How to Restore GRUB After Installing Windows: A Step-by-Step Guide

If you’ve recently installed Windows on a dual-boot system with Linux, you may find that your GRUB bootloader has been overwritten, preventing you from accessing your Linux distribution. Restoring GRUB is a crucial step to regain control of your system and boot into your preferred operating system. In this comprehensive guide, we’ll walk you through the process of repairing GRUB after a Windows installation, ensuring a smooth and seamless dual-boot experience.

Preparing for GRUB Restoration

Before we dive into the restoration process, it’s essential to ensure that you have the necessary tools and information at hand. You’ll need a live Linux environment, such as a bootable USB drive or a live CD/DVD. Additionally, you should know the partition where your Linux distribution is installed and the type of partitioning scheme used (MBR or GPT).

To determine the partition and partitioning scheme, you can use the `fdisk` command in a terminal. Open a terminal and run the following command:

sudo fdisk -l

This will display a list of all the partitions on your system. Look for the partition labeled with your Linux distribution (often “Linux” or “ext4”). Make a note of the partition number and the partitioning scheme used (MBR or GPT).

Restoring GRUB in a Legacy BIOS System (MBR)

If your system uses a legacy BIOS and MBR partitioning, follow these steps to restore GRUB:

1. Boot into the live Linux environment.
2. Open a terminal and run the following commands:

    sudo mount /dev/sdaX /mnt sudo grub-install --root-directory=/mnt /dev/sda 

   Replace `X` with the partition number where your Linux distribution is installed (e.g., `sda3`). The second command installs GRUB on the MBR of the first hard drive (`/dev/sda`).

3. Run the following command to generate a new GRUB configuration file:

   sudo grub-mkconfig -o /mnt/boot/grub/grub.cfg

4. Reboot your system, and you should now be able to see the GRUB menu and boot into your Linux distribution.

Restoring GRUB in a UEFI System (GPT)

If your system uses UEFI and GPT partitioning, the process is slightly different:

1. Boot into the live Linux environment.
2. Open a terminal and run the following commands:

    sudo mount /dev/sdaX /mnt sudo mount /dev/sdaY /mnt/boot sudo mount /dev/sdaZ /mnt/boot/efi 

   Replace `X` with the partition number where your Linux root filesystem is mounted, `Y` with the partition number for the `/boot` directory, and `Z` with the partition number for the EFI system partition.

3. Chroot into the mounted Linux environment:

   sudo chroot /mnt

4. Install the GRUB packages:

   sudo grub-install /dev/sda sudo grub-mkconfig -o /boot/grub/grub.cfg 

5. Exit the chroot environment and reboot your system. You should now see the GRUB menu and be able to boot into your Linux distribution.

If you encounter any issues or errors during the restoration process, it’s recommended to consult the official documentation of your Linux distribution or seek further assistance from the community forums.