There is one singular quality I look for in any candidate, regardless if they are a system administrator, software engineer, or any technical position. It's the ability to research and learn.
I was interviewing a system administration candidate for another group and the classic question I ask is, "When moving from administrating a few machines to 1000s of machines, what difficulties do you imagine you'll come upon?"
This particular candidate had actually setup and administered a small 16ish node cluster before and said something along the following:
When I setup this cluster, I realized FOO was running really slow. I went online to see how other people solved the problem. I found someone else who used pdsh to make FOO run better. So I downloaded pdsh, set it up and FOO was working better.
I can't even remember what FOO was, but it was really irrelevant. The candidate:
A) Realized something was running poorly or sub-optimal
B) Researched online a mechanism that would be better
C) Set it up/implemented the solution
D) The solution was deemed much better than the prior situation
Because my group had developed pdsh that was sort of bonus points for the candidate, but I absolutely loved this candidate's answer. It was so simple and basic, yet illustrates exactly the quality that you want in an engineer. Going online to research, learn, figure new things out, and find better solutions. It's actually a quality that is often difficult to find in many candidates.