Netstat is a tool in the Linux which can be used to monitor network services. It dictates you about the processes that are using a port. Netstat displays all the ports in use and used by all of the processes, however, you can limit those to only a specific port simply by using the “grep” command.

If you wish to see, which service is running on the port 25, execute the following command:

# netstat -ant | grep 25

If you wish to check the number of connections on port 25, execute the following command:

# netstat -an |grep :25 |wc –l

If you wish to see, which ports your server is listening on, enter the following:

# netstat -ant | grep LISTEN