I’ve got a very odd problem with an old G5 of mine. It's a 2.3GHz Dual-Core G5 with Mac OS X 10.5.8. Sometimes, though not always (about 50/50), when putting the computer to sleep, it wakes up after a couple of seconds. This is really puzzling and I just can’t figure out what the problem is. I've had this computer for many years now, and it started just recently, but I can't pinpoint the exact time.

So far, I can rule out the following potential causes:

  • Wake for ethernet network administrator access (turned on or off, doesn’t matter)
  • Any network traffic - the problem can occur when the G5 is not connected to the network
  • External USB hubs (none connected)
  • Bluetooth (doesn’t have BT)
  • Modem (doesn’t have one)
  • Software (clean installation of OS X: same problem)
  • Keyboard or Mouse waking it up - the problem can even occur when none are connected and I put it to sleep via SSH
  • Graphics card/monitor: problem can occur when there is no monitor connected and I put the G5 to sleep via SSH.
  • Power fluctuations

The logs don’t help me. The Wake event is always 0020, regardless whether it's an intentional wake or not.

When the G5 woke up, I can put it back to sleep and then it will stay in sleep mode. So it’s no big deal but I still would love to know what the problem is.

Edit (21-June-2012): Thank you all for your suggestions and pointers. Unfortunately my G5 recently had a failing power supply, and it won't wake up from that anymore.

  • 1
    Have you tried resetting the System Management Unit (SMU)? support.apple.com/kb/HT1436 Commented Nov 27, 2011 at 9:18
  • Unfortunately resetting the SMU didn't change anything :(
    – René
    Commented Nov 28, 2011 at 19:00
  • 1
    Have you checked the power specific logs using the following command? "pmset -g log" Commented Dec 1, 2011 at 5:35
  • Interesting. I didn't know this existed. Unfortunately, pmlog -g doesn't offer the "log" argument on Leopard. pmlog -g pslog works, but only shows me "Waking", regardless if intentionally or not.
    – René
    Commented Dec 1, 2011 at 9:23
  • I think we're having the same problem, though I have a 2011 iMac with Lion: apple.stackexchange.com/questions/27862/… If you restart, does the problem go away temporarily? Commented Dec 26, 2011 at 15:14

8 Answers 8


Have you tried Reseting the SMU

The SMU (System Management Unit) is a microcontroller chip on the logic board that controls all power functions for your computer. If your computer is experiencing any issues regarding these functions, resetting the SMU may resolve the issue. The functions controlled by the SMU include:

  • It tells the computer when to turn on, turn off, sleep, wake, idle, and so on.

  • It handles system resets from various commands.

  • It controls the fan.

Note that resetting the SMU does not reset the PRAM.

Steps to reset the SMU on:

Power Mac G5 (Late 2005)

To reset the SMU on a Power Mac G5 (Late 2005) computer, either use the steps listed above for the Power Mac G5 (Late 2004) or:

  1. Turn off the computer by selecting Shut Down from the Apple menu or by holding the power button until the computer turns off.

  2. Open and remove both the metallic outer door and the inner plastic air deflector.

  3. Remove the fan assembly immediately to the left of the processor module.

  4. Press the SMU reset button on the logic board.

  5. Replace the fan assembly, air deflector, and outer door.

  6. Turn on the computer.

The SMU reset button is located underneath the lower bank of system memory slots, as shown below:

SMU Location on G5

Unlike earlier models of Power Mac G5 or Power Mac G4 computers, the Power Mac G5 (Late 2004) and (Late 2005) models do not have a PMU. This functionality has been replaced by the SMU.


Check Schedule in the Energy Saver preference panel.

  • There's no schedule set. It also wouldn't explain why it wakes up just seconds after putting it to sleep.
    – René
    Commented Nov 26, 2011 at 14:54

The "Zombie Wake-Up". I have an intel iMac that does the same thing. If I sleep it from the keyboard with ShiftCmdEject, it's likely to wake up again in a couple of seconds. In fact, it will be exactly one "breathing" cycle of the power light if it's going to do it at all.

