What is the need of the lines:

in the /etc/sudoers file??

Doesn't root have ANYWAY full powers on the system?

Try using visudo to edit sudoers and remove that line.

I bet sudo would then block root. So, `sudo ls -l` by root would fail; whereas, obviously, `ls -l` directly by root would work just fine. You can repair the "damage" by doing `vi /etc/sudoers`. vi just won't syntax check for you when you are done, and you could break things if you mess up.

On my Mac OS X system, that same line appears with %admin. So, an admin user can do anything with sudo.

Full disclosure: I haven't tried it, and don't want to mess with my servers. But it seems perfectly logical.

Thanks for the answer. That seems logical to me as well and I'll check out just to be sure.

Anyway, my central doubt remains:

Why should root bother issuing he command 'sudo ls -l' instead of plain 'ls -l'?

When his fingers are used to typing sudo first.

Having root `sudo ls -l` was just an example.

I think that as a matter of principle, sudoer is set up to not deny access to root. But, as a matter of flexibility, it is done in the configuration of the sudoers file. I would guess that makes the coding more straightforward as well, since there wouldn't be any exceptions for root that have to be coded in throughout the code.