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I've been running Ubuntu 12.04 for a while now with no problems. Overall, the only kind of instability I've had is that the system will occasionally lock up completely under prolonged full cpu usage.

My current problem, though, is that Unity constantly freezes. Often, the whole thing doesn't freeze. Usually, only part of it freezes. For example, any open windows will lock up but the launcher will remain responsive, or vice-versa.

I can find no abnormal resource use associated with these freezes, though. That and the fact that I can often restore responsiveness by clicking somewhere on the status bar at the top make me inclined to think that this is a bug in Unity, and not, say, an issue with the graphics driver.

If it's of any use, though, I do have a PCIE Radeon card for which I am using the proprietary drivers, but I was able to use this for a month before I encountered this problem.

Another thing that I've noticed is that the problem often manifests itself the most soon after a start-up. As soon as the system runs for a few minutes, the problem becomes significantly reduced. Has anyone experienced something similar, and, of so, how did you fix it?

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marked as duplicate by Jorge Castro, Eliah Kagan, stephenmyall, hhlp, Tom Brossman Feb 15 '13 at 17:17

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Welcome to Ask Ubuntu! I recommend reporting this as a bug. (This question also has some good information about bug reporting.) This will probably be closed, in accordance with the FAQ and this policy. It's very likely that, as @RolandiXor says, a running process is using lots of CPU--but no APT-related process should be able to cause this serious interface disruption. Can you tell what's using the CPU? – Eliah Kagan Feb 15 '13 at 16:01
APT-related processes don't generally run at a high enough priority that they could cause this without a bug in something else, but some processes, like pulseaudio, do. To report the bug and have any likelihood of the report resulting in a bug fix or workaround, you have to know what process or processes are using the CPU. How do you know the CPU is maxed out (if it's frozen, how do you look at this)? However you've discovered this, it's likely you can see per-process CPU usage as well. If you cannot, please let us know. Also, does this problem happen every login or just after booting? – Eliah Kagan Feb 15 '13 at 16:04
Either way, please try logging out, selecting Ubuntu 2D as your session type on the login screen, logging in, and then rebooting. Ubuntu 2D will remain the default session type. You had problems moving windows, and Ubuntu 2D uses Unity 2D rather than Unity, which uses the metacity window manager rather than compiz. This is important diagnostic information. If there's no high priority process taking up CPU, the bug might be in the window manager (or in graphics drivers), and this could reveal that. Did the problem start after an update? – Eliah Kagan Feb 15 '13 at 16:06
Please note that Ask Ubuntu isn't a good place for in-depth investigation of bugs, so once we figure out what package to report this bug against, the rest of the work should be done on Launchpad. (Some of this general freeze question's answers may help, too; some of the answers there are about troubleshooting.) – Eliah Kagan Feb 15 '13 at 16:08

From what you described, it sounds like your experiencing a common issue with apt's update check, which runs as soon as you log in for the first time, and causes the CPU usage to spike for a while. It's harmless, and usually goes away after a few minutes.

In such cases, the best thing to do is to be patient and not do too much immediately after starting the system, since most systems (think, core2duo, 4GB Ram, and such like :), will not be able to handle the workload too smoothly.

Unfortunately, I don't know of any sure fire fix for this at this point in time.

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