Essas linhas existem no seu /etc/default/grub
? Se não, adicione-os.
GRUB_TIMEOUT=10
GRUB_TIMEOUT_STYLE=menu
execute update-grub
para atualizar /boot/grub/grub.cfg
Você pode verificar se as mudanças necessárias ocorreram dessa maneira:% grep -i timeout /boot/grub/grub.cfg
A saída deve conter tais valores:
set timeout_style=menu
set timeout=10
No manual do grub :
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. If GRUB_TIMEOUT_STYLE is set to countdown or hidden, the timeout is instead counted before the menu is displayed.
GRUB_TIMEOUT_STYLE
If this option is unset or set to menu, then GRUB will display the menu and then wait for the timeout set by GRUB_TIMEOUT to expire before booting the default entry. Pressing a key interrupts the timeout. If this option is set to countdown or hidden, then, before displaying the menu, GRUB will wait for the timeout set by GRUB_TIMEOUT to expire. If ESC is pressed during that time, it will display the menu and wait for input. If a hotkey associated with a menu entry is pressed, it will boot the associated menu entry immediately. If the timeout expires before either of these happens, it will boot the default entry. In the countdown case, it will show a one-line indication of the remaining time.