When I access GRUB at boot I don't see any entry listed.
I can see I'm in GRUB because some Debian Grub menu splashdown in the background is displayed. But no entry is listed and nothing happens if I press E.
If I press Enter I just boot normally into my Ubuntu installation.
How can I get Grub to display the entries? Thanks a lot in advance.
An addition to the answer by Vivek S Panicker: in file /etc/default/grub, there are two lines
GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
If they are not commented out, or at least the latter one, that means that the GRUB2 menu will never be shown on boot, unless you press the shift key within the number of seconds defined by GRUB_HIDDEN_TIMEOUT. If that value is 0, then you'll never see the GRUB2 menu. Instead, the first item on the menu that would otherwise appear will be booted into.
So, you should also check those lines in your /etc/default/grub file, and if they're there, comment them out with the # character, then save the file, command sudo update-grub, and reboot.
