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How To Fix a Mac Pro Sleep Problem

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Are you facing a sleep problem, for a change not with yourselves but your Mac? Then this article might help you find possible fixes and the reasons why your Mac is getting insomniac!
But before we begin, let us clarify that you might not find the perfect solution to your problem, but will sure zero down on few reasons why your Mac Pro is behaving the way it is.
The Problem
Many a times, when you manually select the Sleep mode for your 2009 Mac Pro, it intermittently behaves strangely. There are times when it goes to sleep, on other occasions wakes up suddenly. If you select sleep again, things operate the way they are supposed to.
This glitch is certainly irritating if you leave your office for some work and put your Mac Pro on sleep mode, only to come back and see it awake.
Possible Reasons Why It Happens
When you investigate a little, you might rule out most of the reasons you think can trigger such events such as a Bluetooth integrated with the Mac. However, a little scrubbing beneath the surface will help you narrow down on the two possible options:
The first Reason
This could be the Mac OS X’s Wake on Demand feature. Working in conjunction with an AirPort Base Station or Time Capsule, this feature allows other network devices to temporarily wake up a sleeping Mac and perform a requested or scheduled action. To activate this option, you need to go to the Energy Saver System Preferences pane. Now select “Wake for network access.” If you have done so for your Mac, the network devices could be the possible reason.
Apple, in its support notes, maintains that Mac Pro behaves this way occasionally for a brief time. It does so to “maintain registrations with the Bonjour Sleep Proxy.”Mac then goes off to Sleep. This is confirmed even at the time of setting up Mac for ‘Wake On demand’ option.
As per Apple, this normally happens once every two hours. And you check your Mac Pro’s Console Pro’s console log, this gets confirmed. You might come across messages such as these while checking the log sheet:
8/25/10 2:22 20 PM Aug 25 kernel Wake reason = RTC
8/25/10 2:22 20 PM Aug 25 kernel RTC: maintenance alarm 2010/8/25 21:22:19, sleep 2010/8/25 19:35:08
8/25/10 2:22 20 PM Aug 25 kernel System Wake
Note: RTC stands for Real Time Clock.
“Maintenance alarm” refers to “Wake on Demand” checks and this is how the console defines it. To check whether you are assuming right and the 2 hour maintenance check is indeed true, simply turn off the ‘Wake On Demand’ option. You will notice that the messages stop coming up.
Coming back to the problem at hand, when you notice the logs, you will realize that this function should not cause the Mac to wake up soon after being put on sleep; at least not automatically. This brings us to the second reason.
The second Reason
Second possible reason could be the Scheduled wake ups. To check this, simply go to Energy Saver System Preferences pane. Now click on Schedule button. This will drop a list. Here you can feed in the time you want Mac to wake up. Suppose if you work around 8:30 or so, you can set your Mac to wake up at 8:30 AM.
If you want to check how the logs look for this option, be aware that scheduled wake ups correspond to an RTC alarm message and not maintenance alarm. The logs will look somewhat like this: (8:30 is GMT 15:30:00)
8/27/10 8:10 01 AM Aug 27 kernel Wake reason = RTC
8/27/10 8:10 01 AM Aug 27 kernel RTC: alarm 2010/8/27 15:30:00, sleep 2010/8/27 14:49:48
8/27/10 8:10 01 AM Aug 27 kernel System Wake

As you can see in the log, everything looks fine. However if Mac awakes at this time, you can possible a message similar to what we saw during our prognosis.
8/26/10 9:38 03 AM Aug 26 kernel Wake reason = RTC
8/26/10 9:38 03 AM Aug 26 kernel RTC: alarm 2010/8/26 15:10:00, sleep 2010/8/26 16:38:02
8/26/10 9:38 03 AM Aug 26 kernel System Wake
The message looks the same as the previous ones, however there is one exception.
The 15:30:00 time comes earlier than 16:38:02, the time when we put our Mac Pro to sleep manually. In fact it was like if the Mac could speak, it will shout out loud saying “Sorry for missing the earlier alarm time, I am making amends and waking up now”
However, once you do this the second time, Mac goes to sleep and wakes up next morning at 15:30.

Now the big question is: how and why does this happen?
The scheduled wake up time and day is stored in a com.apple.AutoWake.plist file. It is located in /Library/Preferences/SystemConfiguration
The only plausible explanation to this is the file not getting updated correctly. Many reports suggest that deleting this file and letting Mac create a new one can solve this issue but it has not been tested before this article.

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