How can I repair grub? (How to get Ubuntu back after installing Windows?)
When you install Windows, Windows assumes it is the only operating system (OS) on the machine, or at least it does not account for Linux. So it replaces GRUB with its own boot loader. What you have to do is replace the Windows boot loader with GRUB. I've seen various instructions for replacing GRUB by mucking around with GRUB commands or some such, but to me the easiest way is to simply chroot
into your install and run update-grub
. chroot
is great because it allows you to work on your actual install, instead of trying to redirect things here and there. It is really clean.
Here's how:
- Boot from the live CD or live USB, in "Try Ubuntu" mode.
-
Determine the partition number of your main partition.
sudo fdisk -l
,sudo blkid
or GParted (which should already be installed, by default, on the live session) can help you here. I'm going to assume in this answer that it's/dev/sda2
, but make sure you use the correct partition number for your system!If your main partition is in an LVM, the device will instead be located in
/dev/mapper/
, most likely,/dev/mapper/{volume}--{os}-root
where{volume}
is the LVM volume name and{os}
is the operating system. Executels /dev/mapper
for the exact name. -
Mount your partition:
sudo mount /dev/sda2 /mnt #Replace sda2 with the partition from step 2
If you have a separate
/boot
,/var
or/usr
partitions, repeat steps 2 and 3 to mount these partitions to/mnt/boot
,/mnt/var
and/mnt/usr
respectively. For example,sudo mount /dev/sdXW /mnt/boot sudo mount /dev/sdXY /mnt/var sudo mount /dev/sdXZ /mnt/usr
replacing
sdXW
,sdXY
, andsdXZ
with the respective partition numbers. -
Bind mount some other necessary stuff:
for i in /sys /proc /run /dev; do sudo mount --bind "$i" "/mnt$i"; done
-
If Ubuntu is installed in EFI mode (see this answer if you're unsure), use
sudo fdisk -l | grep -i efi
or GParted to find your EFI partition. It will have a label ofEFI
. Mount this partition, replacingsdXY
with the actual partition number for your system:sudo mount /dev/sdXY /mnt/boot/efi
-
chroot
into your Ubuntu install:sudo chroot /mnt
-
At this point, you're in your install, not the live session, and running as root. Update grub:
update-grub
If you get errors or if going up to step 7 didn't fix your problem, go to step 8. (Otherwise, it is optional.)
-
Depending on your situation, you might have to reinstall grub:
grub-install /dev/sda update-grub # In order to find and add windows to grub menu.
-
If Ubuntu is installed in EFI mode, and EFI partition UUID has changed, you may need to update it in
/etc/fstab
. Compare it:blkid | grep -i efi grep -i efi /etc/fstab
If current EFI partition UUID (from
blkid
) differs from the one in/etc/fstab
, update/etc/fstab
with current UUID. -
If everything worked without errors, then you're all set:
exit sudo reboot
At this point, you should be able to boot normally.
If you cannot boot normally, and didn't do step 8 because there were no error messages, try again with step 8.
- Sometimes giving GRUB2 the correct configuration for your partitions is not enough, and you must actually install it (or reinstall it) to the Master Boot Record, which step 8 does. Experience helping users in chat has shown that step 8 is sometimes necessary even when no error messages are shown.
The Windows installer doesn't care about other OS in the system. So it writes own code over the master boot record. Fortunately the solution is easy too.
You need to repair the MBR. Do the following
Boot using a live usb/cd of ubuntu.
Use boot-repair
to fix the problem.
After booting with live usb/cd, run following command in terminal:
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair
Use Recomended Repair
.
More info - https://help.ubuntu.com/community/Boot-Repair
Boot from a live Ubuntu USB pendrive or CD
and
Install Boot-Repair on ubuntu by following steps
Open the terminal and run the following commands
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install boot-repair
After completing the installation you can launch it from System->Administration->Boot-Repair menu if you use Gnome, or search "boot-repair" in the dash if you use Unity. Then follow the following screenshots:
Method 1
- Click on the advanced options
- Tick the options shown below
- Change the tab to Grub Location Tab and Tick The options Shown in the figure
Press Apply and Reboot the system
Method 2
- Select the recommended Boot repair options as shown in the first screenshot
Documentation :