Failing to Finish Updating macOS on an External Disk
Apple today seeded the fourth beta of an upcoming macOS Sequoia 15.5 update to developers for testing purposes, with the software coming a week after Apple released the third macOS Sequoia 15.5 beta.
My update/installer/storage issues continue. I tried updating my external drive several times, but each time when Software Update restarted the Mac it booted from the internal SSD rather than the drive where the update was installed. I don’t recall this ever happening before. Each time I tried the update it had to redownload it, and then in failed in the same way. What eventually worked was using Startup Disk to set the external drive as the preferred boot drive.
Previously:
- Failed Software Update on the External Drive of an Apple Silicon Mac
- How External Bootable Disks Work With Apple Silicon Macs
- Error 702 Installing macOS on an External Drive
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A week ago I had the same boot issue on my internal drive, trying (only once) to update macOS 14.7 to 14.7.5. It just booted into my main macOS, 15. First time too.
I tried to repeat it now but it went smoothly. The main parameter that I know changed is that I have 20 GB of available disk space (out of 256) versus 10 or so last week.
After successfully updating, restarting brought up macOS 14 again (with an incorrect keyboard layout, “ABC”). My startup disk had been set to macOS 14, automatically.
Other times, even with "Apple - System Settings - General - Startup Disk" configured to boot from the external portable SSD fails to cold boot the Mac, showing black screen with flashing folder with question mark (above), and support.apple.com/mac/startup (below). You must force shutdown pressing the power button and try again to cold boot.
Apple should fix such issue. Having an external portable SSD is great to boot a powerful desktop Mac with large Apple display at work and other identical one at home with all your stuff in the external portable SSD.
