guestfish

open a image file

guestfish --rw -a ./ubuntu-20.04-server-cloudimg-amd64.img
Welcome to guestfish, the guest filesystem shell for
editing virtual machine filesystems and disk images.

Type: ‘help’ for help on commands
      ‘man’ to read the manual
      ‘quit’ to quit the shell

><fs>
><fs> run
><fs> list-filesystems
><fs> mount /dev/sda1 /
><fs> cat /etc/shadow
><fs> quit