How do I find out which process is using a particular network socket?

This is handy for when you need to know what process is using a particular network socket.

e.g. What process is using socket TCP port 443?

netstat -tapn | grep 443

Example output:

netstat -tapn | grep 443
tcp        0      0 :::443                      :::*                        LISTEN      6996/sshd
tcp        0      0 ::ffff:192.168.11.5:443     ::ffff:192.168.11.3:3190    ESTABLISHED 7065/sshd: troyski

Here we can see that process 6996 (sshd) is using tcp 443.

Note : you have to be root for this to work right.