The Nmap aka Network Mapper is an open source and a very versatile tool for Linux system/network administrators. Nmap is used for exploring networks, perform security scans, network audit and finding open ports on remote machine. It scans for Live hosts, Operating systems, packet filters and open ports running on remote hosts.
Full article here:
29 Practical Examples of Nmap Commands for Linux System/Network Administrators (Tecmint)
Beginner’s Guide to Using nmap (Make Tech Easier)
Advanced Uses For Nmap (Make Tech Easier)