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My computer has been acting a little wonky today (it's been running a little slow), so I decided to open up the task manager to look at CPU usage.

This is what I got.

Why does the top CPU usage not add up to the total at the bottom? I've never seen this happen before, and it leads me to suspect a process is hiding itself.

Any thoughts? Is there a command to get CPU usage of all processes in a list much like the task manager from the command line (since user-mode hooks/rootkits don't generally hook console applications)?

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up vote 3 down vote accepted

You need to check the "Show processes from all users" checkbox. Its right above the square box around 18% you drew on your image. There are processes under the user "SYSTEM" you are not seeing. Once you do that, the CPU usage will add up correctly. If you sort CPU descending after you click "Show processes from all users", you will see "System Idle Process." This is the percent of CPU not being used.

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Yes, no SYSTEM account is a dead giveaway –  AthomSfere Mar 21 '13 at 4:08
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Aha, that makes me feel like a sufficient idiot. Thanks! –  Qix Mar 21 '13 at 4:33
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