Types of files

The types of files recognized by the system are either regular, directory, or special. However, the operating system uses many variations of these basic types.

The following basic types of files exist:

All file types recognized by the system fall into one of these categories. However, the operating system uses many variations of these basic types.

Regular files

Regular files are the most common files and are used to contain data. Regular files are in the form of text files or binary files:

Text files

Text files are regular files that contain information stored in ASCII format text and are readable by the user. You can display and print these files. The lines of a text file must not contain NUL characters, and none can exceed {LINE_MAX} bytes in length, including the newline character.

The term text file does not prevent the inclusion of control or other nonprintable characters (other than NUL). Therefore, standard utilities that list text files as inputs or outputs are either able to process the special characters or they explicitly describe their limitations within their individual sections.

Binary files

Binary files are regular files that contain information readable by the computer. Binary files might be executable files that instruct the system to accomplish a job. Commands and programs are stored in executable, binary files. Special compiling programs translate ASCII text into binary code.

Text and binary files differ only in that text files have lines of less than {LINE_MAX} bytes, with no NUL characters, each terminated by a newline character.

Directory files

Directory files contain information that the system needs to access all types of files, but directory files do not contain the actual file data. As a result, directories occupy less space than a regular file and give the file system structure flexibility and depth. Each directory entry represents either a file or a subdirectory. Each entry contains the name of the file and the file's index node reference number (i-node number). The i-node number points to the unique index node assigned to the file. The i-node number describes the location of the data associated with the file. Directories are created and controlled by a separate set of commands.

Special files

Special files define devices for the system or are temporary files created by processes. The basic types of special files are FIFO (first-in, first-out), block, and character. FIFO files are also called pipes. Pipes are created by one process to temporarily allow communication with another process. These files cease to exist when the first process finishes. Block and character files define devices.

Every file has a set of permissions (called access modes) that determine who can read, modify, or execute the file.