Configuration file
Encyclopedia
In computing
, configuration file
s, or config files configure the initial settings for some computer program
s. 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 applications provide tools to create, modify, and verify the syntax
of their configuration files; these sometimes have graphical interfaces. For other programs, system administrators
may be expected to create and modify files by hand using a text editor. For server processes and operating-system settings, there is often no standard tool, but operating systems may provide their own graphical interfaces such as YaST or debconf
.
Some computer programs only read their configuration files at startup
. Others periodically check the configuration files for changes. Users can instruct some programs to re-read the configuration files and apply the changes to the current process, or indeed to read arbitrary files as a configuration file. There are no definitive standards or strong conventions.
variants hundreds of configuration-file formats exist. Each application or service may have a unique format. Historically, Unix
operating system settings were often modified only by editing configuration files. Almost all formats allow entries to be disabled by prepending a special comment character, turning that entry into a comment.
The configuration files on Unix-type operating systems are traditionally documented using manpages, though other forms of online help are also used. In many cases the default configuration files distributed with a program contain extensive internal documentation in the form of comments. It is rare for a file to be completely undocumented, except in cases where a graphical configuration tool is the preferred method of configuring a program.
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 or a location defined by the system administrator.
Configuration files also do more than just modify settings, they often (in the form of an "rc file") run a set of commands upon startup (for example, the "rc file" for a shell
might instruct the shell to change directories, run certain programs, delete or create files —- many things which do not involve modifying variables in the shell itself and so were not in the shell's dotfiles); according to the Jargon File
, this convention is borrowed from "runcom files" on the CTSS operating system; see run commands
for details. This functionality can and has been extended for programs written in interpreted language
s such that the configuration file is actually another program rewriting or extending or customizing the original program; Emacs
is the most prominent such example. The "rc" naming convention of "rc files" was inspired by the "runcom" facility mentioned above and does not stand for "resource configuration" or "runtime configuration" as is often wrongly guessed.
On UNIX
variants dot files remain "hidden" from listing by default. On Mac OS X these files are sometimes called "hidden files" although other mechanisms exist on Mac OS X to hide a file from view in various tools. The Explorer
interface of Microsoft
Windows XP
does not allow the user to rename a file with an initial '.' though it does allow access to such files, and Windows' Notepad program does allow files to be saved with such names. Where Unix programs that use dotfiles are ported to Windows, they are sometimes modified to accept some other naming convention; for example, GNU Emacs permits its configuration file to be named _emacs instead of .emacs.http://www.gnu.org/software/emacs/windows/Installing-Emacs.html
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.
family of operating systems and their attendant applications utilize a similar system of configuration files. Windows 3.0
had an API for INI files (from "initialization"). Many Windows programs abandoned configuration files to use the Windows Registry
to store information.
uses a binary format, also with a .INI suffix, but this differs from the Windows versions.
It contains a list of lists of untyped key-value pairs.
Two files control system-wide settings: OS2.INI and OS2SYS.INI.
Application developers can choose whether to use them or create a specific file for their applications.
configurations. These are frequently not Turing complete (nor need to be, by definition). A notable exception is Lua, which started out specifically as a configuration language for use in other programs. It evolved into a complete programming language, but retains a phrasing that allows configuration descriptions to be read directly into a native, stateful, tabulated set of variable-key pairings accessible to other programs (via a library), as well as allowing (self or external) invocation of commands to augment configuration activities.
The class includes all markup languages. The trend in the increase of XML
and YAML
(among other formats) for use as configuration-file formats is at least partially attributable to the increase in popularity of open source
and platform neutral
software applications and libraries. Moreover, the specifications describing these formats are routinely made available to the public, thus increasing the availability of parsers and emitter
s across programming languages.
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, configuration file
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
s, or config files configure the initial settings for some computer program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
s. They are used for user applications
Application software
Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...
, server processes
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
and operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
settings. The files are often written in ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
(rarely UTF-8
UTF-8
UTF-8 is a multibyte character encoding for Unicode. Like UTF-16 and UTF-32, UTF-8 can represent every character in the Unicode character set. Unlike them, it is backward-compatible with ASCII and avoids the complications of endianness and byte order marks...
) and line-oriented, with lines terminated by a newline
Newline
In computing, a newline, also known as a line break or end-of-line marker, is a special character or sequence of characters signifying the end of a line of text. The name comes from the fact that the next character after the newline will appear on a new line—that is, on the next line below the...
or carriage return
Carriage return
Carriage return, often shortened to return, refers to a control character or mechanism used to start a new line of text.Originally, the term "carriage return" referred to a mechanism or lever on a typewriter...
