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When I do

sudo umount /media/KINGSTON

I got

umount: /media/KINGSTON: device is busy.

By using

fuser -c /media/KINGSTON


cat /proc/<pid>/cmdline

I found that the process is thunar--deamon. I closed all file manager windows. When I try to umount it by right cliking on the desktop, it also gave an error :

An application is preventing the volume "KINGSTON" from being unmounted

I am affraid that killing Thunar is going to impact other process running in other terminal. How can I tell it that I don't need this usb key anymore so it stop using it?

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If nothing is writing to the usb stick and you're out of other ideas, unplug it. – Martin Owens -doctormo- Nov 6 '10 at 19:27
sudo fuser -mv /media/KINGSTON will show the process name (instead of needing to do the separate cmdline command). – Kees Cook Nov 7 '10 at 1:51

If you know that the media device is synchronised (there're no outstanding writes), then use the -f switch to umount (force unmount).

From the unmount man page, the -l switch does a "lazy" unmount, which detaches the filesystem now, and cleans up all references later.

sudo umount -f /media/KINGSTON


sudo umount -l /media/KINGSTON
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