Recently I was compiling a list of Linux commands that every sysadmin should know. One of the first commands that came to mind was nmap.
nmap is a powerful network scanner used to identify systems and services. nmap was originally developed with network security in mind, it is a tool that was designed to find vulnerabilities within a network. nmap is more than just a simple port scanner though, you can use nmap to find specific versions of services, certain OS types, or even find that pesky printer someone put on your network without telling you.