hoakley January 20, 2017 Macs, Technology

Power Management in detail: using pmset

The Energy Saver pane in System Preferences does not give you full access to all the capabilities of your Mac. Even desktop models have more than a dozen different controls to determine their sleep and related behaviours. The best way to gain full access, whether you’re trying to fix your Mac’s aberrant sleeping habits, or tweak something crucial, is to use pmset at the command line.

Inspecting

Macs differ in their power management capabilities, so the first command that you’ll need is
pmset -g cap
which lists what is available. On this iMac17,1, it runs to
Capabilities for AC Power: displaysleep disksleep sleep womp autorestart halfdim gpuswitch standby standbydelay powernap ttyskeepawake hibernatemode hibernatefile autopoweroff autopoweroffdelay

There is an additional system-wide power setting, DestroyFVKeyOnStandby, which determines whether the FileVault key is destroyed when your Mac goes into standy or hibernate mode. Normally that is set to 0, which preserves the key, but if you want to secure your encrypted hard disk, you will probably want to set it to 1: then waking it from hibernation will require the user to enter the FileVault passphrase, and if they fail to do so, they cannot try to recover the key from memory.

The meaning of these settings is generally obvious:

displaysleep is the time in minutes before the display is put to sleep; 0 indicates that the display is never put to sleep;
disksleep is the time in minutes before hard disks are spun down and put to sleep; 0 means never;
sleep is the time in minutes to system sleep; 0 means never;
womp is 1 if you want your Mac to wake when it receives a ‘magic’ network packet, which is the same as wake for network access in the pane;
autorestart sets whether your Mac will automatically restart when power loss has occurred and power has been restored;
halfdim sets whether an intermediate (rather than full) dimming is used for display sleep;
gpuswitch sets GPU behaviour during sleep, and appears to be undocumented;
standby sets whether to hibernate when a Mac has been asleep for a set period; this writes memory to disk and powers down memory;
standbydelay is the delay in seconds between going to sleep and switching to standby mode;
powernap sets whether your Mac will take Power Naps, where supported;
ttyskeepawake can prevent sleep when a text input, such as a remote login session, is active;
hibernatemode is set to 0 for plain sleep (desktops), 3 to store a copy of memory to disk and keep memory powered up (laptops), or 25 for full hibernation in which memory is powered down too;
hibernatefile sets the location of the cache to be used when going into standby mode, which must be on the boot disk;
autopoweroff sets whether to go into low-power sleep or standby mode;
autopoweroffdelay is the delay in seconds between going to sleep and going into low-power sleep or standby mode;
lidwake sets a laptop to wake when its lid is opened;
sms sets whether to use the Sudden Motion Sensor to park hard disk heads if there is a sudden jolt.

There are a couple of other settings which you can view using man pmset.

You can inspect current settings using
pmset -g
which here returns:
System-wide power settings: DestroyFVKeyOnStandby 0 Currently in use: standby 1 Sleep On Power Button 1 womp 1 halfdim 1 hibernatefile /var/vm/sleepimage powernap 0 gpuswitch 2 autorestart 0 networkoversleep 0 disksleep 0 sleep 0 autopoweroffdelay 28800 hibernatemode 0 autopoweroff 0 ttyskeepawake 1 displaysleep 180 standbydelay 10800

UPS

If you have a supported uninterruptible power supply (UPS) connected, you can check its settings using
pmset -g ups
which will typically return something like
UPS settings: haltlevel off 0 haltafter on 2 haltremain off 0

The three settings here are:

haltlevel – the % battery level at which to start an emergency shutdown,
haltafter – the time in minutes after switching to UPS power at which to start an emergency shutdown,
haltremain – the remaining time in minutes available on UPS power at which to start an emergency shutdown.

So according to my settings above, when my Mac is running off its UPS battery, it will start making an emergency shutdown after two minutes on that supply. These match the settings you can make in the Energy Saver pane.

Even though you might have your laptop connected to a UPS, portable Macs do not use UPS emergency shutdown settings; in the event of power outage, including the UPS shutting down during a prolonged mains failure, laptops use their internal batteries and follow their own sleep and shutdown settings instead.

You can also schedule automated power on, shutdown, wake, and sleep events, which are detailed in man pmset.

Setting

Using pmset to change Power Management settings requires you to have elevated privileges, so must be prefaced by sudo. For example, to set a Mac so that it destroys its FileVault key when going to standy/hibernation mode, you should enter
sudo pmset -a DestroyFVKeyOnStandby 1
then authenticate with your admin password.

