lsof

Lists information about open files (similar to fstat(1))

Lsof (LiSt Open Files) lists information about files that are open by the running processes. An open file may be a regular file, a directory, a block special file, a character special file, an executing text reference, a library, a stream or a network file (Internet socket, NFS file or Unix domain socket). See also fstat(1) in the base system.