macOS 15.4 update failed on external disk

I have the same issue and error report. This has happened consistently after trying to install the macOS 15.4 update on an external drive.

Device info:

• M1Pro MacbookPro 14in
• 512 GB internal SSD
• 2 TB external SSD connected via Thunderbolt 3

I have tried:

• Removing my laptop from FindMy
• Turning off SIP on the internal drive
• Downloading and running the full installer to install to the external drive
• Using Recovery to install to the external drive
• Using the bless command from the Recovery mode terminal. (See: screenshot)

So based on the screenshot and my attempt to enable SIP on the external drive after installation failed it looks like a local boot policy is never set due to a preboot error.

Anyone have any luck with a fix?

I've the same problem with M1 MacBook Pro and update on internal SSD.

So yesterday I've downloaded the update from macOS 15.3.2

After the download from Settings it starts to update.

After that it shows a window where it ask for my FileVault password (never seen before).

So, I've inserted it.

After that, only boot loop. No log given.

So, I've seen using Terminal that in Macintosh HD - Data there are all my folders and files.

I've tried:

• Restarting in Safe Mode: same problem
• Create a macOS 15.4 update from USB stick created from another mac: after install, it keeps bootlooping and no log provided.
• Using S.O.S. from Disk Utility it shows a lot of warnings on snapshots.
• Restore window shows "Install Monterey" that is four years old.

So, now, how can I do?

Since this morning I'm with Apple Support but no guidelines to solve the problem.

I don't want to loose all my data for a minor update (I've done a cp operation using Terminal on a external SSD but probably I've missed some path/folder to backup).

I’ve had the same problem, except mine is with two different volumes on the internal SSD on my M1 Macbook Pro. My work side updated absolutely fine, but I was unable to update my personal side - it rebooted in a similar way to yours, but then just had an “We ran into a problem” style prompt with the option to report.

As there are a fair few vulnerabilities addressed with this update and I had not rebuilt my personal volume since I got the device, I thought I’d try installing from scratch but I’m hitting the same problem with just trying to install the OS on the separate volume, it doesn’t complete successfully and now I’m stuck with just my work volume.

Planning on doing some more troubleshooting at the weekend when I have some more time, but this isn’t ideal.

I had the same problem on my M1 MBP -- after a number of failed attempts, it finally worked for me after I moved the external drive so that it was not connected to the "DFU port" -- this is just one of your USB-C / thunderbolt ports, and not plugging external bootable drives into this port is documented by Apple as a requirement, but it seems that after the initial install, the boot itself might work from any port, but upgrade does not? At least, that is my working theory.

I did not disabled File Vault on the internal drive (it was never on for the external). I did also allow the password for a user with rights to decrypt the internal drive to be stored in my keychain; I'm unsure if this was a factor.

How to identify the DFU port on Mac - Apple Support (NZ)

Install macOS on an external storage device and use it as a startup disk - Apple Support (NZ)

Falko Zurell wrote:

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.

I just managed to update my external hard drive to 15.4 after first turning off fire vault. I think I already did that in the past and it failed so it could be that Apple partially fixed the installer

I'm not sure what factors led to the successful update. My steps were as follows to successfully update the external disk to macOS 15.4:

1. Upgrade the internal disk to the latest macOS, which was 15.4 at that time.

2. Turn off the FileVault for both the internal and external disks.

3. Boot in the internal disk and download macOS Sequoia 15 from the App Store, then install it on the external disk.

(Note: Make sure to download and install 15.4 from the App Store on the internal disk. Doing it on the external disk will fail.)

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.

I tried changing Thunderbolt cable to an Apple one, that didn't work (pleased really as a certified Thunderbolt cable should be the same as an Apple Cable). I didn't know about DFU port (which coincidently I was plugged into). I changed the port my external drive was connected to - success, I now have the latest MacOS installed! At last!

The same update failure issue occurred when I upgraded from macOS 15.4 to 15.4.1.

The following is my solution:

1. Turn off FileVault on the external disk and the internal disk.

2. Close Find My Mac on Settings.

3. Normal update on Settings.

Then I successfully updated to macOS 15.4.1 from 15.4.

Good work my friend!