MacOS – Mountain Lion won’t wake up after an extended sleep

macbook promacossleep-wake

I've recently upgraded my MacBook Air to Mountain Lion. Now whenever the machine sleeps for a long time (more than two hours or so) while disconnected from the mains, it won't wake up. I had to hold the power button to reboot the machine.

Is there a solution to this problem?

Best Answer

This is a known issue that hasn't been fixed as of 10.8.1. When Mountain Lion hibernates (either directly or as part of standby mode), it couldn't wake up and thus need to be restarted.

The current workarounds are:

Disable hibernate mode.
Disable standby mode.

I've written an article how to get around this issue by preventing OS X from hibernating.

For Apple folks: please see rdar://1212084 - Thanks.

Related Solutions

MacOS – Lion – Macbook randomly wakes up from sleep when lid is closed

It is possible to determine what caused the system to wake

Open Console (/Applications/Utilities/Console)
Set the search filter to 'wake'

You're looking for the latest entry that has something like this:
```
Wake reason = EC LID0
```
(In the example above, opening the display clamshell caused the machine to be woken)

Here's a list of wake 'reasons' from OSXDaily

This should shed some light on what is waking the machine, then you can go from there.

Mac – Why won’t the Mac Pro wake from sleep at the scheduled time

Try resetting the System Management Unit (SMU); the SMU is typically responsible for tracking when your Mac is scheduled to wake up.

With regard to your Mac Pro appearing not to keep time, this is not a problem. It is expected behaviour for the menu bar clock to update a few seconds after your Mac has woken up.

The process controlling the clock needs to get a change in time notification before updating; it will not match your Mac's internal clock immediately upon waking up.

Best Answer

Related Solutions

MacOS – Lion – Macbook randomly wakes up from sleep when lid is closed

Mac – Why won’t the Mac Pro wake from sleep at the scheduled time

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