I have found this in the Ubuntu forums, and the original source is not longer online.
So, I’ll put it here to me and anyone.
Howto Recover Grub2 After Windows Installation Posted by Binbash on Jun 21, 2009 Labels: grub2, Howto, jackalope, jaunty, karmic, koala, linux, recover, ubuntu, windows Today i destroyed my Grub2 via installing windows on my notebook which i write blog posts.(I quit smoking , so i have to play some games : ) No rush). It may be hard to recover it since there are not much (i did not find anything) howtos around the net about recovering Grub2.Here is the step by step guide to recover it : You will need a LIVE cd if you are going to recover an Ubuntu Box.Download Ubuntu Jaunty, Karmic whatever you want.Open the system with Live CD (I assume you are using Ubuntu Live CD).Press Alt+F2 and enter gnome-terminal command.And continue by entering : $sudo fdisk -l This will show your partition table.Here is my table to understand it better : /dev/sda1 29 8369 66999082+ 83 Linux /dev/sda2 * 8370 13995 45190845 7 HPFS/NTFS /dev/sda3 13996 14593 4803435 5 Extended /dev/sda5 13996 14593 4803403+ 82 Linux swap / Solaris Now i will mount Linux (sda1 here), i have no external boot partition as you can see.(IF YOU HAVE external one, do not forget to mount it! ) $sudo mount /dev/sda1 /mnt $sudo mount --bind /dev /mnt/dev $sudo mount --bind /proc /mnt/proc The following command is optional (it copies resolv.conf) $sudo cp /etc/resolv.conf /mnt/etc/resolv.conf Now chroot into the enviroment we made : sudo chroot /mnt After chrooting, you do not need to add sudo before your commands because from now, you will run commands as root. You may want to edit /etc/default/grub file to fit your system (timeout options etc) #nano -w /etc/default/grub Play with the options if you want.(But do not forget to give grub-update command if you saved it ) Now install/recover Grub2 via : #grub-install /dev/sda command.However you may get errors with that code like me.If so please use this command : #grub-install --recheck /dev/sda Now you can exit the chroot, umount the system and reboot your box : #exit $sudo umount /mnt/dev $sudo umount /mnt/proc $sudo umount /mnt $sudo reboot