Nixpkgs/Modifying Packages

To modify the behavior of a Nix package, you typically have more than one option. The first approach you may consider is changing its runtime configuration: passing command line options, environment variables or configuration files that exist outside the package itself. Not modifying the definition of a package has the benefit of being able to use the publicly available Hydra build cache.

If the software as packaged does not have the flexibility you need, you have various options.

Conceptually the most simple option is to duplicate the package definition in a local file where you make your changes. You will be able to install and use it locally, while only having to learn the basics of Nix packaging.

If you expect your changes to be generally useful to others, you may consider creating a pull request for nixpkgs on github. This has the benefit that others can help maintaining the package and that a binary of your package will be available for you to download.

If upstreaming into the official NixPkgs is not an option, consider creating an overlay. This is slightly more involved at first, but is easier to maintain than a NixPkgs fork and, unlike a fork, it can be combined with other overlays. In an overlay, you can also choose not to redefine the package, but only override part of the arguments or derivation attributes. For example, you may only need to change one of the stdenv build phases.