How to override 2 (two) packages in Nixos configuration.nix

Question

I have some package to override in my configuration.nix. So I write the code as follows:

nixpkgs.config = {
  allowUnfree = true;
  packageOverrides = {
    pkgs:         


        

Answer 1

The proper solution is:

nixpkgs.config = {

  allowUnfree = true;

  packageOverrides = super: let self = super.pkgs; in {

    mumble = super.mumble.override { pulseSupport = true; };

    linuxPackages = super.linuxPackages // {
      e1000e = super.linuxPackages.e1000e.overrideDerivation (old: {
        name = "e1000e-3.3.3-${config.boot.kernelPackages.kernel.version}";
        src = fetchurl {
          url = "https://www.dropbox.com/s/pxx883hx9763ygn/e1000e-3.3.3.tar.gz?dl=0";
          sha256 = "1s2w54927fsxg0f037h31g3qkajgn5jd0x3yi1chxsyckrcr0x80";
        };
      });
    };
  };
}

The variable super refers to the Nixpkgs set before the overrides are applied and self refers to it after the overrides are applied. It's important to distinguish these two explicitly to avoid infinite recursions, etc.

Also, note that your override

linuxPackages.e1000e = pkgs.linuxPackages.e1000e.overrideDerivation ...

replaces the linuxPackages attribute set with one that contains nothing but the (overriden) e1000e derivation. That's probably not what you want.