hibernatemode = 3 is appropriate for portable Macs, and will write sleepimage to disk so that a battery-powered Mac can remove power to RAM while it sleeps for power conservation. That is the reason for the sleepimage file creation. It's not related to using a UPS, which you can configure to sleep or shut down the Mac at programmed limits of time or battery charge. There is no difference to the Mac - it will either sleep or shut down in the same exact manner, with or without a UPS.
If a desktop loses power the sleepimage file is not used to restore RAM upon a subsequent startup. Although the sleepimage file is being written to disk every time your Mac sleeps, it can convey no benefit, so hibernatemode should be set to zero.
I believe you can reset hibernatemode to its default value of zero by resetting the NVRAM.
NVRAM reset:
- Shut down your Mac.
- Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the Command-Option-P-R keys before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
If that does not reset it to zero use Terminal:
sudo pmset -a hibernatemode 0
There are also third party hacks and utilities to manipulate system sleep variables that may have caused it to change from the zero value that it should have been. I don't recommend using such things.
