urlmapping.html revision 2fbcb47faf267c01a8254429378b444b51d9207b
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
<TITLE>Mapping URLs to Filesystem Locations - Apache HTTP Server</TITLE>
</HEAD>
<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
<BODY
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#000080"
ALINK="#FF0000"
>
<!--#include virtual="header.html" -->
<h1 align="center">Mapping URLs to Filesystem Locations</h1>
<p>This document explains how Apache uses the URL of a request to
determine the filesystem location from which to serve a file.</p>
<ul>
<li><a href="#documentroot">DocumentRoot</a></li>
<li><a href="#outside">Files Outside the DocumentRoot</a></li>
<li><a href="#user">User Directories</a></li>
<li><a href="#redirect">URL Redirection</a></li>
<li><a href="#rewrite">Rewrite Engine</a></li>
<li><a href="#notfound">File Not Found</a></li>
</ul>
<hr>
<table border="1">
<tr><td valign="top">
<strong>Related Modules</strong><br><br>
</td><td valign="top">
<strong>Related Directives</strong><br><br>
</td></tr></table>
<h2><a name="documentroot">DocumentRoot</a></h2>
<p>In deciding what file to serve for a given request, Apache's
default behavior is to take the URL-Path for the request (the part of
the URL following the hostname and port) and add it to the end of the
your configuration files. Therefore, the files and directories
underneath the <code>DocumentRoot</code> make up the basic document
tree which will be visible from the web.</p>
<p>Apache is also capable of <a href="vhosts/">Virtual Hosting</a>,
where the server receives requests for more than one host. In this
case, a different <code>DocumentRoot</code> can be specified for each
virtual host, or alternatively, the directives provided by the module
dynamically determine the appropriate place from which to serve
content based on the requested IP address or hostname.</p>
<h2><a name="outside">Files Outside the DocumentRoot</a></h2>
<p>There are frequently circumstances where it is necessary to allow
web access to parts of the filesystem that are not strictly underneath
offers several different ways to accomplish this. On Unix systems,
symbolic links can bring other parts of the filesystem under the
<code>DocumentRoot</code>. For security reasons, Apache will follow
setting for the relevant directory includes
<code>FollowSymLinks</code> or <code>SymLinksIfOwnerMatch</code>.</p>
directive will map any part of the filesystem into the web
space. For example, with</p>
</code></blockquote>
href="mod/mod_alias.html#scriptalias">ScriptAlias</a> directive works
the same way, with the additional effect that all content located at
the target path is treated as CGI scripts.</p>
<p>For situations where you require additional flexibility, you can
href="mod/mod_alias.html#scriptaliasmatch">ScriptAliasMatch</a>
directives to do powerful regular-expression based matching and
substitution. For example,</p>
<blockquote><code> ScriptAliasMatch ^/~([^/]*)/cgi-bin/(.*)
<p>will map a request to
resulting file as a CGI script.</p>
<h2><a name="user">User Directories</a></h2>
<p>Traditionally on Unix systems, the home directory of a particular
<em>user</em> can be referred to as <code>~user/</code>. The module
the web by allowing files under each user's home directory to be
accessed using URLs such as the following.</p>
<p>For security reasons, it is inappropriate to give direct
access to a user's home directory from the web. Therefore, the <a
href="mod/mod_userdir.html#userdir">UserDir</a> directive
specifies a directory underneath the user's home directory where web
files are located. Using the default setting of <code>Userdir
public_html</code>, the above URL maps to a file at a directory
<p>There are also several other forms of the <code>Userdir</code>
does not contain the location of the home directory.</p>
<p>Some people find the "~" symbol (which is often encoded on the web
as <code>%7e</code>) 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 <a
href="mod/mod_alias.html#aliasmatch">AliasMatch</a> directive to
achieve the desired effect. For example, to make
<code>AliasMatch</code> directive:</p>
<blockquote><code>
AliasMatch ^/upages/([^/]*)/?(.*) /home/$1/public_html/$2
</code></blockquote>
<h2><a name="redirect">URL Redirection</a></h2>
<p>The configuration directives discussed in the above sections tell
Apache to get content from a specific place in the filesystem and
return it to the client. Sometimes, it is desirable instead to inform
the client that the requested content is located at a different
URL, and instruct the client to make a new request with the new URL.
This is called <em>redirection</em> and is implemented by the
example, if the contents of the directory <code>/foo/</code> under the
<code>DocumentRoot</code> are moved to the new directory
<code>/bar/</code>, you can instruct clients to request the content at
the new location as follows:</p>
<blockquote><code>Redirect permanent
<p>This will redirect any URL-Path starting in <code>/foo/</code> to
<code>/bar/</code> substituted for <code>/foo/</code>. You can
redirect clients to any server, not only the origin server.</p>
<p>Apache also provides a <a
href="mod/mod_alias.html#redirectmatch">RedirectMatch</a> directive
for more complicated rewriting problems. For example, to redirect
requests for the site home page to a different site, but leave all
other requests alone, use the following configuration:</p>
<blockquote><code>
RedirectMatch permanent ^/$ http://www.example.com/startpage.html
</code></blockquote>
<p>Alternatively, to temporarily redirect all pages on a site to one
particular page, use the following:</p>
<blockquote><code>
RedirectMatch temp .* http://www.example.com/startpage.html
</code></blockquote>
<h2><a name="rewrite">Rewriting Engine</a></h2>
<p>When even more powerful substitution is required, the rewriting
be useful. The directives provided by this module use
characteristics of the request such as browser type or source IP
address in deciding from where to serve content. In addition,
mod_rewrite can use external database files or programs to determine
how to handle a request. Many practical examples employing
mod_rewrite are discussed in the <a href="misc/rewriteguide.html">URL
Rewriting Guide</a>.</p>
<h2><a name="notfound">File Not Found</a></h2>
<p>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 <a href="#redirect">URL
redirection</a> 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.</p>
<p>Another common cause of "File Not Found" errors is accidental
mistyping of URLs, either directly in the browser, or in HTML links.
(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, mod_speling 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.</p>
<p>An especially useful feature of mod_speling, 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 mod_speling 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.</p>
<p>If all attempts to locate the content fail, Apache returns an error
page with HTTP status code 404 (file not found). The appearance of
this page is controlled with the <a
be customized in a flexible manner as discussed in the <a
href="misc/custom_errordocs.html">International Server Error
Responses</a> documents.</p>
<!--#include virtual="footer.html" -->
</BODY>
</HTML>