How to Change the root Password and add a Public SSH Key to a QCOW2 Image and Flash That Image to an SSD

  • Create the password hash:
openssl passwd -6 'MyNewPassword'
  • Use guestfish to open the qcow2 image:
sudo guestfish --rw -a ./image.qcow2 -i
  • Edit the shadow file:
edit /etc/shadow
  • Find the root line and add in the hashed password like so:
root:$6$k1ZzD3M5$z2lFtIYwREEXAMPLEHASH/sCEzF/:19956:0::7:::
  • For the public key, open the authorized_keys file. If you don’t already have a public/private ssh key pair, generate it with ssh-keygen -t rsa -b 4096:
edit /root/.ssh/authorized_keys

  • Add your public ssh key to the bottom of the file.

  • exit from the image.

  • Provide the following permissions on the local if needed:

chmod 700 /root/.ssh
chmod 600 /root/.ssh/authorized_keys
  • Convert the qcow2 image into raw format:
qemu-img convert -f qcow2 -O raw image.qcow2 image.raw

  • When copying the image onto the USB stick, make sure the USB’s filesystem is either XFS or EXT4. Create the partitions on the USB stick with fdisk and then sudo mkfs.xfs /dev/<partition> for the filesystem. Change the file permissions as well afterwards with sudo chown howard:howard ./

  • Copy the raw image over to a USB stick and boot the target machine into the Rocky Linux recovery shell via a Ventoy USB (Rocky Linux 8.10 is a good choice).

  • Flash the image and boot:

sudo dd if=image.raw of=/dev/sdX bs=4M status=progress conv=fsync

Updated: