Chapter 12. 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 the desired operating system. Note GRUB restores files only if they are not corrupted. 12.1. 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 Reinstall GRUB on the device where it is installed. For example, if sda is your device: Reboot your system for the changes to take effect: Additional resources grub-install(1) man page on your system 12.2. 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 Reinstall the grub2-efi and shim boot loader files: Reboot your system for the changes to take effect: 12.3. 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 Determine the disk partition that stores GRUB: Reinstall GRUB on the disk partition: Replace partition with the identified GRUB partition, such as /dev/sda1 . Reboot your system for the changes to take effect: Additional resources grub-install(1) man page on your system 12.4. 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 Remove the configuration files: Reinstall packages. On BIOS-based machines: On UEFI-based machines: Rebuild the grub.cfg file for the changes to take effect. On BIOS-based machines: On UEFI-based machines: 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. Follow Reinstalling GRUB procedure to restore GRUB on the /boot/ partition.

Commands:
grub2-install /dev/sda
reboot
yum reinstall grub2-efi shim
reboot
bootlist -m normal -o sda1
grub2-install partition
reboot
rm /etc/grub.d/ * rm /etc/sysconfig/grub
yum reinstall grub2-tools
yum reinstall grub2-efi shim grub2-tools
grub2-mkconfig -o /boot/grub2/grub.cfg
grub2-mkconfig -o /boot/grub2/grub.cfg