linux ports in use by process 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: linux query port use by pid

$ sudo netstat -nlp | grep :80
tcp  0  0  0.0.0.0:80  0.0.0.0:*  LISTEN  125004/nginx

Example 3: linux check what process is using port

$ netstat -ltnp | grep -w ':80'

Example 4: how to open port by fuser

root@exampleuser-X55CR:~# fuser -k  123/tcp
123/tcp:             11543