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I have a 4 Gig USB drive that I'd like to format.

I go to the Disk Utility, and try to format it, but it says that the device is busy. (This same error occurs no matter whether I tried to format the whole drive, or just the partition.)

So, I do some research, and figured out how to disable automount. It's now disabled.

To be on the safe side, I first unplug then reconnect the USB stick then tried:

sudo umount /dev/sdb
sudo umount /dev/sdb1
sudo umount /dev/sdb*

Now, the Disk Utility STILL gives me the same error - usually "/dev/sdb is busy" or "/dev/sdb1 is mounted" or similar.

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Why don't you use GParted which will allow you to unmount from the context menu and do whatever you want to do (chech, format, label, etc.) easily? – Sadi Jan 24 '13 at 12:30
Oh, man, I forgot about GParted. I had that a while back, I loved it. After I had to reinstall Ubuntu, I sort of forgot about it... Thanks for reminding me about that! I actually figured out the problem, though: I'd left the Startup Disk Creator open, and for some reason, it was auto-mounting my flash drive... – JamesTheAwesomeDude Jan 24 '13 at 14:37

Run df -h in terminal and make sure there is nothing mounted that looks like /dev/sdb*. I had /dev/sdb11/ and /dev/sdb8 mounted so I had to run umount /dev/sdb11 and umount /dev/sdb8.

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In my case the disk was umounted and the problem persisted. I had to use gparted to delete the partition, restart (as requested by the app) and try to format it again. After that I was able to.

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