Basic knowledge and background questions. It wasn't a "How would you solve this problem" type thing, more of a "What kind of experience do you have with XYZ..." Having read my resume, they knew I had been doing this work for a very long time, so didn't waste my time with a lot of very basic unix-type questions. Instead, for the things I didn't already have experience with, they asked if I would be willing to learn - which, of course, I was more than happy to do. Like most people in this industry, I always like learning new technologies.