When your terminal is dumb or you request GRUB to hide the menu
interface explicitly with the command hiddenmenu
(see hiddenmenu), GRUB doesn't show the menu interface (see Menu interface) and automatically boots the default entry, unless
interrupted by pressing <ESC>.
When you interrupt the timeout and your terminal is dumb, GRUB falls
back to the command-line interface (see Command-line interface).
Published under the terms of the GNU General Public License
