How to find out what application that using specific port

Just a case if you want to know some application or service who is running under specific port :

$ netstat -tulpn | grep :80

Sometimes you need to run with sudo to see all services :

$ sudo netstat -tulpn | grep :80

Output :

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      1393/nginx.conf

It turns out that 1393 is the pid of service