After you mount a new file system for the first time (as described in Mounting file systems), you need to change the owner and group owner. This topic explains why this step is necessary.

To begin with, the hierarchical file system is used to store data and organize it in a hierarchical way by using file system entries such as directories and files. These file system entries have certain attributes, such as ownership, permission bits, and access time stamps. The data and the attributes of a file are stored with the file in the file system. All file attributes are stored in a control block that is sometimes called the inode.

Mounting a file system creates a binding for the duration of the mount. The binding is between a directory that is already in the file system hierarchy, called the mount point, and the entry point into the file system about to be mounted, called the root of this file system. The mount point directory and the root are connected until unmount time. When a file system is mounted on a mount point, it overlays the contents of the mount point directory. Files, symbolic links, and subdirectories within the mount point directory are no longer accessible and are hidden until the file system is unmounted.

See Figure 1 to see what happens when Jane's file system is mounted on directory /u/jane.

Figure 1. Mounting a file system

The root directory of a file system, like any other entry, also has attributes, but the directory does not have a name. At mount time, the mount point directory lends its name to the root directory of the file system that is to be mounted. The root, however, keeps its attributes. Logically, the directory (which is an entry in another directory, one level up the hierarchical tree) no longer points to its own inode. Instead, it points to the inode of the mounted root. Thus, the attributes and the content of a directory are hidden as long as a file system is mounted on it.

Remember that the root of a file system always keeps the attributes that it had at unmount time. The same attributes are used again when the file system is mounted later. The attributes do not depend on the actual mount point.

The automount facility and the ISPF shell can be used to define either a HFS or zFS file system. For more information about the automount or z/OS UNIX System Services Command Reference.