A File System Defined

A file system is a collection of files and directories stored on disk in a standard Unix file system (UFS) format. All disk-based computer systems have a file system. In Unix, file systems have two basic components: files and directories. A file is the actual information as it is stored on the disk, and a directory is a list of the filenames. In addition to keeping track of filenames, the file system must keep track of files' access dates, permissions, and ownership. Managing file systems is one of the system administrator's most important tasks. Administration of the file system involves the following:

• Ensuring that users have access to data. This means that systems are up and operational, file permissions are set up properly, and data is accessible.

• Protecting file systems against file corruption and hardware failures. This is accomplished by checking the file system regularly and maintaining proper system backups.

• Securing file systems against unauthorized access. Only authorized users should have access to files.

• Providing users with adequate space for their files.

• Keeping the file system clean. In other words, data in the file system must be relevant and not wasteful of disk space. Procedures are needed to make sure that users follow proper naming conventions and that data is stored in an organized manner.

You'll see the term file system used in several ways. Usually, file system describes a particular type of file system (disk-based, network based, or virtual). It might also describe the entire file tree from the root directory downward. In another context, the term file system might be used to describe the structure of a disk slice, described later in this chapter.

The Solaris system software uses the virtual file system (VFS) architecture, which provides a standard interface for different file system types. The VFS architecture lets the kernel handle basic operations, such as reading, writing, and listing files, without requiring the user or program to know about the underlying file system type. Furthermore, Solaris provides file system administrative commands that enable you to maintain file systems.