Red Hat SummitChapter 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 the desired operating system.
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.
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
sdais your device:# grub2-install /dev/sdaReboot your system for the changes to take effect:
# reboot
13.2. Reinstalling GRUB on UEFI-based machines
You can reinstall the GRUB boot loader on your UEFI-based system.
Ensure that the system does not cause data corruption or boot crash during the installation.
Procedure
Reinstall the
grub2-efiandshimboot loader files:# yum reinstall grub2-efi shimReboot your system for the changes to take effect:
# reboot
13.3. Reinstalling GRUB on IBM Power machines
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.
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:
# bootlist -m normal -osda1Reinstall GRUB on the disk partition:
# grub2-install partitionReplace
partitionwith the identified GRUB partition, such as/dev/sda1.Reboot your system for the changes to take effect:
# reboot
13.4. Resetting GRUB
Resetting GRUB removes all GRUB configuration files and system settings. It reinstalls the boot loader and restores all configuration settings to their default values. This process fixes failures caused by corrupted files and invalid configuration.
The following procedure will remove all the customization made by the user.
Procedure
Remove the configuration files:
# rm /etc/grub.d/* # rm /etc/sysconfig/grubReinstall packages.
On BIOS-based machines:
# yum reinstall grub2-toolsOn UEFI-based machines:
# yum reinstall grub2-efi shim grub2-tools grub2-common
Rebuild the
grub.cfgfile for the changes to take effect.On BIOS-based machines:
# grub2-mkconfig -o /boot/grub2/grub.cfgOn UEFI-based machines:
# grub2-mkconfig -o /boot/grub2/grub.cfgWarningThe path to rebuild
grub.cfgis same for both BIOS and UEFI based machines. Actualgrub.cfgis present at BIOS path only. The UEFI path has a stub file that must not be modified or recreated usinggrub2-mkconfigcommand.
-
Follow Reinstalling GRUB procedure to restore GRUB on the
/boot/partition.
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