lsof
$ lsof [-p pid] [-d fd] [-u login/UID] [-g PGID] [filename]List open files of a processes. This can mean actual files in the file system, sockets, pipes, etc.
-p pid: Select by PID-d fd: Select by file descriptor-u login/UID: Select by login/UID-g PGID: Select by process group IDfilename: Filename