What is the best way to limit users access to a server?
 

I need to config my server so that users only be able to access some ports like as mysql or mail! what is the best way to do that?and what services are more appropriate to do it?

That's firewall
That's a group control, not firewall, you have to open the mysql port on the firewall, but access to the engine is controlled by group (mysql group) rights
See mysql

Try this, type "#groups" and figure out what every one of those groups is for. If you get stuck, post back, but that will give you a better grasp of how to control access to your server.

You can define iptables rules for specific group or specific user.
Here is the hint, how can you do this.
http://www.linux-noob.com/forums/ind...ports-and-ips/