[Skriticos]

I have a copy of "Advanced Programming in the UNIX Environment, Second Edition" (featuring very good description of C/POSIX/SuS/XSI protocols/api's and programming techniques for Linux/BSD/OSX/Solaris/other UNIX systems). Anyone who seriously wants to do thread safe multiprocessing or other complex low level stuff on UNIX platforms should have a copy of it. It's basically "the book" on the topic.

[sophacles]

This is one of a very small number of books older than 5 years which I still regularly reference. Amusingly, most of the books on that list were written by W Richcard Stevens as well.

[leoc]

The Linux-specific /Linux Application Development/ by Johnson and Troan is very good too. http://ladweb.net/