Rescuing a Non-Booting GRUB2 Environment

When the GRUB bootloader fails to find its configuration file or its partition, you are dropped into one of two shells: the GRUB Shell (grub>) or the GRUB Rescue Shell (grub rescue>). This guide covers how to access these shells and manually boot your system.

Accessing the GRUB Shell

If the system doesn’t drop you into a shell automatically, you may need to interrupt the boot process manually.

Depending on your system configuration (BIOS vs. UEFI), use the following keys immediately after the BIOS/Manufacturer splash screen:

BIOS/Legacy: Hold the Shift key.
UEFI: Tap the Esc key repeatedly.

2. Entering Command Mode

Once the GRUB menu (the list of available kernels) is visible:

Press c: This opens the GRUB shell (grub>).
Press e: This allows you to edit the boot parameters of the selected entry.

Scenario A: The GRUB Shell (`grub>`)

This shell appears when GRUB can load its modules but cannot find the grub.cfg file.

1. Identify Partitions

List all partitions known to GRUB:

grub> ls

2. Find the Boot Files

Inspect the partitions to find your kernel (vmlinuz) and initrd files:

grub> ls (hd0,1)/

Note: If you have a separate /boot partition, the files will be in the root of that partition. If not, look in (hd0,1)/boot/.

3. Set Root and Load Kernel

Once identified, set the root partition and point to the specific kernel and initrd versions:

grub> set root=(hd0,1)
grub> linux /boot/vmlinuz-3.13.0-29-generic root=/dev/sda1
grub> initrd /boot/initrd.img-3.13.0-29-generic

4. Boot

grub> boot

Scenario B: The GRUB Rescue Shell (`grub rescue>`)

This limited shell appears when GRUB cannot find its own directory (/boot/grub).

1. Set the Environment

Tell GRUB where its modules and root partition are located:

grub rescue> set prefix=(hd0,1)/boot/grub
grub rescue> set root=(hd0,1)

2. Load Normal Mode

grub rescue> insmod normal
grub rescue> normal

Note: If normal loads successfully, you will transition to the standard grub> prompt.

3. Load Linux and Boot

If the system stays in the rescue environment after normal, load the Linux module manually:

grub rescue> insmod linux
grub rescue> linux /boot/vmlinuz-3.13.0-29-generic root=/dev/sda1
grub rescue> initrd /boot/initrd.img-3.13.0-29-generic
grub rescue> boot

Post-Boot: Permanent Fixes

Manual booting is temporary. Once you are back in your OS, you must repair the bootloader.

For Debian/Ubuntu Systems:

sudo grub-install /dev/sda
sudo update-grub

For RHEL/AlmaLinux/Fedora Systems:

sudo grub2-install /dev/sda
sudo grub2-mkconfig -o /boot/grub2/grub.cfg