I've not had to do this myself but a quick search on the net yields:
REQUIREMENTS FOR BOOTING WITHOUT A KEYBOARD
The following steps are required to get the system to boot without a
keyboard attached.
Halt the system and at the "{1} ok" prompt, type the following (in bold):
{1} ok setenv input-device ttya
input-device = ttya
{1} ok setenv output-device ttya
output-device = ttya
{1} ok reset
The system will begin to boot, so remove the keyboard.
The system will continue to function without a keyboard even thru reboots
and power cycles.
REQUIREMENTS FOR BOOTING WITH A KEYBOARD
However, should you wish to use a keyboard and monitor with either of these
boxes int the future, then you must reset the NVRAM (Non-Volatile Random
Access Memory)
as follows:
Reboot the system, and during the reboot, press and hold Stop-N (as in
Nancy). This resets the NVRAM and puts the system back into the state where
it wants to have a keyboard and monitor. You must now attach the keyboard
and monitor, since the system will now , not fully boot without them .
Later on, of course, since you will want to remove the keyboard and monitor
to run "headless" once again, the steps in SECTION A must be performed.
Hope this is what you're looking for :)
