anchor.diff:  
       in
         # Declare the ISO as a build product so that it shows up in Hydra.
  -      runCommand "nixos-iso-${config.system.nixosVersion}"
  +      scrubDrv (runCommand "nixos-iso-${config.system.nixosVersion}"
           { meta = {
               description = "NixOS installation CD (${description}) - ISO image for ${system}";
               maintainers = map (x: lib.getAttr x lib.maintainers) maintainers;
  
positive.code: 
      in
        # Declare the OVA as a build product so that it shows up in Hydra.
        runCommand "nixos-ova-${config.system.nixosVersion}-${system}"
          { meta = {
              description = "NixOS VirtualBox appliance (${system})";
              maintainers = lib.maintainers.eelco;
  
negative.code:           mkdir -p $out/nix-support
            fn=$(echo $ova/*.ova)
            echo "file ova $fn" >> $out/nix-support/hydra-build-products
          '') # */
  
    );
  
  