C Programming in Linux
This is a free, online textbook offered by Bookboon.com. "Using a series of web development examples, this free book 'C Programming in Linux' will give you an interesting glimpse into a powerful lower-level world.
C is tight and spare and economical, and in the current world climate people who know C will ensure critical systems keep running.
A knowledge of C is now and has been for years a pre-requisite for serious software professionals and with the recent popularity and maturity of Open Systems this is even more true. The book refers to a C source code bundle which you can download" at the site.