Find the ports listening on Linux

The netstat and the lsof are the two main commands to check the tcp/udp listening ports in Linux.

Netstat Installation:

CentOS and Debian:

yum install net-tools
apt install net-tools

netstat --listen or netstat -l

To show established tcp connections :

netstat -vatn

To show only UDP connections:

netstat -vaun

If you are looking for a specific service listens to which port :

netstat -ntpl | grep ssh

Filter with specific port number :

netstat -ltnp | grep -w ':80' 

l- tells netstat to only show listening sockets.
t – tells it to display tcp connections.
n – instructs it show numerical addresses.
p – enables showing of the process ID and the process name.
grep -w – shows matching of exact string (:22).

lsof is another command used to list all open ports and files in your system. Installation for CentOS and Debian:

yum install lsof	        
apt install lsof		

To display all open Ports:

lsof -i

To display all open files :

lsof

To display all tcp listen:

lsof -iTCP -sTCP:LISTEN

To show a specific port :

lsof -i :80

To show only IPV4 addresses in MacOS:

netstat -f inet -rn