fix bug where nix store DB would not be loadable if root was not mounted on /

        Whether to configure the sd image to expand it's partition on boot.

      '';

    };

    nixPathRegistrationFile = mkOption {

      type = types.str;

      default = "/nix-path-registration";

      description = ''

        Location of the file containing the input for nix-store --load-db once the machine has booted.

        If overriding fileSystems."/" then you should to set this to the root mount + /nix-path-registration

      '';

    };

  };

  config = {

        ${pkgs.parted}/bin/partprobe

        ${pkgs.e2fsprogs}/bin/resize2fs $rootPart

      '';

      nixPathRegistrationFile = config.sdImage.nixPathRegistrationFile;

    in ''

      # On the first boot do some maintenance tasks

      if [ -f /nix-path-registration ]; then

      if [ -f ${nixPathRegistrationFile} ]; then

        set -euo pipefail

        set -x

        ${expandOnBoot}

        # Register the contents of the initial Nix store

        ${config.nix.package.out}/bin/nix-store --load-db < /nix-path-registration

        ${config.nix.package.out}/bin/nix-store --load-db < ${nixPathRegistrationFile}

        # nixos-rebuild also requires a "system" profile and an /etc/NIXOS tag.

        touch /etc/NIXOS

        ${config.nix.package.out}/bin/nix-env -p /nix/var/nix/profiles/system --set /run/current-system

        # Prevents this from running on later boots.

        rm -f /nix-path-registration

        rm -f ${nixPathRegistrationFile}

      fi

    '';

  };