Cannot eject Time Machine drive from MacBook Pro

This has not been my experience. I've always been able to eject my attached Time Machine SSD as long as it is not involved in an active Time Machine operation. Others have described a systemmigrationd situation, and this occurred for me after a system restore from my Time Machine drive. Killing systemmigrationd" was the appropriate fix.

Removing it from Time Machine does not help. systemmigrationd still dissents from the unmount.

Killing the systemmigrationd process (no -9 needed) released it and allowed diskutil unmount to work.

Something must have changed in 26.?. I never used to have this problem and my use case hasn't changed. For the last several months I see this on both my iMac and my MBA every time I plug in their portables to do an TM backup to normally offline media. Plug the disk in. Come back later, find TM has completed one or more backups to the disk and appears to be just sitting there waiting to do another. Try to eject the disk. Fail. One or more programs has disk in use. So far my workaround is a reboot and pulling the plug when I hear the ding. Very annoying. I suppose I could Force Eject but TM backups are fragile enough as it is.

Per Reddit thread on this subject, recent origin,:

dick@Mac ~ % diskutil unmountDisk "/Volumes/AirMac_TM_2TB" 

Unmount of disk5 failed: at least one volume could not be unmounted

Unmount was dissented by PID 1776 (/System/Library/PrivateFrameworks/SystemMigration.framework/Versions/A/Resources/systemmigrationd)

Dissenter parent PPID 1 (/sbin/launchd)

What is systemmigrationd and why is it holding onto this drive?!?

The Finder dialog doesn't tell you which program is using the drive. Open a Terminal window and type "diskutil eject /Volumes/<drive name>" and that will tell you which process is using the drive. If there's an active Time Machine backup running--which would be indicated by the TM menubar item--then TM would be the culprit; however, in most of the cases in this thread, the culprit is systemmigrationd for some reason.

I am also seeing this since updating to Tahoe and like others systemmigrationd seems to be the culprit.

Last login: Sat May 30 14:03:38 on console

Sam@MacBook-Pro-2 ~ % diskutil eject /Volumes/TIME2 

Unmount of disk7 failed: at least one volume could not be unmounted

Unmount was dissented by PID 1789 (/System/Library/PrivateFrameworks/SystemMigration.framework/Versions/A/Resources/systemmigrationd)

Dissenter parent PPID 1 (/sbin/launchd)

Sam@MacBook-Pro-2 ~ % 

I am considering to try delete from time machine, format, add as new time machine volume and start over. I don't need the ability to go back and wonder if there is a long running (months?) process touching all the backups that occurred prior to Tahoe?

It is a nuisance because while I normally leave a time machine backup target drive plugged in I have two and swap them every two weeks. I also eject it to hook up another external to the same power supply and USB cables to clone my other external drive which houses all my RAW photo files. This now requires me to power off and make the swap while powered off.

A solution at last; I have been working with a developer named Aaron Hampton who created Ejecta. It was one of several app/utilities I tried which did not solve my problem ejecting Time Machine EHD from my M1 MBP.

I contacted him about this for a refund and he happily refunded my one time purchase price along with his apologies. He also asked me if I could tell him what happened when I tried to eject with his app.

Over several weeks we fed back and forth and today I received his last update taking into account what I had already posted him about systemmigrationd

Bottom line is, IT WORKS!

He has generously allowed me to keep a free copy of the app and the best thing about it is, it does not kill the systemmigrationd process. After ejecting my TM backup I checked Activity Monitor and as you can see, there it is;

His app can be found on his home page here; https://www.ejecta.app/en/

I'll try running "sudo lsof | grep" on my volume to see if I can pinpoint a cause.

That's a fine idea but it still shouldn't be necessary to resort to such conniptions.

There MUST be some underlying process that is holding the drive hostage and preventing it from ejecting properly.

EtreCheck may help. Post its report here.

Another thought. Is it possible that TM backup drive has been in service for a very long time, perhaps before Time Machine imposed its complete and total dominance over it?

Same! Since updating to macOS 26.6 I have been able to swap time machine disks as before without shutting down. So far so good it appears to be resolved.

Cerebro, like you updating to 26.6 seems to have fixed the issue for me too. Prior to that I was using Ejecta to overcome the persistent "systemmigrationd" process temporarily which worked fine now the Control Click or Right Click menu works on its own so maybe, someone at Apple actually reads this stuff and the problem has been resolved at the system level in 26.6 ? Either way its good news for me and I hope others too.🙏

I am having this same issue, new to me since I regrettably upgraded to Tahoe. I'm now running 26.5 and the issue is not fixed. For what it's worth, I just tried this suggestion (quitting the "systemmigrationd" process) while the OS was attempting to eject the external TM drive, and once I returned to the dialogue box and clicked try again, the external drive unmounted. Restarting the Finder did not work. I have FileVault turned off on my internal drive and on the TM backup as well. I have no idea for how long this trick will work. Quite a kludgy workaround for something that used to be seamless. But that's Tahoe for you.

Thanks for the suggestion.

Force

As previously reported, I've tried all of the solutions. While some didn't work, others did, most notably deleted systemmigrationd. Unfortunately, that success was short lived.

I just shut down all running programs and used CleanMyMac to delete all user logs, caches, DNS, etc. I then rebooted my MBP and, lo and behold, no problem ejected the Time Machine Backup Drive.

I unmounted and remounted it multiple times with success. I then ran a backup and then ejected the drive without a problem. I then mounted/ejected the drive multiple times, also with success.

However, I'm not going to be lured into thinking "problem solved" but will continue to eject/remount the drive at various times during the day and see if good fortune prevails.

After struggling with the same issue for weeks, I've finally figured out the solution that works every single time!

All you have to do is make sure you Open Time Machine Settings. If that window is open (in system settings,) you'll be able to instantly eject your external disk every time.

I had the same issue. Tried your solution of shutting down with the drive still connected, unplugging the drive, restarting my MPB 2021 running Tahoe 26.5, connecting my drive. I then ejected the drive without a problem!

Will keep my eye on this and -- hopefully -- there will not be a recurrence.

Reported resolved in the next release of macOS. Another member of my local computer user group who also saw this as a reproducible problem on macOS 26 has shared that updating that machine to running the next release of macOS resolved the problem. He says we can hope a fix may be included in an update macOS Tahoe but no one at Apple has given any indication about that.

I can confirm that the problem is consistent with the minor update to macOS Tahoe 26.5.2 and I am waiting for 26.6 and the next release of macOS with I believe some reasonable hope. I think waiting for Apple to fix this and in the meantime shutting down the Mac to swap drives is the most conservative approach I don't recommend anything else. Various people suggest shenanigans and terminating processes that belong to macOS yourself just to eject a volume is probably a bad idea.

Tahoe 26.5 seems to have fixed the bug. See if you agree.