It can be useful to determine what processes or users are currently
accessing certain files. Suppose, for example, you want to unmount a
file system mounted at
umount returns "device is busy."
The command fuser
can then be used to determine what processes are accessing the device:
$ fuser -v /mnt/* USER PID ACCESS COMMAND /mnt/notes.txt jj 26597 f.... less
Following termination of the less process, which was running on another terminal, the file system can successfully be unmounted.