How to Check (Scan) for Open Ports in Linux
This article describes several approaches to find out what ports are opened to the outside on your Linux system. An open port is a network port that accepts incoming packets from remote locations.
Netcat (nc) Command with Examples
Netcat (or nc) is a command-line utility which reads and writes data across network connections, using the TCP or UDP protocols. Netcat is cross platform and it is available for Linux, macOS, Windows and BSD.