This error message has come up on a number of occasions and I’m sure many people have wondered what is the best way to deal with this. This is for macOS, OSX, Macintosh operating system. For historical sake, I’m currently running High Sierra.
I have found a few main things that cause this error on my machine…
1) There is some application with a file open on that disk (the obvious one). Double check you have no apps with files open on the disk first.
2) There is a terminal open, and you have changed directory onto the ejectable disk in terminal. Check any open terminals and close them if this is the case.
3) QuickLookUIService was holding on to the disk and needed to be Force Quit. Open Activity Monitor, find QuickLookUIService, and click the x button and Force Quit! Or you can do it on the terminal with
There is an application called “What’s keeping me” that can help you find which process is keeping your disk from ejecting http://www.hamsoftengineering.com/products/wkm/wkm.html . Using this tool was helpful in finding QuickLookUIService for me. So far, I have not come across any other system process giving the same trouble as QuickLookUIService.
I hope this was useful. Have fun ejecting your disks!