nmap

If you have ever needed to survey a large group of systems to find out which of them supported some particular service, such as ftp, telnet, ssh or some other particular application, you have probably thought of numerous ways to query the systems for the required information and display it in some usable fashion. Many methods of obtaining information from servers, however, require some sort of login or a remote shell request that either takes more time than you want to spend or requires you to configure some sort of trust on the part of the systems with the information for the system on which it is being collected. In today's column, we will look at a way to find out about services running on systems without setting up any access ahead of time.