Setting a root password on Ubuntu systems brings risk and you should probably avoid it… If you want to run commands set aside for the root user, you should use the sudo command… However, if you insist to set a password for the root user and use it to logon, even with all the risks, then run the commands below:

Ubuntu Linux root Password - Find default root user Dec 02, 2018 How to Change Password in Ubuntu [for Root and Normal Users] Oct 09, 2019 How to change root password in Ubuntu Linux - nixCraft Dec 02, 2018 What is the default password for Ubuntu 16.04 LTS? - Quora

The default password for the user 'ubuntu' on Ubuntu is blank. If you want to run the 'Live CD' from your hard disk then there's no need to make an image of it using dd. You can simply copy the casper directory to your hard disk and create an entry in grub which looks like:

Apr 17, 2020 Nagios Default Password for nagiosadmin CentOS Nagios XI Network analyzer Default Username and Password for CentOS Ubuntu, Debian, Fedora Linux. Nagios default Web Admin Password. Nagios Web interface uses htpassword, which is …

$ kinit ubuntu/admin@EXAMPLE.COM Password for ubuntu/admin@EXAMPLE.COM: Note. kinit doesn’t need for the principal to exist as a local user in the system. In fact, you can kinit any principal you want. If you don’t specify one, then the tool will use the username of whoever is running kinit.

Service - Kerberos | Server documentation | Ubuntu