File-System Mounting

• Just as a file must be opened before it is used, a file system must be mounted before it can be available to processes on the system.
• The mount procedure is straightforward. The OS is given the name of the device and the mount point -the location within the file structure where the file system is to be attached.
• Typically, a mount point is an empty directory. Next, the OS verifies that the device contains a valid file system.
• Finally, the OS notes in its directory structure that a file system is mounted at the specified mount point.
• This scheme enables the OS to traverse its directory structure, switching among file systems as appropriate.
• To illustrate file mounting, consider the file system depicted in Fig. 16, where the triangles represent sub-trees of directories that are of interest. At this point, only the files on the existing file system can be accessed.

  Figure 16: File system. (a) Existing system. (b) Unmounted volume.

  
• Figure 17 shows the effects of mounting the volume residing on $/dev/disk$ over $/users$.

  Figure 17: Mount point.