whoami

Hi! I'm Arnout Engelen and I've been a NixOS contributor since 2019 and committer since 2021. I'm keeping some notes here about how I use NixOS that work for me but about which I'm not completely confident yet that they should go into the upstream docs. If you see anything you'd like to discuss further, feel free to get in touch!

Why NixOS

Part of the reason I'm so fond of free/open source software is because it blurs the line between 'producers' and 'consumers', which I think can be very empowering.

NixOS vs Debian

i have been a Debian user for about 20 years. I like their principled approach to open source and their tendency to look beyond Debian itself: it seems pretty common for Debian maintainers to work closely with upstream to fix bugs there, and there seem to be quite a number of projects that get significant input from Debian even though (e.g. Reproducible Builds, X.org).

What made me look beyond Debian is that the round-trip time between doing a contribution and seeing it generally available is rather large, widening the gap between maintainers and regular users.

NixOS vs Arch

I tried Arch for a while, but it didn't stick: I'm not a fan of the "we refuse to create a nice installer because typing in commands yourself will be an educational experience" attitude.

The tooling for contributing to AUR seemed clunky: weird use of git (because of some compatibility with svn it appears), and AFAICS no structured way to have shared maintainership of packages.

NixOS selling points

Especially as a developer, NixOS can be frustrating because build systems may make assumptions about your system that do not hold on NixOS. With a shell.nix you can often fulfill these assumptions, however, and getting familiar with the nix language makes it easier to contribute to the upstream package tree later on. It has the additional advantage that this allows you to specify per-project dependencies instead of installing everything globally.

Notes

flakes

I see advantages of flakes: having the split between flake.nix describing 'abstractly' what version you want to run, and the flake.lock describing the *actual* version you're running right now, is helpful. Also the new structure provides some opportunities for caching.

It does introduce some dilemmas: checking in flake.lock seems rather restrictive on downstream users, and will be likely to cause merge conflicts when you collaborate using forks.

Also, I really like working from a local nixpkgs checkout, but that is not very well-supported by flakes yet: it copies it to the nix store each time, which takes a lot of disk space and is slow. Work on this is underway at https://github.com/NixOS/nix/pull/6530 but seems to be stalled.

/etc/nixos/configuration.nix vs nix-env

I am running NixOS on a laptop where I am the only user, so I try to do all my configuration by editing /etc/nixos/configuration.nix and "nixos-rebuild switch". I avoid nix-env.

using a fork of a packaged project

Sometimes, you want to use a packaged project, but with a slight twist: perhaps changing something in the packaging, or perhaps just updating the version or pointing to a different branch. My approach to that is to use 'git worktree' to check out a copy of the nixpkgs collection to ~/nixpkgs-foo. Then I can make any changes I'd like in that directory, and use it from /etc/nixos/configuration.nix like so:

# Edit this configuration file to define what should be installed on
# your system.  Help is available in the configuration.nix(5) man page
# and in the NixOS manual (accessible by running ‘nixos-help’).

{ config, pkgs, lib, ... }:

let
  nixpkgs-vscode = import (/home/aengelen/nixpkgs-vscode) { 
    config.allowUnfree = true;
  };
in
  ...
  environment.systemPackages = with pkgs; [
    ...
    nixpkgs-vscode.vscode
    ...

A nice thing with this approach is that if you're happy with your local changes, you can use them immediately like this, but also send a PR upstream to have your change incorporated in the official tree.

/lib64/ld-linux-x86-64.so.2

If you download a random binary from the internet, typically it will not work because it explicitly uses /lib64/ld-linux-x86-64.so.2 as interpreter.

applications

If it's an application, you can write a `shell.nix` to `patchelf` it before running it:

with (import <nixpkgs> {});
mkShell {
  shellHook = let
    libPath = lib.makeLibraryPath [
      zlib stdenv.cc.cc.lib
    ];
  in ''
    patchelf --set-interpreter "$(cat $NIX_CC/nix-support/dynamic-linker)" path/to/the/executable;
  ''
}

simple builds

If it's a resource that is being downloaded as part of another project or build system, you can use write a 'shell.nix' that builds a temporary FHS-like structure with buildFHSUserEnv:

{ pkgs ? import <nixpkgs> {} }:

(pkgs.buildFHSUserEnv {
  name = "akka-grpc";

  targetPkgs = pkgs: [ pkgs.sbt pkgs.glibc pkgs.jdk ];
}).env

more complicated builds

If you also want to use a more complicated shell.nix setup, such as for android (https://discourse.nixos.org/t/building-an-android-app/5043), I'm not sure how to achieve this. I cheated and just created a /lib64/ld-linux-x86-64.so.2...

running nixos-unstable

I've been running nixos-unstable from the beginning, and this has been a great experience. Being able to roll back and forth in case of trouble has worked out fine, and allowed me to test with newer versions/patches without interfering with regular work.

Overall upgrading is fast because binaries can be loaded from hydra, with the exception of graalvm.

building graalvm

building graalvm needs some extra swap on my (32g) machine:

   dd if=/dev/zero of=swapfile count=4096 bs=1MiB
   mkswap swapfile
   swapon swapfile

If I understand correctly there is good progress on getting this to compile on hydra again underway in https://github.com/NixOS/nixpkgs/pull/86244 which depends on https://github.com/NixOS/nixpkgs/pull/85902

codium

Loading extensions as documented at VSCodium seems to have stopped working recently, now on 467ce5a9f45aaf96110b41eb863a56866e1c2c3c . Time to bisect.

sweethome3d

depends on p7zip which has been marked insecure
https://discourse.nixos.org/t/glx-not-recognised-after-mesa-update/6753/5

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