Post-macOS update, systemmigrationd prevents ejecting Time Machine drive

Happened for me following 26.5.1 to 26.5.2 upgrade. Time Machine disk was not attached during upgrade. I attached it post-upgrade to perform a backup and the `systemmigrationd` process will not release the drive for unmounting.

A simple `sudo kill <PID>` of the `systemmigrationd` worked to release the drive and allow me to unmount it. Since it didn't require any escalation flags for the kill command, I think that feels pretty safe, although definitely annoying.

JLG89 wrote:

After a macOS update, a Time Machine backup drive cannot be ejected because the systemmigrationd process is using it. Once I allow the system to sit for an extended period of time (over a weekend seems to be sufficient), the problem resolves. What is systemmigrationd doing with the backups? Is there a way to monitor the process?

Currently on macOS 26.5, but have been seeing this behavior on multiple systems for at least a couple of update cycles.

You can reference this thread, read through the 2 pages:

Cannot eject Time Machine drive from MacBook Pro note your "systemmigrationd"

Cannot eject Time Machine drive from MacB… - Apple Community

addendum: Activity Monitor User Guide for Mac

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

JLG89 wrote:

The issue is not resolved, because we don't know why systemmigrationd randomly grabs the external drive and won't let go. Force eject works, obviously, as does killing the systemmigrationd process (via either CLI or Activity Monitor), but neither of those answers the original question.

Well you may never get answer to your "original question" since it seems related to 26.5...

there is no magic insight here, so beyond your control or mine.

File a bug report / submit your feedback here: Feedback - macOS - Apple

Maybe with enough feedback macOS 26.6 will resolve the issue...

JLG89 wrote:

Hrmph. I searched the forums for "systemmigrationd" and that thread didn't come up. Apparently the AI search engine is more A than I.

?

More importantly here was your issue resolved(?) your feedback is apopreciated....