To allow hibernate mode, you should have the same mount of free space as physical memory plus 750Mb.
Here are possible values:
hibernatemode 0 = suspend to RAM only (default on desktops) hibernatemode 1 = suspend to disk only hibernatemode 3 = suspend to disk + RAM (default on laptops)
To see your current hibernatemode
# pmset -g | grep hibernatemode
So, to enable Sleep Safe, open a Terminal console (spotlight search for Terminal) and enter
# sudo pmset -a hibernatemode 3
It will ask for your password to run this command, and create /var/vm/sleepimage file containing a dump of your memory when you will close the laptop.
With this option, it will now enter regular Sleep mode first (consuming minimal power). It will only enter Safe-Sleep if the battery is very low, or is unplugged.
If you prefer to skip regular sleep, and use deep mode instead (note: it takes a few seconds more to sleep and wake-up) enter:
# sudo pmset -a hibernatemode 1
To disable Safe Sleep:
# sudo pmset -a hibernatemode 0
The Mac does not need to be restarted to set the changes to hibernate mode.
Put the Mac to sleep and wait for the light to start pulsing, in new models it won’t show you any light. Wait until you won’t hear any noise. Wake it normally (by hitting the space bar for example).
Open Console and view system.log, or simply open the file /var/log/system.log.
Look for a line indicating that the process worked. It is similar to:
Nov 11 12:15:33 computername kernel: System SafeSleep