Q: when you umount /mnt/usb it shows: um… Apr 22, 2009 • edyliu Q: when you umount /mnt/usb it shows: umount: /mnt/usb: device is busy umount: /mnt/usb: device is busy A: > lsof +D /mnt/usb find the PID of using /mnt/usb, kill it or quit the application.