What are default owner and group permissions on an external volume?

Solution 1:

For MacOS (née OS X), the default owner and group permissions on a freshly formatted external drive are (in several parlances):

• 775
• drwxrwxr-x
• user group
• whichever-user-formatted-the-external-drive staff

For example, I just hooked up an external drive, my username is mrcook, so the permissions shown for the drive via Terminal and the ls -pal command are:

drwxrwxr-x mrcook staff

To change permissions on an external drive with MacOS, run chmod to change the permissions like read, write, etc. Run chown to change the owner and group. Both chmod and chown can be run without using sudo if you are the administrator of your Mac.

You can read more about chmod and 'chown` on the extremely useful SS64 website which has a list of (most?) MacOS shell commands and their switches.

Update to add information about the "ignore ownership on this volume" checkbox option in the Finder's Get Info

The "ignore ownership on this volume" is checked by default so "everything just works" as Apple likes to say. This option sets the permissions as described above. However, if you uncheck the "ignore ownership on this volume" option, the drive permissions change to system wheel.

I was able to use sudo vsdbutil -c /Volumes/DiskName recommended by this Mac OS X Hints page from 2002 to check the status of the permissions on the drive. The other suggestions worked as well:

• sudo vsdbutil -a /Volumes/DiskName to check the option
• sudo vsdbutil -d /Volumes/DiskName to uncheck the option

YMMV though depending on the version of MacOS you are using. I highly recommend this previous question on how to change "ignore ownership on this volume" from the command line because the changes made via vsdbutil may not stick after mounting and remounting the drive.