The Cuckoo's egg is a must read for anyone persuing a career in Devops or Security - It covers such a wide range of debugging techniques and ways to track down unusual behavior, that it's still a relevant read and great primer. The early anecdote about 'mirroring' the typing if his hacker by hooking up line printers to phone lines is particularly ingenious - using `tee` as a tool for the same effect has saved my hide many a time, and helped me understand complex systems. Introspecting median output is great tool (see also printf debugging).
On a different note, Cliff Stoll is himself a great dude, fun and witty and very friendly. I bought a Klein bottle[1] from him as a present for my father, who loves it, but the real treat was for me - I went in person, and he gladly took an hour of his time to show me his warehouse and custom robot he uses to manage it, and chatted about everything - Life, The Universe, his book and his business and software problems (I was at a videoconferencing startup, and he'd also done some work with telcos that proved relevant and illuminating). If you have a chance, buy a bottle and have a chat.