/line feed pair, depending on the operating system. They may be considered a simple database
Flat file database
A flat file database describes any of various means to encode a database model as a single file .- Overview :...
.
Some applications provide tools to create, modify, and verify the syntax
Syntax
In linguistics, syntax is the study of the principles and rules for constructing phrases and sentences in natural languages....
of their configuration files; these sometimes have graphical interfaces. For other programs, system administrators
System administrator
A system administrator, IT systems administrator, systems administrator, or sysadmin is a person employed to maintain and operate a computer system and/or network...
may be expected to create and modify files by hand using a text editor. For server processes and operating-system settings, there is often no standard tool, but operating systems may provide their own graphical interfaces such as YaST or debconf
Debconf (software package)
debconf is a software utility for performing system-wide configuration tasks on Unix-like operating systems. It is developed for the Debian GNU/Linux distribution, and is closely integrated with Debian's package management system, dpkg....
.
Some computer programs only read their configuration files at startup
Booting
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
. Others periodically check the configuration files for changes. Users can instruct some programs to re-read the configuration files and apply the changes to the current process, or indeed to read arbitrary files as a configuration file. There are no definitive standards or strong conventions.
UNIX/Linux
Across the UnixUnix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
variants hundreds of configuration-file formats exist. Each application or service may have a unique format. Historically, Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
operating system settings were often modified only by editing configuration files. Almost all formats allow entries to be disabled by prepending a special comment character, turning that entry into a comment.
The configuration files on Unix-type operating systems are traditionally documented using manpages, though other forms of online help are also used. In many cases the default configuration files distributed with a program contain extensive internal documentation in the form of comments. It is rare for a file to be completely undocumented, except in cases where a graphical configuration tool is the preferred method of configuring a program.
Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
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
Full stop
A full stop is the punctuation mark commonly placed at the end of sentences. In American English, the term used for this punctuation is period. In the 21st century, it is often also called a dot by young people...
, 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 or a location defined by the system administrator.
Configuration files also do more than just modify settings, they often (in the form of an "rc file") run a set of commands upon startup (for example, the "rc file" for a shell
Shell (computing)
A shell is a piece of software that provides an interface for users of an operating system which provides access to the services of a kernel. However, the term is also applied very loosely to applications and may include any software that is "built around" a particular component, such as web...
might instruct the shell to change directories, run certain programs, delete or create files —- many things which do not involve modifying variables in the shell itself and so were not in the shell's dotfiles); according to the Jargon File
Jargon File
The Jargon File is a glossary of computer programmer slang. The original Jargon File was a collection of terms from technical cultures such as the MIT AI Lab, the Stanford AI Lab and others of the old ARPANET AI/LISP/PDP-10 communities, including Bolt, Beranek and Newman, Carnegie Mellon...
, this convention is borrowed from "runcom files" on the CTSS operating system; see run commands
Run Commands
The term rc stands for the phrase "run commands". It is used for any file that contains startup information for a command. It is believed to have originated somewhere in 1965 from a runcom facility from the MIT Compatible Time-Sharing System system....
for details. This functionality can and has been extended for programs written in interpreted language
Interpreted language
Interpreted language is a programming language in which programs are 'indirectly' executed by an interpreter program. This can be contrasted with a compiled language which is converted into machine code and then 'directly' executed by the host CPU...
s such that the configuration file is actually another program rewriting or extending or customizing the original program; Emacs
Emacs
Emacs is a class of text editors, usually characterized by their extensibility. GNU Emacs has over 1,000 commands. It also allows the user to combine these commands into macros to automate work.Development began in the mid-1970s and continues actively...
is the most prominent such example. The "rc" naming convention of "rc files" was inspired by the "runcom" facility mentioned above and does not stand for "resource configuration" or "runtime configuration" as is often wrongly guessed.
