Linux · critical · Day-to-day operations

grub rescue> — "no such partition" or "unknown filesystem"

GRUB's first stage loaded but cannot find its own modules, so it drops to a minimal shell with almost no commands.

What you see

Boot lands at a `grub rescue>` prompt. Most commands are unavailable; only ls, set, insmod and a few others work.

What is actually wrong

A partition was resized, moved or renumbered, another OS overwrote the boot sector, or /boot was on a disk that has changed device order.

Codes and articles

grub rescueno such partitionunknown filesystemerror: file '/boot/grub/i386-pc/normal.mod' not found

Fixes (2)

Boot once from the rescue prompt

grub rescue> prompt20 minuteslow riskreversible

No live media to hand. This gets you booted once; it does not repair anything permanently.

List the partitions GRUB can see.
Shell
```
ls
```
It prints things like (hd0) (hd0,gpt1) (hd0,gpt2). These are GRUB's names, not Linux's — gpt2 here is roughly /dev/sda2.
Find which one holds /boot/grub by inspecting each in turn.
Shell
```
ls (hd0,gpt2)/boot/grub
```

Point GRUB at it and load the modules.

Shell

set prefix=(hd0,gpt2)/boot/grubset root=(hd0,gpt2)insmod normalnormal

The full menu should appear. Boot the system normally.
Once booted, make it permanent — otherwise the next restart lands right back here.
Shell
```
sudo grub-install /dev/sdasudo update-grub
```
Do not skip this. Everything above lives only in memory.

On RHEL-family use the other tool name.

Shell

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

Confirm it workedThe machine restarts into the normal GRUB menu.

Shell

sudo grub-install --version && lsblk -f

If you need to undo itNone — nothing on disk is changed until the grub-install step.

Reinstall GRUB from a live USB

Live USB session45 minutesmedium riskreversible

The rescue prompt route failed, or /boot itself is damaged.

Boot the live USB and identify the partitions.
Shell
```
lsblk -fsudo blkid
```
Mount the root filesystem, activating LVM first if used.
Shell
```
sudo vgchange -aysudo mount /dev/sda2 /mnt
```
Mount /boot and, on a UEFI machine, the EFI partition.
Shell
```
sudo mount /dev/sda1 /mnt/bootsudo mount /dev/sda1 /mnt/boot/efi
```
Only mount boot/efi if they are separate partitions — check the fstab of the mounted root with `cat /mnt/etc/fstab` rather than assuming.

Bind the virtual filesystems and enter the installation.

Shell

for d in dev dev/pts proc sys run; do sudo mount --bind /$d /mnt/$d; donesudo chroot /mnt /bin/bash

Reinstall the bootloader. For BIOS/MBR, target the DISK not a partition.
Shell
```
grub-install /dev/sdaupdate-grub
```

For UEFI, install to the EFI directory instead.

Shell

grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntuupdate-grub

Leave and unmount cleanly.
Shell
```
exitsudo umount -R /mntsudo reboot
```

Confirm it workedThe machine boots to the GRUB menu and into the system.

Shell

sudo efibootmgr -v

If you need to undo itReinstalling GRUB is repeatable and non-destructive to data.

Related faults

Where this stops. This write-up was written and checked by hand. It says what each step changes, how to confirm it worked and how to reverse it, and anything destructive is flagged before you reach it. If it does not match what your machine is doing, search the Support Centre for the exact code or message — and when something needs a person, get in touch.