Nixpkgs/Building RPM DEB with nixpkgs

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How it works

To build deb/rpm packages with nix/nixpkgs, it is critical to understand the process. Hence a short intro:

To build a deb or rpm package with nixpkgs, the build process needs a disk image which it then uses to boot a virtual machine (as in Qemu). Inside this virtual machine, the deb/rpm package is compiled from a tarball and then packaged using the respective tools for deb/rpm packaging.

Luckily, all that requirements are shipped inside nixpkgs itself.

Preparation of the host machine

The host machine has to be prepared for the build process.

In the evaluation for this article, a CentOS 7 amd64 machine running in vmware was used. On the machine, the nix package manager was installed via curl https://nixos.org/nix/install | sh as suggested on https://nixos.org/nix/ > "Get Nix".

The configuration file /etc/nix/nix.conf was edited for the following contents:

sandbox = false
system-features = [ kvm nixos-test benchmark big-parallel ]

This step might not be necessary on a NixOS installation.

How to build a deb/rpm with nixpkgs

The following approach can be used to try out building a .deb package with nixpkgs:

1. Clone the official nixpkgs repository into ~/nixpkgs
2. Add a file to the nixpkgs repository ./deb.nix with the following contents:

(In this scenario, ncurses was built for testing the whole approach)

let
  pkgs = (import ./default.nix {});
  vm    = pkgs.vmTools.diskImageFuns.centos7x86_64 {};
  args = {
    diskImage = vm;
    diskImageFormat = "qcow2";
    src       = pkgs.ncurses.src;
    name      = "ncurses-deb";
    buildInputs = [];
    meta.description = "No descr";
  };
in pkgs.releaseTools.debBuild args

and then this file was called: nix-build ./deb.nix.

This loads the relevant disk images from the channel mirror and spins up the Qemu VM to build the package. The deb file (in this case, as we're building a deb with the expression from above) is located in ./result/debs/ after a successful build.