How to Reinstall GRUB2 from Rescue Mode on RHEL, AlmaLinux and Rocky Linux

Updated: 28 September 2026 · Applies to: GRUB 2.06 and 2.12 on AlmaLinux and Rocky Linux 9 and 10 and RHEL 9 and 10 (BIOS and UEFI); notes for Ubuntu and Debian

If a server stops at a "grub>" or "grub rescue>" prompt, or no longer finds its operating system after a disk change, the boot loader must be reinstalled. You do this from the installation or rescue media, by entering the installed system with chroot. The steps depend on whether the server boots with BIOS (legacy) or UEFI, and they follow Red Hat's documented procedure.

Before you start

• You need the server's console: IPMI or KVM on a dedicated server, or your VPS panel's console. If you cannot attach installation media yourself, ask your provider's support.
• Boot the AlmaLinux, Rocky Linux or RHEL installation image of the same major version and choose Troubleshooting › Rescue. Let it mount the installed system: it is placed under /mnt/sysroot.

1. Enter the installed system

chroot /mnt/sysroot

Check which boot mode you are in: if /sys/firmware/efi exists, the server boots with UEFI; otherwise with BIOS.

2a. BIOS servers

1. Find the boot disk (not a partition) with lsblk, for example /dev/sda.
2. Install GRUB to it:

   grub2-install /dev/sda

   With software RAID 1, install it to every disk in the array so the server can boot from either.
3. Regenerate the menu:

   grub2-mkconfig -o /boot/grub2/grub.cfg

2b. UEFI servers

Do not run grub2-install on UEFI systems. Reinstall the boot loader packages instead, which puts the signed boot files back in the EFI partition:

dnf reinstall grub2-efi shim grub2-tools grub2-common
grub2-mkconfig -o /boot/grub2/grub.cfg

On RHEL 9 and 10, /boot/efi/EFI/*/grub.cfg is a small stub that points to /boot/grub2/grub.cfg; do not overwrite it with grub2-mkconfig. If the firmware lost its boot entry, recreate it with efibootmgr (check the existing entries with efibootmgr -v).

3. Leave and reboot

exit
reboot

Remove the rescue media so the server boots from its disk.

Ubuntu and Debian

Boot a live or rescue system, mount the root file system on /mnt (and /mnt/boot/efi on UEFI), bind-mount /dev, /proc and /sys, run chroot /mnt, then grub-install /dev/sda (BIOS) or grub-install (UEFI), followed by update-grub.

Official documentation: Reinstalling GRUB (Red Hat).