Since upgrading to Mountain Lion, the display sleep function appears not to work, and the screen saver is flaky. I can leave my machine for a couple of hours and when I come back the screen is as I left it.

I would expect the display sleep to be in effect, and if not that, at least the screen saver should appear. I have tested with various settings. In particular the screen saver set for 1 minute, and the display sleep set for 2 minutes. These functions just are not working. Note: I have Computer Sleep set to never, and usually 10 minutes for display sleep.

There have been no hardware changes to my system, and blue tooth is turned off. The system is on a LAN, but wake on network access is turned off. I am not sure if these network connections should affect the screen sleep/saver functions, but have heard of such issues in the past so have set them so as not to interfere.

I don't have any special programs running that should interfere with the display. Time Machine is running. However, before this upgrade, I did not notice a problem with any programs.

Here is the output from pmset:

$ pmset -g
Active Profiles:
AC Power        -1*
Currently in use:
 hibernatemode        0
 halfdim              1
 womp                 0
 networkoversleep     0
 sleep                0 (sleep prevented by )
 powerbutton          0
 ttyskeepawake        1
 hibernatefile        /var/vm/sleepimage
 autorestart          0
 disksleep            10
 displaysleep         2

Any ideas?

Addendum: while this issue has been going on for several days since the upgrade to ML, I notice that today the issue appears to be gone. Both the screen saver and the screen sleep are working.

Since the problem has been in existence for about a week solid, but has corrected itself without any action by me, I am not that confident that it is actually solved. No changes to the machine have been done.

  • Try resetting the SMC.
    – duci9y
    Sep 22, 2012 at 18:29
  • SMC has was reset after upgrade to ML, due to another issue that I was having. Sep 23, 2012 at 20:41

1 Answer 1


After a long while now, the problem has come back.

I found very detailed and useful info at http://web.archive.org/web/20150405031645/http://mactips.dwhoard.com/mactips/system/display-sleep. For me the workaround was just to logout and login again. Then test and the problem is fixed. The referenced page gives other, perhaps better workarounds.

Please note that the normal "why doesn't my Mac sleep" issues such as given at http://support.apple.com/kb/HT1776 are not the problem, and that some bug is the problem.

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