Specifications

David R. Butenhof: "Programming with POSIX Threads", Addision Wesley, ISBN 0-201-63392-2.
Bradford Nichols, Dick Buttlar and Jacqueline Proulx Farrell: "Pthreads Programming", O'Reilly
& Associates
"Git Community Book"
See http://book.git-scm.com/ or download the PDF version.
Articles
The GNU C Library: http://www.linuxselfhelp.com/gnu/glibc/html_chapter/libc_toc.html
General Linux Programming: http://www.linuxselfhelp.com/cats/programming.html
Multi-Threaded Programming With POSIX Threads:
http://users.actcom.co.il/~choo/lupg/tutorials/multi-thread/multi-thread.html
Brad Hards: The Linux USB Input Subsystem, Part I
http://www.linuxjournal.com/article/6396
Brad Hards: Using the Input Subsystem, Part II
http://www.linuxjournal.com/article/6429
Ulrich Drepper: Position Independent Binaries: "Text Relocations"
http://people.redhat.com/drepper/textrelocs.html
Ulrich Drepper: "How to Write Shared Libraries"
http://people.redhat.com/drepper/dsohowto.pdf
Ulrich Drepper: "What Every Programmer Should Know About Memory"
http://people.redhat.com/drepper/cpumemory.pdf
David Goldberg: "What Every Computer Scientist Should Know About Floating-Point Arithmetic"
http://www.physics.ohio-state.edu/~dws/grouplinks/floating_point_math.pdf
More Ulrich Drepper stuff: http://people.redhat.com/drepper/
How to optimize DSOs by identifying unused non-exported functions and data.
http://blog.flameeyes.eu/articles/2008/01/17/today-how-to-identify-unused-exported-functions-and-variables
A quite complete history of the UNIX family can be found here: http://www.levenez.com/unix/
Unix Manual, first edition, 3 November 1971: http://cm.bell-labs.com/cm/cs/who/dmr/1stEdman.html
John Graham-Cumming: Debugging Makefiles
http://newsletter.embedded.com/cgi-bin4/DM/y/e4Kd0G1ErD0FrY0E3FS0EZ
Binutils / ld documentation: Linker Scripts
git ready - learn one git command at a time: http://gitready.com/
Standards:
POSIX.1-2008, IEEE Std 1003.1-2008, The Open Group Technical Standard Base Specifications,
Issue 7: http://pubs.opengroup.org/onlinepubs/9699919799/mindex.html
Linux Standard Base: http://refspecs.freestandards.org/lsb.shtml
Single UNIX Specification, Version 3 (needs registration even for online viewing)
Single UNIX Specification, Version 2
PCI Bus Bindings - Standard for Boot Firmware:
http://playground.sun.com/1275/bindings/pci/pci2_1.pdf
International standardization working group for the programming language C:
http://www.open-std.org/jtc1/sc22/WG14/
12.2.4. Network Programming
Books
W. Richard Stevens: "TCP/IP Illustrated, Volume 1 - The Protocols", Addision Wesley, ISBN
0-201-63346-9
Books 139