Comment 7 for bug 1813662

OK. Thanks for the link and explanation. So it doesn't have to be the exact image of the kernel that is running? just a reasonable image?

If it is not strictly necessary ot be the image of the running kernel, I see a better solution to this bug, which I also consider a better design of virt-builder:
Put a/the kernel image into the file that is downloaded, i.e. http://libguestfs.org/download/builder/ubuntu-18.04.xz, and use that image file when building an OS/VM because apparently virt-builder cannot count on kernel images being available on all supported operating systems (hereamong Ubuntu/Debian).