The prerequisites for unmounting file systems include the following:
You must be superuser or assume an equivalent role.
A file system must be available for unmounting. You cannot unmount a file system that is busy. A file system is considered busy if a user is accessing a directory in the file system, if a program has a file open in that file system, or if the file system is being shared. You can make a file system available for unmounting by doing the following:
Changing to a directory in a different file system.
Logging out of the system.
Using the fuser command to list all processes that are accessing the file system and to stop them, if necessary. For more details, see How to Stop All Processes Accessing a File System.
Notify users if you need to unmount a file system that they are using.
Unsharing the file system. For information about unsharing a file system, see unshare(1M).