Recovery from a bootable USB drive

How to boot from a bootable Recovery USB and recover the boot loader.
This is useful if you cannot boot your Operating System from disk.
Please note: You can follow this guide to create a bootable USB drive.

1 Cannot boot

If you can't access your operating system or its recovery menu, it can be repaired from a bootable USB drive.
Firstly, insert the USB drive and turn on your computer whilst repeatedly tapping the F7 key.
This will bring up the boot menu.
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2 Boot Recovery USB

Use the arrow keys to select your USB drive and press enterto boot from it. You need to use the live mode of the USB. There are a few different terminologies used but typically it is Live, Tryor **Start.**On Ubuntu, the option to select is Try Ubuntu.
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3 Check disk path

Open the GNOME Launcher and open Terminal.
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To check the path of the disk, type in the below command:

sudo fdisk -l | grep 'nvme|sda'

4 Partition of disk

This will reveal the partition of the disk that needs mounting. This will either reveal sda or nvme
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5 Mount partitions

Most installs will only have the 2 partitions shown.
Run the below commands to mount them:

mount /dev/nvme0n1p2 /mnt
mount /dev/nvme0n1p1 /mnt/boot
sudo mount --bind /dev /mnt/dev
sudo mount --bind /dev /mnt/dev/pts
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys

6 Enable network

Depending on what you need to do in the recovery mode, you may want to enable internet access with:

sudo cp /etc/resolv.conf /mnt/etc/resolv.conf

7 Connecting to installation

From here, we need to chroot into the disk with:

sudo chroot /mnt /bin/bash

8 Connected to installation

This will take you to a terminal window running as root on your SSD.
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9 Ready to diagnose

From here we are ready to perform further diagnostics on the installation.

  • fsck - Check file system
  • GRUB Repair - Update bootloader
  • dpkg - Repair broken packages

The most common reason for attempting recovery from a USB drive is an interrupted update - which results in getting stuck at a grub prompt. To resolve this issue, enter the below commands:

sudo dpkg --configure -a
sudo apt -f install

See further guide on using recovery mode

Oct 14, 2021

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