Mac OS X provides a hibernation feature, which allows you to save the current state of the system to memory or the hard drive. You might wish to use this feature if you are going to be away from the system for awhile and don't want to close all of the applications you have open or you can't power the system from a wall electrical outlet and wish to conserve battery power.
OS X supports five different hibernate modes. The default mode is "3", which means when you put the system to "sleep" it saves the current state of the system to Random Access Memory (RAM), blanks the display, and goes to a low power consumption state.
- 0 - Old style sleep mode, with RAM powered on while sleeping, safe sleep disabled, and super-fast wake.
- 1 - Hibernation mode, with RAM contents written to disk, system totally shut down while “sleeping,” and slower wake up, due to reading the contents of RAM off the hard drive.
- 3 - The default mode on machines introduced since about fall 2005. RAM is powered on while sleeping, but RAM contents are also written to disk before sleeping. In the event of total power loss, the system enters hibernation mode automatically.
- 5 - This is the same as mode 1, but it‘s for those using secure virtual memory (in System Preferences –> Security).
- 7 - This is the same as mode 3, but it‘s for those using secure virtual memory.
You can determine the current hibernate mode by opening a Terminal window
(use the Finder to go to Applications then Utilities
then double-click on Terminal) using
pmset -g | grep hibernatemode.
$ pmset -g | grep hibernatemode hibernatemode 3
You can change the hibernation mode by using sudo pmset -a
hibernatemode n where n is one of the above integers
representing a supported hibernation mode. E.g., to write the current state
of the system, which includes the open applications and files in memory,
to the hard drive and completely shut down the system, you can set the
hibernatioon mode to 1. This is akin to hibernate mode on a
Microsoft Windows system.
$ sudo pmset -a hibernatemode 1 Password: $ pmset -g | grep hibernatemode hibernatemode 1
To put the system in hibernation, you can click on the Apple icon in the upper, left-hand corner of the screen and select Sleep. The system will then be put in the selected hibernate mode.
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