Hack: Accessing Time Machine backups

September 20, 2018

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A natural choice for macOS backup is to use Time Machine to output to an external device. To protect the data, the backup disk is encrypted and each backup is encrypted independently. That’s all standard functionality for Time Machine.

Time Machine works great when you wish to recover a deleted file or overwritten file. We don’t often see the need as we working in the cloud (versioning automatically on GDrive) or using Git (which is a time machine in its own right) but the safety net is reassuring.

In the last week, we had reason to access a backup but the computer in question had been reformatted for a different purpose, we couldn’t use it to access its own backup.

What doesn’t work

The theory is you can access another computer’s Time Machine by clicking on the Time Machine icon in the menu bar and then holding down holding Option (alt). (You can add the Time Machine icon to the menu bar using System Preferences). When you press Option ‘Enter Time Machine’ changes to ‘Browse other backup disks…’ which prompts for a backup disk.

Sadly, selecting the other machine’s Time machine backup doesn’t seem to work for us. It always displayed our current machine’s backup. A quick search shows others have seen the same problem.

Disk Utility to the rescue

Access your backup server in Finder - it’ll be listed in the Shared section in the Sidebar. You can log in (with your disk encryption password) and navigate to the folder where your backups are stored.

They are .sparsebundle files, in recent versions of Time Machine. If you haven’t been using encryption, you can probably review them just by right-clicking and selecting ‘Show Package Contents’.

If you are using encryption, then ‘Show Package Content’ issues an error box, stating ‘Device not found’.

Load up Disk Utility. Then use the menu to File > Open Disk Image and navigate to the backup you want. You should enter your backup encryption password when prompted. It’ll take a moment to think, but then your backup will be mounted and accessible in Finder.

The backups are organised into folders which are timestamped ‘date and time of backup’ and their content is ‘what has changed since the last backup’. It is not that easy to find the latest content of a folder, but that’s the way it is. Copy the files you want out of the Backup.

Warnings

  • Don’t change or add files in the backup. It’s probably fine but you want your backup to work. This is an emergency!
  • Always unmount your backup volume when you are done. Otherwise, next time to try to access it you may get an error saying it’s locked.

Use at your own risk!

Credit: Photo by James Newcombe on Unsplash

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