Lsof is an extremely powerfiul unix diagnostic tool. Its name stands for LiSt Open Files, and it does just that. It lists information about any files that are open by processes currently running on the system. It easily pinpoints which process is using each network connection / open port.
You can download it from the following link: https://packetstormsecurity.com/files/download/23085/lsof_4.51_W.tar.gz
Source: https://packetstormsecurity.com/files/23085/lsof_4.51_W.tar.gz.html