Recovering GRUB After Installing Windows 7

With the imminent release of Windows 7, I decided to give it a try on my own machine.  Windows 7 RTM (Release to Manufacturer) has already been released through MSDN, and as a UofT student I was able to grab my own copy through MSDNAA @ UofT.

A clean installation of Windows 7 is actually quite painless.  The setup process is quite fast, and it installed most of the necessary drivers from the get-go.

However, you’ll run into a spot of trouble if you’re running a dual boot *nix <-> ‘doze box.  Windows 7 will obliterate your GRUB and you’ll be able to boot into Windows only.

Well, that’s really no biggie as it happens with all Windows installations, not just 7.   With a bit of Googling, I found a nice blog post that walks you through how to get GRUB back.

However, the instructions above assume that your new Windows partition is located at (hd0,0), and that might not actually be the case.  For my own installation, my Windows partition was indeed installed in the harddrive’s first partition, but booting into the Windows option at the GRUB screen gave me a “BOOTMGR is missing” error. I tried to run the disk repair off of the original Windows 7 DVD, but that didn’t fix it.

After a bit of Googling and a bit of investigation on the disk partitions, I found out that Windows 7 makes two partitions when you first install it.  If you fire up GParted, you’ll see that there is a small (1 – 8mb, the size varies) partition right before the actual Windows partition.

Because of this, you’ll need to modify the line root (hd0,0) under Windows in your GRUB menu.lst file to point to your actual partition, which would be at (hd0,1)!  Or better yet, follow the instructions in the link and use the proper hdd partition reference so you don’t have to mess around with menu.lst.