How to Repair/Restore/Reinstall Grub 2 using a Ubuntu Live CD

How to Repair/Restore/Reinstall Grub 2 using a Ubuntu Live CD.

If you have installed Windows after installing Ubuntu on your computer, then Windows Boot Menu will be the default boot menu on your computer. Since Windows Boot Menu won't detectUbuntu you can't boot into Ubuntu. To fix this you need to install GRUB which is the boot menu of Linux. To install GRUB boot in to your Ubuntu CD or aPendrive which has Ubuntu. For that insert your CD or Pendrive to your computer. Restart your computer and press F12 until a box appears. On that box you will see 2 or 3 items. If you inserted a Ubuntu CD then Select CDROM.
Note :- Boot menu might change according to the computer manufacture.
After selecting you will enter in to Ubuntu CD.
You will get a screen now. Select RUN Ubuntu without installing. You will now boot in to Ubuntu.

See More : Boot From CD

First, open the Terminal.

Mount the partition you Ubuntu Installation is on. If you are not sure which it is, launch gparted (included in the Live CD) and find out. It is Usually a EXT4 Partition. Replace the XY with the drive letter, and partition number. Example: sudo mount /dev/sda5 /mnt. Then bind the directories, you need, like so:

sudo mount /dev/sdXY /mnt

sudo mount --bind /dev /mnt/dev

sudo mount --bind /proc /mnt/proc

 Then we need to be the root of the installed Ubuntu. For that use chroot.

sudo chroot /mnt

Now install, check, and update grub. This time you only need to add the partition letter (usually a) to replace X. Example:grub-install /dev/sda, grub-install –recheck /dev/sda 

grub-install /dev/sdX

grub-install --recheck /dev/sdX 

update-grub

Now you can exit you mounted hard disk, and unmount.

exit

sudo umount /mnt/dev

sudo umount /mnt/proc

sudo umount /mnt

Shut down and turn your computer back on, and you will get the default Grub screen.
NOTE : Sometimes when you reboot you night not see Windows. To fix this do as below.

Boot in to Ubuntu and press CTRL + ALT + T.

A terminal window appears. Then paste the following command and press enter.

sudo update-grub

It will ask for your password. Type it and press enter.
Reboot your computer and you will see Windows now.

If you have any problems comment on this post. I will help you.