Suppose that we want to unmount a file system under /mnt:
$ mount -l | grep /mnt /dev/sda on /mnt type ext2 (rw,noexec,nosuid,nodev,noatime,user=jj)
The attempt to unmount it fails:
$ umount /mnt umount: /mnt: device is busy
To find out which processes are accessing the files in the /mnt directory, enter:
$ 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.