OpenSUSE Install :: Kill The Entire Session (as Root) For A User?

I've got a somewhat anemic box, resource-wise, set up in the office where any authorized user plus a guest account can log on. Guest is tightly restricted, but we get a lot of people passing through who need one-time or occasional access - this isn't the big problem. What's causing me problems is that a user will log in, walk away or go to the john and the screen locks. Next user (or this one comes back) and winds up doing another login. At the end of a week or so, I may have a couple of dozen sessions listed when I ask for "users". Since some of these session contain open applications they eat up an awful lot of a marginal amount of available memory. How do I kill the entire session (as root) for a user? Gotta be simple but it's not obvious to me.