Open a port to listen on in Linux

The following command you can use to open a port to if you are getting a connection refused error on specific port number :

iptables -A INPUT -p tcp --dport <Port>2 -j ACCEPT

How to list open ports in ubuntu lunux.

Open and listening ports :

netstat -anltp | grep "LISTEN"

Established ports :


netstat -anltp | grep "ESTABLISHED"