Knoppix 6.4.4 and knoppix 6.7 were reported by a few people to be extremely slow to start in virtualbox. The platforms were not well established but at least on my computer where the host is Linux, it can take a long time, long enough to make one think it is blocking forever. Which it did not, eventually everything seems to work out fine after a long waiting.

After a lot of debugging, I have come to conclusion that the system is blocking at "udevd --daemon". The best part is if you start up knoppix with cheat code "knoppix debug", the system starts up faster than without the cheatcode.

I can't seem to find out why such thing should happen, at this moment. But suffice to say that, I disabled the "progress" update on the screen, then everything works out fine. It boots up as fast as it can be.