How could a Mac fully Restart itself after a power cut?

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How could a Mac fully Restart itself after a power cut?

After a power cut, my Mac fully Restarted itself, skipping the expected Log-in process.

FYI, this is a Retina 5K, 27-inch, 2019 iMac running macOS Sequoia 15.7.9… though I have no idea what difference that might make…

I expected the Mac to Restart itself so far as to present me with a Log-in window but what I got was in effect a complete return to the previous working state, with no Log-in or other security process.

My Mac re-opened all its previous apps, which I thought should be impossible.

'In effect a complete return…' here means at least one app, Google Chrome, opened only so far as to ask whether I wanted to re-open previous Windows. That's exactly what I'd have expected if the only problem had been re-launching Chrome after that app alone had crashed and again, how could my Mac have got that far by itself?

My second, older iMac, failed to Restart at all, about which I have no query… I don't happen to remember what response I'd asked of that one in the event of a power cut…

iMac 27″, macOS 10.13

Posted on Sep 12, 2026 1:59 PM

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Answer 1

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PreCognition

Level 6

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Sep 12, 2026 2:26 PM in response to Robbie Goodwin

That can happen if two separate settings are involved.

First, the iMac can be set to restart automatically after a power failure. Second, if automatic login is enabled, macOS can continue into the user account without stopping at the login window. It can then reopen apps from the previous session. Chrome asking whether to restore its windows would be consistent with an unexpected shutdown.

I’d check System Settings > Users & Groups > Automatically log in as, and also whether FileVault is enabled. With FileVault enabled, automatic login isn’t available.

One detail is a little confusing: you mention Sequoia 15.7.9, but the post is tagged macOS 10.13. Which version is actually installed on that iMac?

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Answer 2

Sep 12, 2026 3:20 PM in response to Robbie Goodwin

You’re right on both points.

The “restart automatically after a power failure” setting explains why the Mac started again, but not why it apparently got past the login screen.

And automatic login wouldn’t normally be something that happens only after a power cut. If a normal restart usually stops at the login window, then my earlier explanation doesn’t account for that part.

The apps reopening is separate: after an unexpected shutdown, macOS can use the last “Reopen windows when logging back in” setting, so Chrome’s behavior makes sense. But if **Automatically log in as** is Off and the Mac really did reach your desktop without authentication, I’d regard that as the part still needing an explanation rather than normal restart behavior.

Apple describes the app-reopening behavior here:

Prevent apps and windows from reopening on Mac - Apple Support

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Answer 3

den.thed

Level 10

97,502 points

Sep 12, 2026 3:21 PM in response to Robbie Goodwin

How long was the power cut off...?

Does it go back to your desktop if the power is cut off for 30 seconds..? 1 minute...?

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Answer 4

leroydouglas

Level 10

207,038 points

Sep 13, 2026 9:40 AM in response to Robbie Goodwin

Robbie Goodwin wrote:

After a power cut, my Mac fully Restarted itself, skipping the expected Log-in process.

FYI, this is a Retina 5K, 27-inch, 2019 iMac running macOS Sequoia 15.7.9… t

To be proactive you can file a bug report / submit your feedback here: Feedback - macOS - Apple

Feedback - macOS - Apple

You might expect to see this after a pending automatic point-update or macOS upgrade returning you to a previous state of the user account...

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Answer 5

Robbie Goodwin Author

Level 6

19,971 points

Sep 12, 2026 3:18 PM in response to PreCognition

Thanks and two things:

First, do you really think this Question could have arisen if the Mac was not set to restart automatically after a power failure?

Second, will you say how automatic login could continue into the account without stopping at the login window only following a power cut, and not in any other circumstances?

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Answer 6

Robbie Goodwin Author

Level 6

19,971 points

Sep 14, 2026 12:45 PM in response to PreCognition

Thanks, Everyone.

I apologise for lumping so much together and I hope everyone agrees, it's better not to split a Thread into separate streams…

Thanks, PreCognition. Yes, my Mac really did reach the Desktop without authentication, and I'm glad you agree that still needs an explanation.

I hope everyone knows, the Link provided won't help.

Now that PreCognition has clarified my OQ, I still hope to concentrate on whether anyone else has shared my particular experience and whether anyone has a specific explanation.

Thanks, Leroydouglas. I take your suggestion as well meant, and I'm sorry I failed to point out that since System 6, nearly 40 years ago, I've seen many dozens of Macs recover after power cuts and this is the sole instance of a recovery proceeding that far.

If Apple knew about a significant number of cases under whatever OS, that should have been incorporated into exactly such resources as the link provided.

That being so, how seriously do you suppose Apple would take a bug report about a single case, observed as a simple fact without supporting details? Doesn’t the nature of the incident suggest ’supporting details…’ could be available only to deep-level techie User and even then, largely only with prior notice of the event?

You might expect to see what I saw after a pending automatic point-update or OS upgrade but I never would. Can you cite a specific UD/UG?

Thanks, Den.thed. Will you say what difference the length of any power cut could make, please? Are you suggesting time might make my Mac see a Restart after a power cut differently than a commanded Restart?

A commanded Restart should not, and a power-cut-enforced Restart very well might introduce problems but how might time matter?

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Answer 7

Robbie Goodwin Author

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19,971 points

Sep 12, 2026 3:11 PM in response to PreCognition

Thanks and the version actually installed on that iMac is Sequoia 15.7.9, but apart from simple accuracy, how might that make a difference?

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