Comment 3 for bug 537849

Experienced Same issue:

error: unknown terminal 'serial'
error: unknown command `terminal'.

Have been testing multiple configurations with limited success.

This command throws errors:
GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1"

This command seems to stop the errors.. but I can't get the boot menu to appear or shift key to be recognized:
GRUB_SERIAL_COMMAND="serial --speed=115200"

I have also messed with toggling GRUB_TERMINAL vs. GRUB_TERMINAL_INPUT / GRUB_TERMINAL_OUTPUT... tried various combinations of the lines below...
GRUB_TERMINAL=serial
GRUB_TERMINAL_INPUT="serial console"
GRUB_TERMINAL_OUTPUT="console"

Basically been adjusting the following lines with little to no success... I have been unable to get the menu to display at all via serial port. (Prior GRUB 1 configurations in Ubuntu 8 have been deployed to many servers with no problems... so this is starting to feel like a GRUB2 error).

#GRUB_CMDLINE_LINUX_DEFAULT=""
#GRUB_CMDLINE_LINUX_DEFAULT="quiet"
#GRUB_CMDLINE_LINUX=""
#GRUB_CMDLINE_LINUX_DEFAULT=""
#GRUB_CMDLINE_LINUX="text console=tty0 console=ttyS0,115200n8"
#GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8"

# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console
#GRUB_TERMINAL=serial
#GRUB_SERIAL_COMMAND="serial --speed=115200"
#GRUB_TERMINAL_INPUT="serial console"
#GRUB_TERMINAL_OUTPUT="console"
#GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200"
#GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1"