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Chapter 13. Reinstalling GRUB

You can reinstall the GRUB boot loader to fix certain problems, usually caused by an incorrect installation of GRUB, missing files, or a broken system. You can resolve these issues by restoring the missing files and updating the boot information.

Reasons to reinstall GRUB:

  • Upgrading the GRUB boot loader packages.
  • Adding the boot information to another drive.
  • The user requires the GRUB boot loader to control installed operating systems. However, some operating systems are installed with their own boot loaders and reinstalling GRUB returns control to those operating systems.
Note

GRUB restores files only if they are not corrupted.

13.1. Reinstalling GRUB on BIOS-based machines

You can reinstall the GRUB boot loader on your BIOS-based system. Always reinstall GRUB after updating the GRUB packages.

Important

This overwrites the existing GRUB to install the new GRUB. Ensure that the system does not cause data corruption or boot crash during the installation.

Procedure

  1. Install grub2-pc: 

    # grub2-pc
    Copy to Clipboard

  2. Reinstall GRUB on the device where it is installed. For example, if sda is your device: 

    # grub2-install /dev/sda
    Copy to Clipboard

  3. Reboot your system for the changes to take effect: 

    # reboot
    Copy to Clipboard

13.2. Reinstalling GRUB on UEFI-based machines

You can reinstall the GRUB boot loader on your UEFI-based system.

Important

Ensure that the system does not cause data corruption or boot crash during the installation.

Procedure

  1. Reinstall the grub2-efi and shim boot loader files: 

    # dnf reinstall grub2-efi-x64 shim
    Copy to Clipboard

  2. Reboot your system for the changes to take effect: 

    # reboot
    Copy to Clipboard

13.3. Reinstalling GRUB on IBM Power machines

You can reinstall the GRUB boot loader on the Power PC Reference Platform (PReP) boot partition of your IBM Power system. Always reinstall GRUB after updating the GRUB packages.

Important

This overwrites the existing GRUB to install the new GRUB. Ensure that the system does not cause data corruption or boot crash during the installation.

Procedure

  1. List the disk partition that stores GRUB: 

    # bootlist -m normal -o
sda1
    Copy to Clipboard

  2. Reinstall GRUB on the disk partition: 

    # grub2-install partition
    Copy to Clipboard

    Replace partition with the identified GRUB partition, such as /dev/sda1.

  3. Reboot your system for the changes to take effect: 

    # reboot
    Copy to Clipboard

13.4. Resetting GRUB

Resetting GRUB completely removes all GRUB configuration files and system settings, and reinstalls the boot loader. You can reset all the configuration settings to their default values, and therefore fix failures caused by corrupted files and invalid configuration.

Important

The following procedure will remove all the customization made by the user.

Procedure

  1. Remove the configuration files: 

    # rm /etc/grub.d/*
# rm /etc/sysconfig/grub
    Copy to Clipboard

  2. Reinstall packages.

    • On BIOS-based machines: 

      # dnf reinstall grub2-pc grub2-tools
      Copy to Clipboard

    • On UEFI-based machines: 

      # dnf reinstall grub2-efi shim grub2-tools grub2-common
      Copy to Clipboard

  3. Rebuild the grub.cfg file for the changes to take effect: 

    # grub2-mkconfig -o /boot/grub2/grub.cfg
    Copy to Clipboard

    This applies to both, BIOS and UEFI based systems.

    Warning

    The path to rebuild grub.cfg is same for both BIOS and UEFI based machines. Actual grub.cfg is present at BIOS path only. The UEFI path has a stub file that must not be modified or recreated using grub2-mkconfig command.

  4. Follow Reinstalling GRUB procedure to restore GRUB on the /boot/ partition.
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