lsof, the least talked about Unix tool
Apparently this is one of the least talked about, but most useful Linux/Unix tools.
lsof lists information about files opened by processes, and according to these articles, that is more useful than it sounds.
- http://dmiessler.com/study/lsof/
- http://0xfe.blogspot.com/2006/03/troubleshooting-unix-systems-with-lsof.html
Heard about this on http://reddit.com