Mac Pro won't sleep any more The past couple days, command-option-eject no longer puts my Mac Pro to sleep.  I haven't done any software updates in that time.  No process seems to be doing anything very interesting, or CPU-intensive.

What's stopping my Mac from being able to sleep?  How can I figure out what it is?
Using the Terminal application on macOS Sierra 10.12 or later you can run the following:

log show --last 2d|grep "Wake reason"

This will provide a list of the various reasons your system is not sleeping. Unfortunately the list will likely contain a few things that are not immediately clear, but a quick search on those messages should lead you in the right direction.