It is the mystery for most Ubuntu Linux users. You didn’t set a root password, so what is it? The root user (also known as superuser), is a user on Ubuntu Linux and Unix-like systems with full administrative privileges (full access). So using the root account for daily work can be very dangerous, and you may damage your working system.
Ubuntu Linux and root account password
By default root account is locked under Ubuntu Linux. Therefore, you cannot log in as root or use ‘su -‘ command to become a superuser. To run all administrative command use the sudo command on Ubuntu. sudo allows a permitted user to execute a command as the superuser or another user. Ubuntu setup your default account (the one created during installation) to run all administrative commands. For example create a new user called bar, you need to type sudo command as follows:
$ sudo adduser bar
When sudo asks for a password, you need to supply YOUR OWN password. In other words a root password is not needed. Here are few more examples.
Start / stop / restart services stored in /etc/init.d/ directory
$ sudo /etc/init.d/ssh stop
$ sudo /etc/init.d/networking restart
$ sudo systemctl restart ssh
Avoid typing sudo each and every time on Ubuntu Linux
Note that this is not recommended until and unless you are an expert and aware of what you are typing or doing:
$ sudo -i
$ sudo -s
Above command will start /bin/bash as a root shell so that you can enter a root user command without using sudo command.
Open the terminal application and simply type the following sudo command
$ sudo bash
$ sudo -s
Supply your password and you will become a root user.
So, what is the default root password for Ubuntu Linux?
Short answer – none. The root account is locked in Ubuntu Linux. There is no Ubuntu Linux root password set by default and you don’t need one.
Long answer from the official wiki page:
By default, the root account password is locked in Ubuntu. This means that you cannot login as root directly or use the su command to become the root user. However, since the root account physically exists it is still possible to run programs with root-level privileges. This is where sudo comes in – it allows authorized users to run certain programs as root without having to know the root password. This means that in the terminal you should use sudo for commands that require root privileges; simply prepend sudo to all the commands you need to run as root.