Thanks to the following site, I’m able to use the “root” login on Ubuntu 11.10.
http://www.debuntu.org/2006/04/24/34-ubuntu-default-root-password-or-the-sudo-way 

Copied below for local reference:

Root is created without predefined password, it does not have a password, but it does not have an empty password either, you just can’t login!!!

I actually like to be logged as root when I’ve got many this to do. I find sudo usefull when only one or two actio are to be done, but when doing administration task, typing sudo all the time just drive me cray .

One way to gain root prompt is to launch a shell as root. Therefore, using sudo you can type:

:~$ sudo sh
Password:
sh-3.1#

And there you are, you have a root shell.

If you want to be able to login as root, you need to define a password for root:

:~$ sudo passwd
Password:
Enter new UNIX password:
Retype new UNIX password:

Now you can login as root with su.