macOS 15.4 update failed on external disk

Question

Level 1

63 points

macOS 15.4 update failed on external disk

I've got a maybe somewhat odd setup here. MacBook Pro M2 Max with macOS Sequoia 15.4 running on the internal SSD (APFS, encrypted). In addition I have an external NVMe SSD (Samsung T7) where I've also installed macOS Sequoia to be used as StartUp-Disk if need be. With that setup I keep my private and my corporate macOS installations physically separated. "Just" using the same MacBook Pro to run them.

Now I tried to apply the latest update from macOS 15.3 to 15.4 on my external SSD. The update shows, the external disk is set as StartUp Disk and the update process starts. It looks like it does the update with multiple reboots and all. But after it's finished and log in to the macOS it still shows the update 15.4 as available. There were no apparent errors during the update process. But I noticed that wen I log in after the update the system complains that it was improperly shut down and whether it should report that.

Any idea how to debug this? The update worked just fine on the internal SSD without any issue.

MacBook Pro 14″, macOS 15.4

Posted on Apr 1, 2025 5:54 AM

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Answer 1

NowApple

Level 1

13 points

May 9, 2025 2:58 AM in response to Falko Zurell

I have a similar issue here.

I have been trying to install MacOs on external drive without any success, here what I have tried:

SSD EMTEC 480GB
sigle portion as APFS with GUID boot partition
downloaded installer macOS Sequoia version 20.2.05
launching installer and followed all the steps selecting the external SSD
after a while it shows up the same message:

An error occurred preparing the update.

Failed to personalise the software update. Please try again.

tried to connect the external SSD to the non-DFU port (which is the leftest on the MacBook Air M1 2020.
having the same error message.

Any help please?

Many Thanks

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Answer 2

NowApple

Level 1

13 points

May 9, 2025 5:41 AM in response to ameenjuz

We have installation issue 15.4 on external drive to MacBook Air M1

which one Mac model you are using

Does it mean I should be able to install Sonoma on external drive instead?

If so, how can I download the Sonoma version?

Many Thanks

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Answer 3

May 9, 2025 11:42 AM in response to Falko Zurell

Thank you for the articles you posted, I guess I was in luck when I did a clean install. The articles help me understand about external disks and ownership. I guess a Mac is never really yours these days, with all the safety stuff Apple has implemented. I hope my update issues will not prevail with the next updates.

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Answer 4

Falko Zurell Author

Level 1

63 points

Apr 2, 2025 5:48 AM in response to tbirdvet

Were the clones created before the 15.4 update? How did you update the TB drives to 15.4?

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Answer 5

tbirdvet

Level 6

16,988 points

Apr 2, 2025 5:54 AM in response to Falko Zurell

All drives had 15.3.2 I booted each one up and then applied the 15.4 update as any normal process would follow.

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Answer 6

Falko Zurell Author

Level 1

63 points

Apr 2, 2025 7:59 AM in response to tbirdvet

interesting. That's pretty much what I tried. But it didn't work for me.

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Answer 7

Apr 2, 2025 7:37 PM in response to Falko Zurell

my problem is after upgrade to 15.4, my M4 Mac mini can't boot from external SSD , it just shows a blank screen and keep reboot for a while. I have reinstalled the OS, and still get a blank screen.

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Answer 8

ameenjuz

Level 1

8 points

Apr 2, 2025 10:07 PM in response to aransh

I have a same issue macOS Sequoia 15.4 during installation on External drive but in internal drive no issue

i think that it has installer bug

we hope Apple fix this issue

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Answer 9

gio259

Level 1

12 points

Apr 3, 2025 1:45 AM in response to gio259

And the problem also occurred on a clean installation of 15.3.2 after the above. Which means that 15.4 changes the Firewall settings on Mac

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Answer 10

gio259

Level 1

12 points

Apr 3, 2025 2:00 AM in response to Petr.Podzimek

Exactly the same. I believe that it will be fixed quickly and 15.4 will finally be released on the Appstore which until now did not exist !

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Answer 11

tbirdvet

Level 6

16,988 points

Apr 3, 2025 4:41 AM in response to ameenjuz

No issue here. I've done two different external drives and all installs no issue and both boot fine using 15.4. My external drives stared with 15.3.2 before updating.

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