Ownership & Permissions On An External SSD

[Buadhai]

This on a 2017 iMac Running Catalina.

I have an older WD Elements dive on which there is a volume called Media. On this volume I keep videos, photographs and lots of other stuff, including iMazing backup files.

I decided to buy a Samsung T7 SSD on which to store this stuff. I partitioned the drive into two volumes, one of which is formatted as Mac OS Extended, as is the volume on the old WD drive.

I used CCC to copy the old Media volume onto the new drive. Both volumes have the same owner/group (root/staff) and permissions (755). Neither volume has "Ignore ownership" enabled.

iMazing refused to work with the new volume insisting that it didn't have read/write permission on the drive. I eventually gave up trying to fix this and simply changed the permissions to 777 after which iMazing was happy.

A couple of questions:

• Why would iMazing be able to r/w from one drive and not the other?
• What should the ownership and permissions be on an external drive? I want all users to be able to read and write from the drive. root/staff 755 seems odd to me, but has worked fine with the volume on the older drive.

 

[Fishrrman]

Easiest way to overcome permissions problems on an external drive is to:
a. click on drive (or partition) icon in finder
b. bring up the "get info" box
c. at the bottom, click lock and enter password
d. put a check into "ignore ownership on this volume" in sharing and permissions.

Works every time for me.

 

[Buadhai]

This has always seemed to me to be kind of a lazy, sledgehammer approach to a screwdriver problem. I've had external drives on Macs for decades now and have never had to resort to a solution like this for permissions problems. I didn't have to do this on the drive which was replaced by the new SSD. Why now?

 

[Fishrrman]

Look at my avatar.
I'm a "sledgehammer kind of guy".
I do the "ignore permissions" in get info as a matter of course on EVERY external drive I have...

 

[Buadhai]

OK. Got the picture. I figure that if I use the sledgehammer approach I don't learn anything.

Question: What ownership and permissions do you have on EVERY external drive? (You'd actually have to uncheck the "ignore" box to see what the pre-sledgehammer ownership is.)

 

[chown33]

I've always just used the Ignore Ownership feature, or I've copied files onto the drive so I'm the owner.

I don't see the problem with Ignore Ownership, but maybe I don't understand exactly what you're trying to accomplish.

If I happen to have an external disk where I want ownership enforced, then I create it that way in the first place, and I copy things to it from a suitable account. That could be my admin account, a non-admin account, or whatever I want, depending on what I'm trying to accomplish by enforcing ownership.

Sometimes when I'm developing software, I want a fairly specific access-control environment, including owneship, normal Unix permissions, or ACLs. I put that on a disk-image (usually sparse bundle), and make sure Ignore Ownership is disabled.


If all the actual permissions are set to 777 (or 666), then anyone can R/W anything anywhere, but the permissions of files or folders can only be changed by root (the owner). Conversely, if Ignore Ownership is activated, then you get the same R/W ability, but you also get the ability to change permissions (should one wish). So that's something one can do under Ignore Ownership that isn't doable with a disk-wide setting of full-open permissions.

Another thing is that Ignore Ownership can be easily and quickly reversed, simply by unchecking the box. The underlying action is to change the volume's mount flags (use 'mount' cmd in Terminal to observe). In order to change all the permissions across the disk, one would need to run a recursive 'chmod' cmd, or use Finder's Get Info window to change permissions recursively. Either one will likely take longer than simply unchecking a box.

Ignore Ownership may seem like a sledge-hammer, but needing to run recursive 'chmod' seems like a swarm of a thousand mosquitos. No one thing is a big problem, but the sheer number is a different story.


I can't answer your question about iMazing, since I've never used it.

 

[Buadhai]

Thank you for taking the time to write such a clear and understandable explanation.

As for what I'm trying to accomplish; it's simply to understand why I've never had to use ignore ownership in the past and why root/staff and 755 on my previous Media volume worked fine for me, but failed to work as expected when I created a new Media volume (via a CCC clone) with the same ownership and permissions.

 

[chown33]

As for what I'm trying to accomplish; it's simply to understand why I've never had to use ignore ownership in the past and why root/staff and 755 on my previous Media volume worked fine for me, but failed to work as expected when I created a new Media volume (via a CCC clone) with the same ownership and permissions.

Well, I can't offer any help on that, because it seems to be related only to iMazing.

 

[Buadhai]

I guess that's why I called it a sledgehammer. Yeah, ignoring permissions solved the problem, but I didn't learn anything about what caused the problem in the first place.