Inactivity logout systems are something that date back to the days of timesharing. They didn't work well then, and they fell out of favor once workstations and personal computers became prevalent.
One of the major reasons they fell out of favor is that there's no good way to do it right. Sure, you can just shoot the user's jobs, but that works until someone is doing an hour's worth of editing and gets called away from their desk and they lose their work.
There's no good way to suspend the user's tasks so the user can come back to them. If you just log them off, they'll lose work. There is no unified OS way to tell jobs, "Save your work, you're going away."
What problem are you trying to solve? What is the situation you're faced with that you need to do this?
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This was first published in March 2002