notes after installing http://nerdvittles.com/?p=26675 VirtualBox disk image:
- /boot must be at least 200MiB, better 500MiB. 100MiB is not enough. have you tried to run yum upgrade? it fails on not enough space on /boot.
- disk size must not be 20.7GiB, many KVM offerings start from 15 or 20
- knockd.FAQ is out of date - provided command sequence does not works since nmap now makes multiple tries on each port and requires at least --max-retries 0 and may be even -Pn