Netstat is a very useful tool for showing network status. It displays the contents of various net-work-related data structures. There are a number of output formats, depending on the options for the information presented.

Netstat:

-a Show the state of all sockets and all routing table entries; normally, sockets used by server processes are not shown and only interface, host, network, and default routes are shown.
-n Show network addresses and ports as numbers. Normally netstat attempts to resolve addresses and ports, and display them symbolically.

For Unix use: netstat -an | grep "ESTABLISHED". This will show established connections on port 80 (http) in this form:

On FreeBSD you can also use sockstat -4c command, which is also very usefull to list connected sockets (established connections) on the server. It combines netstat with lsof.

Of course, output from both commands sockstat -4c and netstat -an | grep "ESTABLISHED" can be redirected to grep or/and wc -l in order to count and/or filter established connections you are interested in.

Bookmarks:

Echo "List established connections on Unix servers" around: