Let's assume our server paniced and rebooted but then fails because the filesystem is complete full.
From the xscf prompt reboot the system by sending a panic signal.
reset -d 0 panic
Once the system starts rebooting, take a close look to the console.
console -d 0 -y
Jumping back to the xscf console (#.) can allow you to perform a sendbreak. Multiple attempt might be needed.
sendbreak -d 0 -y
Once you are on the OK prompt you can boot as next to correct the problem:
Boot in single usermode : boot -sw
Boot in failsafe mode : boot -F failsafe
Happy recovering :-)