A configuration file, a.k.a. config file, is a file that stores

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

used to configure a

software system A software system is a system of intercommunicating software component, components based on software forming part of a computer system (a combination of Computer hardware, hardware and software). It "consists of a number of separate Computer progr ...

such as an application, a server or an

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

. Some applications provide a tool to create, modify, and verify the

syntax In linguistics, syntax ( ) is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure (constituenc ...

of their configuration files sometimes via

graphical user interface A graphical user interface, or GUI, is a form of user interface that allows user (computing), users to human–computer interaction, interact with electronic devices through Graphics, graphical icon (computing), icons and visual indicators such ...

(GUI). For context,

system administrator An IT administrator, system administrator, sysadmin, or admin is a person who is responsible for the upkeep, configuration, and reliable operation of computer systems, especially multi-user computers, such as Server (computing), servers. The ...

s may be expected to create and modify

text Text may refer to: Written word * Text (literary theory) In literary theory, a text is any object that can be "read", whether this object is a work of literature, a street sign, an arrangement of buildings on a city block, or styles of clothi ...

config files via a text editor. For server processes and operating-system settings, there is often no standard tool, but operating systems may provide graphical interfaces such as YaST or debconf. Some computer programs only read their configuration files at

startup A startup or start-up is a company or project undertaken by an entrepreneur to seek, develop, and validate a scalable business model. While entrepreneurship includes all new businesses including self-employment and businesses that do not intend to ...

. 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. Gnu grub config file

RAPHICS_QUALITY HIGH_FPS=2 #0-Off, 1=60FPS, 2=120FPS MODEL_QUALITY=2 # Medium-High model detail (ad EFFECT_QUALITY=2 # Medium-High skill effects

File format

In general, a config file can have any format. The format that applies to a particular system is determined by the design of that system. Often, a standardized format is used since it allows for using tools designed for the format even if not designed for the consuming system. In particular, general-purpose

serialization In computing, serialization (or serialisation, also referred to as pickling in Python (programming language), Python) is the process of translating a data structure or object (computer science), object state into a format that can be stored (e. ...

formats, such as

JSON JSON (JavaScript Object Notation, pronounced or ) is an open standard file format and electronic data interchange, data interchange format that uses Human-readable medium and data, human-readable text to store and transmit data objects consi ...

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...

, and

YAML YAML ( ) is a human-readable data serialization language. It is commonly used for configuration files and in applications where data is being stored or transmitted. YAML targets many of the same communications applications as Extensible Marku ...

, are often used in

open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

and platform-neutral software. The

specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard. There are different types of technical or engineering specificati ...

for these formats are generally publicly available to support wide-spread use. The following table compares notable formats used for configuration data. The ''syntax typing'' column indicates whether the

supports

data type In computer science and computer programming, a data type (or simply type) is a collection or grouping of data values, usually specified by a set of possible values, a set of allowed operations on these values, and/or a representation of these ...

s. A format has syntax-typing if a value's type is specified by syntax – e.g. true is a Boolean while "true" is a

string String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...

. A format does not have syntax-typing if a value's type is based on

semantics Semantics is the study of linguistic Meaning (philosophy), meaning. It examines what meaning is, how words get their meaning, and how the meaning of a complex expression depends on its parts. Part of this process involves the distinction betwee ...

– e.g. true and "true" are both Boolean if the parser expects a Boolean. Opinions on the value of syntax-typin
vary

Examples

The following are examples of config files organized by the

s on which they are commonly used.

Unix and Unix-like

Many different file formats are used on

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

and

Unix-like A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...

operating systems. Even so, there is a strong tradition of using human-editable, plain text formats including simple key–value pair. Filename extensions of .cnf, .conf, .cfg, .cf or .ini are often used. Many formats allow comments, in which case, individual settings can be disabled by prepending with the comment character. Often the default configuration files contain extensive internal documentation in the form of commentshttps://opensource.apple.com/source/postfix/postfix-174.2/Postfix.Config/main.cf.default. http://opensource.apple.com/source/apache/apache-769/httpd.conf. and man files are also typically used to document the format and options available. System-wide software often uses configuration files stored in /etc, while user applications often use a " dotfile" – a file or directory in the home directory prefixed with a period, which in Unix hides the file or directory from casual listing. Since this causes pollution, newer user applications generally make their own folder in the .config directory, a standardized subdirectory of the home directory. Similar to config files, a

run command The Run command on an operating system such as Microsoft Windows and Unix-like systems is used to directly open an application or document whose Path (computing), path is known. Overview The command functions more or less like a single-line com ...

