ubuntu find program using a port code example

Example 1: linux how to see ports in use

# Any of the following
sudo lsof -i -P -n | grep LISTEN
sudo netstat -tulpn | grep LISTEN
sudo lsof -i:22 # see a specific port such as 22
sudo nmap -sTU -O IP-address-Here

Example 2: cli check what is listening on port

lsof -i tcp:53 #Check what is listening on port 53
lsof -t -i tcp:53 #Return the process PID listening on port 53