grub: terminal_input
16.2.2 terminal_input
---------------------
-- Command: terminal_input [--append|--remove] [terminal1] [terminal2]
...
List or select an input terminal.
With no arguments, list the active and available input terminals.
With '--append', add the named terminals to the list of active
input terminals; any of these may be used to provide input to GRUB.
With '--remove', remove the named terminals from the active list.
With no options but a list of terminal names, make only the listed
terminal names active.
Info Catalog
grub: serial
grub: General commands
grub: terminal_output