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Is it possibile to change default permissions /dev/disk*?

In Linux this is done in the udev configuration files; which is the equivalent on OS X?

I'd like to give group write permissions so members of the group operator will be able to perform write operations to external hard drives without using sudo (e.g. run virtual machines from external usb drives).

I tried to sudo chmod g+w /dev/disk2* but it doesn't persist as when the first write attempt permissions revert to 640 instead of the changed permissions.

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    Why is access to the device file necessary? To let other users run virtual machines on an external USB drive you can mount it, create a directory, give the operator group write access to it and put the virtual machines in there. Am I missing something in your setup? – jaume Feb 20 '14 at 7:40
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    Without wishing to confuse the question: amongst the advanced topics for VirtualBox, there's Using a raw host hard disk from a guest. Many times I tried but failed to get what's suggested working on OS X … some of my experiments involved attention to the modes of devices, and so this question interests me. – Graham Perrin Jul 23 '14 at 22:02
  • Not easily. What software runs your virtualization? Perhaps we can get you to your actual destination without messing with default permissions. It might be as simple as changing the permissions on the mount point in /Volumes once you script the mounting of the filesystem. – bmike Sep 18 '14 at 16:02
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As far as I can tell, Apple locks this stuff down pretty hard to the point where it's not reasonably possible.

However, considering what you want to do with it, I'm certain that what you're actually wanting is to give write access to the external HDD which can be found in /Volumes/ (after you plug it in). Now, most external HDDs I've used (that are formatted properly*) will allow anyone to write to 'em unless an Admin chmod 'em to say otherwise.

*NTFS-formatted drives are read-only through the Mac OS. As far as I know, there is no way around this without reformatting the drive.

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