I run FreeBSD in virtual machines using both VMWare and Microsoft Virtual PC 2007. Both applications seem to stuff with the virtual machine's system clock, resulting in messages such as..
calcru: negative runtime of -12728437.., etc.
These errormessages pop up at the most inconvenient of times (like half way through a vi session) - not that there's ever a good time for an error alert.
Microsoft Virtual PC 2007
In FreeBSD and other distros, disabling the Advanced Configuration and Power Interface (ACPI) can force the guest operating system to fall back on the IRQ timers.
Using a text editor, add the following line to the end of FreeBSD's /boot/device.hints:
Note you may need to make the file writable first..
chmod 777 /boot/device.hints
..and reset it to read-only afterwards..
chmod 444 /boot/device.hints
Edit the virtual machine's .vmx file and add the following line to the end of the file..
host.useFastclock = "FALSE"
Save and exit the file and restart the virtual machine.
The above entry may need to be moved further up the .vmx file to work.. (VMWare 5.x, FreeBSD 6.2).