grub2: terminal_input
16.2.2 terminal_input
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-- 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
grub2: serial
grub2: General commands
grub2: terminal_output