Unmounted drives become mounted (after the Mac awakens from sleep) (macOS 26.4.x?)

TidBITS Talk
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I am wondering if anyone has run into this problem lately, and if so, are there any decent workarounds? –>

I believe this behavior began in macOS version 26.4.x: When I unmount a drive, it does appear to be unmounted, but, the drive becomes mounted again, when, for me, the Mac awakens from sleep.

Actually, there does seems to be at least one triggering mechanism, which re-mounts the drive, after being unmounted. For example, if you put the Mac to sleep, when you wake it up, the previously unmounted drives, once again appear mounted. I am not sure if there are any other triggering mechanisms.

I have two Macs, a 2020 Mac-Mini M1, and a 2022 MacBook Air M2, both running macOS 26.4.1, and the problem appears on both Macs.

Background: I believed what happened is the following: Apple was trying to fix a problem, in that for some users, it was difficult (or impossible) to get some drives to mount. So in trying to “fix” this problem, Apple created a new problem/bug, in which the opposite condition gets created, that is, now (once the triggering new bug occurs, for example, awakening from sleep), a previously unmounted drive becomes mounted, regardless. Note: I had never experienced the original problem Apple was trying to fix in this case, that is, I never had a problem mounting a drive, when I needed the drive access.

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2

I think I found out how to fix this issue, simply, quickly.

Contact me if you want for details.

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I found this on the Carbon Copy Cloner “issue tracking” webpage:

macOS Tahoe 26.4 will remount all external volumes when the display sleeps

Starting in macOS 26.4, macOS has developed an annoying behavior in which all external volumes are remounted whenever the display sleeps. This is not related to any CCC activity, and can be reproduced with these simple steps:

1. Unmount all external volumes
2. Sleep the system or sleep the display (e.g. with a hot corner)
3. Wake the system/display

Result: the external volumes remount. This behavior started with the macOS 26.4 update.

We have reported this to Apple (FB22369073, March 30) and we’re awaiting their response (or hopefully just a fix in 26.5).

https://support.bombich.com/hc/en-us/articles/20686463881367-macOS-Specific-Issues-That-We-re-Tracking

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I have this too, since 26.4 and also unchanged now with 26.4.1. There’s an additional twist with me, in that if I eject a drive, it will sometimes a little later mount again, uninvited and with the machine still awake. In the meantime, Phil pmvtutor, could you post your simple, quick fix?

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Hello,
The simple fix is to invoke a one-line UNIX command from the Terminal app (on your Mac), followed by a reboot of your Mac.

The specific UNIX command and procedure is included within the following site:

External Hard Drives Randomly Re-mounting after Tahoe 26.4 Update

https://discussions.apple.com/thread/256271120?sortBy=rank

travel down this webpage to “batutta” entry from 11Apr2026 8:02 AM (which begins with the note “IGNORE!”), and enter this UNIX command, then reboot your Mac. (In essence, this sets a key flag to the FALSE value. I wanted to give proper credit to the person who revealed the fix.)

Let me know if this method worked for you.

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Ta, Phil, will give it a whirl. I trust this sort of command is safe to deploy?

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Oh, and I should add re the CCC post that I reported this to Apple as well, soon after it arose in 26.4.

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I am rather cautious in general, especially when it comes to applying a UNIX command.
What I can say is that this fix worked for both my Macs, and I haven’t noticed anything untoward since on either Mac.

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Looking at the latest posts on that Apple Discussion it seems that batutte found that his suggested Terminal command did not permanently fix the problem. It seems that Apple needs to fix the bug as there is no simple workaround.
As it happens I have held off “upgrading” to Tahoe and will stay on Sequoia for a while longer!

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I have to say, I always considered the fix from “battuta” a workaround, and am also convinced that Apple needs to fix the bug they introduced. See my original post.

If you wish to not update to Tahoe, of course that is your choice.

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I think I’ll wait for Apple’s update/fix. It’s annoying, the random mounting thing, but I can live with it for now. I too am wary of deploying Unix commands. Maybe we’ll see a 26.4.2 MacOS soon?

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If anyone is, like me, waiting for an Apple fix for this, the just-released MacOS 26.5 does seem to have fixed it, certainly for me.

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OS 26.5 Adds Encrypted RCS Messaging, Fixes Bugs
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Thanks for the news update. I will update to 26.5 soon, to check it out for myself.

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No problems regarding re-mounting when unwanted, for me, after updating to macOS 26.5.

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