"Cannot access the Hardware Clock via any known method."

Downloaded the latest VirtualBox, version 2.1.2, for my now-ancient Windows XP main PC, and wondered if I could finally get Ubuntu server to boot on it. Having tried previously with the old 1.6 version and failed. Got the same problem, couldn't boot, but fixing it was as simple as enabling PAE (processor architecture extensions) in the settings for the VM. I don't know whether that option wasn't there in 1.6 or whether I was just being exceptionally dense that day, but anyway it's solved now.

During the Ubuntu boot process there was another odd message though, even when it was successfully booting: "Cannot access the Hardware Clock via any known method." Sounded like the hardware was being hidden a little too successfully. Sounded like something that a lot of people would come across, but the only solution I found was on a German website.

In brief, there are two files in /etc/init.d :

hwclockfirst.sh

and

hwlock.sh

You need to edit both of them. There's a line that defines an (empty) environment variable, HWCLOCKPARS; it looks like this:

HWCLOCKPARS=

Edited that line to look like this:

HWCLOCKPARS="--directisa"

And Ubuntu server now boots in the VM without any problem.