Backup seems to be changing permissions

[Duncan H]

I hope this hasn't already been covered elsewhere, but I couldn't find it here.

I'm running 10.4, and copying from one backup disk to another: neither are boot discs.

One is a drive I call "shared", which has ignore ownership on this drive ticked. This copies some directories that I want to back up to another drive called "backup 1", which has permissions set so that only I can write to it, and no other users.

Everything copies perfectly, but once the copy has run, the "shared" drive has its ignore ownership tick box unticked, and the "backup 1" drive has permissions for all users set to read/write. Exactly the same problem occurs when backing up another set of files to a different drive.

It's annoying, as after every use of Super Duper I have to remember to go into the drives, and reset the permissions manually. I can't see what I've done that causes the permissions on the source and destination drive to change, but they do every time.

The copy is set to "copy newer files", rather than do a smart backup. I guess I need to tell it to ignore something, but I'm not sure what. And even then I can't see why it should remove the "ignore ownership" tick from the source drive. Surely this drive shouldn't be affected by a copy...

[dnanian]

Duncan:

That's totally us. We consciously enable ownership on all drives we copy to: otherwise, you lose the ownership when you copy files -- and thus wouldn't be a "good" copy!

Why would you want to keep ownership turned off?

[Duncan H]

Duncan:

That's totally us. We consciously enable ownership on all drives we copy to: otherwise, you lose the ownership when you copy files -- and thus wouldn't be a "good" copy!

Why would you want to keep ownership turned off?

OK - that does make sense for the drive I'm copying to. But I'm still a little confused as to why the source drive is changing as well.

The "shared" drive contains iTunes and iPhoto data, so that several users can share, and alter, the same data. It's easiest to do this by ignoring ownship on the drive (from my experience).

But I also want to back up this data, onto drives that I don't want anyone else to be able to see/touch/change/destroy in case there is an accident.

When I backup the data, the source drive loses its 'ignore ownership on this drive' tick. Surely only the destination drive should change, not the source.

[dnanian]

Because if ownership is not turned on for the source, the files on the source don't have their true owners displayed. Instead, you get fake, floating values.

The best way to allow groups of users to share files is to use group or "other" (as opposed to individual) permissions, rather than to turn ownership off. Ownership off is a pretty nasty hack in OSX, and I'd really, really strongly advise you to not use it. Instead, work "within" the system to do it the real way...

[Duncan H]

Because if ownership is not turned on for the source, the files on the source don't have their true owners displayed. Instead, you get fake, floating values.

The best way to allow groups of users to share files is to use group or "other" (as opposed to individual) permissions, rather than to turn ownership off. Ownership off is a pretty nasty hack in OSX, and I'd really, really strongly advise you to not use it. Instead, work "within" the system to do it the real way...
Thanks for the help. Or at least, the explanation.

I know I ought to get round to properly learning how group permissions work, so maybe this will give me the impetus to actually do it. I've tended to only pay attention to the "owner" and "others" field, and ignored the group.

[dnanian]

I'm really not trying to be a pain here, Duncan, and not give you a solution -- I'm trying to point you in the best direction.

But, if you want to turn off ownershi for the volume automatically after the backup, you could use a "site customization script", similar to what I've provided in the FAQ entry for spotlight.

What you'd do is use the "vsdbutil" command to turn ownership off. The command line is:

vsdbutil -d "/Volumes/the-volume"

In the site customization script, you'd use the parameter passed in for the source volume, perhaps after checking to see if it's the one you want it to be: I discuss these scripts in the User's Guide.

Hope that helps!