By default, if the boot process fails in Ubuntu, the Grub timeout for the next boot will be disabled and the menu shown instead. This results in a situation that some keyboard input will be required in order to proceed. Obviously, this isn't convenient for headless machines, servers and virtual machines.
This default behaviour is easy to disable. Add the following to <i>/etc/default/grub</i> (assuming it doesn't already exist
# disable getting stuck in menu after fail GRUB_RECORDFAIL_TIMEOUT=0
and execute
update-grub