Checking port status in Linux

By default, ports are blocked for incomming requests

1) Enable ufw

sudo ufw enable

2) Add port

sudo ufw allow http (or) sudo ufw allow 80/tcp
sudo ufw allow ssh (or) sudo ufw allow 22

3) Deny port

sudo ufw deny http

4) List all open ports

sudo ufw status

        To                         Action      From
        --                         ------      ----
        22                         ALLOW       Anywhere
        80                         ALLOW       Anywhere
        22 (v6)                    ALLOW       Anywhere (v6)
        80 (v6)                    ALLOW       Anywhere (v6)

List the listening ports

Suppose we have a nginx server listening on port 80, we can check it with teh following command

sudo netstat -ntlp | grep :80