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Time Machine has started to fail when I try to backup. I am running Big Sur 11.6.1 and have APFS both on my Mac and external USB drive. The Time Machine log shows:

2022-02-05 10:07:36  Not starting scheduled Time Machine backup: Automatic backups disabled
2022-02-05 10:07:36  Starting age based thinning of Time Machine local snapshots on disk '/System/Volumes/Data'
2022-02-05 10:07:36  Starting age based thinning of Time Machine local snapshots on disk '/Volumes/Macintosh HD - Datos2'
2022-02-05 10:07:36  Starting age based thinning of Time Machine local snapshots on disk '/Volumes/Macintosh HD - Data'
2022-02-05 10:07:36  Starting age based thinning of Time Machine local snapshots on disk '/System/Volumes/Update/mnt1'
2022-02-05 10:07:36  Failed to wait for snapshot deletion to complete on disk '/System/Volumes/Update/mnt1', error: Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"
2022-02-05 10:07:36  Skipping age based thinning of Time Machine reference snapshot 'com.apple.TimeMachine.2022-02-04-184432.local' on disk '/System/Volumes/Data'
2022-02-05 10:07:36  Skipping age based thinning of Time Machine reference snapshot 'com.apple.TimeMachine.2022-02-04-184432.local' on disk '/Volumes/Macintosh HD - Data'
2022-02-05 10:07:36  Skipping age based thinning of Time Machine reference snapshot 'com.apple.TimeMachine.2022-02-04-184432.local' on disk '/Volumes/Macintosh HD - Datos2'

Looks like I need to get rid of the Update mount. Is that the correct thing to do? If so, how do I do it?

Thanks

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  • The error usually indicates that the snapshot is mounted. To list all mounted volumes, use mount. However, not able to delete snapshot is not usually a reason for Time Machine to fail completely. There might be something else that happened. Potentially the errors might be in the log file in the Time Machine backup directory.
    – Joy Jin
    Feb 5, 2022 at 12:38
  • Thanks. On further checking the details of the back up: log show --predicate 'subsystem == "com.apple.TimeMachine"' --info --last 4h | grep error I found there was a file that was corrupted and couldn't be copied. I couldn't delete it using Finder but did from a terminal. Once gone, the backup worked fine.
    – Tim
    Feb 5, 2022 at 20:09
  • You should (could?) post your solution as an answer (and explain it in more detail) and mark it as the accepted answer.
    – Joy Jin
    Feb 6, 2022 at 11:10
  • Good idea Joy. Let's see if I can figure out how to do so...
    – Tim
    Feb 7, 2022 at 9:10
  • Great! Now you should accept your own answer. Click on the check mark which should be left of your answer.
    – Joy Jin
    Feb 7, 2022 at 13:19

1 Answer 1

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OK, so after searching around on Google I found a way to actually see what the real error message was:

printf '\e[3J' && 
    log show --predicate 'subsystem == "com.apple.TimeMachine"' --info --last 6h \
    | grep -F 'eMac' | grep -Fv 'etat' \
    | awk -F']' '{print substr($0,1,19), $NF}' 

This showed me that I had some obscure file that was refusing to be copied into the backup and hence cause TM to stop! Since the file was very old and of no importance I tried to delete it from Finder, no luck. It wouldn't let me. So I started a Terminal and went to the folder and deleted it using rm. After that, my backups worked perfectly.

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