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.
[root /etc]# lsof /var COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME cryptoran 186 root txt VREG 85,3 26680 201645 /var (/dev/md/dsk/d3) syslogd 299 root 5w VREG 85,3 197526 22414 /var/adm/messages syslogd 299 root 7w VREG 85,3 68201 78419 /var/log/syslog syslogd 299 root 9w VREG 85,3 197526 22414 /var/adm/messages syslogd 299 root 10w VREG 85,3 3456678 78429 /var/log/lpr [snip]
Vic Abell's Home Page: The author of LSOF.
Sam Nelson's PCP script, is an alternative to "lsof -i" for Solaris.