Apple tried replacing the IR sensor board, then the whole main board, and then blamed my environment and asked (told!) me not to bring it back again. I found if I sleep it from the Apple menu, it doesn't re-awaken. I haven't tested it using hot-corners, but I'm guessing that would be equally effective.


Try checking the G5's internal clock battery. It is located to the left of the SMU button. Since the machine is from 2005-2006 it may be going bad and not be able to maintain proper voltage, which may be causing the SMU, PRAM, or other settings to become corrupt and maybe cause the random waking from sleep to show up as a side effect.


Without any additional information, it's difficult to say specifically what is causing the issue. It could be any of the other issues mentioned here, but to make sure, go into terminal and use pmset -g log for more information.


Got a question, your computer, was it part of the logic board fault issues, and was it ever replaced? I only ask because this was a known issue with the logic boards.

If not, then there are three things I'd try.

  1. Reset the PR Ram.
  2. Check to see if your prefs are set to wake up for any reason whatsoever, you may be having your computer do it's daily checkup for updates at that time and not know it.
  3. If you are running OS X, as you are, around that time CHRON jobs are activated. Your computer may be waking up to do them, this also comes into play of point 2, so you may need to just check extra carefuly in your prefs to make sure that nothing is accidently activating the computer without you knowing about it.

Apple provide the following list of possible reasons for Mac OS X 10.7, aka Lion, not sleeping or staying asleep:

OS X Lion: If your Mac computer won’t go to sleep or stay in sleep

If your Mac doesn’t go to sleep when you expect it to, or if it wakes up unexpectedly, you may need to change your sleep preferences or something may be waking your computer.

  • Make sure your computer’s sleep settings are set the way you want. In Energy Saver preferences, use the slider that controls the computer’s sleep.
  • Other users may be waking your computer remotely to use its shared resources. If you don’t want this to happen, open Energy Saver preferences and deselect “Wake for network access.”
  • Bluetooth devices can wake your computer. If you don’t want a Bluetooth keyboard or mouse to be able to wake the computer, open Bluetooth preferences, click Advanced, and then deselect “Allow Bluetooth devices to wake this computer.”
  • Key presses and mouse or trackpad clicks can wake your computer. If your computer wakes when you’re not present, something may be pressing the mouse button or keyboard.
  • Applications that access a disk can keep your computer from going to sleep. For example, iTunes accesses your disk to read the songs it plays, and DVD Player accesses the optical disc drive to play movies.
  • People using shared services on your computer can prevent it from sleeping. For example, they may be using a printer connected to your computer or accessing shared files stored on it. In Sharing preferences, turn off any services you don’t need to use by deselecting the On checkbox next to the service.
  • If Spotlight is indexing your hard disk, your computer won’t go to sleep. Click the Spotlight icon on the right side of the menu bar and check whether it says it’s indexing. Indexing your files can take several hours, depending on the number of files on your computer.
  • Malfunctioning USB, FireWire, and Thunderbolt devices may keep your computer from going to sleep. Disconnect your USB, FireWire, and Thunderbolt devices and see if your computer goes to sleep. If it does, reconnect each device, one at a time, until you find the one that’s malfunctioning. Contact that device’s manufacturer for more information.
  • Some PCI extension cards intentionally prevent a computer from going to sleep. Refer to the documentation that came with your card.

Try to delete the .plist file below as the root user. Below is the steps needed to create a backup of the file in case you need it later and delete the file:

  1. Launch Terminal
  2. su root
  3. cd /Library/Preferences/SystemConfiguration
  4. cp com.apple.PowerManagement.plist com.apple.PowerManagement.plist.bak
  5. rm com.apple.PowerManagement.plist

Reboot your system to make sure the changes take effect.

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