Nix

Nix-caliga does not require the nix package itself, or a nix-daemon to be on the bootc images it creates.
However you may still want nix and the nix-daemon to be available on your system. config.nix.enable sets the nix-daemon up.
This module is functional, but it is not yet fully featured, some aspects of the nix configuration are not easily accessible.

Enabling config.nix.enable requires config.caliga.core.etc-usr.enable, config.caliga.core.systemd.enable, config.caliga.core.tmpfiles.enable, and config.caliga.core.users.enable to all be true.

Writable /nix Overlay

On a bootc system /nix is part of the read only image. To allow the Nix daemon to install packages and manage the nix store, we create an overlay mount over /nix with its upper directory at /var/nix/upper and work directory at /var/nix/work (/var being mutable and persistant). The overlay mount only occurs on systems where /nix is actually read only. In a container the overlay mount won’t actually be created.

Nix Daemon

The nix-daemon service and socket units are pulled in through config.systemd.packages from the Nix package itself. It’s not tested, but other “nix” packages should work in place.

Image Nix Database

If the nix-daemon is enabled, config.layeredImage.includeNixDB (see buildImage) is set to true so that the Nix database from the image build is included. This allows the daemon to be aware of store paths that were baked into the image.

Nix Configuration

A nix.conf is placed at /etc/nix/nix.conf with flakes and the nix-command experimental features enabled along with the nixpkgs path set from the flake input. Additional settings can be configured through config.nix.settings.
Eventually the nix-caliga nix-daemon will be more configurable. Hopefully pulling in more of the configuration directly from NixOS.

Options

• config.nix.enable
  • Enable the Nix package and daemon.
• config.nix.package
  • The Nix package to use. Defaults to pkgs.nix.
• config.nix.nrBuildUsers
  • Number of Nix build users to create. Defaults to 32.
• config.nix.settings
  • Additional settings for nix.conf as an attrset. Merged with the (currently) fixed defaults (build-users-group, experimental-features, nix-path).