DirectoryIndex

DirectoryIndex is a configuration directive used by web servers to specify the default file name to serve when a client requests a URL that maps to a directory rather than a specific file. It lists one or more filenames.

In Apache HTTP Server, DirectoryIndex is provided by the mod_dir module and can be set globally in httpd.conf or per-directory in .htaccess or <Directory> blocks. Syntax: DirectoryIndex index.html index.php index.htm. The first existing file among the listed names is served.

If a request targets a directory and none of the listed index files is present, the server's behavior depends on configuration: it may return a 403 Forbidden, 404 Not Found, or generate a directory listing if the Options Indexes setting is enabled.

The directive is commonly used to prefer PHP-backed index pages or static HTML. It interacts with other modules such as mod_negotiation for content negotiation and with Web frameworks that create index.php as the front controller.

Security note: Relying on DirectoryIndex to hide files is not a complete security measure; ensure directory listings are disabled when not intended. In other servers, Nginx uses an index directive; IIS uses Default Document.

See also: mod_dir, Directory, httpd.conf, index directive in Nginx, Default Document in IIS.