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Since a few weeks ago, i am unable to backup my mac using time machine. It finds my backup drive, but each time i get a message that reads : failed to create a local snapshot.

I have already reinstalled a fresh installation using the apple recovery utility, and also tried to use a different backup drive. Note that i did not try to erase my data yet.

Edit: I wanted to point out the fact that this issue is impacting two macbook at this time, while six others are being backed up fine, using the same release and the same backup disc.

Edit: Using this command sudo tmutil listlocalsnapshots /, I get this output:

Snapshots for volume group containing disk /:
com.apple.TimeMachine.2020-06-18-194222.local
com.apple.TimeMachine.2020-06-18-203811.local
com.apple.TimeMachine.2020-06-18-213808.local
com.apple.TimeMachine.2020-06-18-223858.local
com.apple.TimeMachine.2020-06-18-233809.local
com.apple.TimeMachine.2020-06-19-004440.local
com.apple.TimeMachine.2020-06-19-014255.local
com.apple.TimeMachine.2020-06-19-024125.local
com.apple.TimeMachine.2020-06-19-033808.local
com.apple.TimeMachine.2020-06-19-043810.local
com.apple.TimeMachine.2020-06-19-053809.local
com.apple.TimeMachine.2020-06-19-064356.local
com.apple.TimeMachine.2020-06-19-083809.local
com.apple.TimeMachine.2020-06-19-095017.local
com.apple.TimeMachine.2020-06-19-104256.local

So, snapshots are indeed created despite time-machine's error message.

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  • All the Macbooks are on the exact same version of macOS, yes? – Nathan Jun 19 '20 at 12:26
  • Yes, all Macbooks are on the exact same version of macOS. – f.thoorens Jun 19 '20 at 13:37
  • Have you checked the aailable memory on the 2 MacBooks? – Natsfan Jun 19 '20 at 15:26
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    that has also been checked. both have way more than 10% of available space. – f.thoorens Jun 19 '20 at 15:48
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Timemachine has changed a lot between different OSX versions. Some settings were still linked to an old version. The root cause appears in the Console logs. You can filter Timemachine error in Console.app by searching backupd.

In this particular case, we've figure out the error was: Illegal permissions or ownership discovered on local snapshot directory !

We've removed the local snapshot folder: solution from Macrumors

1. command-r boot to recovery
2. csrutil disable in Terminal to disable SIP
3. reboot to command-r recovery again
4. in Terminal cd /Volumes/Macintosh\ HD/Volumes (or whatever your normal boot drive is named)
5. rm -rf com.apple.TimeMachine.localsnapshots
6. csrutil enable in Terminal to enable SIP
7. reboot

And then finally, set the permissions correctly on the default "Catalina Timemachine local path":

sudo chmod -R 755 /Volumes/Macintosh\ HD/com.apple.TimeMachine.localsnapshots

And finally it works!

Main advice: Time machine error messages are not always complete. Look at logs in Console.app while triggering Backup now for full logs.

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As suggested, the only solution was to back up the whole system using a rsync command, and reinstall the OS from scratch.

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