How to use the NMAP Security Scanner on Linux

Nmap is a free and open source network discovery and security auditing utility that is widely used in the Linux users community as it is simple to use yet very powerful. Nmap works by sending data packets on a specific target (by IP) and by interpreting the incoming packets to determine what posts are open/closed, what services are running on the scanned system, whether firewalls or filters are set up and enabled, and finally what operation system is running.