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Low End Mac's Safe Sleep FAQ

Dan Knight - 2009.06.15 (updated) - Tip Jar

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Apple introduced a new feature, Safe Sleep, with Mac OS X 10.3.x. When enabled, Safe Sleep writes the contents of your Mac's memory to a file named "sleepimage" on its hard drive before putting the computer to sleep (this works like the Hibernate command in Windows). In case the Mac loses power while sleeping, it can restore the state of memory using this file - complete with open documents. This is a lot faster and more efficient that restarting the computer, relaunching your applications, and resuming where you left off with your documents and Web browsing.

It generally takes about 20 seconds for your Mac to write the sleepimage file to its hard drive. The computer should not be moved during this time. Once the file is written, your Mac will enter sleep mode.

Which Macs Support Safe Sleep?

Most Macs introduced since Sept. 2003 support Safe Sleep. It has been reported to work with "the majority of G4s" including the following Macs:

  • iBook G4, all models
  • aluminum PowerBook G4, 1 GHz and faster models (reports of problems with the fan not running on the 867 MHz 12" PowerBook)
  • eMac, 1 GHz
  • Mac mini
  • some G4 Power Macs

Apple's list of models that support Safe Sleep is much shorter. We will update this list as we learn of other Macs that support Safe Sleep.

Why Would I Want to Use Safe Sleep on a Desktop Mac?

Just as a notebook wakes up faster and resumes its state after losing power if Safe Sleep is enabled, a desktop Mac will do the same thing. This can be especially helpful if you're moving a Mac mini or supported iMac from one location to another.

Why Would I Want to Disable Safe Sleep?

If you want to be able to Sleep your Mac and be able to move it right away, disable Safe Sleep. If Safe Sleep is enabled and you move your Mac, there is potential for damaging the hard drive while it is writing the sleepimage file.

How Much Hard Drive Space Does Safe Sleep Use?

The sleepimage file will take as much drive space as the amount of physical RAM installed in your Mac. If your hard drive does not have sufficient free space for the sleepimage file, it will not create it. The file will be deleted when you shut down or restart your Mac.

Do I Have to Enable Safe Sleep?

Intel-based Mac notebooks introduced since Fall 2005 have Safe Sleep enabled by default. iBooks, PowerBooks, and Intel-based MacBooks produced prior to that have it disabled by default.

How Do I Disable/Enable Safe Sleep Mode?

There are Terminal commands for turning Safe Sleep on and off, but there's an easier way. The freeware SmartSleep preference pane and the DeepSleep Widget let you choose one of three sleep options:

  1. Sleep without Safe Sleep.
  2. Safe Sleep.
  3. Safe Sleep and power off computer.

According to the SmartSleep page, some Mac OS X 10.4 users find that it doesn't work, and some users report that the Sleep command no longer functions when SmartSleep is installed. The page includes full instructions for removing SmartSleep if that is the case.

Another option is the Deep Sleep widget, which supports Mac OS X 10.4.3 and later and offers five different options.

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