hello all
say im logged in to account ar root , but I can't change any thing there ( like username )
if someone is already logged in also . how can I know who is ( user name ) also connected to the user im using ?

If both are logged in as root, you could possibly tell from the output of the who command - just associate the terminal connection with the userid (found with ps -ef|grep root). Then, with the who command, look for that terminal to see where they are coming from - you would then have to look on that server to try to find who was logging in as root (if this is what they are doing).

If a person logs in as root on console, then you don't have a way of doing this (unless there are console logs which may or may not have information on the person).

If you are in charge of this server, you should consider setting up the root account so it can only be accessed from console - so anyone signing in can not log in as root (and this will make it easier to find who is using it via the su logs).

If your people are using a MS Windows PC, it is pretty easy. Shoot the command who -u | grep user and look at the output :

unix:/ # who -u | grep user
user pts/t3f Feb 28 09:36 . 13390 10.1.1.30

or anything you get. If your UNIX box talks to DNS or is DNS you might see the Machine name instead of IP address. Then you can browse the Windows machine and look at the most recent account and find out you is using that account. Hope it is what you are looking for.