I have a Mac Pro that draws about 250 watts (so I read somewhere) when it's running full-bore. It apparently draws less than 90 when it's sleeping. For whatever reasons I like to leave it on overnight, but I'd like it to sleep for cost and eco reasons. However, something I have installed keeps waking it up. I've done a fresh reboot, and then told it to sleep once it's fully up and running and before launching any other apps. It won't stay asleep for as long as a half hour (approximately, I haven't timed it) and it certainly won't stay asleep overnight.

By sleep I mean the monitors go dark and the hard drives spin down and the fan stops and power draw is minimised. By wake up I mean a jet takes off in my Mac Pro tower as all the fans and drives spin up together loudly enough to be heard in another room. The monitors may or may not come on, they seem to sleep all right.

FWIW I'm running Snow Leopard on a first-generation Intel Xeon quad-core Mac Pro with 10 GB of RAM, 4 internal hard drives and two monitors, but I think this is a software thing, not hardware, so that shouldn't matter.

How do I find out what process/app/plugin/background operation/preference pane/whatever is waking up my Mac?


  • Look in console log as an admin user and see if anything shows there.
    – mmmmmm
    Jan 16, 2012 at 18:04
  • FWIW I think the actual power consumption numbers for the 1st-generation quad-core Mac Pro are about 300W full-bore, but closer to 100W powered on under a light load (what it spends most of its time doing if you're not intentionally taxing it) and under 10W asleep.
    – metamatt
    Jan 16, 2013 at 18:44
  • Also: I had one of these machines (2006 model, first generation, MacPro1,1) and then replaced it with a 2009 model (first Nehalem generation, MacPro4,1). The 2009 model does sound like a jet engine for a few seconds every time it wakes from sleep -- I know well the phenomenon you're describing -- my 2006 model didn't do that though; that one could wake up from sleep without running the fans full speed.
    – metamatt
    Jan 16, 2013 at 18:46

3 Answers 3


You can see a log of power events with pmset -g log or or syslog.

$ pmset -g log | grep ' Wake  ' | tail -n5
10/29/12 10:31:20 PM GMT Wake      Wake due to EHC2/HID Activity: Using BATT (Charge:99%)                       
10/30/12 12:51:56 AM GMT Wake      Wake due to EC.LidOpen/Lid Open: Using BATT (Charge:68%)                     
10/30/12 8:50:33 AM GMT+ Wake      Wake due to EC.LidOpen/Lid Open: Using AC (Charge:100%)
10/30/12 5:12:32 PM GMT+ Wake      Wake due to EC.LidOpen/Lid Open: Using AC (Charge:99%)                       
10/31/12 12:58:01 PM GMT Wake      DarkWake to FullWake due to HID Activity: Using AC (Charge:44%)              
$ syslog | grep 'Wake reason' | tail -n5
Oct 30 03:14:26 MacBook-Air kernel[0] <Debug>: Wake reason: EC.LidOpen (User)
Oct 30 17:12:05 MacBook-Air kernel[0] <Debug>: Wake reason: ?
Oct 30 17:12:31 MacBook-Air kernel[0] <Debug>: Wake reason: EC.LidOpen (User)
Oct 30 23:08:18 MacBook-Air kernel[0] <Debug>: Wake reason: EC.ACAttach EHC2 (Maintenance)
Oct 31 12:57:52 MacBook-Air kernel[0] <Debug>: Wake reason: ?

The post at OS X Daily has descriptions of the abbreviations.

  • OHC: stands for Open Host Controller, is usually USB or Firewire. If you see OHC1 or OHC2 it is almost certainly an external USB keyboard or mouse that has woken up the machine.
  • EHC: standing for Enhanced Host Controller, is another USB interface, but can also be wireless devices and bluetooth since they are also on the USB bus of a Mac.
  • USB: a USB device woke the machine up
  • LID0: this is literally the lid of your MacBook or MacBook Pro, when you open the lid the machine wakes up from sleep.
  • PWRB: PWRB stands for Power Button, which is the physical power button on your Mac
  • RTC: Real Time Clock Alarm, is generally from wake-on-demand services like when you schedule sleep and wake on a Mac via the Energy Saver control panel. It can also be from launchd setting, user applications, backups, and other scheduled events.
  • Wow, thanks for that. I (thought I) knew about pmset's -g option, but "pmset -g log" is a whole new world, and hugely useful. That just enabled me to solve my problem. Kudos.
    – metamatt
    Jan 16, 2013 at 18:42

Go to System Preferences and click Energy Saver. Then, uncheck "Wake For Network Access." That is the most likely problem. Good luck!

  • re: thekmc Disabling "Wake For Network Access" worked for me. The reason seems to be that when Apple updated to Mavericks, they bundled a bunch of features to sync with Apple Cloud. More background can be found on this thread: forums.macrumors.com/showthread.php?t=1548254
    – user910028
    Sep 30, 2014 at 14:40

Better answer: http://osxdaily.com/2010/07/17/why-mac-wakes-from-sleep/

Let the people find out for themselves. Don't guess for them

  • 3
    Why is this answer better? And because links may break rendinging your answer useless in the future, could you please summarize the linked page in your answer?
    – nohillside
    Oct 31, 2012 at 5:03
  • Welcome to Ask Different! Answers on Ask Different need to be more than just a link. It's okay to include a link, but please summarize or excerpt it in the answer. The idea is to make the answer stand alone. Please take a look at the FAQs for more info. Thank you :)
    – gentmatt
    Oct 31, 2012 at 10:26

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