Online version of The Art of Unix Programming book. Same as the print version from Addison Wesley. Good guide about creating application on unix, philosophies and things at the level of code and interaction with the unix kernel and subsystems.
http://www.faqs.org/docs/artu/index.htmltags: books ebook linux programming unix
free online ebook about the principles of synchronization for concurrent programming.
http://greenteapress.com/semaphores/