14 years UNIX support, training and research

Maurice Bach "The Design of the UNIX operating system"

PC A Power User's Guide - Harry Fairhead

Unix Power Tools - O'Reilly

System Performance Tuning - O'Reilly

Termcap and Terminfo - O'Reilly

A Quarter Century Of Unix - P Sulcas

SCO Unix Internals course attended with Peter Kettle 1994 (approx)

Understanding the Linux Kernel - Daniel P Bovet & Marco Cesati - O'Reilly (has a really excellent Source Code Structure list at the back of the book.)

Sebastian Spitzner - Phyrix Systems (Pty) Ltd.