The fuser Command

Before you can unmount a file system, you must be logged in as the administrator (root), and the file system must not be busy. A file system is considered busy if a user is in a directory in the file system or if a program has a file open in that file system. You can make a file system available for unmounting by changing to a directory in a different file system or by logging out of the system. If something is causing the file system to be busy, you can use the fuser command, described in Table 5-7, to list all the processes accessing the file system and to stop them if necessary.