depending the channel used.

The system channel and the git repository should be up to date before hacking

To update the system channel, as root run:

# nixos-rebuild switch --upgrade

This will update the channel, all the configuration options and the packages.

Then we have to update the nixpkgs-channel repository:

# git pull

Configuration modules are located under nixos/modules.

To test the changes, as root run:

nixos-rebuild -I nixpkgs=<path> switch

where <path> should be the full path to the local nixpgs-channel, for example:

nixos-rebuild -I nixpkgs=/home/nix-user/Projects/nixos/nixpkgs-channels/ switch

If something goes wrong, it is possible to rollback:

nixos-rebuild switch --rollback

In case the changes can benefit to all users, it is a good idea to send a pull request to nixpkgs.

Fork and clone locally nixpkgs, details in github forking guide.

then generate a patch file from the changed nixpgs-channel repository:

# git diff > /tmp/my.patch

Then from the forked nixpkgs repository, create a branch and apply the patch:

# git checkout -b my-branch
# patch -p1 < /tmp/my.patch

Be sure to follow naming convention for the commit and pull request from the contributor guide.

Commit and send the pull request from github.