Why iMac & Mac Mini Powers Off after Hours of Sleep (Hibernates/Turns Off)
(FYI: This post is from Feb 2013 - Apple doc listed 2012 and later mac models affected.)
An updated Apple support article (on 2/28/2013) (HT1757 - "Mac computers: Progress bar appears after waking from sleep", no longer online) explains why newer Macs (including Late 2012 mini and iMacs) go into hibernate (and power off) after hours of sleep even when on AC power. Per the Apple doc, added in OS X 10.8.2 supplemental update 2.0 to comply with European Energy Standards.
I had mentioned this behavior in an article on HDMI tests with a late 2012 mac Mini in fall 2012 (that covered other things) and linked to an Apple forum thread on it ("Mini hibernates despite pmset saying it shouldn't") that discusses changing PMSET options.
(Note the tip below is targeted to desktop/AC powered Macs with this behavior, not notebooks that run on battery power that needs to Hibernate/power off if the battery runs very low.)
Tip to Prevent Mac from Powering Off in Sleep:
From the OS X Terminal app, try these PMSET changes:
sudo pmset autopoweroff 0
and
sudo pmset standby 0
Verify the settings by entering "pmset -g" (without quotes).
(The above settings tip was reported to still work as recent as summer 2015.)
BTW: This is for later Macs that support Standby. [Before Disabling BOTH autopoweroff and standby, I had tried setting both autopoweroffdelay and standbydelay from the default 4200 (seconds) to 86400 (i.e. 24 Hours). Did not try a number like 9999999.]
(Update: 4/4/2014 reply to news post on new Cylinder Mac Pros also turning off in sleep)
"Re: About Modern Macs Not Waking after Hours of Sleep
No idea why, but I've now seen at least 2 cases where "sudo pmset autopoweroff 1" and "sudo pmset standby 1" worked but "sudo pmset autopoweroff 0" & "sudo pmset standby 0" didn't!?
(What mac models and OS X version were those 2 using?)
-BDAqua"
Agreed that does seem odd (opposite of expected setting), but if any readers find that helps (where 0/disabling didn't), let me know.
(previous/older posts follow)
FYI on sleepimage file (created by hiberate):
If your Mac goes into hibernate and you don't plan to ever let that happen again (i.e. with desktop macs) you can save Gigabytes of disk space (especially important for SSD users) by removing the "sleepimage" file written when the mac hiberates. (This was covered here years ago in a 2009 post Tips for OS X SSD Users on Disabling Hibernate mode/deleting sleepimage file.) The sleepimage file is written to the /var/vm/ directory. Using the Terminal, cd to that directory and sudo rm the file to delete it. (Size of the Sleepimage file depends on amount of RAM installed.)
(Update) Sleepimage File Keeps Reappearing despite Hibernate Disabled:
I just noticed this recently (mini w/Mtn Lion 10.8.4) but I hadn't checked earlier for the sleepimage file 'reappearing' after deleting it. Regardless of hibernate mode being disabled and deleting the sleepimage file, it will later reappear. Deleted it via sudo rm (file located in /private/var/vm/ or /var/vm/) - ls check shows file is gone. I verify (via pmset) that hibernate mode is disabled yet the sleepimage file reappears - even if the mac had not been in sleep at all. In fact, I noticed the file was recreated again after a few minutes. (System/drives, even Display were set to never sleep - deleted the Sleepimage file, let the mini sit idle for 5-10 minutes (no wifi/internet connection active, only the terminal open). Checking /private/var/vm/ again showed the sleepimage file was back (with a new timestamp.)
My first thought was to create a small sleepimage file and write protect it, but curious if anyone has a better suggestion. (For now I'm just leaving it alone.)
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