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Apple Mac OS X tips and tweaks

Date: 10th April 2011

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Change hibernation mode settings on MacBooks

There is an interesting command you may not have come across called pmset and it has lots of useful functions. You may not have met it yet because it can only be used from a Terminal window and some people never use the Terminal. You should though, because you can do some powerful things with it.

You can see Apple's documentation for the pmset command here, but don't worry if it looks complicated because we will examine one simple function here. Pmset is short for Power Management Settings and one of its functions is to set the way that the Mac or MacBook sleeps. There are two ways that it can do this and it can keep RAM alive, but at the cost of using a bit of power, or it can completely power off. When a Mac or MacBook is woken from sleep mode with a keypress or the power button, it carries on exactly where you left off with all your applications running and windows open. If the Mac sleeps with the RAM alive then it can resume more quickly. If you completely power off then you save power, save battery charge on MacBooks, and it is environmentally friendly when the Mac is to be sleeping for extended periods. The choice is yours.

Hibernate mode 0

Hibernate mode 0 powers down most internal components to save energy, but the contents of RAM is kept powered up. This means the Mac can be woken quickly, but if there's a power cut you'll lose the contents of RAM, which may include unsaved documents or information. It's the default for desktop Macs. Run Terminal in the Utilities folder and enter: sudo pmset -a hibernatemode 1

Hibernate mode 3

Hibernate mode 3 is the same as mode 0, but the contents of RAM are also saved disk. It's the default for MacBooks. When waking from sleep mode the MacBook just powers up and carries on like a desktop Mac, but if the battery ran out in sleep mode and the contents of RAM was lost, it reloads it off the disk. You can use this mode for desktop Macs too for extra security. Run Terminal in the Utilities folder and enter: sudo pmset -a hibernatemode 3

Hibernate mode 25

Hibernate mode 25 saves the contents of RAM to disk and then shuts off the power completely. No power is consumed in sleep mode and so it makes MacBook batteries last longer and is more environmentally friendly for desktop Macs because no power is consumed. It takes longer to put to sleep and longer to wake up because RAM has to be saved to disk and read back, but you may consider it a small price to pay for the benefits. Run Terminal in the Utilities folder and enter: sudo pmset -a hibernatemode 25


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