External Hard Drives Changing Permissions to Read Only

To add an addendum to this thread for those like me looking for an answer to the problems of write errors to external drives.

I have a brand new 6TB external Lacie drive onto which I'm loading a body of work form a failing raid array in one of my 2 Mac Pros. The drive is formatted for Mac so no problems there. What was weird about this was that while I could read and write normally form the machine to which it was attached over a network I couldn't write to it and in some folders couldn't display the files to other machines. The permissions appeared to be OK on the local machine and it was set to not use permissions as well but on the networked machines the show info box gave me 'custom access' message and no option to change them.

I was stumped until I used Kappy's trick of going into terminal and resetting the permissions that way. It seems that the wysiwyg interface doesn't accurately reflect the state of the permissions settings on the drive and you have to use terminal to access them fully.

I'm on Yosemite on 2 machines and Snow Leopard on the third.

If you already had a working filesystem and you get the read only situation (i.e. the -50 error), double check the SATA cable going to your drive. I had all my user directories on the second drive (first partition) and workspaces on the same drive (in a second partition) - both were showing as read only (huge hint).

I read about a possible cable issue and decided to try it, guess what.... it was simply a bum cable (or one that had worked it's way lose with vibration). I spent a few bucks and got a replacement SATA cable with metal latches on each end - problem solved, hours of reinstallation / reconfiguration averted.

Reminding you that you still need to backup invaluable data (or at least have it on icloud, box.com, dropbox, gdrive, or your fav).

Turn it off an on again...

Hello, I hope everyone has fixed their problems with the external drives suddenly changing to Read Only. It happened to me recently, after years of using about 4 drives. After searching through many posts, I realised I'd changed my set up recently, and instead of turning off power to the drives at night, I was just shutting down my laptop, but leaving power plugged in.

I decided to try a turn-it-off-and-on-again approach before doing anything more technical, and it has worked (so far). I switched off the power to the drives, started up the macbook, then plugged in the drives (via a usb hub) and turned the power back on. They're all back to normal now.

Thanks for all your posts and suggestions, which have been informative and entertaining. I hope this one will be of help, too.

Hi, Kappy. My Toshiba external drive format changed to NTFS when I used it on a Windows PC. This had happened once before and an Apple-authorised service centre engineer had been able to change the 'read only' permission so that I was able to write onto the drive without formatting it. Can you please show me how to do it? I can't afford to format my drive. Also, there are no 'owner/group/admin' user options on my drive info like you've asked for at the beginning of this thread. Thanks in advance!

thanks al lot! finally manage to move files from my mac to the external HD without erasing or formatting my HD. i don't know why after updating my software from el capitan to sierra my HD automatically turn to NTFS but thanks to you again save a lot of my time back up 7 formatting my HD

Looks like gist of this issue ends up being with NTFS formatted drive. I found this good article on the subject.

https://www.engadget.com/2011/09/19/mac-101-format-choices-for-usb-flash-drives/

Basically, you cannot write to an NTFS from Mac but can read from it.

To add to my post, I have a 2004 G5, running 10.5.8.

I have the same problem since today.

Maybe i shoud switch back to ubuntu :/