Time Machine couldn’t complete the backup to “TimeMachine”. An error occurred while preparing the backup

Hey there! For this, I may, as I posted before, (Appears the OP’s cause was something different, due to the logs), I would:

Disconnect any external drive you use for Time Machine, (Eject first).

Turn OFF Automatic backups in System Preferences > Time Machine.

Open Terminal in Finder > Applications > Utilities.

Paste this command to clear the Time Machine snapshots, and press Return afterwards.

sudo tmutil thinlocalsnapshots / 999999999999999 4

Once it finishes, Restart, re-connect the external drive, re-enable Time Machine and test again.

PS: Before running the command, also delete the incomplete backup in Finder:

Double click the external drive on the Desktop, or in the Finder Sidebar.

Open “Backups.backup”, open the name of your Mac, scroll to the bottom, (Usually), and move the tile of the incomplete backup, “Usually says In Progress”. Then try the steps above.

Otherwise, how is your Mac and external drive’s storage? Hope that helps!

Hi there!

I’ve come across this multiple times and read the replies to you and the OP.

It sounds like, to me, especially if you can’t backup to any external drive, even after reformatting properly, it may be an OS/content issue as you stated.

First:

Are there any connected drives to your Mac(s) that are also set to be backed up? Of course if so, eject, disconnect and try again.

Your suggestion of excluding files or directories from being backed up is also right on, there is one setting to allow/remove by default, which makes it easier, is I believe System files and Apps, that’s a good test. You can add that to be excluded from Time Machine Advanced Preferences, restart and test.

I know you’ve also probably run first aid, etc. which is another good step if all else fails. Otherwise:

IF the first backup completes okay, but the subsequent ones don’t, then I’d try clearing the Time Machine snapshots, restarting and trying again.

You can do this by opening Terminal from Finder > Applications > Utilities. Then run and enter the following command:

sudo tmutil thinlocalsnapshots / 999999999999999 4

(Yes, that’s 15 9’s)

Restart your Mac and try again.

Otherwise, if all else fails, I may delete the Time Machine plist/restart:

Open Finder > Go > Computer > Macintosh HD (Usually) > Preferences.

Save a copy them delete com.apple.timemachine.plist, then delete the file from that location, restart and test again. If you do this, you will have to choose your backup disks again, however if it is an issue with this property list, it may just fix the problem.

You can also use Terminal to check the Time Machine status, it’s not much, but you can run and enter:

tmutil status

And of course, testing the backup process while in Safe Mode or in another active user account is a good test/solution.

Knowing, of course if another Mac has the same issue with the same external drive, or the same Mac has an issue with another external drive would be revealing. Hope something here helps!

I had the same problem early today. Open the time machine preferences, select disk, remove the disk you are using, then if you are on AirPort, make sure the name on the drive you are using is not duplicated on finder locations. if you are using an external make sure the name is not duplicated in finder locations. After that, on backup disk click on the one you want to designate and use that disk. this worked for me without loosing my prior backups.

I hope this help!

I had similar problems that I could not pinpoint - my problem was due to a corrupted file which was stopping the backup

this worked for me

Get the Time machine logs

https://discussions.apple.com/thread/250226175

look through them and see if you can see a file name or some other error that is causing it

here is my last post in the thread that helped me the most

https://discussions.apple.com/thread/253012759?answerId=255778958022

SOLVED !

ok I removed the snapshots & restarted

still didn't work

tried to find "com.apple.timemachine.plist" but it simply isn't there - maybe BigSur does it a different way

anyhow I sourced the log file again and found the following mention of a file named

"Iggy & The Stooges/1-01 Search and Destroy.mp3"

that file was added from a download around the same time as the problem started

I imagine Iggy Pop corrupting something ... unthinkable !!

anyhow I removed the file and all seems to be working fine now

here is the error showing in the logs

2021-08-24 07:21:57 Failed to copy '/Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/iMac/2021-08-24-071250/Macintosh HD - Data/Users/user/Music/iTunes/iTunes Music/Iggy & The Stooges'to '/Volumes/mac backup/2021-08-24-071251.inprogress/Macintosh HD - Data/Users/user/Music/iTunes/iTunes Music', error: -48, srcErr: NO

2021-08-24 07:21:57 Failed to copy '/Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/iMac/2021-08-24-071250/Macintosh HD - Data/Users/user/Music/iTunes/iTunes Music/Iggy & The Stooges/1973 - Iggy & The Stooges/1-01 Search and Destroy.mp3'to '(null)', error: -8062, srcErr: NO

2021-08-24 07:21:57 Failed copy from volume "Macintosh HD - Data"

Thanks so much. Just tried the thinning command and remaining steps. Unfortunately, same result. Pasting the logs below in the hopes that someone might have an idea. At this point, I have received a new backup drive, but if it is TM that is corrupt, I'm thinking that opening and installing that drive will have no impact but will have cost me $180. Wondering if I should:

1.) Try the new drive and hope that it works (just doesn't make logical sense that it would), but I don't claim to understand how all this works.

