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I had MBP 2015 in the past and used Time Machine on it. Last September, I switched to MBP 16'' 2019 and did a fresh installation / manual copy of most of my home directory files, maintaining the layout.

Note: I wanted to do a fresh installation for various reasons but if I were to compare the filesystems in the end, they are almost the same – my home directory is still /Users/borekb, the folder layout under it is exactly the same, etc.

Now I'm trying to set up Time Machine again but I'd like to continue with my previous line of backups – for example, I want to see last year's versions of files that are on the same path. Also, my first backup on this new Mac should be "incremental" – I'd like Time Machine to compare what is on my current Mac with the latest state of my previous backups (from September 2020) and does a diff as usual.

The key to this seems to be the tmutil inheritbackup command, which I've successfully ran:

$ sudo tmutil inheritbackup /Volumes/time-machine/Borek’s\ MacBook\ Pro.backupbundle
Password:
Mounting disk image...
Unmounting disk image...
Inheriting disk image for machine...
Successfully inherited disk image '/Volumes/time-machine/Borek’s MBP 16.backupbundle'

/Volumes/time-machine is a mounted network folder (I backup wirelessly to a Synology NAS) and the command seemed to work well – it did this rename:

Borek’s MacBook Pro.backupbundleBorek’s MBP 16.backupbundle

I then went to Time Machine UI, selected the time-machine disk, entered my previous password for encryption, etc.:

Everything seemed fine so far.

However, when I start backing up, it does a full initial backup to a new folder inside the .backupbundle that is called after my new computer's name: Borek’s MBP 16. This is what it looks like after I mount the sparse bundle and browse the /Volumes/Time Machine Backups/Backups.backupdb folder:

I somehow want to tell Time Machine keep using the original Borek’s MacBook Pro folder (the one that was last modified on 22 Sep 2020).

How to do that?


UPDATE 1: I tried changing my computer's name to match the old one but Time Machine still insists on creating a new set of backups from scratch – it just calls the new "machine directory" Borek’s MacBook Pro 2:

I have also ran this script, found here (as Big Sur doesn't seem to support -a), to run tmutil associatedisk an all folders found under the original backup location:

for f in /Volumes/Time\ Machine\ Backups/Backups.backupdb/Borek’s\ MacBook\ Pro/*; do
  if [[ -d "$f" ]]; then
    sudo tmutil associatedisk /Volumes/Macintosh\ HD "$f"/Macintosh\ HD;
  fi;
done

This also worked correctly but Time Machine still doesn't see my older backups and is attempting to create Borek’s MacBook Pro 2 when I try to run a backup.


UPDATE 2: I've successfully verified backups which was a solution in this answer. The preferences UI still report "no backups" so I'm now trying to run a new backup, which was Step 2 in that answer and the author wasn't sure if it's necessary or not. I'll report back in a few hours...

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  • This is a prickly operation at best. I would refrain from making any more changes to the destination - especially since the inherit failed to set all the magic bits that track the sources and destinations. What was the macOS version and build in the past (if you know what was in play previously) and what version are you now? – bmike Mar 21 at 21:53
  • Also, you may not want this advice, but for me I would immediately start a new backup on a new drive and then open a case with Apple Engineering if you can. That way you’re covered for how ever long it takes to pick apart why the inherit failed by looking at tmdiagnose – bmike Mar 21 at 21:55
  • @bmike The inheritbackup command worked fine, for example, I can see my hardware UUID written to one of the .plist files in the backup. I just can't get my new Mac to use the old "machine directory" (if that's the right term within the backupbundle) – it keeps insisting on creating a new one. – Borek Bernard Mar 21 at 22:39
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If you tap the option key while clicking the time machine icon in the menu bar, you can browse backups from previous or other computers.

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  • And how can this be used to reconnect to a previous backup so that new backups get added there? – nohillside Mar 22 at 12:17

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