When Ubuntu boots, you normally briefly see a screen that says "GRUB loading. please wait… Press Esc to enter the menu…"

If you are hacking around your system and would prefer to always see the GRUB menu (to enter command-line options, for instance), there's an easy fix.

Open up the /boot/grub/menu.lst file in your favorite text editor. I'm using gedit:

sudo gedit /boot/grub/menu.lst

Now find the section that looks like this:

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
hiddenmenu

Put a # before hiddenmenu to comment that line out:

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu

Save the file, and you should see the menu the next time you reboot.