You may notice on Ubuntu that you don't have a root password. There are times that you will install software and it requires that you enter a root password but you don't have a root password. In some cases, you can just run sudo su and then change to root through sudo, but other times you actually need a real root password on Ubuntu.
Here's all you do...
If you need a real root password, then just run the following command from a terminal:
sudo passwd root
If you do that, you'll first be asked for the password of your user account (twice). And then you'll be asked what you want your root password to be. That's all. It's very simple.