This question already has an answer here:
I am running Xubuntu 13.04, I got in the habbit of closing my Acer Netbook and forgetting about it for a week+. I open it up to find it has still been running. How do I set it to shutdown after 15 minutes of inactivity? I don't want to set it to lid close because I often get up and close the lid so kids don't get at it. Also, due to the sometimes long stretches I go without touching it, I would like to make sure it is completely shutdown.
I'm sure I'm just missing some little check box. I've never had a setup that didn't shut itself down, or wasn't able to with a few click.
I already Googled the question for a bit and wasn't able to get the keywords right to get a relevant answer.