Restoring the MBR

[pokeyThePenguin]

I installed Ubuntu onto an external hard drive hooked up to my laptop. The MBR was overwritten, so now my laptop can only boot when I boot from the external.

I have Ubuntu (and only Ubuntu) on my laptop, and that's where all my precious things are. I have absolutely nothing of importance on my external right now.

In order to restore the MBR on my laptop, do I have to boot from a LiveCD and somehow do it that way? What are the steps for restoring the MBR?

I'm running Karmic Koala on a 32-bit Toshiba laptop.

[oldfred]

You can use the liveCD.

How to restore the Ubuntu/XP/Vista/7 bootloader (Updated for Ubuntu 9.10)
http://ubuntuforums.org/showthread.php?t=1014708

But if with the external installed you can boot into your install you just have to reinstall grub from there. I am assuming grub2, ask if not.

reinstall from working system - first find Ununtu drive:
sudo fdisk -l
if it's "/dev/sda" then just run:
sudo grub-install /dev/sda
If that returns any errors run:
sudo grub-install --recheck /dev/sda
Then:
sudo update-grub