Brian “Beej” Hall has written a couple of really useful guides on topics of interest to Unix programmers:
- Beej’s Guide to Unix Interprocess Communication (IPC) – signals, pipes, FIFOs (named pipes), sockets, shared memory, message queues, memory mapped files, etc.
- Beej’s Guide to Network Programming – client/server programming with BSD sockets in C
He has links to all of his guide at this page.
The guides have the occasional typo but are otherwise very well written, concise, and easy to understand. They are not exhaustive, like say the W.R. Stevens books, but rather were written to be short and to the point and quick to read.