Mounting QCOW2 Disk Images and Resetting the Root Password Without Booting the VM in Ubuntu/Debian

This guide explains how to mount a QCOW2 disk image on your host server and reset the root password without starting the virtual machine.

Step 1 – Install the nbd package

sudo apt install nbd-client qemu-utils

Step 2 – Load the NBD kernel module

sudo modprobe nbd

Step 3 – Connect the QCOW2 image as a network block device

sudo qemu-nbd --connect=/dev/nbd0 /PATH_TO_IMAGE/image.qcow2

Step 4 – Identify partitions in the QCOW2 image

sudo fdisk -l /dev/nbd0

Step 5 – Mount the root filesystem

In many cases, the bootloader is on the first partition, so you’ll likely want to mount the second partition:

sudo mount /dev/nbd0p2 /mnt/

Step 6 – Bind required filesystems

sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo mount --bind /run /mnt/run

Step 7 – Chroot into the mounted environment

sudo chroot /mnt

You are now inside the VM's root filesystem.

Step 8 – Reset the root password

passwd root

Follow the prompt to set a new root password.

Step 9 – Exit and unmount all filesystems

exit
sudo umount /mnt/run
sudo umount /mnt/dev
sudo umount /mnt/proc
sudo umount /mnt/sys
sudo umount /mnt

Step 10 – As the last step, disconnect and unload the kernel module

sudo qemu-nbd --disconnect /dev/nbd0
sudo rmmod nbd