I didn't do that, I just used the CD to get the boot prompt, then entered the bootcode. In my case, it was knoppix26 home=/dev/hdb5 myconf=/dev/sda1 bootfrom=/dev/hdb1/k*.iso

I must have misunderstood your question, because I thought you were asking about the command itself. Sorry I couldn't help more. I'm actually trying to work on booting from USB drive.

jd