Should my iMac hibernate automatically I've got a 2009 iMac (Intel Core 2 Duo) and I've noticed that the disks never sleep. I ran a power monitor and the iMac is using a third of our electricity every day!

I've checked via pmset that hibernatemode is set to 1 and when I purposefully click Apple > Sleep the iMac sleeps by saving state to RAM. However, if I just leave the device the screen sleeps but the disk never does.

I've unplugged all USB devices and made sure that bluetooth is not allowed to wake the device and that wake-on-lan is off

maxi:~ pauldambra$ pmset -g
Active Profiles:
AC Power        -1*
Currently in use:
 hibernatemode  1
 halfdim    1
 womp       0
 sleep      2
 powerbutton    1
 disksleep  2
 hibernatefile  /var/vm/sleepimage
 ttyskeepawake  1
 autorestart    0
 displaysleep   1


I'm pretty new to Macs and Unix so I'm not really sure how I go about checking what is keeping the disks awake (or indeed if I've understood how disksleep works on a mac)

Many thanks in advance

Paul
Your iMac should automatically spin down its disks and go to sleep.

Use the following command to view a detailed log showing your iMac's power history:

pmset -g log


Look out for applications that may be keeping your Mac awake and active. Applications and other processes can keep your Mac awake if they are providing a service, such as file sharing or remote access.

Do you have an active ssh session or terminal session running? This can also be responsible for keeping your iMac awake.

Be aware that Apple does not officially support hibernation on desktop Macs. Your setting hibernatemode suggests you have this feature enabled.

Disclaimer: I am involved with a commercial product called Power Manager, it can help make your Mac sleep more predictably.