Problems on Mac OS X with owners and groups? For solution, read on...

Lee Cullens lee_cullens at
Tue Aug 30 15:23:23 GMT 2005

Martin Koistinen wrote:

> All,
> This message is placed here for the aid of others in the future.  I 
> have search the archives for this solution, but sadly, only found a 
> couple of (rather old) messages from people exhibiting having the same 
> problems, but without any replies for this solution.
> Please forgive me as I seem to ramble on here, I do so with the intent 
> of making this solution more findable by others having this issue but 
> don't exactly know what they are searching for.
> The problem is characterized by copies made by rsync have reset owner 
> and group information -- in my case to root : unknown -- regardless of 
> the switch settings for rsync.  So, for example:
> # rsync -aog source dest
> will copy all files from source to dest, but will not preserve the 
> owner and group settings of the source files, even though the 
> (redundant) flags for -a , -o and -g are all set.
> To make matters worse, because of the problem, the whole --link-dest 
> functionality doesn't save space in a backup/snapshot scheme for 
> unchange files, since rsync will find that the dest files in the 
> previous backup will have different ownership than the source files 
> (unless the source files also happen to have root:unknown ownership, 
> that is)
> This problem is most likely to occur with those of us who have added 
> extra disks to the system (probably) via firewire or USB.
> The issues is not rsync, but rather a setting in the OS.  OS X has 
> newly formatted disks marked with a flag to "ignore ownership details 
> on this volume" by default.  To fix this, select the volume you wish 
> to check/change in the finder.  File -> Get Info (Apple-I), in the 
> multi-panel, info-window for your disk, open the section "Ownership & 
> Permissions:", and verify/uncheck the checkbox for "Ignore ownership 
> on this volume".
> Voila, the "rsync" issue is now gone.
> I suspect that this ownership flag is set by default to emulate disk 
> insertion behavoir prior to OS X on the Mac (where it was ignorant of 
> ownership and/or permissions).
> It would be great if rsync could verify that ownership settings 
> actually took when they are set and report in the verbose output 
> and/or logs if there is a discrepancy.  This would help to aid those 
> of us in setting up rsync-based backups and will forewarn us of 
> related problems during full recovery of a backup.
> I hope this helps someone and/or aids the future development of rsync.
> -- MKoistinen

You would see that and more in my article <a 

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