HOWTO: Restore Grub2 Menu after Windows Reinstall

How to Restore GRUB2 after installing Windows:

Boot from an Ubuntu Live CD or Live USB
Once up and running, Open a Terminal
Type sudo su (press enter after typing each command)
Type fdisk -l
Note which device contains your Linux partition (IE: /dev/sda1)
Type mount /dev/sdx# /mnt (replacing x# with your actual device and partition number)
Type mount —bind /dev /mnt/dev
Type mount —bind /proc /mnt/proc
Type cp /etc/resolv.conf /mnt/etc/resolv.conf
Type chroot /mnt
Type grub-install —recheck /dev/sdx (replacing x with your actual device)
Type reboot (to reboot your PC)
Make sure to remove your Live USB or CD. Upon reboot you should be presented with a GRUB2 menu. However, Windows is missing. Now, I show you how to fix that.

Making GRUB 2 detect Windows Installs:

Proceed to boot into your Linux environment.
Open a terminal and type sudo update-grub (enter your root password when prompted)
If all went well, grub should have updated it's menu entries to reflect what it detected. Including existing Windows partitions.