When setting values, you will normally need to specify which group of settings are to be affected. This is determined by options:

-b changes a setting when on battery power (laptops),
-c changes a setting when on charger (mains) power (laptops),
-u changes a setting for the UPS, as detailed above,
-a changes a setting for all circumstances (laptops and desktops).

To set the time before a Mac goes to sleep to 20 minutes, you can therefore use the commands

sudo pmset -b sleep 20 for a laptop running off its internal battery,
sudo pmset -c sleep 20 for a laptop running off its mains charger,
sudo pmset -a sleep 20 for any Mac and all circumstances.

If you get the settings into a mess and don’t know what to do,
sudo pmset restoredefaults
should work just like the button to restore defaults in Energy Saver (which you could use instead), and sets everything back to the default settings for that model.

To set a desktop Mac to start emergency shutdown when it has been running on UPS power for 5 minutes, you would use
sudo pmset -u haltafter 5

There are a couple of other useful features in pmset:

pmset resetdisplayambientparams
will reset the ambient light parameters for those Apple displays which support ambient light adjustments;

caffeinate
can create an ‘assertion’ in OS X / macOS which will prevent sleeping of a particular system. It is fully documented by man caffeinate

Like the Energy Saver pane, settings are stored in a preference file, and acted on through the Power Management system and your Mac’s power management hardware. Until recently (Sierra 10.12.2), settings have been kept in /Library/Preferences/SystemConfiguration/com.apple.PowerManagement.plist, with scheduled events in /Library/Preferences/SystemConfiguration/com.apple.AutoWake.plist. However, in 10.12.2 the former file has moved back to /Library/Preferences/com.apple.PowerManagement.plist for unknown reasons, and in 10.12.3 the file is now named PowerManagement.[UUID].plist, where [UUID] is replaced by your hardware UUID.

They are also shown in the Power item in System Information (About This Mac, then click on System Report).

Diagnostics

You can use pmset to diagnose odd sleep behaviour in laptops. For example, if your MacBook Pro seems to keep going to sleep suddenly when it has less than 50% of its battery remaining, open a window in Terminal and type
pmset -g pslog

Then when the problem next occurs, wake your Mac and look for sudden falls in the indicated power remaining, such as a drop from 30% to almost nothing. These are typical of an ageing battery which needs to be replaced.

(Updated 23 January 2017 for 10.12.3)

18Comments

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1

Alex Santos (@_alex_santos) on February 20, 2017 at 11:56 am

Great article! You have one heck of a site. Packed with news. How do you do it?

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- 2
  
  hoakley on February 20, 2017 at 12:11 pm
  
  Thank you.
  I have written Mac Q&A sections for a very long time – first for MacUser, the UK magazine, and now for MacFormat. I therefore have to keep on top of all this information, something that I enjoy doing anyway. So why not share the information to help others?
  Howard.
  
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3

Manoli on February 28, 2018 at 3:30 pm

Dear Howard,

maybe i missed that in your article but could you please explain the difference between low-power sleep and standby mode?

Some machines have set both, like my iMac have autopoweroff set by default to 1, but also standby 1, autopoweroffdelay 28800, standbydelay 10800 and hibernatemode 0.

I’m a bit confused now what and when will actually happen? Looks like it’s kind of mix of everything and I cannot identify which settings have priority?

Otherwise great stuff all over here, I really enjoy this site a lot, thanks Howard, bye bye.

Manoli

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- 4
  
  hoakley on February 28, 2018 at 4:05 pm
  
  Thank you.
  For a desktop Mac (normally), you have three sleep levels. ‘Plain old sleep’, in which hibernatemode = 0, maintains power to memory, and wakes using the contents of memory. Hibernation, in which hibernatemode = 25, writes the contents of memory to disk and powers down memory. When waking, memory has to be powered up, its contents restored from disk, and it is thus slower. The third option is very similar, but designed to comply with a European Directive – again, memory contents are written to a hibernation image and memory powered down. There may be some additional chipsets which are powered down, beyond those in normal hibernation.
  Laptops normally have hibernatemode = 3, which is in between 0 and 25, in that memory is not powered down.
  Apparently, hibernatemode = 25 is only set by pmset.
  With your settings, after the standbydelay period of normal sleep, your Mac will go into one of the two deeper sleep modes, in which memory contents are written to a hibernation image and memory is then powered down. Because your autopoweroffdelay is longer than standbydelay, it shouldn’t have any effect.
  This assumes that your hardware supports these modes. Many don’t!
  Howard.
  
