In computing, netstat (network statistics) is a command-line network utility that displays network connections for Transmission Control Protocol (both incoming and outgoing), routing tables, and a number of network interface (network interface controller or software-defined network interface) and network protocol statistics. Wikipedia.

Installation in Debian-like systems (Ubuntu, Kali Linux, ParrotSec OS, etc...):

sudo apt install net-tools -y

Display all sockets (default: connected):

netstat -a | more

Enumerate all TCP ports:

netstat -at

Enumerate all UDP ports:

netstat -au

Enumerate all locally running applications and its listen ports:

netstat -tlnp

Show process name and PID:

netstat -pt

Show all active connections:

netstat -t -n -v | grep ESTABLISHED