Macbook pro doesn't go to sleep after left inactive
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