Hierarchical file system concepts
A hierarchical file system consists of:
- Files, which contain data or programs. A file containing a program object, shell script, or REXX program is called an executable file. Files are kept in directories.
- Directories that contain files, other directories, or both. Directories are arranged hierarchically, in a structure that resembles an upside down tree, with root directory at the top and the branches at the bottom. The root is the first directory for the file system at the peak of the tree and is designated by a slash (/).
- Named pipes, links, and other UNIX items, such as character special files like /dev/console that are used by applications like syslogd. See z/OS UNIX System Services Planning for more information about UNIX items like character special files.
- A logical collection of files, directories, named pipes, links, and other UNIX items and metadata that are arranged in a hierarchy.
- A particular instance of a logical collection of these items that are arranged in a hierarchy. They might be on local or remote disks or in computer memory.
- A program that is designed to provide the functions and data of one type of file system.
The context indicates which meaning is intended. Often more than one meaning is intended; this is an industry convention.
To the z/OS® system, the file hierarchy is a collection of file systems. Additional instances of local or remote file systems might be mounted (logically connected) on directories of the root file system or of additional file systems.
Several types of file systems are supported by z/OS, including the following file systems:
- z/OS File System
Each instance of z/OS File System is in a linear data set.
- HFS (hierarchical file system)
Each instance of HFS is in an HFS data set.
- TFS (temporary file system)
Each instance of TFS is in computer memory.
- NFS (Network File System)
NFS server provides access to file systems that are on other computers.
For most application programs, these types of file systems are interchangeable. The root file system is the first file system that is mounted. Subsequent file systems can be logically mounted on a directory within the root file system or on a directory within any mounted file system.