MicrOS

MicrOS is a small, experimental operating system designed for embedded situations. It is based heavily on NixOS, but compiles down to a microscopic kernel¹, an initrd and a ~50mb squashfs.

Runit is used instead of systemd, with some degree of abstraction over services. This is not as robust as NixOS systemd module, nor is it in any way portable (i.e., additional init systems are not yet possible) but it results in a small and fast image for low-resource scenarios, e.g., embedded development.

Why

NixOS is great, it fits under most use-cases and it is extremely flexible on what you might use it for. Unfortunately for us, it is quite large even after you go out of your way to "debloat" it by applying various overlays that create a butterfly effect in the module system, breaking things you did not even know were called by your system. This is not unexpected, as Nixpkgs is quite large, but it is also very annoying.

MicrOS aims to be a robust solution to building small, minimal, and functional systems for various use cases. More specifically, embedded Linux and containerization.

Building

Micros is a build system more so than it is a collection of hardware modules. It should be utilized primarily as a module system to reduce friction in building images for embedded systems.

Construct your own system with lib.microsSystem. This functions almost identical to lib.nixosSystem that you might be familiar with.

lib.microsSystem {
  modules = [
    {
      not-os.rpi1 = true;
      not-os.rpi2 = true;

      system.build.rpi-firmware = raspi-firmware;

      nixpkgs.hostPlatform = {system = "armv7l-linux";};
      nixpkgs.buildPlatform = {system = "x86_64-linux";};

    }
  ];
};

Above configuration enough to construct a basic system. You may build different components of the configuration, available under config.system.build to create different build artifacts for different workflows.

Contributing

Contributions are always welcome. If you have anything you'd like to see implemented, and would like to work on implementing it then please create an issue so that we may figure out next. Please remember to write comments in particularly complex areas if adding new modules, or refactoring existing modules.

You may visit runit/runscripts for additional services that could be upstreamed to MicrOS.

License

Note

Work here is based heavily on the awesome not-os. I worked on something similar until I realized I was duplicating effort for no reason. This repository diverges (and will continue to diverge from not-os) in terms of module structure, coding conventions and goals on what should and should not be provided. In addition to the aggressive repository restructure, I will be working to provide more idiomatic Nix code that follows best practices and focuses on purity.

MicrOS is a soft-fork of not-os, plain and simple. Any and all work here is available under the MIT license, following upstream. I do not make any claims on the code provided here. Please support the original author and contributors.

The nature of MicrOS does not quite allow for a dependency on nixpkgs due to its tight integration with systemd. Although, we borrow modules from nixpkgs at times to avoid duplicating work, or to avoid reinventing the wheel as as square. A copyright notice is hereby provided that some modules in MicrOS are directly copied from nixpkgs, also available under the MIT license.

Please see LICENSE for details.

Footnotes

1. For the time being MicrOS attempts to boot the mainline kernel as development is most steadily pacing on x86_64-linux and we would like minimum amount of rebuilds possible. In the future, likely after there is some CI infrastructure, alternative kernels aiming at achieving smaller kernels might become a priority. ↩