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I have a 13-inch Mid 2012 Macbook Air running 10.9.3. I usually run with the lid closed plugging into 2 Apple cinema displays. Everything works great, except when I accidentally bump the power cable, at which point it goes to sleep.

Is there any way to prevent this? Clearly it isn't a power issue, because with the lid open and no power cable it drives all 3 monitors just fine.

  • I think it's possible, if you're comfortable with terminal stuff. Back in a moment with that... – krs013 Jul 17 '14 at 19:58
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The power adapter is required for closed display mode on any Apple portable machine, without it you can't use closed display mode.

Reference: http://support.apple.com/kb/ht3131

There is however a third party solution, called Caffine. Which when enabled, forces the mac to stay on until the battery dies, it won't ever sleep.

http://lightheadsw.com/caffeine/

  • Thanks, the issue is that now I have to remember to enable/disable Caffeine when I want to switch between these behaviors. It would be nice if there was something conditional on the power adapter. – RaresMan Jul 29 '14 at 20:43
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I was hoping to figure out how to do this with the pmset utility (man page). I feel like it's possible, but I couldn't see anything obvious (to me) looking through the options.

Anyway, here's another app that will do what you want: https://code.google.com/p/macosx-nosleep-extension/

  • Bummer, I've looked into the no sleep extension, and again the issue is I have to remember to enable/disabled it. For now I just moved my laptop into a spot where it's a lot harder to accidentally bump the power cable. – RaresMan Jul 29 '14 at 20:44
  • It could be done still. What you would need to do would be to make a daemon that periodically checks if an external display is connected, and when it is, place a no sleep assertion or run one of those utilities. This might help you get started: superuser.com/questions/278082/… – krs013 Jul 30 '14 at 3:19
  • Thanks for the tip, that looks like the only way to do it. I was looking into Scenario (itunes.apple.com/us/app/scenario/id423444193?mt=12) but it looks like it doesn't detect when external power is plugged in or not. – RaresMan Jul 31 '14 at 23:46

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