Intel BIOSes require the Bootable flag on partitions

Not much on my tech blog these days, but here's a quick solution to what seems to be a common gotcha. We recently got new machines for our lab, and they all run a 946 chipset. The installs went smoothly with grub getting installed, but after rebooting, the BIOS refused to boot from the hard disk, pretending as if it wasn't there at all!

It turns out the BIOS on these machines refuse to boot from the hard disk if none of the partitions has the bootable flag set. This is a bit crazy, and can make you go hunting for unconnected hard disks and stuff like that.

Here's the quickest solution, for the above mentioned problem:

1. Boot from CD, I used the Ubuntu CD.
2. Choose "Boot from Hard Disk" or equivalent.
   
3. In the resulting grub menu, press 'c' to get to the prompt, and execute the following commands, where hd(X, Y) is your boot/root partition:
   

   
   root (hdX,Y)
   makeactive
   

   This will set the bootable flag on (hdX, Y).
   
4. Press 'Esc' to get back to the menu, and boot normally.