how to launch grub menu for ubuntu guests in virtualbox?

I have ubuntu 12.04 alpha installed in virtualbox. When the virtual machine is started, it boots directly to the login screen without showing the grub menu. How can I get the grub menu to show up on start?

Please note: the graphics is broken after recent updates, so i cannot login and make the changes. it is stuck at the screen "Ubuntu is running on low graphics mode" and the mouse and other keys do not work.


Hold the shift key as the VM boots.

If that fails, boot a desktop iso, mount the root partition at /mnt, and manually edit what you need or make an update in a chroot.