reuse Microsoft Office USB stick with 7.9 GB - Error: -69877: Couldn't open device - dd: /dev/disk9: Permission denied I have a USB stick from Microsoft, which was used to ship Office 2016 for Mac. I don't use Office 2016 for Mac, so wish to use this stick for other purposes.

/dev/disk9 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *7.9 GB     disk9
   1:               Windows_NTFS Office 2016 for Mac     7.9 GB     disk9s1

&gt; diskutil eraseDisk ExFAT DiskName /dev/disk9
Started erase on disk9
Unmounting disk
Error: -69877: Couldn't open device

&gt; sudo dd if=/dev/zero of=/dev/disk9
Password:
dd: /dev/disk9: Permission denied

&gt; sudo diskutil unmountDisk force /dev/disk9
Forced unmount of all volumes on disk9 was successful

&gt; diskutil eraseDisk ExFAT DiskName /dev/disk9
Started erase on disk9
Unmounting disk
Error: -69877: Couldn't open device


Is this USB stick somehow readonly? How to use it?
After doing a little research on this, my conclusions are that you can try:


Restarting your machine. If you haven't restarted your machine since plugging in the USB drive then I would try that. Once you do, try reformatting the USB.
Running as root. In Terminal type in sudo su, press enter and then type in your password. Then issue the commands, being careful to type them in exactly as you need.
Booting into Safe mode. Another method is using Safe Mode, as this should allow you to encounter fewer errors than using terminal as a regular user. To boot into Safe Mode, immediately press and hold the Shift key down after booting up - keep it down until you see the login screen.


Finally, did you ever interrupt the formatting process at any time? Doing that can pose issues, so booting into Safe Mode is a good option.

Resources:  


https://origin-discussions-us.apple.com/thread/4806895?start=0&amp;tstart=0
https://apple.stackexchange.com/a/225061/242879  
https://askubuntu.com/a/771326