(rc)

shell script A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be command languages. Typical operations performed by shell scripts include file manipu ...

can configure a

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

session. Often, such scripts are named with an rc suffix after the consuming program's name such as .xinitrc, .vimrc, .bashrc, xsane.rc. By contrast,

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

's AIX uses an Object Data Manager (ODM) database to store much of its system settings.

MS-DOS

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...

primarily relied on the CONFIG.SYS config file; a plain text file with simple key–value pairs (e.g. DEVICEHIGH=C:\DOS\ANSI.SYS). MS-DOS 6 introduced the INI-file format. Similar to an rc file, the

batch file A batch file is a Scripting language, script file in DOS, OS/2 and Microsoft Windows. It consists of a series of Command (computing), commands to be executed by the command-line interpreter, stored in a plain text file. A batch file may contain a ...

named AUTOEXEC.BAT ran commands on

. Both these files were retained up to

Windows 98SE Windows 98 is a consumer-oriented operating system developed by Microsoft as part of its Windows 9x family of Microsoft Windows operating systems. It was the second operating system in the 9x line, as the successor to Windows 95. It was released ...

, which still ran on top of MS-DOS. An example CONFIG.SYS: DOS=HIGH,UMB DEVICE=C:\DOS\HIMEM.SYS DEVICE=C:\DOS\EMM386.EXE RAM DEVICEHIGH=C:\DOS\ANSI.SYS FILES=30 SHELL=C:\DOS\COMMAND.COM C:\DOS /E:512 /P DOS applications used a wide variety of individual configuration files, most of them binary, proprietary and undocumented - and there were no common conventions or formats.

Windows

Early

Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

operating systems heavily utilized plain-text INI files which served as the primary mechanism to configure the operating system and applications. The

API An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build ...

s to read and write from these still exist in Windows, but after 1993, Microsoft began to steer developers away from using INI files and toward storing settings in the registry, a hierarchical database to store configuration settings, which was introduced with

Windows NT Windows NT is a Proprietary software, proprietary Graphical user interface, graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Original ...

. Later systems use XML and other formats instead of the registry.

macOS

The

Property List In the macOS, iOS, NeXTSTEP, and GNUstep programming frameworks, property list files are files that store serialized objects. Property list files use the filename extension .plist, and thus are often referred to as p-list files. Property l ...

is the standard configuration file format in

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

(as well as in

iOS Ios, Io or Nio (, ; ; locally Nios, Νιός) is a Greek island in the Cyclades group in the Aegean Sea. Ios is a hilly island with cliffs down to the sea on most sides. It is situated halfway between Naxos and Santorini. It is about long an ...

NeXTSTEP NeXTSTEP is a discontinued object-oriented, multitasking operating system based on the Mach kernel and the UNIX-derived BSD. It was developed by NeXT, founded by Steve Jobs, in the late 1980s and early 1990s and was initially used for its ...

GNUstep GNUstep is a free software implementation of the Cocoa (formerly OpenStep) Objective-C frameworks, widget toolkit, and application development tools for Unix-like operating systems and Microsoft Windows. It is part of the GNU Project. GNUst ...

and Cocoa applications). It uses the

filename extension A filename extension, file name extension or file extension is a suffix to the name of a computer file (for example, .txt, .mp3, .exe) that indicates a characteristic of the file contents or its intended use. A filename extension is typically d ...

.plist.

IBM OS/2

IBM's

OS/2 OS/2 is a Proprietary software, proprietary computer operating system for x86 and PowerPC based personal computers. It was created and initially developed jointly by IBM and Microsoft, under the leadership of IBM software designer Ed Iacobucci, ...

uses a binary format, also with a .INI suffix, but this differs from the Windows versions. It contains a

list A list is a Set (mathematics), set of discrete items of information collected and set forth in some format for utility, entertainment, or other purposes. A list may be memorialized in any number of ways, including existing only in the mind of t ...

of lists of untyped key–value pairs.
The OS/2 INI Files
' by James J. Weinkam. Two files control system-wide settings: OS2.INI and OS2SYS.INI. Application developers can choose whether to use them or to create a specific file for their applications.

HarmonyOS and OpenHarmony operating systems

HarmonyOS HarmonyOS (HMOS) ( zh, s=鸿蒙, p=Hóngméng, tr=Vast Mist) is a distributed operating system developed by Huawei for smartphones, tablet computer, tablets, smart TVs, smart watches, personal computers and other smart devices. It has a microk ...

and

OpenHarmony OpenHarmony (OHOS, OH) is a family of open-source distributed operating systems based on HarmonyOS derived from LiteOS, donated the L0-L2 branch source code by Huawei to the OpenAtom Foundation. Similar to HarmonyOS, the open-source distrib ...

-based operating systems use JSON config files, named . The platform IDE, DevEco Studio, provides methods for editing config.json.

References

{{DEFAULTSORT:Configuration File