Sleeping M4 iMac shuts down and hard to reboot

Since Tahoe (now 12.6.1) has been installed, on two occasions when I try to awaken my sleeping M4 iMac I find it is shut down. I then find it is difficult to start it up again. It is reluctant to get to the login page, and then when I get there with some fiddling (try again, etc.) it is reluctant to start up. When I try that again the computer requires two or three logins, and then finally on line with home screen and all working OK.

I do realize that a brief ac electric power loss could lead to the sleeping computer's shutdown, but it has happened twice now. And was hard to start up both times as described above, which leads me to believe something else is going on.

Has anyone else seen this? And if so, do you know of a fix? And how best to restart the computer without the difficulties I mentioned above if it does happen?

iMac 24″, macOS 26.0

Posted on Oct 28, 2025 11:01 AM

Top-ranking reply

jimpal Author

Level 2

232 points

Posted on Nov 3, 2025 7:22 AM

BopCat, I think you have provided the best help for me to solve my shutdown when sleeping, and difficult restarts issue. I have two drives attached to my M4 iMac, one for Time Machine, and one for SuperDuper backups of my whole computer. The first is about 8 years old, and the second is probably 12 years old.

Since I don't know which one may be causing the problem, I will have to test a bit. I have already disconnected the older drive and tried two shutdowns and restarts. They were totally fast and normal this time, which may mean I have identified the culprit. Of course, I won't know for sure until I have operated this way for a time, and see if the shutdowns no longer occur when my computer is sleeping. If that shutdown problem reoccurs, of course, I will try operating with only the newer drive I use with Time Machine disconnected to see what happens then.

Thanks for your post. I think it is the one which offers the solution to my problem. We will see.

View in context

19 replies

jimpal Author

Level 2

232 points

Nov 5, 2025 4:12 PM in response to BopCat

Sorry to learn that you are still having these problems. It looks like it goes beyond your having a faulty drive connected.

Now I'm not sure that is my problem either. Even though I thought it was in my most recent post. All is working perfectly for me now with both drives connected. I was going to use that setup to troubleshoot, and disconnect the drives one at a time if more shutdown and booting problems occur. Now it looks like I have a dreaded intermittent problem that will return when I will least expect it.

I've gone out of my way to use both drives more as part of my troubleshooting. Perhaps the bad acting culprit just needed some exercise.

I will post again when and if my problem shows up again. And I will bet it will.

BopCat

Level 1

58 points

Nov 6, 2025 8:44 AM in response to Owl-53

FYI - my 2nd partition was named “Passport_CCC”. It was a while ago, but I believe I was meaning to use your CCC (I have it - works great), but not sure I did. It was suggested there might be an issue with any special characters, so I renamed it (Disk Utility recovery mode) to Passport C, and renamed the other partition from Passport to Passport (same name). After erasing the Passport Time Machine partition I was finally able to mount the Passport C drive using WD Utilities. Even that didn’t work for days, but I was finally able to mount just the Passport C drive, and files are slowly downloading as we speak.

Owl-53

Level 10

102,439 points

Nov 6, 2025 9:32 AM in response to BopCat

From Carbon Copy Cloner is regards to using 1 Physical Drive for More than One Purpose

Follow the guidance of CCC's Backup Volume Setup Assistant

The Backup Volume Setup Assistant is designed to get your backups started off on the right foot. This assistant asserts that the destination will be used exclusively for this backup task, and offers alternative options if the selected volume cannot be used exclusively. This assistant also takes care of volume formatting, snapshot support, and makes it easy to enable encryption (which is optional).

BopCat

Level 1

58 points

Nov 5, 2025 2:32 PM in response to Owl-53

Multiple backups of everything was messing me up. I’d open a backup file by mistake because an identical folder showed up in finder.

Sleeping M4 iMac shuts down and hard to reboot