SHELL

check open port linux

netstat -lntu

open port on linux

sudo ufw allow <PORT_NUMBER>

used port linux

# Linux
ss -ltn

# windows
netstat -a -p -n tcp | findstr LISTENING

# SOURCE 
https://solace.community/discussion/26/how-to-find-a-free-tcp-port-for-testing-pubsub-with-docker

Linux port

# to kill port 80 simply use
sudo fuser 80/tcp -k