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5

Joss on August 30, 2018 at 10:49 pm

I’m still trying to wrap my head around this. For security reasons I want to hibernate (safe sleep) almost immediately on my 2018 MBP, and also destroy the FileVault keys, so that’s pm setting 25 for hibernate (safe sleep) and 1 for DestroyFVKeyOnStandby, then for hibernation to work also set standby to 1. For accidental sleep, I have a standbydelay of 10, and maybe I’ll go a little higher later. I’ve set powernap to 0, because I’ve read about problems in this context. I’ve set autopoweroff to 0, because hibernation with FVKey destruction is enough imho. I don’t think you need both. (But I’m not sure I correctly understand the differences between the two modes.) I’m still testing a couple of settings, because I’ve experienced bridgeOS panics & hard reboots after waking from hibernation after a couple of hours. I currently still have womp set to 1, and ttyskeepawake as well. Don’t know if this can cause problems in terms of magic packets making the MBP try to wake from hibernation and fail, because it can’t load the FileVault key without user interaction. But how could a Mac wake due to network access if it’s hibernating, i.e. powered down? In normal sleep, yes, but safe sleep? Anyone know the optimal settings for secure sleep, i.e. load RAM contents to disk (hibernate) and destroy FileVault key? (High Sierra or Mojave)

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- 6
  
  Joss on August 31, 2018 at 7:03 am
  
  I’ve found this: https://github.com/bfleischer/hibernate:
  
  Quote (Apple): “Portable Macs with Wake on Demand enabled will only wake on demand if they are plugged into power, and either the built-in display is open or an external display is attached.”
  
  Quote (@bfleischer): “But the above statement does not apply to hibernation mode. When in hibernation mode, a portable Mac will wake up in regular intervals to broadcast its Bonjour services to a local Bonjour proxy (even if there is none) despite not being plugged into power or the lid being closed. To prevent this from happening, the “Wake on Demand” feature is disabled while in hibernation mode.”
  
  And that’s (probably) what causes the bridgeOS panics: MBP wants to wake from hibernation, FileVault key is destroyed, can’t reload key because user is afc, ergo panic. Strange thing is that my MBP works fine at first, accepts the FileVault key, but then only crashes while reloading the previous state.
  
  Another headscratcher is this: http://bendeegan.com/2016/04/19/how-to-make-a-mac-hibernate-properly-and-consistently/ … the author says that the proper hibernation would be by setting standby to 0. So standby seems to be a different thing from hibernation (safe sleep).
  
  I’ll first test the womp 0 setting, but that would mean that Find My Mac stops working. So you gain & you lose some security with hibernation.
  
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- 7
  
  hoakley on August 31, 2018 at 7:12 am
  
  I wish you success: I have the feeling that sometimes, no matter what you set, the SMC tries to fit that with its idea of what it will or can do, so you end up with its behaviour even though that may not be quite what you wanted. This seems very model-specific.
  Howard.
  
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8

Joss on November 15, 2018 at 10:22 am

Mojave changed something again, actually a nice new feature in pmset. You now have a highstandbythreshold, which is set to 50 by default (i.e. 50 percent battery capacity). Instead of one standbydelay argument you now have two: standbydelayhigh and standbydelaylow. If you’re above 50, the high delay is used, if you’re below 50 percent battery, the low delay kicks in.

What I noticed, though, is that this new setting seems to disable safe sleep (standby a.k.a. hibernation) when the AC is plugged in. But there might be a solution: so far I’ve successfully tested AC-hibernation twice after setting the highstandbythreshold to 100. But this needs to be tested further. (In case people are wondering: if you have FileVault enabled, and if you pmset to destroy FileVault keys on standby, then hibernation is a great security measure; and wake from safesleep is super-fast on Macs with NVMe SSDs.)

PS: the autopoweroff arguments were all removed in Mojave, which is a thankworthy move by Apple, because that was the same thing as safesleep, just named differently because of some European regulation, and it only caused confusion.

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- 9
  
  hoakley on November 15, 2018 at 10:37 am
  
  Thank you.
  This is the problem with pmset and the Energy Saver pane: there are complex interactions which seem to vary with different models, making behaviour something of a gamble. It also isn’t helped by the almost complete lack of documentation, leaving us guessing at so much, or just having to try it out and see.
  Howard.
  
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10

Daniel Cohen on December 10, 2018 at 3:35 pm

I have just got a 2018 Mac Mini, and am trying to solve some problems with it not sleeping. The Energy Saver panel is as you show it (rather than the older form which has separate sliders fo display and system sleep). pmset shows sleep 1. That can’t possibly have the meaning the manual shows, as that would be system sleep after 1 minute. I suspect it is means system sleep 1 minute after display sleep.
I might ask you about my specific problem later.

