If you've got a working build of libguestfs from git, please try this and see if it fails for you: while make -C tests/guests clean windows.img \ LIBGUESTFS_DEBUG=1 LIBGUESTFS_TRACE=1 >& /tmp/log ; \ do echo -n . ; done For me it fails after ~ 100 iterations in a VM. (Unfortunately it seems to happen all the time in Koji). It doesn't appear to fail on baremetal at all, but most likely that's because it runs "too fast" to show up the race. You can see the error here: https://kojipkgs.fedoraproject.org//work/tasks/6637/7316637/build.log (look for: "/dev/sda1: No such file or directory") Compare to the code that is running: https://github.com/libguestfs/libguestfs/blob/master/tests/guests/guest-a... It's a bit of mystery why this happens repeatedly for this make-windows-img script but never anywhere else. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v