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Command-Tab [still] freezes system (sporadically) - any resolutions?

Someone must know how to kill the offending process (I hope).

This problem has been around for a few years now (i.e., both in Panther and Tiger) - but unfortunately, no one that I know of has posted a solution on the net as to how to recover usual operations from those times when the 'Application Switcher' (i.e., the one activated by command-tab) is stuck on screen.

The only thing that moves on screen is the mouse (usually stuck as a hand for me). No other keyboard shortcut makes any difference. I can ssh into the machine from another computer. But killing the dock, Finder or similar apps leaves zombie processes around and does not bring the gui back to life.

It seems to occur if you are too quick for the system (i.e., are able to command tab fast enough either to have done so before the panel appears on screen or have let go of the command key prior to it being able to get its required resources or something).

The only process on the system that has this problem of locking up the machine is the application switcher - there must be some way of killing when it hangs when such a thing occurs, but I've no idea what to kill.

Has anyone had success with recovering from this without rebooting the system from a remote system or holding down the power key?

Powerbook G4, 1.66 Ghz Mac OS X (10.4.9) 1 Gig Ram

Posted on May 2, 2007 9:03 PM

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24 replies

Jun 27, 2007 12:57 PM in response to lhmd

I'm having the same problem. It used to occur every few days, but I hadn't seen the issue in over a week. I thought it was over until it happened again last night. I've traced back posts that were created over two years with the same problem, and it still hasn't even been acknowledged by Apple.

http://www.joemaller.com/2006/09/19/os-x-gui-lockup-with-command-tab/
http://simplygenius.com/geekblog/2006/01/26/os-x-ui-freeze/
http://forums.macrumors.com/showthread.php?t=209009
http://discussions.apple.com/thread.jspa?messageID=701265
http://guruza.com/question/122/reward-100.00

The only solution I've heard is to completely use a different application switcher (which is ridiculous).

I do agree that it seems to be when I'm working too quick for the system. Because it's usually when I'm frantically trying to get something done, and the fact that my machine gets the "Command-Tab of Death" doesn't help. I'd personally rather experience a BSOD -- at least it's more meaningful.

Macbook Mac OS X (10.4.9) C2D 2.0GHz

Jul 27, 2007 9:59 AM in response to TailOfTheSun

I have been having the same problem for a couple of years. I have installed LiteSwitch X trial version to see whether it fixes the problem. And actually 10 minutes ago I had the problem again. Alternative application switchers do not seem to solve this problem. I would say that LiteSwitch X is an excellent application, and it's worth buying it if you want its features which are not offered by the default switcher, but anyway it's not the solution of this issue.

Can anyone guess what the problem is when it is not in the switcher application?

Aug 9, 2007 12:10 PM in response to shgaki

This is a follow-up of my previous post.

I keep using LiteSwitch X trial and actually I haven't experienced any more freeze since that I reported in the previous post. Because this issue occurs sporadically, I need more days before I form the conclusion, but it is possible that the alternative switcher at least reduces the possibility of freeze. There's also another possibility that the last freeze I experienced was caused by a totally different reasons and have no connection with the issue discussed here although it looked like exactly the same problem.

Anyway I rushed to a conclusion in the previous post. I would say it might be worth trying the alternative switcher if you are in trouble with this problem.

Aug 22, 2007 2:00 PM in response to lhmd

This just happened to me (again). Seems to creep up every few weeks. It's totally unpredictable.

My MPB is connected to a Cinema Display & closed (built-in screen off). This time I was able to make the Mac sleep by opening & closing the clamshell, but upon wake, the display was just black with only the pointer (hand) still moveable with the trackpad. A hard reset got it going again.

There was no crash log written... so I have no way to know what is causing this.

So frustrating to get derailed by a dirty restart.

Aug 28, 2007 9:19 PM in response to TailOfTheSun

Chiming in - still happening for me too ( http://simplygenius.com/geekblog/2006/01/26/os-x-ui-freeze/ )- this is really annoying, I'm getting tired of having to reset my machine so often! I've just switched to Witch for an app switcher, lets see if this helps any, but I'd much rather a fix from apple as I prefer the way the built in App Switcher works.

Since I can ssh into my machine when the problem is exhibiting itself, I'd be happy to run any tests/diagnostics/postmortems that would help an engineer figure this out. I'm a software engineer myself, so don't be shy with any esoteric commands that would give us the slightest chance of debugging this - e.g. maybe attach to a process with gdb to get a stack trace/core dump - just need to know which ones to attach to.

Sep 12, 2007 5:19 AM in response to lhmd

Me too. I've had the same problem both on my old Powerbook Pro as well as on my new Macbook Pro.
Learning that this problem has been existing for so long is rather saddening, since i thought Apple does not make business by the M$ way, which simply doesn't care about the "last 10%" of bugs.
That kind of nullifies that long-standing slogan "It just works".

Best regards,
Gabriel.

Sep 16, 2007 9:47 PM in response to GabrielZ

That is true.

The point I'm making is: Does the act of connecting and using an external display make the video driver unstable? (So that even if it's disconnected, the freeze may still occur.)

My pic of the "public app switcher freeze" [above] was the first time that particular MacBook owner had experienced the freeze on his 1-year-old machine, freezing midway through his thirty-minute presentation. It was also the first time he'd used an external display with his machine.

Coincidence?

Command-Tab [still] freezes system (sporadically) - any resolutions?

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