skip to content
Keshav Mohta

Grub issue fix in ubuntu

/ 3 min read

ubuntu , grub

Here’s a summarized version of the main commands and steps to recover from a deleted OS situation using a live USB environment, including troubleshooting for common issues like disk space:

Summary: Recovering GRUB and Restoring Deleted OS Data

Prerequisites:

  • Bootable Ubuntu 24.04 live USB. ( although I has 23.10 USB while system installed was 24.04 but it worked)

1 Mount partitions

  1. Boot into the live USB and open a terminal.

  2. Identify the partitions:

Terminal window
sudo fdisk -l

You will see 2 partition, one is EFI ( sometimes it is not there ) and one is Linux FileSystem

Device             Start       End   Sectors   Size Type
/dev/nvme0n1p1      2048    206847    204800   100M EFI System
/dev/nvme0n1p2    206848    239615     32768    16M Microsoft reserved
/dev/nvme0n1p3    239616 211358180 211118565 100.7G Microsoft basic data
/dev/nvme0n1p4 211359744 294244351  82884608  39.5G Microsoft basic data
/dev/nvme0n1p5 294246400 295315455   1069056   522M Windows recovery environment
/dev/nvme0n1p6 295315456 500115455 204800000  97.7G Linux filesystem
  1. Mount the root partition (replace /dev/nvme0n1p6 with your actual root partition):
Terminal window
sudo mount /dev/nvme0n1p6 /mnt
  1. If there’s an EFI partition (typically small, like 100MB):
Terminal window
sudo mount /dev/nvme0n1p1 /mnt/boot/efi

2 Copy data from os_deleted to root

actually the osuninstaller command moved files from root partition to os_deleted; you can check whether /etc, /proc, /sys, /run directories are under root partition (i.e./dev/nvme0n1p1_ ) or not and if these directory are under os_deleted folder then we have to follow below step

  1. If your data was moved to os_deleted:
Terminal window
sudo rsync -av /mnt/os_deleted/ /mnt/

This command copies the contents of os_deleted back to the root partition.

If “No space left on device” error occurs:

Remove large or unnecessary files:

Terminal window
sudo rm -rf /mnt/var/cache/apt/*
sudo rm -rf /mnt/var/log/*

Use find to locate large files:

Terminal window
sudo find /mnt -type f -size +100M

Then remove any unnecessary large files:

Terminal window
sudo rm /mnt/path/to/large/file

in my cae there are images and video files so removed those

3 chroot into the system

  1. Bind the required directories:
Terminal window
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo mount --bind /run /mnt/run
  1. Enter the chroot environment:
Terminal window
sudo chroot /mnt

if above command gives error: failed to run command /bin/bash : No such file or directory means you do not have all required files in root directory

you can run sudo fsck /dev/nvme0n1p4 to check corrupted files

4 Reinstall GRUB

  1. Install GRUB for UEFI systems:
Terminal window
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=ubuntu
  1. Update the GRUB configuration:

update-grub

  1. If you encounter “unable to allocate pty”, run:
Terminal window
mount -t devpts none /dev/pts

5 Exit chroot and unmount

  1. Exit chroot:

exit

  1. Unmount the bound directories:
Terminal window
sudo umount /mnt/dev
sudo umount /mnt/proc
sudo umount /mnt/sys
sudo umount /mnt/run
sudo umount /mnt/boot/efi  # If mounted
sudo umount /mnt

6 Reboot

  1. Reboot the system to check if GRUB is restored:
Terminal window
sudo reboot

Troubleshooting tips:

If “target is busy” during unmount, use:

Terminal window
sudo umount -l /mnt

To list processes using a mount point:

Terminal window
sudo lsof +D /mnt
sudo fuser -vm /mnt
sudo fuser -k /mnt  # To kill processes

Use rsync with —exclude to temporarily skip non-essential data if space is an issue:

sudo rsync -av --exclude='home/*' /mnt/os_deleted/ /mnt/

This should help for restoring the system and resolving common errors encountered during the process.

Hope it helps