What Is The Default Root Password In Ubuntu Linux

How to login as root user ?

1. Goto Applications –> Accessories –> Terminal.
2. Simply type the following command:
$ sudo -s
OR
$ sudo bash

How to set the default root password ?

You can assign a new root password in Ubuntu Linux.
1. Goto Applications –> Accessories –> Terminal.
2.Type the following command,
$ sudo passwd root
3. Follow the instructions to set and confirm your new password.

Additional Stuff:

In Pc Linux Os Distribution,the default username and password for root user is same. 
Username: root
Password: root