OS X GUI lockup with Command-Tab
Every once in a while, probably twice this month, my GUI locks up after pressing Command-Tab to bring up the Application Switcher. Everything on screen is stuck behind the switcher display, the mouse still works but nothing can be clicked.
Most infuriating is that the guts of the machine are working normally, I can SSH in and run any non-GUI app I want and everything works fine. I’ve tried working up the ladder of apps to kill (via SSH), but nothing I’ve found manages to restore the computer to working order. Except restarting by holding the power button (or the shutdown command via SSH).
Today the screen froze while iTunes was playing, iTunes finished the song it was playing then stopped. No Apple Events work (ie. osacript -e’tell application “Finder” to quit’)
At least two, maybe three other people are having this problem too; Matthew Conway, poster lazydog on MacRumors and Rich Collins (who’s having it much worse and is willing to pay $125 for a fix.)
The machine is in otherwise excellent health. Disks are regularly checked and permissions repaired (FWIW). Nothing unusual seems to be appearing in the logs and there isn’t anything particularly funky running on the machine. Since it’s so irregular, trying to recreate this in a second user account isn’t a realistic option.
This has happened a few times and I’m totally at a loss as to why. That people are seeing it on non-Intel hardware is reassuring that it’s not a hardware failure. Any ideas about how to fix/prevent this are welcomed. If you’re having this problem, please leave a comment.
More from Apple Discussions: Command-Tab freezes system (sporadically)
I deleted the com.apple.dock.plist file, here’s hoping that works.
Update: I seem to have a partially failing stick of RAM, which may or may not be related. It passes Apple’s Hardware Test, but the computer won’t boot if that chip is installed by itself, or in the lower slot (where it was before I discovered this?!), it boots and seems to run fine in the top slot. I installed a new chip this morning (Sept 21), no issues so far.
I still have this problem as well. I’ve had it for years, first with a Powerbook G4, and now with a MacBook Pro. I’m pretty sure it is related to multiple displays, as I have never noticed a correlation between the freeze and any particular application or other action. Also, the multiple display and display detection functionality on Apples has always been buggy, similar to the sleep/wake functionality. Seems to me that these are both pretty fundamental operations to a laptop, and given the longstanding bugginess of both, you’d think they’d have addressed this by now. I guess that’s just me venting, but I laugh anytime someone says, “Apples never crash”. Bullshit.
Anyway, for me, it only happens after
1) I’ve been connected to an external monitor, then slept the machine, disconnected from the monitor, then sometime later awakened the machine and worked on it for awhile.
2) #1 + another sleep, then reconnecting to the external display, awakened the machine and started working.
I would say #2 is the way it happens about 99% of the time.