In computing, configuration files, or config files, are used to configure the initial settings for some computer programs. They are used for user applications, server processes and operating system settings. The files are often written in ASCII (rarely UTF-8) and line-oriented, with lines terminated by a newline or carriage return/line feed pair, depending on the operating system. They may be considered a simple database. Some files are created and modified using an ASCII editor. Others are created and modified as a side-effect of changing settings in a graphical user interface (GUI) program. The formats of configuration files are often poorly documented. Originally, the word computing was synonymous with counting and calculating, and a science that deals with the original sense of computing mathematical calculations. ... A computer file is a collection of information that is stored in a computer system and can be identified and referenced in its entirety by a unique name. ... The terms computer program, software program, applications program, system software, or just program are used to refer to either an executable program by both lay people and computer programmers or the collection of source code from which an executable program is created (eg, compiled). ... Application software is a loosely defined subclass of computer software that employs the capabilities of a computer directly to a task that the user wishes to perform. ... In information technology, a server is a computer system that provides services to other computing systems—called clients—over a network. ... An operating system (OS) is an essential software program that manages the hardware and software resources of a computer. ... For other uses, see ASCII (disambiguation). ... UTF-8 (8-bit Unicode Transformation Format) is a variable-length character encoding for Unicode created by Ken Thompson and Rob Pike. ... In computing, a newline is a special character or sequence of characters signifying the end of a line of text. ... Originally, carriage return was the term for the key, lever, or mechanism on a typewriter that would cause the cylinder on which the paper was held (the carriage) to return to the left side of the paper after a line of text had been typed, and would often move it... In computing, line feed (LF) is a control character indicating that one line should be fed out. ... A database is an organized collection of data. ... A graphical user interface (or GUI, often pronounced gooey) is a method of interacting with a computer through a metaphor of direct manipulation of graphical images and widgets in addition to text. ... In general terms, documentation is any communicable material (such as text, video, audio, etc. ...

Some applications provide tools to create, modify, and verify the syntax of their configuration files. For server processes and operating system settings, the only documentation may be the source code. Some configuration files are partially described by man or help pages. Syntax, originating from the Greek words συν (syn, meaning co- or together) and τάξις (táxis, meaning sequence, order, arrangement), can in linguistics be described as the study of the rules, or patterned relations that govern the way the words in a sentence come together. ... The man page on man Almost all substantial UNIX and Unix-like operating systems have extensive documentation known as man pages (short for manual pages). The Unix command used to display them is man. ...

Some computer programs only read the configuration files at startup. Others periodically check the configuration files for changes. Some can be told to re-read the configuration files and apply the changes to the current process. There are no standards or strong conventions.

Recently, XML and YAML have become popular as configuration file formats. They have the advantages of having well-defined syntaxes, and tools to validate and verify the syntax of the files that are created in those formats. The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language for creating special-purpose markup languages, capable of describing many different kinds of data. ... YAML is a human-readable data serialization format that takes concepts from languages such as XML, C, Python, and Perl, as well as the format for electronic mail as specified by RFC 2822. ...

UNIX

Among the Unix variants, there are hundreds of configuration file formats. Each application or service may have a unique format. Historically, Unix operating system settings were often modified only by editing configuration files. Since the formats were poorly documented and there were no syntax checking tools for the configuration files, it was easy to misconfigure the operating system or service. Some configuration files have sample entries that can be used as templates. However, the examples may be out-of-date or incorrect. Some formats allow entries to be disabled by prepending a special comment character. Unix user applications often create a file or directory in the home directory of the user upon startup. To hide the file or directory from casual listing of the contents of the home directory, the name of the file or directory is prepended with a period, giving rise to the nickname "dotfile" or "dot file". Server processes often use configuration files stored in /etc, but they may also use their installation directory, the root directory, or a location defined by the system administrator. Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... A full stop or period, also called a full point, is the punctuation mark commonly placed at the end of several different types of sentences in English and several other languages. ... The Filesystem Hierarchy Standard (FHS) defines the main directories and their contents in Linux and other Unix-like computer operating systems. ...

On UNIX variants dot files are 'hidden' from listing by default, On OS X these files are called "hidden files." The Explorer interface of Microsoft Windows XP does not allow you to rename a file with an initial '.' though it does allow access to such files. Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... Windows Explorer running on Windows XP Windows Explorer is an application that is part of modern versions of the Microsoft Windows operating system that provides a graphical user interface for accessing the file systems. ... Microsoft Corporation (NASDAQ: MSFT, SEHK: 4338) is an international computer technology corporation with 2005 global annual sales of US$39. ... Windows XP is the name of a line of operating systems developed by Microsoft for use on general-purpose computer systems, including home and business desktops, notebook computers, and media centers. ...

IBM's AIX uses an Object Data Manager (ODM) database to store some system settings, some of which need to be available at boot time. For other uses, see IBM (disambiguation). ... AIX (Advanced Interactive eXecutive) is a proprietary operating system developed by IBM based on UNIX System V. Before the product was ever marketed, the acronym AIX originally stood for Advanced IBM Unix. ...

Microsoft Windows

Within the Microsoft Windows family of operating systems and their attendant applications, the situation is similar. Windows 3.0 had an API for INI files (from "initialization"), but that format is deprecated and modern Windows programs forgo configuration files to use only the Windows Registry to store information. As of 2006, Microsoft Windows is the worlds most popular operating system for use on personal computers. ... The Windows 3. ... An initialization file, or INI file, is a configuration file that contains configuration data for Microsoft Windows based applications. ... In computing, the Windows registry is a database which stores settings and options for the operating system for Microsoft Windows 32-bit versions and Windows Mobile. ...

IBM OS/2

IBM's OS/2 uses a binary format also named INI but it is different from the Windows versions. It contains a list of lists of untyped key-value pairs^[1]. There are two files for system-wide settings, OS2.INI and OS2SYS.INI. Application developers can choose whether to use them or create a specific file for their applications. OS/2 is an operating system created by Microsoft and IBM and later developed by IBM exclusively. ...

Implementation Shortcomings

Some of the common problems with configuration file implementations are:

• No defined behavior if the configuration file is missing, truncated, unreadable, unwritable, or has inappropriate ownership
• No defined minimum or maximum file size
• No defined minimum or maximum entry size
• No revision control
• No defined precedence—i.e., if there are two identical entries, does the program use the value of the first, the second, or both?
• No formal syntax definition
  • No defined character set
  • No defined line-continuation syntax
  • Poorly defined comment syntax
  • undefined or idiosyncratic treatment of whitespace

Reference

1. ^ The OS/2 INI Files by James J. Weinkam.

External links

• dotfiles.com – a site for users to share configuration files for Unix applications and utilities
• libprf1 - alpha cross-platform, multi-language support for accessing the Preferences Registry Format (PRF) 1.0 configuration files
• www.libelektra.org - Elektra provides a universal and secure framework to store configuration parameters in a hierarchical key-value pair mechanism, instead of each program using its own text configuration files
• gconf - GConf is a system for storing application preferences. It is intended for user preferences; not configuration of something like Apache, or arbitrary data storage
• rc.conf - BSD system startup configuration file
• libconfig - Libconfig (LGPL) is a simple library for parsing structured configuration files, with a file format that is more compact and more readable than XML. And unlike XML, it is type-aware, so it is not necessary to do string parsing in application code. The library includes bindings for both the C and C++ languages.
• GetPot GetPot (LGPL) is a sophisticated command line and input file parsing library, contained in a header file.