It can be seriously annoying when you want your Mac to sleep but it wants to stay up late, playing video games, eating cheese doodles and generally not doing “lights-out.” Wait, maybe that’s my kids. Anyway, when it’s your Mac that won’t get to sleep, today’s tip should help you get to the bottom of it.
I keep my Mac Mini at my bedroom desk, and it’s always spinning up and waking up when I don’t want it to, so maybe today’s tip is more about me than you, but that’s ok, right?
Launch Terminal, found in the Utilities folder, which itself is in the Applications folder on your Macintosh’s hard drive. Once launched, type or paste the following command in:
pmset -g assertions
The first bit of output will show you the status of PreventSystemSleep and PreventUserIdleSystemsSleep – if either one is shown to have a status of the number 1, that means it is currently triggered, keeping your system awake.
The second part shows which processes “own” the assertions that are enabled, so check down there to see what’s keeping your Mac up. If you don’t at first figure out what process is being named, you can launch Activity Monitor, also in the Utilities folder, and visually see what process is being named.
You will then be able to quit the program, kill the offending process, or at least know why your Mac is awake when you really want it snoring away like the gentle sleeping, er, Lion, that it is.
- Source Macworld