I can now ssh in while the system is hung up, and I have attached logs captured during a recent hang up. Top showed Xorg using 100% CPU at the time. When I killed xorg (signal 9) I got a fresh, working X. The shutdown I requested was aborted. The timing is a little surprising, since things had been mostly working for awhile. It might be relevant that there was a second X session active when I requested the shutdown.
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