Update error: A snapshot is currently set to boot that is not the currently booted snapshot [solved]

macos_snapshot_fix.md

Fix for "A snapshot is currently set to boot that is not the currently booted snapshot" issue

I spent a while figuring this one out. Here is what I did to render it [Solved] on my Dad's new Sonoma iMac. (BTW: I caused this problem in the first place by enabling his nfsd service, then adding and tagging the snapshot as bootable)

1. Boot into recovery mode, open the terminal and disable SIP

   csrutil disable

2. Reboot at this point back into Recovery mode and this time open up DiskUtil

   You should now be able to see the system snapshot that is causing the issue, however you will not be able to delete it (since it is the active boot snapshot) So, instead, take careful note of the previous snapshot - it might have a name like:

   com.apple.os.update-5E4DF785AD9E60757D57924284549E29EECDBFE5942B5587D41DEAD049A903BE

3. Now exit DiskUtil and go back into Terminal, then mount the booting hard disk as rw:

   mount -uw /Volumes/Macintosh\ HD

4. Now 'tag' the official snapshot as the next bootable one:

   /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs_systemsnapshot -r "SnapshotName" -v /Volumes/Macintosh\ HD

   (replace SnapshotName with the name of your snaphot. (like the one I showed)

5. Now exit the terminal and go back into DiskUtil

   Now you can view the snapshot and should be able to delete the offending one if you want to. (select it and click the minus sign at the bottom left)

6. Exit DiskUtil and go back to the terminal (last time I promise) and re-enable SIP:

   csrutil enable

7. Reboot back into MacOS and your apple sanctioned update should proceed without any errors

@sirfragalot, thanks, this is good to know.

@loshlee it sounds like CCC created the snapshot, and it also sounds like the one it created is the currently active one (and hence greyed out since you can't delete a snapshot if you have just booted from it)

If CCC created, then it should say this to the RHS of the snapshot list (under the 'Kind' column heading) if you were using time machine, then it would say "Time Machine Snapshot", if this field is blank, then maybe something else created it?
It does seem strange though as CCC and Time Machine do not normally create snapshots over the system snapshot.

If you can get to step 4 in my instructions and then reboot, in theory the snapshot should be no longer active and you should be able to delete it.

It wasn’t Time Machine, but it was current, apparently, because attempting to delete it in Recovery mode using Disk Utility resulted in “read-only file system” error and renaming it caused Recovery's restart to require an overlay (in-place) installation of macOS Sequoia (15.3.1). The vexing issue is still that Finder began showing 45G less available space and Disk Utility began revealing the apfs snapshot in question at the same time and only a few days ago. Thanks.

Ahh ok, that explains it. Thanks for the update.

diskutil apfs listSnapshots /disk3s1

can directly get the snapshot's name from the terminal.

You can execute

diskutil list 

to know how many disk you have in the computer.