Global FHS environment for NixOS

Possible thanks to OCI containers!

Warning I tested this module on my dev host. It may not work on yours. If it doesn't, open an issue!

I recommend you use this in a setup where / gets wiped every reboot.

Installation using flakes

/etc/nixos/flake.nix

{
  inputs = {
    # ...
    fhs.url = "github:GermanBread/nixos-fhs/stable";
    # ...
  };

  outputs = { ..., fhs, ... }: {
    nixosConfigurations.<host> = nixpkgs.lib.nixosSystem {
      # ...
      modules = [
        # ...
        fhs.nixosModules.default
        # ...
        ./configuration.nix
        # ...
      ];
      # ...
    };
  };
}

IMPORTANT: You need to enable this module in your configuration.nix

{
  services.fhs-compat = {
    enable = true;
    # other options here
  };
}

Also enable podman:

{
  virtualisation.podman.enable = true;
}

Module definition

services.fhs-compat.distro

default:
  "arch"

example:
  one of [ "debian", "ubuntu", "alpine", "arch", "manjaro", "gentoo", "void" ]

description:
  Which distro to use for bootstrapping the FHS environment.

services.fhs-compat.tmpfsSize

default:
  "5G"

description:
  How big the tmpfs mounted on $mountPoint should be.
  This also affects the tmpfs size for temporary storage of the container.
  Sizes must have a valid suffix.

services.fhs-compat.mountPoint

default:
  "/.fhs"

description:
  Where the FHS environment will be installed to.

services.fhs-compat.stateDir

default:
  $mountPoint/.state

description:
  A directory where the service itself stores data

services.fhs-compat.mountBinDirs

default:
  false

example:
  true

description:
  Whether or not to put a bind mount over /bin and /usr.
  Both will redirect to their counterparts in $mountPoint.

  This option does not affect /sbin.

services.fhs-compat.packages

default:
  []

example:
  [ "neofetch" "sdl2" ]

description:
  Which packages to install. Package names vary from distro to distro.

services.fhs-compat.persistent

default:
  false

example:
  true

description:
  Try to persist the FHS environment across reboots.

services.fhs-compat.preInitCommand

default:
  null

description:
  Which command to run on a fresh container.

  WARNING:
  Multiline strings have to be escaped properly, like so:
  foo && \
    bar

services.fhs-compat.postInitCommand

default:
  null

example:
  "pacman -R neofetch sdl2";

description:
  Which command to run after packages have been installed.

  WARNING:
  Multiline strings have to be escaped properly, like so:
  foo && \
    bar

services.fhs-compat.maxTimeDelta

default: 60 * 60 * 24; # 1 day

example: 60 * 35; # 35 mins

description: The maximum age any given FHS environment (in seconds). If the env is older than $maxTimeDelta (in seconds), it will be refreshed.