Configuration file

In computing, configuration files, or config files configure the parameters and initial settings for some computer programs. They are used for user applications, server processes and operating system settings.

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; possible because many are human-editable plain text. 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.

Across Unix-like operating systems many different configuration-file formats exist, with each application or service potentially having a unique format, but there is a strong tradition of them being in human-editable plain text, and a simple key-value pair format is common. Filename extensions of .ini, .cnf, .conf, .cfg, .cf and similar are often used.

Almost all 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 comments and man files are also typically used to document the format and options available.

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