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I have OSX Server running on a mac mini in my home. I've been using it for doing Time Machine backups from my MacBook. This worked fine until I changed the password for my user account on the mac mini. At that point, backups on my laptop started failing, indicating that I needed to update the password that the laptop was storing for the mac mini. However, when I try to do so (at System Preferences > Time Machine > Select Backup Disk...), I get the following error:

"You do not have the necessary read, write and append privileges on the selected network backup disk."

The laptop is running OSX 10.9, and the mac mini is running OSX 10.8.

Has anyone using OSX Server for backups experienced something similar to this? Does anyone know how to fix it (without losing all of my previous backups)?

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    Seems this has broken again on Big Sur on an APFS backup volume. None of the solutions below seem to work. – balupton Dec 20 '20 at 1:09
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On my iMacs running macOS High Sierra (version 10.13.6) I had to explicitly add filesystem permissions for Time Machine to function correctly over the network. This resolved the You do not have the necessary read, write, and append privileges on the selected network backup disk error message.

I'm using username_A on both the source and destination iMacs.

On the source iMac, I used username_A when configuring Time Machine to run over the network to the shared network drive.

On the destination iMac (the one sharing out the Time Machine backup disk over my home network), I had to add username_A to the list of allowed users in System Preferences → Sharing → File Sharing. I also had to pull up the Get Info window for the shared disk and add username_A to the Sharing & Permissions list at the bottom of the window. Once I had added username_A in both places on the destination iMac, I was able to get Time Machine running over the network.

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  • Same problem here. It was only when I added the permission to the shared folder from the Get Info window that it allowed the connection. – zkarj Feb 19 '19 at 7:30
  • I only had to set permissions for Everyone to Read/Write in the Get Info Window. – Paul J. Lucas Feb 11 '20 at 4:00
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I still don't know what caused the issue to come up in the first place, but I was able to get around it by going to Server.app > File Sharing > [my backup volume] > Edit Share Point... and then adding my user to the Access section of the page with Read & Write permissions.

I don't know how/why it worked before or why changing the user password caused it to stop working, but doing the above gets around the issue.

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If you've previously connected to said network drive before and are having trouble reconnecting, it's possible, the folder where the time machine back-up resides is locked. I would try navigating to the network folder, look for "TimeMachineBackup" and if you see a locked logo on the folder, simply right click -> get info, and uncheck the locked box, then try initiating the time machine to use the network drive again.

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The same error message occurred in my case. I have a Time Machine set up with netatalk. Initially, I had only one user, but later I added additional users and added them all to a timemachine group, with the single sparse bundles owned by the respective users. Even though a backup already existed and the user has full permissions on the sparse bundle, the Time Machine backup failed.

It turns out that the user also needs write access to the folder where the sparse bundle is located.

I can understand that this is required for an initial backup, where a sparse bundle is created (and renamed). However, the Time Machine client checks for the write permission even if the sparse bundle already exists.

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