GRUB bootloader repair with chroot

I had to do this quite often lately, so I thought it deserves going to the blog… 🙂 If you are having computers with multiple OS to boot sooner or later you will end up in a situation of having GRUB corrupt.

My latest adventure was after Windows 10 Anniversary update. The update messed up the hard drive partition table and on boot the computer ends up to GRUB’s rescue console. You can try the steps from this post and fix GRUB from its rescue console, though it did not work for me and you will notice at the end you still need to reinstall grub and recreate the boot menu:

http://www.legendiary.at/2016/01/04/windows-10-update-changes-partition-table-and-breaks-grub/

So I got one of my flash drives with live Linux on it and went for the well-known classic approach 🙂 Please mind your flash and hard disk Linux kernel architecture /32 or 64 bit/, they must match.

Boot your computer of the flash drive, run a terminal, make sure you are root /or use sudo/ when execute the commands and follow these steps:

1. List your drives and partitions with a command of your choice and make a note of the Linux partition

 

          fdisk –l

 

2. Mount your Linux partition to a folder and link required system folders to their alternatives in that folder. Substitute sdXY below with the correct Linux partition for your system.*

 

          mount /dev/sdXY /mnt

 

          mount –bind /dev /mnt/dev

          mount –bind /dev/pts /mnt/dev/pts

          mount –bind /proc /mnt/proc

          mount –bind /sys /mnt/sys

 

3. Use chroot to change your root directory.

 

          chroot /mnt

 

4. Recreate GRUB menu and install it on the boot drive. This commands are for Debian and its family, for other distributions you have to use the correct commands.

 

          update-grub

 

          grub-install /dev/sdX

 

Reboot your computer and enjoy the boot menu you are used to. 🙂

*You can substitute the multiple mount commands with a single line if you wish to:

          for i in /dev /dev/pts /proc /sys; do mount -B $i /mnt$i; done

** Just a quick addition to the post to bring it up to current times. If your happen to have a EFI bootloader you will have to mount the EFI partition as well, like this:

mount /dev/sdXZ /mnt/boot/efi

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