I have setup a server (slackware 12.0) for one school. There are lot of users and the teachers want to admin the users. Adding users, deleting users.
I set up webmin on it, and limit the users rights for user and group administration only. But I see that the root user can be selected for deleting and the password can be changed too.

I didn't try it but, it is possible that when I select the root user I can delete it. And the password can be changed just by typing new password without the knowledge of old??

Maybe it is a stupid question, but I am affraid that some clever teacher will try this option.

If the user is logged in as a root-level administrator, of course they can delete or modify the root user. How could you expect anything else?

That said, Webmin has an extremely flexible and powerful access control system with users, groups, and ACLs.

What you want to do is create a new group that is limited to only editing users of a certain UID range, and then create all of your professor accounts as members of that group.

This is documented pretty well in the Webmin docs here: http://doxfer.com/Webmin/WebminUsers

If, after reading that, you have any question, feel free to follow up with more questions.

Yes, thats exactly what I need.
I already set up (with help of that documentation) different accounts for each teacher who can admin the accounts of there students.

I just thought that this action will be somehow denied, because I don't see any logical circumstance when the root user should be deleted. I don't even imagine what it can cause if deleted.

You end with a shell prompt like "I have no name!@hostname#" (don't ask me how I know )

But nothing a Live CD (or Slackware install DVD/CD) can't fix (just update /etc/passwd in the mounted / partition)

As if we don't already know....

This begs the doubt: are LiveCDs security threats in an otherwise secure environment? Should organizations prevent employees from using LiveCDs and/or USB sticks at work?

That's why in important PCs you password protect the BIOS and prevent the CD/DVD drive from being bootable. Easy fix. You could also encrypt the partition.

Anyone who has physical access to the computer can be a security threat. Even BIOS passwords can be worked around.

gnashley is right! I remember when I worked as network assistant, there was an IT "engineer" who argued that windows nt passwords were not reset-able, you should have seen his face when I booted from a special linux floppy and reseted the admin password in less than 2min
http://home.eunet.no/pnordahl/ntpasswd/

Logic does not apply to root. root has absolute power over the system.

If you were assuming that root in Webmin is somehow safer than a root login in a shell, it's probably wise to pause in your plans until you've gotten a better grasp on Webmin. A root-level Webmin login is every bit as dangerous (and very nearly as powerful) as a root-level shell. Would you ask if a root-level shell login could delete the root user? (The answer is, of course, "yes, a root-level shell user can delete the root user", thus the same is true of a root-level Webmin user.) ;-)

That's why other accounts can be created, and with arbitrary limits on their powers. Webmin's ACLs are more flexible than standard UNIX permissions, so you can safely use Webmin in ways that a shell account could not be used. User management, for example, is extremely flexible in Webmin, and you can restrict particular accounts to only managing a range of UIDs or other characteristics.

Good point, I didn't think about the root user of webmin that way.

Yes, after the first post I checked out the webmin user administration section (carefully), and now I set up for another user admins an UID range which can they manage.
It is very well designed...