I have an early 2009 24" iMac. Lately, when in sleep mode it will occasionally wake up for around ten seconds with the screen off, then go back to sleep. Wake on LAN is turned off so I can't figure out why this is happening!
IMac – Why Does My iMac Wake Itself Up
imacsleep-wake
Related Solutions
Your iMac should automatically spin down its disks and go to sleep.
Use the following command to view a detailed log showing your iMac's power history:
pmset -g log
Look out for applications that may be keeping your Mac awake and active. Applications and other processes can keep your Mac awake if they are providing a service, such as file sharing or remote access.
Do you have an active ssh session or terminal session running? This can also be responsible for keeping your iMac awake.
Be aware that Apple does not officially support hibernation on desktop Macs. Your setting hibernatemode suggests you have this feature enabled.
Disclaimer: I am involved with a commercial product called Power Manager, it can help make your Mac sleep more predictably.
Macs will wake up in response to many hardware events. Changing a USB/Firewire/Thunderbolt cable or even plugging in / powering on a connected device will wake Macs that are sleeping. Keyboard presses, clamshell sensor detecting an open of the display lid will also wake up a sleeping Mac. These are pretty well known and obvious, even if you don't realize a pet or power fluctuation can cause a wake event.
Two software items will also wake a sleeping mac and both rely on the power management / system management controller. Both are seen in the Energy Saver preference pane. This is how applications can do the same thing as hardware and wake your mac.
For macs with a battery - the power adapter needs to be connected and powered for much of this to work. The Wake for network access is both the standard WakeOnLan (WOL) as well as Apple's Bonjour Sleep Proxy. I like the article About Wake on Demand that explains how Apple has extended the concept of WOL and made a service.
If you disable these two items - software can no longer wake your sleeping mac and you can know if it's a hardware event or a software event. The other answers go into how to look at the logs to know which event has made a specific wake up request. Hopefully this helps frame the bigger picture of how your mac can take a cat nap with one eye open.
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Best Answer
There are a number of possible reasons, and the system actually logs the cause of each 'wake from sleep'.
Open a terminal and enter:
syslog | grep -i "wake reason"(or, on Sierra or newer
log show | grep -i "wake reason")This may take some time to return a result, but when it does, you should get a series of lines that look something like the following:
Here are the possible 'Wake Reason' codes (lifted from OSXDaily)
Happy hunting!