I've just had my first Mountain Lion lockup. The screen was entirely frozen in place (I have seconds displayed on my clock in iStat Menu and even that wasn't moving) BUT the mouse still worked. I could move that around. Nothing else did anything.

I noticed that the keyboard backlight also didn't come on if I typed anything in.

I have SSH access to the machine and that also still worked so it looks like just the GUI was the problem.

Anyone else had this, and have a fix if it happens again?

Its a MBP Retina, 2.6/16/512, with the SMC update from yesterday applied. No optical bay. Graphics: Intel HD4000 integrated, and a discrete Nvidia GT650M.

At the time of the hang it was on mains power, undocked, no external devices plugged in. The NVidia GT650M was in use (it always is, some of my running apps force it on for some reason, postbox for example).

I had Firefox Aurora (their bleeding edge version) active and it was actually in the middle of rendering an Ebay login page as well.

  • I'm experiencing the same issue (3 times now in the same night) on a 2011 MBP 2.3 and upgraded from Lion to Mountain Lion.
    – user26166
    Commented Jul 29, 2012 at 3:46
  • Do you happen to a second HD in the optical bay? Commented Jul 29, 2012 at 16:39
  • 1
    It happened to me when I plugged in a USB tablet... All my tricks (trying to make it sleep, hitting the power button for a short moment, unplugging and replugging power, and a lot of patience) failed. Next, I guess I never forced a shutdown on this mid 2011 MacBook Air, as I was surprised how long I had to hold down the power button. I was just about to boot another computer to Google how to force a restart, when it finally shut down after maybe 10 seconds or more...? But after the reboot, I could plug in and use the tablet just fine. (Still, despite many nasty 10.8 surprises, I love AirPlay.)
    – Arjan
    Commented Jul 29, 2012 at 18:31
  • FWIW, the same (or a similar) thing happened to me in Chrome. Did it seem to be graphics-related?
    – jtbandes
    Commented Jul 31, 2012 at 19:56

3 Answers 3


Suspect an issue affecting the WindowServer process (brief edition for power users)

The symptoms you describe are familiar but not commonplace and in my case, not frequent.

Diagnosis – at the time of the problem, if it recurs


sudo sysdiagnose

After you regain local control, you can analyse the end result.


top -o state

Processes that are stuck should be at or near the top.

Is WindowServer stuck for any length of time?


If WindowServer is stuck, you might kill remotely – 

sudo killall WindowServer

– but this will cause a local log out, so be prepared to lose unsaved changes.

This relatively short answer is tuned to the opening poster's confidence with remote ssh and bleeding edge stuff.

For a more detailed answer, accepted under a similar question where the cause of a problem may be different: Suspect an issue affecting the WindowServer process (long edition)


I had iTunes generating a lot of disk and network I/O for several minutes and blocking anything else during this. Disabling automatic cover art updates seems to have resolved that for now.

  • Ah, this might help explain some "interesting" itunes behaviour I've experienced. I'll try this out. Commented Jul 31, 2012 at 12:52

I have had exactly the same problem twice today after upgrading to ML. Seconds stopped, iTunes was still playing and could move the mouse. Also I noticed that both time this happened when I was hovering my dock. I could also see the first time something about to open in the dock but it halted and I couldn't see what that was.

Happened on a 2012 MBP i5 2.4

Any ideas anyone?

Ok, it may be some kind of a new error handling system which is not working as expected. My software is up to date and I WAS still experiencing the hang-ups. So, because I was pretty convinced that my dock is the faulty one, because 3 times my mac hang when hovering something on the dock, the first thing I thought, is removing all the hovering effects - the magnification. And voila - no more freezes.

I've read that a lot of people are experiencing freezes when coming out of the screensaver or other. So, what I suggest is - try and track the last action right before the freeze. Are you closing an app, opening an app, minimizing, maximizing, hovering, what are hovering or any action above, and try to well - not do that :D If it's pretty global and not app-specific, you can try and change some related settings.

Ok, I'll keep you guys posted.

Havent experienced any more freezes like for 16hrs now. Previously it was every 1-3hrs.

08/13/2012 - Crashed again. Last time was on 07/29/2012

  • In my experience: Dock in Mountain Lion is extremely robust, never contributory to problems with other processes. Commented Jul 30, 2012 at 22:09
  • Exactly the same thing happened to me, I'd have a few windows open and then when I hovered over my dock it would cause this crash (you could see the dock label was stopped about half transparent as it appears). Has to hold power button to shutdown as it never recovered. Happened twice, both last night on Late 2011 13" MBA with ML.
    – Dunhamzzz
    Commented Jul 31, 2012 at 12:52
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    Until the problem for the opening poster is resolved or explained, I'm reluctant to treat other people's problems as the same. The most noticeable symptom – maybe a stuck WindowServer – may be identical, but the root causes of people's problems may be very different. Commented Jul 31, 2012 at 19:55
  • The question within your answer (seeking peoples ideas on your own case) makes me wonder whether you should ask a separate question. Not a criticism – just a thought. Commented Jul 31, 2012 at 20:01
  • 1
    I started a new question here: apple.stackexchange.com/questions/59445/…
    – Dunhamzzz
    Commented Aug 4, 2012 at 19:37

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