How to disable root account?

[Joe Hart]

> kdesu as shipped with Kubuntu asks for the user's password.  Not sure
> if you have the option to change it to ask for the root password or
> not.
>   
Yes, you can.  Although the text of the messagebox doesn't change.  If 
you refer back to an earlier message in this thread you'll see that I 
showed the contents of my sudoers file.  To recap.  If you add rootpw as 
a option to the defaults, it will then require the root password to do 
administrative functions.  That is true for sudo, kdesu and gksu.  That 
one file controls them all.

This is mentioned in the Ubuntu wiki, under enabling root.