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Kenneth Hjulstrom
User level: Level 2 (490 points)

Mac Mini 2018: macOS Sequoia upgrade fails with watchdog timeout

On my Mac Mini 2018, I've been running the entire the entire system from an external non-SSD drive (I have reasons for using this configuration), and it's been running fine until I attempted to upgrade from Sequoia 15.8.0 to 15.8.0. When attempting to do the upgrade, everything seems to run fine until near the end of the process, when the computer shuts down. By logging into the Sequoia 15.8.1 system that's running on the internal SSD drive, I was able to determine that the shutdown was caused by a "userspace watchdog timeout" (see attached report).


I can view the remote drive's contents from the internal Sequoia installation, and have determined the following:

  • From the "Startup Disk" selection screen, the remote drive does have Sequoia 15.8.1 installed
  • I ran Disk First Aid on the remote drive, and no errors were found
  • It appears that all of my data is intact (I expected this to be the case)


I attempted the following MacOS updates for the remote drive:

  • Upgrade to Sequoia 15.8.1 from Software Update, which failed with the machine shutdown (I initially thought that this was just a fluke)
  • A second attempt to complete the Software Update upgrade, which, when I restarted the machine on the internal MacOS instance, showed me the first "Your system shut down due to a problem" report, when I realized that the upgrade failure was due to a watchdog timeout
  • I then attempted an upgrade from Recovery Mode, which also failed with the same watchdog timeout
  • Finally, I attempted a downgrade from Sequoia 15.8.1 to 15.8.0, but this also failed with the same watchdog timeout


For the final two upgrade attempts, I disconnected all peripherals from the Mac Mini except for:

  • HDMI monitor cable
  • USB cable to the external drive (it's connected to the large USB connector)
  • RCA speaker cable
  • USB keyboard cable


The result of all of this is that I'm unable to use the Sequoia installation on the external drive, as the watchdog timeout is shutting down the machine before it displays the login screen. All of the watchdog time errors appear to be identical to each other, pointing to a probable common cause.


Prior to this, every MacOS upgrade that I've done on the external drive installation had been via the Software Update option in System Settings.


My questions are:

  • Has anyone else run into this problem?
  • Is there some sort of solution or workaround that I haven't already tried?


Prior to encountering the same error when attempting the 15.8.0 downgrade, I had reported to Apple Support via phone that I believed that this may have been a subtle bug in the 15.8.1 installer, which still may be the case, but it also appeared in the 15.8.0 installer that I used.


Thanks,


Ken



Userspace Watchdog Timeout Report.log


Posted on Oct 15, 2026 6:29 PM

3 replies

Kenneth Hjulstrom Author
User level: Level 2 (490 points)

Oct 21, 2026 6:42 PM in response to Kenneth Hjulstrom

I wasn't able to solve the userspace watchdog timeout error, but the following workaround worked very well:


  1. The macOS 15.8.1 installation that I wasn't able to log into was installed on a 1 Tb external HDD, with 708 Gb in use, so I wasn't able to transfer everything to the Mac Mini's internal SSD, which was only 256 Gb in size.
  2. I purchased an additional 1 Tb HDD, along with an external SATA enclosure with a USB BM data connector and a USB 3.1 Type C to USB BM cable to allow me to connect it to one of the smaller Type C ports on the Mac Mini, since the USB BA port was already in use by the problematic external HDD.
  3. I connected the second external drive, and from the macOS 15.8.1 installation on the Mac Mini's internal SDD, downloaded the macOS Sequoia installer from the App Store, and used it to install Sequoia onto the second external hard drive.
  4. I tried booting to the second external hard drive, and was successful. However, despite the fact that 15.8.1 had been released a couple of weeks earlier, the installed version was only 15.8. From that 15.8 installation, I ran Software Update, and successfully upgraded that installation to 15.8.1. So far, so good!
  5. From the new 15.8.1 installation on the second external hard drive, I ran Apple Migration Assistant, specifying the problematic external HDD as the source, and accepting all of the pre-selected options ("transfer everything"). I was a bit suspicious about importing the "System Settings", so I asked the Apple support AI to connect me to a live representative, but when it told me that no representatives were available at that time of day (11:00 PM, US Eastern Time), I asked it about the "System Settings, and was told that these these were mostly user settings. So I crossed my fingers, and told the Migration Assistant to transfer everything.
  6. After maybe 30 minutes of the Migration Assistant displaying only "Starting up...", the file transfer began. The first estimate as to how long the transfer process would take shocked me, as it reported "148 hours, 44 minutes" (slightly over six days!), but as the transfer progressed, the estimate dropped quickly, and ended up taking only about 12 hours.
  7. Booting into the 15.8.1 installation on the second external hard drive, I was amazed that this installation appeared to be functionally identical to the old external drive's installation. So far (1 day, 10 hours uptime), the only thing that the Migration Assistant seems to have missed was my weather setting on the menu bar. Additionally, the new installation ran the "Verifying..." verifications for every third-party app that was transferred. I was very impressed with the completeness of the Migration Assistant's operation, and I hope that my experience might help someone else who encounters a similar issue.


Ken

HWTech
User level: Level 9 (78,350 points)

Oct 22, 2026 8:31 AM in response to Kenneth Hjulstrom

I would suggest trying to boot into Safe Mode when trying to boot from the old external HD. If this works, then most likely some third party software or login item is at fault.


Another possibility is the file system is corrupt or that old external HD is failing. For the former, you will want to run Disk Utility First Aid on the hidden Container of the old external boot HD. See the following Apple article for details since the Container is hidden by default:

How to repair a Mac storage device with Disk Utility - Apple Support


Also, even if the First Aid summary says everything is "Ok", click "Show Details" and scroll through the report to see if there are any errors or warnings listed. If so, then run First Aid again until they are gone. If after several scans the errors/warnings remain, then they cannot be repaired and will require erasing the whole physical drive.


To check the health of the external Hard Drive, you can use the third party app DriveDx( free trial period). Post the complete text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar. For Hard Drives any "Warning" or "Failure" notices usually indicate a worn out or failing HD respectively. Note: SSDs are a bit different and cannot be accurately assessed automatically. You will need to install a special USB driver to access the health information of an external USB drive.



den.thed
User level: Level 10 (99,154 points)

Oct 22, 2026 9:23 AM in response to Kenneth Hjulstrom

Another solution!


Is to run macOS on the Mac mini's faster internal SSD and keep your User Libraries on an external SSD or HDD.


Move your Photos library to save space on your Mac - Apple Support

Change where your music files are stored on Mac - Apple Support

Move Logic Pro for Mac and MainStage content - Apple Support

Move your iMovie for Mac library - Apple Support

Move a Final Cut Pro library - Apple Support


Originally posted at discussions.apple.com/thread/256376962