To hibernate my system, all this time (for months) I have been using pmset -a hibernatemode 5. This was working great and I had no complaints.

However, recently I was checking out pmset's man page and it turns out there are no mode 5! In fact it instead recommends mode 25. Worried that my using the undocumented mode might harm my battery I have now moved to using mode 25. However, this has turned out to be far slower hibernate than mode 5.

So, can anybody tell me what exactly is mode 5 and how it is different from 25? Is it still safe to use? Why did Apple remove that from documentation?

I have MacBook Pro Early 2011 series, running Lion 10.7.5.


5 in binary is 0000 0101 - that is, bits 0 and 2 are set. If you read the pmset man page, it doesn't document any meaning for bit 2, so I suspect it doesn't do anything. If I'm right about this, mode 5 is equivalent to mode 1 (bit 0 only), which just enables hibernation. Mode 25 is binary 0001 1001, which enables hibernation (bit 1) with aggressive pageouts to minimize the sleepimage size.

I don't know of any problems that mode 5 should cause, but the undocumented bit 2 worries me a little. I'd be tempted to try mode 1 and see if that behaves the same. If it does, I don't see any real problem with using it...

  • Nopes behavior of modes 5 and 1 are not similar. – AppleGrew Jan 27 '13 at 10:42
  • @AppleGrew: In that case bit 2 is doing something undocumented, and I have no idea if mode 5 is safe to use. Therefore, I cannot recommend using it... – Gordon Davisson Jan 27 '13 at 17:42
  • Yup.. because of that I too have stopped setting that bit. However, before this I have using that for last 7-8 months without any apparent issue. – AppleGrew Jan 27 '13 at 18:01

It seems that the mysterious "bit 2" is for indicating whether to use secure memory in the sleepfile.

I don't know where this originated, but there are over a thousand results for the exact phrase,

"This is the same as mode 1, but it’s for those using secure virtual memory."

So I would assume it's somewhere in the documentation. Most of the people saying this are on forums, but I did find something a bit more reputable here,


EDIT: I would assume however, that perhaps the reason "bit 2" is no longer mentioned in the man page is that activating secure virtual memory encrypts the sleep image for you;
at some point I would like to test this theory though...

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