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I have a 15 GB USB that I want to use as a macOS installer, and it got corrupted.

I tried to reset it, but Finder and the normal Disk Utility does not recognize it, the Recovery Disk Utility loops on loading drives and Terminal throws an error if I tried to reset it.

What can I do to make it work again?

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When I run into this kind of problem, I first identify the device with:

diskutil list

(e.g., /dev/disk3 -- BE SURE TO GET THE CORRECT DEVICE OR YOU WILL HAVE DATA LOSS)

Then I use the dd command to zero it out.

sudo dd if=/dev/zero of=/dev/disk3 bs=8M

I hardly ever wait to completion, rather just a few seconds (maybe 10-15) and then press Control-C to stop it. This is just enough to wipe out everything at the start of the device that tells how it's formatted.

At that point, I go back into Disk Utility, insert the device, and repartition it, putting on a new formatted filesystem.

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  • 8M gives an unvalid character. Putting only 8 will give me dd: /dev/disk5: Resource busy Oct 28, 2019 at 13:58

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