This book, dating from '97, is actually a beauty. It covers a summary of programming on a UNIX environment without any of the 'fancy' modern stuff. It focuses on getting started with the fundations being C, gcc, make, gdb, emacs and the commandline and focuses on the layer many people just skip nowadays. The book is actually written in a cross-platform mindset (think about the glory days of the DEC Alpha, SGI Irix, Sun Sparc, ...) but translates very well to a more modern embedded mindset and if you can make this click and can get rid of the nostalgia the book hasn't really aged a bit (okay, not true, there is still a chapter on rcs).