anchor.diff:              ''
                 PATH=$PATH:${pkgs.gnutar}/bin:${pkgs.gzip}/bin
                 pushd $out
  -              tar -Szcf disk.raw.tar.gz disk.raw
  -              rm $out/disk.raw
  +              tar -Szcf $diskImageBase.tar.gz $diskImageBase
  +              rm $out/$diskImageBase
                 popd
               '';
  -
  +          diskImageBase = "nixos-${config.system.nixosVersion}-${pkgs.stdenv.system}.raw";
             buildInputs = [ pkgs.utillinux pkgs.perl ];
             exportReferencesGraph =
               [ "closure" config.system.build.toplevel ];
  
positive.code:         { preVM =
              ''
                mkdir $out
                diskImage=$out/disk.raw
                truncate $diskImage --size 10G
                mv closure xchg/
              '';
  
negative.code:     169.254.169.254 metadata.google.internal metadata
    '';
  
    systemd.services.fetch-root-authorized-keys =
      { description = "Fetch authorized_keys for root user";
  
        wantedBy = [ "multi-user.target" ];
        before = [ "sshd.service" ];
  