What to do when a hard drive won’t unmount in OS X El Capitan

When OS X won't let you unmount a flash drive or external hard drive, here's what you can do.

Mac hard drive icon
Apple

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Glenn Fleishman is the author of dozens of books. His most recent include Take Control of Your M-Series Mac, Take Control of Securing Your Mac, Take Control of Zoom, and Six Centuries of Type and Printing. In his spare time, he makes Tiny Type Museums. He’s a senior contributor to Macworld, where he writes Mac 911.