There are two books i have read when i begin my programming carrer.
One is <Advanced Programming in the UNIX Environment> written by W. Richard Stevens. The other is <Linux Device Drivers, 2nd Edition> written by Alessandro Rubini and Jonathan Corbet
When I joined the ASUS company, I was trained to be a Linux programmer. However, <Advanced Programming in the UNIX Environment> was choosen as the teaching material. It tells me lots of features in C which I never knew before. Click HERE to download its source code.
Besides, the author has shared the book <Linux Device Drivers, 2nd Edition> free, Click HERE to downlaod its PDF format version.