Nmap (“Network Mapper”) is a free and open source (license) utility for network discovery and security auditing. Many systems and network administrators also find it useful for network inventory, managing service upgrade schedules, monitoring host or service uptime, and many other tasks.
Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. It was designed to rapidly scan large networks, but works fine against single hosts. Nmap runs on all major computer operating systems, and official binary packages are available for Linux, Windows, and Mac OS X. In addition to the classic command-line Nmap executable, the Nmap suite includes an advanced GUI and results viewer (Zenmap), a flexible data transfer, redirection, and debugging tool (Ncat), a utility for comparing scan results (Ndiff), and a packet generation and response analysis tool (Nping).
Nmap was named “Security Product of the Year” by Linux Journal, Info World, LinuxQuestions.Org, and Codetalker Digest. It was even featured in a dozen movies, including The Matrix Reloaded, The Bourne Ultimatum. Girl with the Dragon Tattoo, and Die Hard 4. Nmap was released to the public in 1997 and has earned the trust of millions of users.