Prevent Mac Laptop from sleeping when closed?

I开发者_StackOverflow'm writing a program in C and want it to have an option that will keep a mac laptop awake even if the lid is closed so processes can continue. There seems to be very little information available on this topic so I really don't know where to begin. If anyone knows how to accomplish this or where I can find more information I would really appreciate (i.e. will I need to work with the BIOS for this or are there built in functions?). Also, if it's easier to do it in another language that is fine as I'm not stubbornly set on using C.

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You need to write a kernel extension for this. The OS doesn't support it by default because the laptops aren't designed to properly cool themselves with the lid closed and internal display enabled. SleepLess is a $10 utility that'll do what you want, too. If you warp the display or something, it's your own fault. :-).

If you want to write something yourself, LidSleep.kext looks like a good start (it does the opposite, i.e. sleeping on lid close) and comes with source code.

(It is possible and supported to wake up some Mac laptops with the screen closed by using an external input device.)

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You can do this using the I/O Kit framework, see QA1340 listing 2 for sample code using IOPMAssertionCreateWithName to temporarily prevent sleep.

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The link to LidSleep.kext listed above is not working, so I can inform that the author of NoSleep has made the source code available here, so you can see for yourself how it can be done:

https://code.google.com/p/macosx-nosleep-extension/

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If your laptop is a reasonably recent model, you don't need to add anything. If you are running Lion, it simply works. If you're running an older OS you have to wake up the laptop by sending it a keystroke or mouse click from an external keyboard or mouse. See http://support.apple.com/kb/ht3131