Whenever I want to download something which is over a gigabyte, I leave my computer, so the download could happen smooth and fast, but that's not to be, when my computer goes to sleep, and the Wi-Fi turns off.
In OS X 10.8 Apple introduced an "aggressive system sleep" to aid laptop power consumption and battery life. This means that applications have to tell the OS when they don't want it to sleep because they are, say, working on a long task that doesn't require user input.
If you're using an application that hasn't been updated to issue these requests (known as power assertions) you can issue them yourself from the command line using the
caffeinate command. To do this open
Terminal.app and enter,
The machine will stay awake until you abort the command with CTL+c. To allow the screen to sleep as per your normal System Settings use,
To make the power assertion expire after a fixed number of seconds (e.g., 1 hour = 3600 seconds) use,
caffeinate -t 3600
Once that expires your normal sleep settings will resume.
There is a nosleep Mac OS X kernel extension.
open terminal.app and type:
sudo systemsetup -setcomputersleep Never sudo pmset -a standby 0
also try the freeware "insomniaX"
"InsomniaX is a small utility that acts as a wrapper to the Insomnia kernel extension. InsomniaX disables either lid and/or idle sleep on your MacBook - any MacBook - allowing you to play music through speakers even while it's closed! or simply just to quickly stop the system from going to sleep on idle"