MacOS – How to prevent the MacBook from sleeping when downloading apps from the App Store

Realised I answered a dupe of this here: How can I download something with display turned off (Ctrl+Shift+Eject)?

My answer to that question below:

I always use this combo as well, however this does not immediately sleep my machine in ML.

I believe this is a separate issue at play here. According to Siracusa's ML review, unlike in previous OS X versions, in 10.8 your system is eligible for sleep immediately upon "user inactivity" (the inactivity delay being set in your energy saver settings) unless the currently running apps make "power assertions".

In this case, that key combo is signalling to the OS that "user inactivity" should be triggered right away. In such a case, if your particular app that's downloading stuff does not make power assertions, your system will sleep.

I have come across the same issue generally (not necessarily related to triggering the screen sleep combo). See: Mountain Lion sleeps too aggressively

1. Have a look at this answer which indicates the commands to help you analyse if any process is blocking the sleep of your MacBook.

2. If nothing is blocking it, then look at :

   egrep -i 'sleep|wake' /var/log/kernel.log
   

   and look if you see a sleep line at the time you close the lid. If you don't, look at any information message in:

   /var/log/kernel.log
   

   around the instant this event should have happened.

3. Create a test account, close your session, and open one with this test account. Is your MacBook entering sleep when you close the lid?