The Finder was not responding, so I control+click'd the Finder icon on the Dock and chose Relaunch… except that it didn't relaunch.
Activity Monitor happened to be visible and I could see that it listed Finder (including the PID) and showed it as "Not Responding."
I was in iTerm, so I tried
killall Finder and was told "No processes belonging to you were found" (or words to that effect).
I tried to send "kill" to the PID I could see for Finder, and was told there was no such PID. This led me to assume that the WindowServer was not showing accurate information anymore.
sudo killall -HUP WindowServer which made the entire GUI go away, and left me with a black screen and some white letters on it (not the panic screen, more like console log messages).
The message was:
Sep 27 17:17:23 Pro kernel: V1.4.0: TrustedData_driver_VendorSpecificType00::vendorSpecificPassThroughIn(): SendCommand failed, task not complete, serviceResponse = 1, TaskStatus: 2
Sep 27 17:17:23 Pro kernel: V1.4.0: TrustedData_UserClient_SCSIType00::vendorSpecificPassThroughIn() returning failure from driver: 3758097084
So now I have a black screen, but and I can type but it has no effect (the letters appear on the screen, but don't actually execute. I've tried control-C and control-Z to no avail.
I can ssh into it from my other Mac.
Of course my first step was
sudo shutdown -r now which sent out the notice that the system was going to shutdown, but didn't.
I have also tried
sudo shutdown -ro now and
sudo /sbin/reboot and
sudo reboot -q to no avail.
Aside: (On a Windows PC, I would have pressed CTRLALTDEL but there is no corresponding Mac keyboard shortcut… not that it would have necessarily worked anyway.)
I am out of ideas.
ps and put the output here if anyone wants to see what is still running.
What else would you try?
(Other than simply holding down the power button until it shuts off.)