How do I enter interactive command mode in GRUB bootloader?

I've accidentally locked myself out of the sudoers file on my desktop machine when trying to get wireshark working.

So I figured that I need to enter single user mode. I've read how to do it in grub, but I can't seem to get the grub menu to appear in my default kubuntu installation.

It is hidden. How do I make it show?

From serverfault Matt

• If you hold Shift during computer boot up, Grub will display its menu.

  From jscott

• I'm pretty sure you can hit Esc to get into the menu.

  From weeheavy