umount: /mnt: device is busy.
A. The kernel has not finished flushing disk writes to the mounted device.
B. A user has a file open in the /mnt directory.
C. Another file system still contains a symlink to a file inside /mnt.
D. The files in /mnt have been scanned and added to the locate database.
E. The kernel thinks that a process is about to open a file in /mnt for reading.