Cannot eject Time Machine drive from MacBook Pro

And that was where my problem started because my TM backup EHD was already encrypted. I solved this, "....because one or more programs may be using it" by going to Activity Monitor, Selecting the Disk tab and searching for systemmigrationd. It came up, I double clicked it and used the button to Quit the process. My TM EHD now ejects without a problem but bear in mind systemmigrationd is important to the system and it will restart after a "cold" boot which is a good thing really. It is definitely not suggested that you permanently disable it which involves disabling SIP via Terminal first.

As I rarely turn my MBP off this is not a problem for me and if I do I know how to temporarily disable systemmigrationd quickly without permananently damaging the device.

I hope this helps.

This what I have discovered. In my case it is systemmigrationd which is a daemon associated with migration assistant but for some reason has has a "handle' on my Time Machine EHD.

In Activity Monitor you will find it if you search under the Disk tab.

Do a search for systemmigrationd and if it is your problem you will find it running. Double click it and Quit/Stop the process.

Your TM EHD should now eject. This does not pose a problem because although systemmigrationd is an essential part of the SIP system it will start up again after a "Cold" Boot.

Do not attempt to permanenently disable systemmigrationd.

Just to reiterate; killing the systemmigrationd process in Activity Monitor > Disk > systemmigrationd has worked flawlessly for me on an M1 MBP running 26.5.1 and no, I did not have this problem prior to macOS 26 Tahoe.

Also worth noting is that shutting down and performing a cold boot will reactivate the systemmigrationd process which is a good thing, because a. It is a necessary part of the System and b. Because it's easy to shut down again. Personally I seldom turn my MBP off so this is not an issue for me.

I've also had this since Tahoe / moving to a new mac. It's somewhat random, but seems to happen more than 50% of the time. I don't think a real "fix" has been found in any of the answers here, you can get fooled by the randomness ;)

What I do is try the eject from the command line, then you quickly get the pid of systemmigrationd, and can kill it and eject, like

~ % diskutil eject /Volumes/TM
Unmount of disk7 failed: at least one volume could not be unmounted
Unmount was dissented by PID 1424 (/System/Library/PrivateFrameworks/SystemMigration.framework/Versions/A/Resources/systemmigrationd)
Dissenter parent PPID 1 (/sbin/launchd)
~ % sudo kill 1424 && diskutil eject /Volumes/TM 
Password:
Disk /Volumes/TM ejected

FWIW, as long as a drive is assigned to Time Machine it is considered in use. You would have to first remove the drive from Time Machine in System Settings > General > Time Machine.

I removed TIME2 from Time Machine, Erased it using disk utility, added it to Time Machine as an encrypted volume, performed the initial backup and then after another backup it was running this morning finished I ejected it. No delay it ejected immediately just as I would expect with Time Machine not actively backing up.

I think my theory that something is processing or updating old backups after the upgrade to Tahoe so far seems reasonable. I would love to know exactly why systemmigrationd seems to be running against time machine backup disks. I will keep an eye on this but it if it does not recur for the next two weeks then I will likely also delete, erase, readd the other time machine disk I rotate TIME1.

First, thank you for all of your research!

The shutdown/unplug/startup/plugin worked only once for me; then the problem recurred.

HOWEVER, I took your advice and quit the systemmigrationd process which immediately solved the problem.

I then rebooted my MacBook Pro and was able to easily eject the Time Machine drive.

I then did a backup and ejected the drive afterwards with success as well!

I checked with Activity Monitor and systemmigrationd was running! So, now it's just to hope that this will last.

I tried several attempts having settings open makes no difference for me.

The culprit consistently remains systemmigrationd and this seems to be a bug that needs to be reported to Apple which is my next step.

Last login: Wed Jun 10 09:17:32 on ttys000

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

Unmount of disk14 failed: at least one volume could not be unmounted

Unmount was dissented by PID 1821 (/System/Library/PrivateFrameworks/SystemMigration.framework/Versions/A/Resources/systemmigrationd)

Dissenter parent PPID 1 (/sbin/launchd)

Sam@MacBook-Pro-2 ~ % 

[Edited by Moderator]

dialabrain wrote:

FWIW, as long as a drive is assigned to Time Machine it is considered in use. You would have to first remove the drive from Time Machine in System Settings > General > Time Machine.

Is that really true? I ask because I have two external drives used for Time Machine connected to my MacBook Pro, running Tahoe. But I (multiple times per day) eject them so I can leave them in the work area and take the laptop somewhere else. Then when returning, I reconnect both drives and one of them immediately starts a Time Machine backup to "catch up" on backups while the Mac was physically elsewhere.

I am wondering if the Jettison software being used by the OP might be a factor in this issue ... the developer web site says "macOS 10.13 through 26.3" ... and has some FAQs one of which is about drives that refuse to eject.

Cerebro wrote:

Okay. I think I, finally, solved my problem.

It seems there are two solutions:

Turn off FileVault on my internal drive.

2. Reformat my TM volume with encryption.

I chose the second one. Now, I haven't seen any errors all week with, either failed disk ejections, or failed back-ups. Hopefully, I'm good to go, now.

Good computing Cerebro ! Apprciate the feedback on your resolve.