Command to Prevent Users accessing server temporarily

Does anyone know a command that can be entered at the server console that will prevent users from accessing the server whilst work is being done on it? I am sure I have used this before but cannot find anything about it. many thanks, Anne

Subject: Command to Prevent Users accessing server temporarily

http://www-1.ibm.com/support/docview.wss?uid=swg21089278

Subject: Thankyou - perfect…

…I very much appreciate your prompt reply, thanks again, Anne