tl;dr: make sure the user and group filesystem permissions (not just the Sharing permissions) are set for the user account that will be used to access the Time Machine disk over the network
My configuration includes a Mac Mini running macOS Catalina with an attached USB HDD, and a MacBook Air (among other MacBooks) running Monterey. I wanted to use the disk attached to the Mac Mini as the Time Machine disk for all systems on the network. I kept hitting permissions issues, including this one. The previous answers here such as the one by jefe2000 were not sufficient to resolve it.
The external disk was formatted as HFS+ (Journaled, Case Sensitive, Encrypted) and mounted by the Mac Mini.
The Mac Mini itself had Time Machine configured and working, backing up to the root of the external disk (
In my System Preferences > Sharing > File Sharing, I had to add a directory inside the external disk (e.g.
/Volumes/ExternalHDD/RemoteBackups) as the shared folder. For this shared folder, I used the following settings
under "Options" (the button on the main File Sharing page) I enabled "Share files and folders using SMB" along with AFP (though I think only SMB ended up being used for this). I did not add any Windows File Sharing users.
RemoteBackups shared folder, under "Users" I added my Mac Mini's primary administrator account for Read & Write. I left System Administrators and System Group to the default (also read & write). I set "Everyone" to "No Access"
When you right-click on the shared folder, you get extra menus including "Advanced Options". For this, I selected "Share over SMB and AFP". I also selected "Share as a Time Machine backup destination"
This is roughly where other users' answers stop. However, it was not enough for me. I could see the Mac Mini's
RemoteBackups shared Time Machine "disk" (really just a directory on a volume), but every time I tried to use it, I would get the same permissions errors.
To debug the situation on my MacBook, in Finder I went to Go > Connect to a Server and entered the address for my Mac Mini;
smb://mymac.local. Use the Mac Mini's system admin account to log in, and you get a menu with shared volumes available. From here, I could see the
RemoteBackups directory. But after opening it in Finder, I could not make any new Folders. Confusingly, if I did a "Get Info" on the
RemoteBackups directory, at the bottom under Permissions it actually said that I had Read & Write access, but any write attempts or attempts to adjust permissions would get blocked with permissions errors.
This indicated to me that while I had the SMB and network sharing settings configured correctly, I was missing a critical piece: the permissions on the disk itself.
Back on the Mac Mini, I pulled up a terminal window and
cd'd over to
/Volumes and could see from
ls -l that the the
ExternalHDD disk had
root ownership and
wheel user group. The same was in effect for the
RemoteBackups subdirectory located on that drive. This appears to be OK for processes running locally on the Mac Mini, but evidently not OK for remote access. I had to run
chown -R myadminusername /Volumes/ExternalHDD/RemoteBackups to give the
RemoteBackups dir ownership to my Mac Mini's local admin user account. For good measure, I also ran
chmod -R ug+rw /Volumes/ExternalHDD/RemoteBackups to make sure everything had read write access under that directory tree.
Another measure I took was to dig through my Keychain app on the MacBook and delete any saved logins for my Mac Mini server, and for Time Machine. I also rebooted the MacBook and Mac Mini a couple times during this whole process for good measure to make sure all the updates were getting applied.
After all this, on my MacBook, I selected the Mac Mini's Time Machine disk
RemoteBackups again (with encryption, logging in with the Mac Mini's admin account), and finally everything works.