Mapping URLs to Filesystem Locations

This document explains how the Apache HTTP Server uses the URL of a request to determine the filesystem location from which to serve a file.

make up the basic document tree which will be visible from the web.DocumentRoot

were set to DocumentRoot/var/www/html

then a request for http://www.example.com/fish/guppies.html

being served to the requesting client.

If a directory is requested (i.e. a path ending with /

directive. For example, if DirectoryIndexDocumentRoot

DirectoryIndex index.html index.php

will cause httpd to attempt to serve the file /var/www/html/fish/index.html

. In the event that that file does not exist, it will next attempt to serve the file /var/www/html/fish/index.php

If neither of these files existed, the next step is to attempt to provide a directory index, if

is loaded and configured to permit that.mod_autoindex

httpd is also capable of Virtual Hosting, where the server receives requests for more than one host. In this case, a different

can be used to dynamically determine the appropriate place from which to serve content based on the requested IP address or hostname.modvhostalias

directive is set in your main server configuration file (DocumentRootapache2.conf

) and, possibly, once per additional Virtual Host you create.

. For security reasons, httpd will follow symbolic links only if the DocumentRoot

setting for the relevant directory includes OptionsFollowSymLinks

Alias /docs /var/web

directive works the same way, with the additional effect that all content located at the target path is treated as ScriptAliasCGI scripts.

For situations where you require additional flexibility, you can use the

directives to do powerful ScriptAliasMatchregular expression based matching and substitution. For example,

ScriptAliasMatch ^/~([a-zA-Z0-9]+)/cgi-bin/(.+) /home/$1/cgi-bin/$2

and will treat the resulting file as a CGI script.

For security reasons, it is inappropriate to give direct access to a user's home directory from the web. Therefore, the

directive specifies a directory underneath the user's home directory where web files are located. Using the default setting of UserDirUserdir public_html

There are also several other forms of the Userdir

Some people find the "~" symbol (which is often encoded on the web as %7e

) to be awkward and prefer to use an alternate string to represent user directories. This functionality is not supported by mod_userdir. However, if users' home directories are structured in a regular way, then it is possible to use the

directive to achieve the desired effect. For example, to make AliasMatchhttp://www.example.com/upages/user/file.html

Redirect permanent /foo/ http://www.example.com/bar/

directive for more complicated rewriting problems. For example, to redirect requests for the site home page to a different site, but leave all other requests alone, use the following configuration:RedirectMatch

Alternatively, to temporarily redirect all pages on one site to a particular page on another site, use the following:

RedirectMatch temp .* http://othersite.example.com/startpage.html

httpd also allows you to bring remote documents into the URL space of the local server. This technique is called reverse proxying because the web server acts like a proxy server by fetching the documents from a remote server and returning them to the client. It is different from normal (forward) proxying because, to the client, it appears the documents originate at the reverse proxy server.

ProxyPassReverse /foo/ http://internal.example.com/bar/

ProxyPassReverseCookieDomain internal.example.com public.example.com

configures the server to fetch the appropriate documents, while the ProxyPass

directive rewrites redirects originating at ProxyPassReverseinternal.example.com

rewrite cookies set by the backend server.ProxyPassReverseCookiePath

It is important to note, however, that links inside the documents will not be rewritten. So any absolute links on internal.example.com

will result in the client breaking out of the proxy server and requesting directly from internal.example.com

For more sophisticated rewriting of links in HTML and XHTML, the

module is also available. It allows you to create maps of URLs that need to be rewritten, so that complex proxying scenarios can be handled.modproxyhtml

can be useful. The directives provided by this module can use characteristics of the request such as browser type or source IP address in deciding from where to serve content. In addition, modrewrite can use external database files or programs to determine how to handle a request. The rewriting engine is capable of performing all three types of mappings discussed above: internal redirects (aliases), external redirects, and proxying. Many practical examples employing modrewrite are discussed in the modrewritedetailed modrewrite documentation.

Inevitably, URLs will be requested for which no matching file can be found in the filesystem. This can happen for several reasons. In some cases, it can be a result of moving documents from one location to another. In this case, it is best to use URL redirection to inform clients of the new location of the resource. In this way, you can assure that old bookmarks and links will continue to work, even though the resource is at a new location.

Another common cause of "File Not Found" errors is accidental mistyping of URLs, either directly in the browser, or in HTML links. httpd provides the module

(sic) to help with this problem. When this module is activated, it will intercept "File Not Found" errors and look for a resource with a similar filename. If one such file is found, modspeling will send an HTTP redirect to the client informing it of the correct location. If several "close" files are found, a list of available alternatives will be presented to the client.modspeling

An especially useful feature of modspeling, is that it will compare filenames without respect to case. This can help systems where users are unaware of the case-sensitive nature of URLs and the unix filesystem. But using modspeling for anything more than the occasional URL correction can place additional load on the server, since each "incorrect" request is followed by a URL redirection and a new request from the client.

, which can be used to map virtual URIs to a real resource, which then serves them. This is a very useful replacement for FallbackResource

when implementing a 'front controller'mod_rewrite

If all attempts to locate the content fail, httpd returns an error page with HTTP status code 404 (file not found). The appearance of this page is controlled with the

directive and can be customized in a flexible manner as discussed in the ErrorDocumentCustom error responses document.

- Maps a request to a CGI script based on the request method, or resource MIME type.mod_dir

- Provides basic mapping of a trailing slash into an index file such as index.html

- Maps a request to a URL based on where a user clicks on an image embedded in a HTML document.mod_negotiation

- Selects an appropriate document based on client preferences such as language or content compression.

Modules | Directives | FAQ | Glossary | Sitemap

Apache HTTP Server Version 2.4