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The workspace between the top and bottom Gnome panels occasionally dims about 25% and holds there for an unpredictable period of time. Sometimes it never recovers to full brightness. The cursor moves but buttons are non-responsive. Most often this happens in Firefox but is not restricted to this one program. The top and bottom Gnome panels remain fully functional.

The processor stays at an approximately steady 40% "User" use. The memory hovers at about a 40% mixture of "User", "Buffers" and "Cached" use. Network and disk activities flatline.

Sometimes the workspace un-dims itself and returns full control. When it does not the only things that work are pressing the automatically presented force quit button, typing "xkill" from a terminal or choosing to restart. Usually the application that dimmed can be restarted without restarting the operating system. I've experienced this in both Karmic and Lucid.

What am I missing?

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What applications does it usually hang on? Typically when you experience that dimming it's because a program is not responding. – Marco Ceppi Aug 28 '10 at 15:21
Usually Firefox. But others too. I get it now that this is normal for Compiz. I find it interesting though that the dimming will come and go sometimes within seconds. Thank you. – robertsandrock Aug 28 '10 at 17:24
This question has upvoted answers, which may even have solved the problem for the OP. Even if not, this potentially applies to most Ubuntu users (the ones who use Compiz) and the answers are valuable. The "too localized" closed reason was dropped from the system by Stack Exchange because it was being abused to close acceptable questions (like this one). Now this is garnering delete votes. We should just reopen it. – Eliah Kagan Mar 15 '14 at 23:21
It follows this answer – wojox Mar 16 '14 at 11:06

Compiz dimms windows that are frozen or don't answer to window management events. The dimming is normal and just a way to inform you that this app is not listening to inputs.

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Thank you. Visual Effects was on "Normal". Now it is "None". – robertsandrock Aug 28 '10 at 17:21

Are you using Compiz when this happens? The way to check this is to go to system / preferences / appearance / visual effects, and see if it's set to anything but "None". If it is set to something other than "None", does the problem go away when you use "None" instead?

Hope this helps, regardless.

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System > Preferences > Appearance > Visual Effects was on "Normal". I changed it to "None" and will wait and see if it goes away. Thank you. – robertsandrock Aug 28 '10 at 17:18

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