How to rescan and remount drives on Ubuntu Hardy or Jaunty?
Try triggering the add rule to udev. The default action is add. ( probably what you want)
# udevadm trigger --subsystem-match=block
you can call
# udevadm settle --timeout=60
to wait for udev to finish doing it's thing. (in this case 60 seconds, default is 180seconds)
sudo unmount -a and sudo mount -a will do the job,but only if the device is not busy(in use).
All of the file systems described in /etc/mtab are mounted or unmounted.But after I tried it with USB,It turned out be OK.