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E.4. Troubleshooting GRUB

In most cases, GRUB will be installed and configured during the initial installation process, unless you used a Kickstart file and specifically disabled this behavior. The installed system should therefore be prepared to boot into your desktop environment or a command line, depending on your package selection. However, in certain cases it is possible that the system's GRUB configuration becomes corrupted and the system will no longer be able to boot. This section describes how to fix such problems.
When troubleshooting GRUB, keep in mind thatthe grub package does not automatically update the system boot loader when the package is updated using Yum or RPM. Therefore, updating the package will not automatically update the actual boot loader on your system. To work around this problem, use the grub-install command manually every time after the package is updated. See Section E.3, “Installing GRUB” for details about the command.


GRUB cannot construct a software RAID. Therefore, the /boot directory must reside on a single, specific disk partition. The /boot directory cannot be striped across multiple disks, as in a level 0 RAID. To use a level 0 RAID on your system, place /boot on a separate partition outside the RAID.
Similarly, because the /boot directory must reside on a single, specific disk partition, GRUB cannot boot the system if the disk holding that partition fails or is removed from the system. This is true even if the disk is mirrored in a level 1 RAID. The following Red Hat Knowledgebase article describes how to make the system bootable from another disk in the mirrored set:
Note that these issues apply only to RAID that is implemented in software, where the individual disks that make up the array are still visible as individual disks on the system. These issues do not apply to hardware RAID where multiple disks are represented as a single device.
The exact steps to fix a broken GRUB configuration will vary depending on what kind of problem there is. The GNU GRUB Manual offers a list of all possible error messages displayed by GRUB in different stages and their underlying causes. Use the manual for reference.
Once you have determined the cause of the error, you can start fixing it. If you are encountering an error which only appears after you select an entry from the GRUB menu, then you can use the menu to fix the error temporarily, boot the system, and then fix the error permanently by running the grub-install command to reinstall the boot loader, or by editing the /boot/grub/grub.conf or /boot/efi/EFI/redhat/grub.conf with a plain text editor. For information about the configuration file structure, see Section E.8, “GRUB Menu Configuration File”.


There are two identical files in the GRUB configuration directory: grub.conf and menu.lst. The grub.conf configuration file is loaded first; therefore you should make your changes there. The second file, menu.lst, will only be loaded if grub.conf is not found.