The GRUB Bootloader plays a crucial role in managing multiple operating systems on your computer. As a key component of dual boot systems, it enables seamless switching between Linux, Windows, macOS, or other OSes.

However, GRUB-related issues can sometimes arise, prompting you to troubleshoot and resolve them. This in-depth guide will help you understand common GRUB bootloader problems in dual boot systems and their solutions.

A Brief Overview of GRUB and Dual Boot Systems

The GRand Unified Bootloader (GRUB) is a vital component of dual boot systems, responsible for managing the computer’s boot process.

When you power on your computer, the BIOS or UEFI firmware loads GRUB, which then displays a menu of available operating systems to boot. This flexibility allows you to choose between various installed OSes on your system.

Common GRUB Bootloader Issues

Despite its versatility, GRUB can sometimes encounter issues that affect its functionality. Some of the most common GRUB bootloader problems include:

A) Absence of GRUB during Boot

Occasionally, GRUB may not appear during the boot process, preventing you from accessing your desired operating system. This issue can result from incorrect BIOS/UEFI settings, hardware changes, or a damaged GRUB configuration.

B) Missing Operating System in the GRUB Menu

In some instances, the GRUB menu may display without one or more operating systems. This issue can occur if the GRUB configuration is outdated or if the OS installation is corrupt.

C) GRUB Entering Rescue Mode

When GRUB fails to load its normal configuration file, it enters rescue mode. This minimal environment, designed to recover from severe GRUB issues, can be challenging to navigate without familiarity with its command-line interface.

D) GRUB Error Messages

GRUB may occasionally display error messages such as “error: unknown filesystem” or “error: no such partition.” These errors may indicate issues with your system’s partition layout or the GRUB configuration.

Effective Solutions for GRUB Issues

A) Resolving GRUB’s Absence during Boot

  1. Verify BIOS/UEFI Settings: Ensure that your BIOS or UEFI settings are configured to boot from the correct drive. Access your system’s BIOS/UEFI settings by pressing the appropriate key during the boot process (usually Del, F2, or F10), then verify that the boot order prioritizes the drive containing GRUB.
  2. Repair GRUB: If your GRUB configuration is damaged, you may need to repair it. Boot from a live Linux USB or CD, then use the following commands in a terminal:
sudo fdisk -l

Identify your Linux root partition (e.g., /dev/sda1), then run the following commands in a terminal, replacing /dev/sdX# with the correct partition:

sudo mount /dev/sdX# /mnt
sudo mkdir -p /mnt/boot/efi
sudo mount /dev/sdX# /mnt/boot/efi
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt
grub-install /dev/sdX
sudo umount /mnt/dev
sudo umount /mnt/proc
sudo umount /mnt/sys
sudo umount /mnt/boot/efi
sudo umount /mnt
sudo reboot

After executing these commands, reboot your computer and check if GRUB now appears.

B) Restoring Missing Operating System in the GRUB Menu

  1. Update GRUB Configuration: Boot into the working operating system and open a terminal. Run the following command to update the GRUB configuration and detect all installed operating systems:
sudo update-grub

Reboot your system to see if the missing entry has been restored.

  1. Manually Add the Entry: If updating the configuration doesn’t work, you can manually add the missing entry by editing the /etc/grub.d/40_custom file. Use the following command to open the file in a text editor:
sudo nano /etc/grub.d/40_custom

Add a new menu entry for the missing operating system, then save and exit the file. Run sudo update-grub again and reboot to see if the issue is resolved.

C) Recovering from GRUB Rescue Mode

  1. Identify Correct Partition: In GRUB rescue mode, run the following commands to identify the correct partition containing your Linux root filesystem:

This command will display a list of available partitions (e.g., (hd0,msdos1), (hd0,msdos2), etc.). Use the ls (hdX,msdosY)/ command to explore each partition until you find the one containing the /boot/grub directory.

  1. Set Root and Prefix: Once you’ve identified the correct partition, run the following commands to set the root and prefix, replacing (hdX,msdosY) with the appropriate values:
set root=(hdX,msdosY)
set prefix=(hdX,msdosY)/boot/grub

3. Load Modules and Boot: Now, load the necessary modules and boot into your Linux system:

insmod normal
  1. Repair GRUB: Once you have booted into your Linux system, follow the steps in “Resolving GRUB’s Absence during Boot” to repair GRUB and prevent future occurrences of this issue.

D) Tackling GRUB Error Messages

  1. Check Partition Layout: Boot from a live Linux USB or CD and use a partition manager such as GParted to inspect your system’s partition layout. Ensure that your partitions are correctly formatted and have not been accidentally deleted or resized.
  2. Repair Filesystem: If you encounter an “unknown filesystem” error, you may need to repair the filesystem on the affected partition. Use the fsck command to check and repair the filesystem, replacing /dev/sdX# with the correct partition:
sudo fsck /dev/sdX#
  1. Repair GRUB Configuration: For other error messages, follow the steps in “Resolving GRUB’s Absence during Boot” to repair your GRUB configuration.

Tips to Prevent Future GRUB Bootloader Issues

To minimize the likelihood of future GRUB issues, consider the following best practices:

  1. Regularly Update Your System: Keep your operating systems and GRUB up-to-date to ensure compatibility and stability.
  2. Use Caution When Modifying Partitions: Avoid making changes to your system’s partition layout unless necessary, and always back up your data before doing so.
  3. Create a Recovery USB: Prepare a live Linux USB with a GRUB repair tool like Boot Repair, so you have a handy recovery option if GRUB issues arise.

While GRUB bootloader issues can be frustrating, understanding the common problems and their solutions is the first step toward resolving them.

By familiarizing yourself with the troubleshooting techniques outlined in this guide, you can effectively diagnose and fix GRUB-related issues in dual boot systems.

Moreover, following the best practices mentioned above can help prevent future bootloader problems, ensuring a smooth and seamless booting experience.


The GRUB bootloader is a powerful tool that allows users to manage and switch between multiple operating systems on their computers.

While GRUB-related issues can occur, this guide has provided detailed instructions to troubleshoot and resolve some of the most common problems you may encounter. By using these techniques, you can maintain the functionality of your dual boot system and switch between operating systems with ease.

As a final note, remember that the GRUB bootloader is a complex and versatile component that may require additional research and learning to understand fully.

However, the information provided in this guide should serve as a solid foundation for addressing most GRUB-related issues. Don’t hesitate to seek additional resources or ask for help from the Linux community if you encounter challenges beyond the scope of this guide.

Good luck with your dual boot system, and happy troubleshooting!

Read also:

Set Up Your Own Headless Linux Media Server with Plex and Docker

Supercharge Your Linux Terminal Workflow with Tmux and Vim

Could not open ‘/lib64/’: no such file or directory?

How to install Linux to windows 10 without an admin password?

How to Remove Linux from Chromebook?

Mastering Linux Mint: A Complete Guide To Editing smb.conf File

Categories: LinuxBlog

James R. Kinley - It Admin

James R. Kindly

My Name is James R. Kindly i am the founder and primary author of Storaclix, a website dedicated to providing valuable resources and insights on Linux administration, Oracle administration, and Storage. With over 20 years of experience as a Linux and Oracle database administrator, i have accumulated extensive knowledge and expertise in managing complex IT infrastructures and databases.

Save 30% on Apple AirPods Pro

Get the coolest AirPods ever released for:  $179,99  instead $249

  • Active Noise Cancellation blocks outside noise
  • Transparency mode for hearing and interacting with the world around you
  • Spatial audio with dynamic head tracking places sound all around you