The Taber Family Blog

I recently had to migrate from one Mac laptop to a new one for work. While this was a nice thing to have happen, I found I had suddenly lost the ability to seamlessly transition my Time Machine hard drive backup to this new machine. It seems that when the removable hard drive I had been using previously was connected to this new machine, Time Machine thought this was an entirely new drive and wanted to start all over again, backing up the machine with no regard to the existing backups already on the removable drive. This will not do! I need Time Machine to see this removable drive and simply pick up where it left off with my previous laptop.

After some research on the Internet, I found that Time Machine works to identify the target for the backup by the MAC address of the machine that had created the backup in the first place. Sort of like a key that connects the source to the proper target. That’s a pretty cool concept, because it means you could use the same removable drive for several machines, if there was enough space available.

So after trying some command line tools to try and change the ACL‘s of the various backup DB’s already on the drive and connect them to the MAC address of my new laptop, I was not successful in getting Time Machine to recognize the drive and start backing up. But then I found this cool little piece of software that will execute the exact command you need to update the ACL’s on the backup DB’s. The original creator of the software and the article I found that helped is here.

You have to do this as root, so make you’ve set up your machine to use “sudo”. You’ll also need to know your new MAC address. You can get this from System Profiler or at the Terminal prompt using “ifconfig -a”.

Here’s what I did to fix this problem.

1. Download the backupswitcher software here and unzip it.
2. Connected the removable drive to laptop.
3. At a Terminal prompt:
   cd to the directory where you unzipped backupswitch
   Then type:
   “sudo ./backupswitch  /Volumes/<YOURDRIVENAME>/Backups.backupdb/<YOURBACKUP> YOURMACADDRESS”
4. The program should end by telling you the old MAC address.
5. Disconnect and reconnect your removable hard drive.

That should be all you need to do and Time Machine will recognize the drive as the proper target for backups and do its thing. Thanks to Devin Lane at Shiftedbits.org.