On UNIX
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
variants dot files remain "hidden" from listing by default. On Mac OS X these files are sometimes called "hidden files" although other mechanisms exist on Mac OS X to hide a file from view in various tools. The Explorer
Windows Explorer
This article is about the Windows file system browser. For the similarly named web browser, see Internet ExplorerWindows Explorer is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface...
interface of Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
does not allow the user to rename a file with an initial '.' though it does allow access to such files, and Windows' Notepad program does allow files to be saved with such names. Where Unix programs that use dotfiles are ported to Windows, they are sometimes modified to accept some other naming convention; for example, GNU Emacs permits its configuration file to be named _emacs instead of .emacs.http://www.gnu.org/software/emacs/windows/Installing-Emacs.html
IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
's AIX
AIX operating system
AIX AIX AIX (Advanced Interactive eXecutive, pronounced "a i ex" is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms...
uses an Object Data Manager
Object Data Manager
Object Data Manager is a database management system and device configuration integrated into IBM's AIX operating system. The ODM is unique to AIX compared to other UNIX operating systems. Data being managed by ODM is stored and maintained as objects with associated attributes...
(ODM) database to store some system settings,
some of which need to be available at boot time.
Microsoft DOS
DOS primarily relies on two files calledCONFIG.SYSCONFIG.SYSCONFIG.SYS is the primary configuration file for the DOS, OS/2 as well as similar operating systems. It is a special file that contains setup or configuration instructions for the computer system.- Usage :...
and AUTOEXEC.BATAUTOEXEC.BATAUTOEXEC.BAT is a system file found originally on DOS-type operating systems. It is a plain-text batch file that is located in the root directory of the boot device...
. These were retained up to Windows 98SE, but were not strictly required to run Windows applications.Microsoft Windows
The Microsoft WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
family of operating systems and their attendant applications utilize a similar system of configuration files. Windows 3.0
Windows 3.0
Windows 3.0, a graphical environment, is the third major release of Microsoft Windows, and was released on 22 May 1990. It became the first widely successful version of Windows and a rival to Apple Macintosh and the Commodore Amiga on the GUI front...
had an API for INI files (from "initialization"). Many Windows programs abandoned configuration files to use the Windows Registry
Windows registry
The Windows Registry is a hierarchical database that stores configuration settings and options on Microsoft Windows operating systems. It contains settings for low-level operating system components as well as the applications running on the platform: the kernel, device drivers, services, SAM, user...
to store information.
IBM OS/2
IBM's OS/2OS/2
OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 " line of second-generation personal...
uses a binary format, also with a .INI suffix, but this differs from the Windows versions.
It contains a list of lists of untyped key-value pairs.
Two files control system-wide settings: OS2.INI and OS2SYS.INI.
Application developers can choose whether to use them or create a specific file for their applications.
Configuration languages
Many language specifications have been created specifically to describe and retainSerialization
In computer science, in the context of data storage and transmission, serialization is the process of converting a data structure or object state into a format that can be stored and "resurrected" later in the same or another computer environment...
configurations. These are frequently not Turing complete (nor need to be, by definition). A notable exception is Lua, which started out specifically as a configuration language for use in other programs. It evolved into a complete programming language, but retains a phrasing that allows configuration descriptions to be read directly into a native, stateful, tabulated set of variable-key pairings accessible to other programs (via a library), as well as allowing (self or external) invocation of commands to augment configuration activities.
The class includes all markup languages. The trend in the increase of XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
and YAML
YAML
YAML is a human-readable data serialization format that takes concepts from programming languages such as C, Perl, and Python, and ideas from XML and the data format of electronic mail . YAML was first proposed by Clark Evans in 2001, who designed it together with Ingy döt Net and Oren Ben-Kiki...
(among other formats) for use as configuration-file formats is at least partially attributable to the increase in popularity of open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
and platform neutral
Cross-platform
In computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...
software applications and libraries. Moreover, the specifications describing these formats are routinely made available to the public, thus increasing the availability of parsers and emitter
Emitter
-In general:*A device used to exude any signal, beacon, light, odor, liquid, fragrance, ionizing particles or any other type of signal.-In horticulture:*A device used in drip irrigation.-In electronics and instrument physics:...
s across programming languages.
See also
- The INI file format is a de facto standard for configuration files.
- .properties.properties.properties is a file extension for files mainly used in Java related technologies to store the configurable parameters of an application. They can also be used for storing strings for Internationalization and localization; these are known as Property Resource Bundles.Each parameter is stored as a...
is a file extension for files mainly used in Java related technologies to store the configurable parameters of an application. - YAMLYAMLYAML is a human-readable data serialization format that takes concepts from programming languages such as C, Perl, and Python, and ideas from XML and the data format of electronic mail . YAML was first proposed by Clark Evans in 2001, who designed it together with Ingy döt Net and Oren Ben-Kiki...
is used by some for more complex configuration formats.
External links
- libprf1 - alpha cross-platform, multi-language support for accessing the Preferences Registry Format (PRF) 1.0 configuration files