how to use netstat on a specific port in Linux

You can use

netstat -pnlt | grep ':portno'

another option , you can use nmap tool for checking open ports on the server

nmap -sT -O localhost

Output

Starting nmap 3.55 ( http://www.insecure.org/nmap/ ) at 2004-09-24 13:49 EDT
Interesting ports on localhost.localdomain (127.0.0.1):
(The 1653 ports scanned but not shown below are in state: closed)
PORT      STATE SERVICE
22/tcp    open  ssh 
25/tcp    open  smtp
111/tcp   open  rpcbind
Device type: general purpose

Netstat Example :

[root@krizna ~]# netstat -pnlt | grep ':80'
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name 
tcp        0      0 :::80                       :::*                        LISTEN      1164/httpd          

use netstat -anp | grep portNumber

I think netstat -nat | grep port | grep LISTEN should do the trick.