FIX Dual Boot: Recover Ubuntu GRUB After Windows Update

Step-by-step guide to restore the GRUB bootloader after a Windows update breaks your Ubuntu dual boot. Boot both OS again without losing data

Published on 14 June, 2025

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Dual Boot GRUB Linux

If you're using a dual-boot system with Ubuntu and Windows, there's a chance you've faced this problem. after a Windows update, your system suddenly boots straight into Windows, and Ubuntu is nowhere to be found. You may even see a scary error message like this one:

What’s Going On?

When you install Ubuntu alongside Windows, a program called GRUB (GRand Unified Bootloader) manages which operating system starts when you turn on your computer. GRUB is stored in a small, special partition called the EFI System Partition (ESP).

Unfortunately, sometime Windows updates overwrites or removes Ubuntu’s GRUB boot files in this partition. This leads to an error where your system can't find GRUB, and it either boots directly into Windows or shows an error like the one above.

Your Ubuntu installation is still there, it's just unreachable until we restore GRUB.

Restore GRUB with Bootable Ubuntu USB drive

All of the following steps must be done from the Bootable Ubuntu USB drive (also called a live USB). When you boot from the USB, choose the “Try Ubuntu” option.

1. Boot into Live Ubuntu

Insert your Ubuntu USB and reboot your system. While it starts, press the appropriate key (like F12, Esc, or F10) to open the boot menu and select your USB drive. Choose “Try Ubuntu without installing.”

2. Open the Terminal

Once Ubuntu has loaded, press Ctrl + Alt + T. This opens the Terminal where we’ll run the necessary commands.

3. Identify the Partitions

We need to find two things:

The partition where Ubuntu is installed
The EFI partition where bootloaders are stored

sudo fdisk -l

Look through the output for:

A Linux partition (ext4) – often something like /dev/sda5 or /dev/nvme0n1p4
A small FAT32 partition marked as EFI System, often /dev/sda1 or /dev/nvme0n1p1

4. Create Mount Point and Mount Ubuntu Partition

Create a proper mount point:

sudo mkdir -p /mnt/ubuntu

Now mount your Ubuntu root partition:

sudo mount /dev/nvme0n1p4 /mnt/ubuntu

Replace /dev/nvme0n1p4 with your actual Ubuntu root partition.

5. Mount the EFI Partition

Create the EFI directory (if it doesn't exist):

sudo mkdir -p /mnt/ubuntu/boot/efi

Then mount the EFI partition:

sudo mount /dev/nvme0n1p1 /mnt/ubuntu/boot/efi

Replace /dev/nvme0n1p1 with your actual EFI partition.

6. Mount System Directories

These system folders are needed for GRUB to be reinstalled properly:

sudo mount --bind /dev /mnt/ubuntu/dev
sudo mount --bind /proc /mnt/ubuntu/proc
sudo mount --bind /sys /mnt/ubuntu/sys

7. Access Your Installed System

Now we’ll enter your real Ubuntu system using chroot, which allows us to run commands as if we had booted into it.

sudo chroot /mnt/ubuntu

You are now inside your actual Ubuntu installation.

8. Reinstall GRUB Bootloader

Now, reinstall GRUB on the disk:

grub-install /dev/nvme0n1
update-grub

If you encounter any errors during the GRUB installation, try running the update-grub command directly:

update-grub

Replace /dev/nvme0n1 with your actual disk (not a partition). Use lsblk to confirm the correct identifier.

9. Exit and Unmount Everything

We’re done! Let’s clean up:

exit
sudo umount /mnt/ubuntu/dev
sudo umount /mnt/ubuntu/proc
sudo umount /mnt/ubuntu/sys
sudo umount /mnt/ubuntu/boot/efi
sudo umount /mnt/ubuntu

10. Reboot and Test

Now, reboot your system:

sudo reboot