If your Mac won't go to sleep but Energy Saver settings say it should, try the following: open Terminal and type what you see above, minus the inverted commas, but with the space after the last word
The above result shows that a process is preventing sleep - it's often something to do with printers, so...
Check all print queues are clear
Turn off printer sharing
Remove redundant printers from 'Print and Scan' preferences
There...now your Mac should get a good night's sleep...zzz
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