iMac restarts instead of shutting down

Hope someone suggests a solution. I have the same problem with my 24" iMac using Snow Leopard. It will do it after automatic shutdown. After restarting, and completing the boot up, it will then shutdown properly.

I am having the exact same issue with my Mac Pro and Snow Leopard. I've tried everything you listed above including unplugging all usb and firewire devices (excluding the mouse & keyboard), reformatting my hard drive and reinstalling a clean OS X 10.6.2 all to no avail. Nothing helps. Hopefully someone from Apple will figure this out as it seems to be something of a common problem in these posts...

I found that deleting the file:

/Library/Preferences/SystemConfiguration/com.apple.Boot.plist

corrected the problem for me. So far, it shuts down properly since then.

My /Library/Preferences/SystemConfiguration/ folder does not contain this file at all. Could this be a problem?

If you have any USB (or FireWire) devices connected to the iMac's ports (including any hubs), try disconnecting everything. If you have standard wired USB keyboard/mouse, you can leave those connected. Then try shutting down.

I've tried that. I've reset the smc @ pram. I've reformatted my hdd and reinstalled snow leopard. Nothing seems to work!

Try starting up from your Mac OS X installation disc; insert disc and restart with the C key held down. When you get to the first Installer screen, try shutting down from there. Does it shut down, or does it still restart.

It does not restart if I boot from my OS X installation CD. When I boot up normally, it will restart when I try to shut down about 75% of the time. It does power down correctly 25% of the time. I have tried just about everything including a clean reinstall of OS X after reformatting my hard drive.

So I don't think it's a hardware problem, if you are able to shut down without this problem when booted off the installation disc. But it is odd that, if you did an erase and reinstall, and BEFORE installing any other third-party software, this problem still recurred. And it is strange that the problem does NOT occur part of the time.

Two other tests to hopefully narrow down the cause further:

(1) Do a +Safe Mode+ startup

http://support.apple.com/kb/HT1455

This will start up with only the essential Apple system extensions loaded. Then, try to shut down.

(2) Create a new admin user account in System Preferences Accounts pane

http://docs.info.apple.com/article.html?path=Mac/10.6/en/8235.html

Log out and log in to the new account. Then, try to shut down, from the new account.

Kenichi,

It seems to shut down normally from safe mode and from the new account. Any suggestions from here?

If it does not happen in the new account (you should try it a few times to make sure), then the cause is usually one of two things, and there is probably not anything wrong with the overall system.

First is a background process that runs in your normal account. Check System Preferences Accounts pane +Login Items+ tab. Remove anything there that you no longer need to have running. Then, with what's left, remove one at a time and test to see if it makes a difference; make sure you note what you removed (and where it is located) so that you can put it back if it was not the cause.

Second are user preference settings. In this case, this is a bit harder to trouble-shoot, because I can't think of any particular user preference file that would make a Mac restart instead of shut down.

If the problem does not happen in a new account, and you can't determine the exact cause, one thing you could do is create a new user account for ongoing permanent use, and transfer your user data from your current account to the new account. Eventually, once everything is working fine, abandon your current account.

Deleting those 3 files, then restarting for regeneration, worked for me :
/Library/Preferences/SystemConfiguration/com.apple.Boot.plist
/Library/Preferences/SystemConfiguration/com.apple.PowerManagement.plist
/Library/Preferences/SystemConfiguration/com.AutoWake.plist

Hey Manuk,

Can you confirm if the problem has come back again after deleting those three files? Has this solution held steady? Thanks.

Also to note...I have a MBP and after deleting the recommended 3 files and shutting down once only com.apple.PowerManagement.plist ended up regenerating. Started up fine and a little faster too. Guess I'll hang onto my backups just to be safe.

This solution works fine.

For me only PowerManagement were regenerated, but I think if I modify boot and wake-up options, other files while be created too.

My bad for dyslexic'ing your name man. Flipped the "U" and "A" like a blind dummy. Cheers for the response nonetheless.

Yup. So far deleting those 3 files has cured the Shut Down/Restart issue on my MBP (late 2009).