On Mon, Dec 28, 2015 at 03:36:53PM -0800, Ryan Sawhill Aroha wrote: The format parameter in the metadata and the --format option are related, but different things. The format= metadata tells virt-builder the format of the original template (ie. centos-6.xz is raw format after decompression). Image format auto-detection is a security risk [although to be fair really not in this particular case], and so it's better to specify the format. The --format parameter is what format the virt-builder end user would like your final image to be. So if format=raw and --format qcow2, then virt-builder knows it must convert the image. This is the code: https://github.com/libguestfs/libguestfs/blob/master/builder/builder.ml#L... The --format command line parameter defaults to raw (and this is documented in the manual). It doesn't matter what the original template format was. So virt-builder is behaving as per specification above. My initial thought was that we could have an `output_format=...' line in the metadata. However that has a couple of problems: (1) Other metadata format like SimpleStreams doesn't support this. (2) It breaks the virt-builder contract because we have documented in the manual that the default output format (ie. if --format is not specified) is raw. However, read on ... We couldn't call it "auto", since --format=auto is used in other virt-* tools contexts to mean to do unsafe autodetection of the format. I don't mind if we called it something else, perhaps `--format=input'? It just has to be a name that could never be used as a real disk format (like 'qcow2' or 'vmdk'). The RFE process is described here: http://libguestfs.org/guestfs-faq.1.html#how-do-i-propose-a-feature https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&produc... Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html