When changing the guest OS password of root, you may encounter an Authentication token manipulation error. This message occurs because the /etc/shadow file is not present. You can add the shadow file by entering 'pwconv', then the root password can be set. See the example below.

bash-3.2# passwd
Changing password for user root.
passwd: Authentication token manipulation error

bash-3.2# pwconv
bash-3.2# passwd
Changing password for user root.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.