Gregory's Serverreading through the 2001 book "Advanced Linux Programming" by Mark Mitchell, Jeffrey Oldham and Alex Samuel (available under an open source license at https://mentorembedded.github.io/advancedlinuxprogramming/ ) and i like the fact it also talks about security and how to avoid the common vulnerabilities that often happen in C code.
the part on sockets seems kinda old, since it doesn't talk about IPv6, here i'd advise people to read Beej's Guide to Network Programming ( https://beej.us/guide/bgnet/ ) instead.
i also wonder if there are any modern books or documents talking about new linux security features, such as #seccomp...