In some situations it is very useful to have the possibility to access the GRUB boot menu from a serial line. For example you could remotely reboot your machine with the new kernel you just compiled.
In my case I have a couple of remote machines linked together by a serial cable. I can log into machine A via ssh and get the Grub menu of machine B through minicom. Thus I can boot whatever OS/kernel I want as if I were in front of the machine. Kind of KVM IP for the rest of us.
Simply add this to Grub’s menu.lst:
serial –unit=0 –speed=9600 –word=8 –parity=no –stop=1