Скрыть меню Grub и нажатие клавиш, чтобы открыть

Я думаю, что вы можете сделать это с помощью переменных конфигурации в /etc/default/grub. Не забудьте запустить update-grub после обновления файла.

GRUB_DEFAULT= 3 #Assuming Windows is the third menu entry
GRUB_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT=0

Согласно документации для каждого варианта:

`GRUB_DEFAULT'
     The default menu entry.  This may be a number, in which case it
     identifies the Nth entry in the generated menu counted from zero,
     or the title of a menu entry, or the special string `saved'.
     Using the title may be useful if you want to set a menu entry as
     the default even though there may be a variable number of entries
     before it.

     For example, if you have:

     menuentry 'Example GNU/Linux distribution' --class gnu-linux {
        ...
     }

     then you can make this the default using:

          GRUB_DEFAULT='Example GNU/Linux distribution'

     If you set this to `saved', then the default menu entry will be
     that saved by `GRUB_SAVEDEFAULT', `grub-set-default', or
     `grub-reboot'.

     The default is `0'.
`GRUB_TIMEOUT'
     Boot the default entry this many seconds after the menu is
     displayed, unless a key is pressed.  The default is `5'.  Set to
     `0' to boot immediately without displaying the menu, or to `-1' to
     wait indefinitely.

`GRUB_HIDDEN_TIMEOUT'
     Wait this many seconds for a key to be pressed before displaying
     the menu.  If no key is pressed during that time, boot
     immediately.  Unset by default.