For sysadmin/ops jobs, I want to see debugging ability in addition to programming skill.
I usually ask about HTTP and DNS (for web-focused) or Kerberos/AD logins (for user focused).
There are a lot of moving parts to either of these, so a question like: "You type a web address into a browser, it doesn't load" can turn into questions about the DNS resolver process, system and network config, split horizon, time setup, etc.
Basically, I want to know if they have a grasp of how things all go together, and how to test the individual parts that make up the whole.