GRUB Bootloader Reinstallation from a Live Environment

Overview

Use this procedure to reinstall GRUB on a Linux system that is unable to boot. The process uses a live boot environment, mounts the target system, enters a chroot environment, and reinstalls GRUB on the target disk.

Prerequisites

Boot the server using a Linux live environment (example: R1Soft BMR boot CD).
Log in as the root user:

 
sudo -i
 

Procedure

1. Create a Mount Point

 
mkdir /r1soft
 

2. Mount the Target Filesystem

Standard Root Partition

 
mount /dev/sda1 /r1soft
 

LVM Root Partition if applicable

First, scan for volume groups and activate them with:

 
vgscan
vgchange -ay

Next, mount the logical volume with:

 
mount /dev/vgname/lvname /r1soft
 

Separate Boot Partition if applicable

 
mount /dev/sda2 /r1soft
mount /dev/sda1 /r1soft/boot

3. Prepare the Chroot Environment

 
mount --bind /proc /r1soft/proc
mount --bind /sys /r1soft/sys
mount --bind /dev/pts /r1soft/dev/pts
mount --bind /dev /r1soft/dev
mount --bind /run /r1soft/run
 

4. Enter the Chroot Environment

 
chroot /r1soft
 

5. Back Up Existing GRUB Directory

Debian-Based Systems

 
mv /boot/grub /boot/grub_bak
 

AlmaLinux/RHEL-Based Systems

 
mv /boot/grub2 /boot/grub2_bak
 

6. Reinstall GRUB

Debian-Based Systems

 
grub-install /dev/sda
 

AlmaLinux/RHEL-Based Systems

 
grub2-install /dev/sda
 

Replace /dev/sda with the appropriate boot disk if different.

7. Regenerate GRUB Configuration

Debian-Based Systems

 
update-grub
 

AlmaLinux/RHEL-Based Systems

 
grub2-mkconfig > /boot/grub/grub.cfg
 

8. Reboot and Validate

Exit the chroot environment.
Reboot the server.
Remove the live media.
Confirm the operating system boots successfully.