Jacek's Blog

Software Engineering Consultant

NixOS Community Oceansprint 2021 Report

December 12, 2021 nix

This is my trip report from the awesome NixOS community hackathon on Lanzarote. For more information please also have a look on the website: https://oceansprint.org

The Sprint announcement

Domen Kožar organized a hackathon for the Nix(OS) community on Lanzarote:

Oceansprint Announcement on Twitter

This was totally amazing news for me and i really wanted to participate immediately. I realized that i need to be quick because there were only ~15 slots. Two days later the next announcement said:

The Oceansprint was booked out 2 days later

The NixOS Community

There is an open source package manager called (nix) (which is a ridiculously understated description) and a GNU/Linux distrubtion called NixOS that is based on top of nix. This is all organized in the NixOS github organization and mostly revolves around the git repository nixpkgs because this is where most of the value is concentrated because this repository represents the largest and most current collection of all Linux package distributions out there:

repology.org graph showing the most vs. the most fresh package collections

Apart from that, the repository also contains a lot of NixOS module descriptions that are used to compose a full NixOS system.

A description of all the value that i pull out of this open source project for myself and my company is worth multiple blog articles alone, so please refer to their homepage if you like to read more.

It’s an unbelievable project. If you are interested in contributing to the largest most-current free software package collection in the world and/or an amazing GNU/Linux distribution on top of that within a very nice and inclusive community, then this project is definitely for you.


The sprint has been cancelled roughly 2 weeks before its start due to the latest Corona related warning level increase in Lanzarote/Spain. Most of the participants travelled to Lanzarote anyway as it was still allowed to meet in smaller groups. Luckily, a few days before the sprint the warning level was decreased based on the latest infection numbers, so we were again able to perform the sprint like initially planned.

All participants have their vaccination. On monday and thursday everyone tested themselves under supervision of each other before joining the group.

Participants of the sprint

The participants who showed up over the week were the following ones:

Real name (nickname), Company


The sprint location was Nejc’s Villa at in Costa Teguise on the Spanish island Lanzarote.

The Oceansprint location

Daily Schedule

The official sprint day schedule began at 9:00 and ended at 17:00. Every day ended with a brief standup meeting where everyone explained what they achieved/struggled with.

The gold sponsor Serokell also gave us a brief overview of job opportunities in a dedicated talk slot. The sprint found a good balance between giving the sponsors enough attention and thankfulness but at the same time not distract any efforts.


Every day we had breakfast and lunch provided in form of a professional buffet. After every productive day, the whole group went out for dinner, trying out several local restaurants. This way we really sticked together the whole week, which facilitated easy get-to-know and socializing a lot: The atmosphere was nice and relaxed!

During the work phases inbetween, everyone either worked alone or in teams depending on their projects. While the great location allowed for sitting outside around the big table, near the pool, on the balcony or inside the living room for concentration phases, it was also very easy to sporadically group up and discuss things. Or to just hang around at the pool and lament together how hard life in the sun is.

Apart from work and food, Nejc also organized several activities like swimming/surfing/hiking trips for whoever wanted to participate. Another group went to surf school together on the weekend.

Sprint Projects

nix.dev UX enhancements

Nejc Zupan started to port the tutorials of https://nix.dev from reStructuredText to Markdown. The goal of this change is to lower the barrier for external contributors, as markdown is simpler and better known than reStructuredText.

Another useful effort that he started is to get all code excerpts on the website automatically tested by the CI. This will avoid frustration for newcomers who might want to start to use nix for its reproducibility, so they don’t run into unreproducible tutorials.


Florian Klink implemented nix-casync, a HTTP binary cache using the casync mechanism internally to efficiently store NAR files in a deduplicated fashion, and provides an outlook on how to use it to speed up substitution.

Blog article about this: https://flokli.de/posts/2021-12-10-nix-casync-intro/

NixOS Composability Optimizations

Robert Hensing, Jonas Chevalier, and Vo Minh Thu experimented with and worked on how to make NixOS systems smaller and more composable. There are different reasons for this:

There were basically two approaches:

Robert created a pull request with a POC that shows how to whitelist NixOS modules into a system. This is different from the usual approach because the NixOS function that evaluates a config imports all the NixOS modules and then lets the user activate/deactivate things at will, but has a lot of things already activated by default. “Blacklisting” features by disabling them one by one in order to arrive at a minimal system is very uncomfortable becasue you end up searching for which nix file enables what. Some things also cannot be (easily) disabled this way. Robert’s approach is creating a function that does not work with a default list of imports. He also added unit tests to facilitate regression-free maintenance and extension of this effort.

Jonas and Thu experimented with not-os, which is a set of custom NixOS modules that remove systemd and create system initialization scripts from scratch in order to reach a minimal system. They resulted in an impressive written overview of what would need to be done to minimize the system further and even reach systems without interpreters. (Blog article coming on Jonas’s blog)

Both approaches seem like they could be combined upstream with some amount of work.


Pointed at an existing pull request from user bergkvist by Robert, Jacek Galowicz stopped participating in the discussion about minimizing NixOS systems and started helping improving and testing an application wrapper that is called makeBinaryWrapper. There is an existing tool called makeWrapper that can substitute any binary or script by another script that first manipulates the shell environment in user-specified form and then calls the original app/script, possibly with prepended command line arguments. The binary wrapper builds a tiny C program and compiles it instead of composing a shellscript. This is interesting for the following reasons:

The wrapper does generally work but must be extended if it is chosen to completely get rid of the default wrapper on NixOS systems, because some derivations stretch the wrapper’s capabilities so much that it’s hard to model the same behavior in simple C programs. This can be changed to the better with follow-up contributions.

NixOS Integration Test Driver Refactoring

After Jacek’s porting of the NixOS integration test driver from Perl to Python in 2019 after the NixCon in Brno, this driver implementation became the standard NixOS integration test driver in Nixos 20.03, and the general interest in using and extending the driver for tests in the community increased. The driver code itself is growing in ways that should not happen in unmoderated fashion, and not without giving it a proper architecture.

As a first step, the driver should be split up in individual files for each of its functionality domains and put in a real Python package, in order to get more improvements afterward.

Jacek introduced these ideas as a project idea for the sprint and Marijan Petričević, Amon Stopinšek, and Vo Minh Thu jumped right into doing this.

The first PR on this has already been merged: https://github.com/NixOS/nixpkgs/pull/149329

NixOS Integration Tests on MacOS

Nejc Zupan, Domen Kožar, and Marijan Petričević started working on the NixOS integration test driver nix expression in order to enable for running the usual integration tests with virtual networks of NixOS VMs, but on MacOS.

Nix Community Ownership Bootstrapping

Bernardo Meurer Costa pointed out that the Nix(OS) community is currently organized in a rather anarchistic fashion. This works very well on one hand in the sense that many contributors maintain and enhance nixpkgs and NixOS together and at the same time keep it stable and working.

On the other hand, recent problems with bogging down RFCs and in general bigger decision processes stalling in endless discussions without any resulting decision, indicate that the governance has potential to improve.

Bernardo studied different voting algorithms and chose which ones to quickly employ for having a bootstrap voting process. The process would start with a list of well-known contributors and the sprint participants to decide who shall be part of an anytial group of leaders who then are able to bootstrap general decision structures and processes. It was a pity that Eelco was not here to share his opinions on this, but he will also be included from the beginning.

Cachix Deploy

Domen Kožar worked on and demonstrated the new cachix deploy feature, which can be explained as “the hail service on steroids”. The cachix website will soon show this new feature.

nixpkgs Refactorings

I don’t have a perfect overview of what was done at the sprint as there were so many things, but i also remember: