# umount /media/usb-vfat/
umount: /media/usb-vfat: device is busy
umount: /media/usb-vfat: device is busy

# fuser -a /media/usb-vfat/
/media/usb-vfat/:    12832c 12833c
 -a        display unused files too

# fuser -k /media/usb-vfat/
/media/usb-vfat/:    12832c 12833c
-k        kill processes accessing the named file

or

check alll processes using "usb-atom"

# /sbin/fuser -m /media/usb-atom/
/media/usb-atom/:     5098c

# ps aux |grep 5098
xxxx     5098  0.0  0.0   5744  1896 ?        Ts   08:59   0:00 -csh

# kill -9 5098

# umount /media/usb-vfat/


* note that /sbin/fuser is for RHEL5.3


reference : http://www.idevelopment.info/data/Unix/General_UNIX/GENERAL_Troubleshootingthedeviceisbusy.shtml
posted by citadel