Lsof is a Unix-specific 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 can also list communications open by each process. Open files in the system include disk files, pipes, network sockets and devices opened by all processes. One use for this command is when a disk cannot be unmounted because (unspecified) files are in use. The listing of open files can be consulted (suitably filtered if necessary) to identify the process that is using the files.