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In Energy Saver settings (System Preferences -> Hardware section) the Mac is set to sleep after 15 minutes, but nothing happens.

Mac drains battery and automatically turns off when battery is low.

If I type pmset -g assertions in terminal, I get this:

3/31/14 5:46:52 AM EDT   
Assertion status system-wide:
PreventUserIdleDisplaySleep    0
PreventSystemSleep             0
PreventUserIdleSystemSleep     1
InternalPreventDisplaySleep    0
ExternalMedia                  0
UserIsActive                   0
ApplePushServiceTask           0
BackgroundTask                 0

Listed by owning process:
  pid 251(coreaudiod): [0x0000000100000d01] 00:17:27 NoIdleSleepAssertion named: "com.apple.audio.'AppleHDAEngineOutput:1B,0,1,1:0'.noidlesleep" 
  pid 251(coreaudiod): [0x0000000100000929] 01:11:47 NoIdleSleepAssertion named: "com.apple.audio.'BoomEngine:0'.noidlesleep" 
  pid 269(helpd): [0x0000000c00000159] 02:37:33 BackgroundTask named:     "com.apple.helpd.sdmbuilding" 

Kernel Assertions: None

How should I read this? Why PreventUserIdleSystemSleep is set to one? How I can set up Mac go to sleep after certain time of inactivity?

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2 Answers 2

In this instance, use Activity Monitor.app to kill process pid 251(coreaudiod).

Tracking Down Idle Sleep Problems

Below is an overview for tracking down why your Mac will not idle sleep.

No Idle Sleep Assertion

A NoIdleSleepAssertion assertion is the most likely reason your Mac is not sleeping.

To see more about which processes are blocking sleep, run this command in Terminal.app:

pmset -g assertions

This will list active assertions and their owning application or process. Expect to see audio visual, network sharing, or printing related responses.

If a hidden process, such as pid 251(coreaudiod), is responsible, you can kill it using Activity Monitor.app. Afterwards rerun the pmset command above to check the assertion has been removed.

Common Causes

This Apple Discussion forum thread, My Mac don't go sleeping since Lion Update, contains numerous people who also encountered this problem. The same causes will affect OS X 10.9.

  • Check for stuck print jobs; a pending print job will keep your Mac awake
  • Check for audio visual or presentation programs that may restrict sleep while playing
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Actually thanks for your detailed report one can see it is the application Boom preventing the sleep mode.

Try one of the following by updating the app Boom to 1.8.1, or disable it to test.

The 1.8.1 has some fixes that might help:

--- Audio clipping(cutting out) issue is now fixed.
--- Kernel task consumption issue has been fixed. Now it functions the same as default OS X with or without Boom.
--- No sound after sleep issue is now resolved.
--- VLC and other media compatibility issue fixed.
--- Volume key sound delay.
Our developers our working with Apple's DST to have a quick fix for this.
--- Audio drop when using Facetime. Mavericks users are advised to turn off Boom when FaceTime is active.
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