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I program my iMac to put the display to sleep after 10 mins. It has always worked till now but not any more. The display stays on all the time whatever I do on the energy save page, so when I am away from the iMac the screen saver starts and it will stay on until I next touch the mouse which can be days if I am away and am running Skype for example. I can only sleep the display manually. Any ideas anyone?

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You can use the pmset command to "ask" power management if there is anything that will prevent sleeping. In this first example, I have recently rebooted, and there isn't anything that should prevent the system from sleeping:

$ pmset -g assertions
5/10/13 8:18:51 AM EDT
Assertion status system-wide:
   PreventUserIdleDisplaySleep             0
   CPUBoundAssertion                       0
   DisableInflow                           0
   ChargeInhibit                           0
   PreventSystemSleep                      0
   PreventUserIdleSystemSleep              0
   ExternalMedia                           0
   DisableLowPowerBatteryWarnings          0
   EnableIdleSleep                         1
   NoRealPowerSources_debug                0
   UserIsActive                            0
   ApplePushServiceTask                    0

Kernel Assertions: None

Then I started iTunes playing a song. Checking now, you can see that sleep will be prevented by the core audio process.

$ pmset -g assertions
5/10/13 8:19:46 AM EDT
Assertion status system-wide:
   PreventUserIdleDisplaySleep             0
   CPUBoundAssertion                       0
   DisableInflow                           0
   ChargeInhibit                           0
   PreventSystemSleep                      0
   PreventUserIdleSystemSleep              1
   ExternalMedia                           0
   DisableLowPowerBatteryWarnings          0
   EnableIdleSleep                         1
   NoRealPowerSources_debug                0
   UserIsActive                            0
   ApplePushServiceTask                    0

Listed by owning process:
  pid 1124: [0x00000464012c001f] PreventUserIdleSystemSleep named: "Nameless (via IOPMAssertionCreate)"
  pid 269: [0x0000010d012c0020] PreventUserIdleSystemSleep named: "com.apple.audio.'AppleHDAEngineOutput:1B,0,1,2:0'.noidlesleep"

Kernel Assertions: None
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  • How do I do that?
    – RUSSELL GILBERT
    May 20, 2013 at 22:15
  • How do you do what? The quoted blocks I show above are commands typed into terminal. Is that what you're asking? The command prompt is '$', so you type what is shown on those lines, which appear in the first line. Then the rest of the text in the block (without the prompt char) is output from the command. Type "pmset -g assertions" into Terminal, and post the output if you need help interpreting it.
    – Tim B
    May 21, 2013 at 1:51
  • Last login: Mon May 20 23:03:13 on ttys000 russells-imac:~ russellgilbert$ pmset Usage: pmset <options> See pmset(1) for details: 'man pmset' russells-imac:~ russellgilbert$ Last login: Mon May 20 23:10:13 on ttys000 russells-imac:~ russellgilbert$ pmset -g assertions 21/05/2013 22:22:00 BST Assertion status system-wide: PreventUserIdleDisplaySleep 0 PreventSystemSleep 0 PreventUserIdleSystemSleep 0 ExternalMedia 0 UserIsActive 0 ApplePushServiceTask 0 BackgroundTask 1
    – RUSSELL GILBERT
    May 21, 2013 at 21:27
  • that shows PreventUserIdelSystemSleep has the value 0, so based on this alone, there isn't anything that should prevent the system sleeping based on the user being idle. Perhaps it doesn't think you're idle.
    – Tim B
    May 22, 2013 at 2:33
  • So what can I do next?
    – RUSSELL GILBERT
    May 23, 2013 at 10:36

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