Comment 8 for bug 726790

Using version 0.12.4+bzr469-0ubuntu1 I also get the exception that the device is busy. When I insert a "run_cmd('sync')" just before the umount command it works OK and building finishes without the exception.

So, the /usr/lib/python2.7/dist-packages/VMBuilder/plugins/ubuntu/dapper.py file contains:

    def unmount_dev(self):
        self.context.cancel_cleanup(self.unmount_dev)
        run_cmd('sync') # added by me
        run_cmd('umount', '%s/dev' % self.context.chroot_dir)