2.) Revert using the TM backup from right before I upgraded to Big Sur (which seemingly has it's own risks)

3.) Use something other than TM for backup (major disappointment).

4.) Take to the Apple store for evaluation.

5.) Some other plan, not currently evident.

Appreciate all the patient support from this group. This is very stressful.

Thanks.

Logs attached as additional text due to character limits.

If you’re 100% sure the drives (with right format and potential repair in dusk utility to be double sure), cables and USB ports are fine, here’s what the complete amateur I am would suggest:

• Check that the folders you want to backup can’t create conflicts and exclude others from the backup options (linked files, cloud-based backup drives like OneDrive, Box or Google Drive)
• Restore your OS and latest backup
• Consider upgrading to a more recent version of OS (if your machine can take it)

Nothing to do with Mac OS. After researching what could be causing the error, I excluded (check your time machine settings, options...) the OneDrive folder from backups... It works like a charm and now time machine resumed with its hourly routine.

[Edited by Moderator]

Having an issue with Time Machine backups

getting an error

Time machine couldn’t complete the backup to “Back Up Catalina”

An error occurred while copying files.

I did a bit of googling to try to see if it was a common problem

seems like it might be a corrupted file

I tried to do a backup to a new drive and the same thing happened so its not the drive

I saw a post about getting the Time machine logs using terminal - which i did

I’ve looked thru it but can’t spot anything that makes any sense to me ;-)

I was hoping it might have showed a file name or something where it has going wrong

I can still go into time machine on the desktop & see older backups

any suggestions?

thanks ... but

cables & usb ports are working fine with these and other disks

all files being backed up are local (no cloud etc)

I have excluded dropbox and another folder that I regularly download to

Did a OS update so now have Big Sur 11.5.2

when the disk is first formatted it seems to do 1 full backup then every time it tries to do the nest auto backup it gives the failed message

when I enter into Time Machine it weird because it show incremental backups on the right of the screen

I am now doing some tests (by creating new folders & files ) to see if they actually do get backed up

No worries.

If you decide to run the command to clear Time Machine snapshots, just disable auto backup in Time Machine Preferences first, you can also eject the external drive, sorry, it’s not imperative but I left that out, but one of those steps should work, cheers.

Good luck!

SOLVED !

ok I removed the snapshots & restarted

still didn't work

tried to find "com.apple.timemachine.plist" but it simply isn't there - maybe BigSur does it a different way

anyhow I sourced the log file again and found the following mention of a file named

"Iggy & The Stooges/1-01 Search and Destroy.mp3"

that file was added from a download around the same time as the problem started

I imagine Iggy Pop corrupting something ... unthinkable !!

anyhow I removed the file and all seems to be working fine now

here is the error showing in the logs

2021-08-24 07:21:57 Failed to copy '/Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/iMac/2021-08-24-071250/Macintosh HD - Data/Users/user/Music/iTunes/iTunes Music/Iggy & The Stooges'to '/Volumes/mac backup/2021-08-24-071251.inprogress/Macintosh HD - Data/Users/user/Music/iTunes/iTunes Music', error: -48, srcErr: NO

2021-08-24 07:21:57 Failed to copy '/Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/iMac/2021-08-24-071250/Macintosh HD - Data/Users/user/Music/iTunes/iTunes Music/Iggy & The Stooges/1973 - Iggy & The Stooges/1-01 Search and Destroy.mp3'to '(null)', error: -8062, srcErr: NO

2021-08-24 07:21:57 Failed copy from volume "Macintosh HD - Data"

Amazing, well done! Too bad though, that’s an awesome record! How could Iggy do that to you!? 🙂.

Just curious, about the logs, did you search Console system log? Or open it in /Library/Logs or ~/Library/Logs?

Nice job finding that, hope you can download it again without issue!

I used terminal

this code give you the logs

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}'

copy & paste the log info somewhere

then "exit" terminal