MacBook – Difference between autopoweroff and standby in pmset

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I just got a new Retina MacBook Pro 15". After getting some downloads interrupted due to the computer going to sleep (even on AC power), I started looking at the man page for the pmset command. I did solve my original problem with sleeping but a few options piqued my interest. In particular, here's the description for the autopoweroff setting from the man page:

autopoweroff – Where supported, enabled per default as an implementation of Lot 6 to the European Energy-related Products Directive. After sleeping for autopoweroffdelay minutes, the system will write a hibernation image and go into a lower power chipset sleep. Wakeups from this state will take longer than wakeups from regular sleep. The system will not auto power off if any external devices are connected, if the system is on battery power, or if the system is bound to a network and wake for network access is enabled.

And then there's the standby mode:

standby causes kernel power management to automatically hibernate a machine after it has slept for a specified time period. This saves power while asleep. This setting defaults to ON for supported hardware. The setting standby will be visible in pmset -g if the feature is supported on this machine.

standby only works if hibernation is turned on to hibernatemode 3 or 25.

standbydelay specifies the delay, in seconds, before writing the hibernation image to disk and powering off memory for Standby.

Now maybe I'm just being thick, but both options seem like they do essentially the same thing. The main difference I see is that standby requires a specific hibernatemode.

Concretely, the way I'd like to configure my computer is for it to do a RAM-only sleep (exactly like hibernatemode 0 does) when first closing the lid, so that it quickly goes to sleep, without writing the RAM contents to disk immediately. However, if I leave the computer sleeping with the lid closed for a certain number of hours (say 4 hours), I'd like it to only then write the RAM contents to disk and power off the computer, so as to save battery in case of an extended sleep. Ideally, I'd also like the second part (writing RAM to disk and power off) to happen only if the computer is running on battery power.

The reasoning here is that, for me, the common use case for sleeping is taking the computer from home to work and back, and there's no point in slowing down the sleep process and wasting SSD write cycles (as well as slowing down the wake-up process, if it does hibernate) if I'm just going to wake it up again in less than an hour; also, since the time it spends sleeping is so short, not much battery would be saved by shutting the computer down for such a short period.

How should I configure the hibernatemode, autopoweroff, autopoweroffdelay, standby and standbydelay options to achieve this behavior?

Best Answer

The autopoweroff feature is also mentioned in http://support.apple.com/kb/HT1757:

With the release of the OS X Mountain Lion v10.8.2 supplemental update 2.0, a new feature was introduced to enter safe sleep after four hours of the computer being connected to AC power. This is an effort to comply with the European Energy Standards (ErP Lot6). This will only occur if there is no wireless or Ethernet activity and no activity from external devices such as USB storage devices.

This is normal behavior for the following models:

  • MacBook Pro (Mid 2012 and later)
  • MacBook Pro (Retina, Mid 2012 and later)
  • MacBook Air (Mid 2012 and later)
  • iMac (Late 2012 and later)
  • Mac mini (Late 2012 and later)

Standby mode is documented in http://support.apple.com/kb/ht4392:

Macs that can use standby mode:

  • MacBook Pro (Retina, 13-inch, Late 2012) and later
  • MacBook Pro (Retina, 15-inch, Early 2013) and later
  • MacBook Pro (Retina, Mid 2012)
  • MacBook Air (Mid 2010) and later
  • SSD and Fusion drive versions of Mac mini (Late 2012) and later
  • SSD and Fusion drive versions of iMac (Late 2012) and later

Mac computers manufactured in 2013 or later enter standby after three hours of "regular" sleep. Earlier computers activate after just over an hour of "regular" sleep.

To enter standby, the computer must:

  • Be running on battery power (if it is a Mac notebook computer).
  • Have no USB devices attached.
  • Have no Thunderbolt devices attached.
  • Have no SD card inserted.
  • Have no external display attached.
  • A computer with a fully charged battery can remain in standby for up to thirty days without being plugged in to an AC power source.

The state of the computer is saved to the flash storage (SSD), then the power to the hardware subsystems turns off to increase the length of the standby. For example, RAM memory and the USB bus are powered off during the standby.

So standby mode and autopoweroff are supported by different models of Macs and they are enabled under different conditions. Standby mode was introduced in 2010 and it was initially only supported by MacBook Airs, but it is now supported by all new Macs except Mac Pros, iMacs with no SSD, and Mac minis with no SSD. autopoweroff was introduced in 2012 and it is supported by all new Macs except Mac Pros.

I don't know if the state of being in standby mode is different from the autopoweroff state. A gray screen with a progress bar is shown when a Mac wakes up from both states.

Note that Apple has used "safe sleep" to refer to both the hybrid sleep and hibernation mode that laptops use by default (like in http://support.apple.com/kb/PH11096) and to the hibernation-only state (like in the first block quote above).

Even if you set standbymode to 0 and disable standby mode and autopoweroff, you won't waste that much energy. New laptops use about 0.7-1W of energy in sleep mode and about 0.2-0.3W when off or in hibernation mode.

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