I've tried upgrade to ros chr to v7.6 directly from v6.48.6[long-term] for testing, but found some weird interfaces that cannot be deleted. The type of these interfaces are "interface", and after some serious thinking, I do remember that these interfaces were created when I was using a x86 version, and these interfaces were actully the virtual interfaces used by kvm.
Holy moly, these interfaces were hidden in system for so many years? Can it be deleted? Or I'll need a fresh install.......