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- 11
  
  hoakley on December 10, 2018 at 3:55 pm
  
  What does it say in System Information’s Power info? That explicitly states the various sleep timers in minutes. pmset may not (yet) be fully reliable with new hardware, perhaps.
  If you can’t make sense, I’d try an SMC reset. If that doesn’t solve it, it’s time to contact Apple Support, and hope that they have finally got their minis to work on.
  Howard.
  
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  - 12
    
    Daniel Cohen on December 10, 2018 at 5:48 pm
    
    That says System Sleep Timer (minutes) 1, which agrees with pmset. And Display Sleep Timer and Disk Sleep Timer both show 10 minutes. Which, on the face of it, makes the system sleep before the display does.
    
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- 13
  
  Joss on December 10, 2018 at 7:48 pm
  
  Right. System sleeps after 1 minute (regular sleep), unless a running process is overriding that setting, and display sleeps after 10 minutes, so the display sleep setting is irrelevant, unless you have a process that is overriding regular sleep. Please also note that the standby delay (high & low), i.e. the time the system goes from regular sleep into safe sleep (hibernation/standby), is in seconds, not minutes. The “standby” setting itself only knows 0 (off) and 1 (on).
  
  Generally speaking, sleep (regular & safe sleep) can be prevented by tty, network activity etc., so you might tweak the settings for powernap, womp, tcpkeepalive & ttyskeepawake. (I’ve set them all to 0 = off.)
  
  Weird thing, though: on my system pmset totally ignores lidwake 0. My MBP still wakes when I open the lid. I’ve tried to replicate my user pmsettings in Recovery Mode, too, but that didn’t help.
  
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  - 14
    
    hoakley on December 10, 2018 at 8:25 pm
    
    Thanks, Joss. I think you’re seeing the gap between what pmset thinks it can do and what your MBP will do, no matter what is set. This is the frustrating think about power management – ultimately, your Mac is going to do what its SMC says.
    Howard.
    
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  - 15
    
    Daniel Cohen on December 10, 2018 at 8:41 pm
    
    I still find it confusing, I guess because I would expect the display to be off if the system is asleep but that doesn’t seem to happen, but I think the Energy Saver and pmset settings are actually confusing.
    
    What I have seen is this. If in Energy Saver “Turn Display off after” is set to one’s choice of (say) 11 minutes, then both Power (in System Information) and pmset show Sleep and DisplaySleep as 11, which is what one would expect. But if you then Restore Defaults, you get Sleep 1 minute, Displaysleep 10 minutes. And if you try to use pmset to set the Sleep time it complains if this is less than the Displaysleep time.
    
    All this is interesting, but what I am really after is to find out why my Mac won’t sleep.even when I choose Sleep from the menu .It’s a 2018 Mac Mini, with several external drives connected through a Thunderbolt 1 dock and so need ing a Thunderbolt 3 to 2 adapeter. Most of the time it just won’t sleep. I thought I had solved the problem at one point when it was working ok, but after a restart it went wrong again. But this does suggest (since it was right for a while) a software problem rather than something to do with a drive or other peripheral.
    
    I can tell things are wrong even with the display off by several clues. First of all, approximately every minute my external speakers give a pop or two and I can see the lights on a hard drive going on and off. Second, I play music through a Squeezebox, which is connected through wifi. If the Mac is not asleep, the Squeezebox display shows date and time, but it goes dark when the Mac is asleep. That makes for a very easy way of seeing if the Mac is asleep, especially as the Squeezebox is in my sitting-room and the Mac is in another room.
    
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    - 16
      
      hoakley on December 10, 2018 at 11:45 pm
      
      I suggest in the first instance you strip your system down to bare essentials, with as few peripherals and external drives as possible. See if it sleeps reliably then. If it doesn’t, you need to contact Apple soonest.
      If a stripped-down system works OK, progressively reassemble it and see what makes the difference – it may be one of your peripherals.
      Howard.
      
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    - 17
      
      Daniel Cohen on December 11, 2018 at 8:55 am
      
      I tried that and thought I had an answer, but then I tried a second time and got inconsistent results. I guess I’ll just have to put several hours aside and try again and make detailed notes. But, as I said, I had at least one occasion after a restart when all was well, which inclines me more to thinking it is a software issue.
      
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18

seajayess on March 4, 2019 at 1:03 am

Howard,

Thank you so much for this post.

many kind regards,

Chris

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