Ubuntu changed to grub 2 and I often find myself looking up how to finagle my way into a single user shell.

Step 1.
   Hold the right shift to display the grub menu at boot time.

Step 2.
   Select the correct kernel, press CTRL+e to edit the boot command.

Step 3.
   Append the two directives   Single init=/bin/bash 

Step 4.
   Press CTRL+x to boot and wait for the root prompt.

Step 5.
   Remount / as read/write with the command:
     # mount -o remount,rw /

When you are finished, issue a reboot -f unless you are fond of kernel panics.