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My Mac OS is OS X Yosemite (Version 10.10.2).

Normally I put the mac in Sleep mode before going to bed, and I realize very often that the machine starts to run in the night just for several minutes and then back to silence.

I guess there is some bad process/software in my Mac that wakes up the system from time to time.

I know that Activity Monitor could check processes, but I have no idea how to see what is wrong...

Could anyone help?

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  • Probably nothing wrong, just doing its maintenance and cleaning, and if you have it backing up stuff to time machine, and synchronizing and...so on. Your Mac actually does not need sleep at all, but you do.
    – Ruskes
    Commented Apr 24, 2015 at 4:34
  • But if you do want to see what is it doing :) open the Console in your utility folder than scroll back to the time it supposed to sleep to see what it was busy with.
    – Ruskes
    Commented Apr 24, 2015 at 4:36

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As of OS X Mountain Lion (10.8), there has been a feature called "Power Nap" that allows the Mac to periodically wake from sleep while connected to a power adapter to retrieve emails, calendar updates, iCloud syncing, or to back up to Time Machine. This would be my guess for the reason why your Mac is waking up and running during the night and not an indication of a bad process on your Mac.

If this is unwanted behavior, it's an easy setting to switch off in System Preferences > Energy Saver:

Energy Saver settings on OS X Yosemite

Note that another option here is "Wake for network access" - which would be along the lines of remote or local file/printer sharing while in sleep. I would doubt this is happening since you are asleep yourself while it's occurring :-)

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  • Downvote without feedback?
    – Ethan Lee
    Commented Apr 25, 2015 at 13:25

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