Debian and other debian-based distros like Ubuntu have, by default, has the root account disabled as a security measure.(thanks to Subbu and PICCORO for the clarification)
To re-enable the root account, just open the command prompt, and type
sudo passwd root
You’ll get the following set of messages:
sathya@sathya-laptop:~$ sudo passwd root
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
To disable root access, just type
sudo passwd -l root
If you’re weary of using the command line(you shoudn’t ;) ) then there’s another way:
Just head over to System > Administration > Login Window > Security > and check mark the box beside Allow local system administrator login.
DISCLAIMER: Christof Baumann mentions in this post as to why you shouldn’t fiddle with the root account:
Be aware of locking the root account if you once activated it. I activated the root account and skipped the %admin ALL=(ALL) ALL line int /etc/sudoers file because i thought i wouldn’t need it anymore. Then i disabled the root account without thinking and now had no chance to start programs with root rights. Luckily i could restore it using a knoppix live cd. Be aware of changing settings concerning the root account.
Also, read this article in Ubuntu Wiki as to why sudo is preferred over standard root account.
PS: Just incase you guys are wondering why I’ve posted this basic info so late, well I’m just getting the hang of Ubuntu.