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      <h3>Apache HTTP Server Version 2.0</h3>
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    <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="#proxy">Reverse Proxy</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 />
         <a href="mod/mod_alias.html">mod_alias</a><br />
         <a href="mod/mod_proxy.html">mod_proxy</a><br />
         <a href="mod/mod_rewrite.html">mod_rewrite</a><br />
         <a href="mod/mod_userdir.html">mod_userdir</a><br />
         <a href="mod/mod_speling.html">mod_speling</a><br />
         <a
        href="mod/mod_vhost_alias.html">mod_vhost_alias</a><br />
         </td>

        <td valign="top"><strong>Related Directives</strong><br />
         <br />
         <a href="mod/mod_alias.html#alias">Alias</a><br />
         <a
        href="mod/mod_alias.html#aliasmatch">AliasMatch</a><br />
         <a
        href="mod/mod_speling.html#checkspelling">CheckSpelling</a><br />
         <a
        href="mod/core.html#documentroot">DocumentRoot</a><br />
         <a
        href="mod/core.html#errordocument">ErrorDocument</a><br />
         <a href="mod/core.html#options">Options</a><br />
         <a href="mod/mod_proxy.html#proxypass">ProxyPass</a><br />
         <a href="mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a><br />
         <a href="mod/mod_alias.html#redirect">Redirect</a><br />
         <a
        href="mod/mod_alias.html#redirectmatch">RedirectMatch</a><br />
         <a
        href="mod/mod_rewrite.html#RewriteCond">RewriteCond</a><br />
         <a
        href="mod/mod_rewrite.html#RewriteRule">RewriteRule</a><br />
         <a
        href="mod/mod_alias.html#scriptalias">ScriptAlias</a><br />
         <a
        href="mod/mod_alias.html#scriptaliasmatch">ScriptAliasMatch</a><br />
         <a href="mod/mod_userdir.html#userdir">UserDir</a><br />
         </td>
      </tr>
    </table>

    <h2><a id="documentroot"
    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 <a
    href="mod/core.html#documentroot">DocumentRoot</a> specified in
    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 <a
    href="mod/mod_vhost_alias.html">mod_vhost_alias</a> can be used
    to dynamically determine the appropriate place from which to
    serve content based on the requested IP address or
    hostname.</p>

    <h2><a id="outside" 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 the <a
    href="mod/core.html#documentroot">DocumentRoot</a>. Apache
    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 symbolic links only if the <a
    href="mod/core.html#options">Options</a> setting for the
    relevant directory includes <code>FollowSymLinks</code> or
    <code>SymLinksIfOwnerMatch</code>.</p>

    <p>Alternatively, the <a
    href="mod/mod_alias.html#alias">Alias</a> directive will map
    any part of the filesystem into the web space. For example,
    with</p>

    <blockquote>
      <code>Alias /docs /var/web</code>
    </blockquote>

    <p>the URL
    <code>http://www.example.com/docs/dir/file.html</code> will be
    served from <code>/var/web/dir/file.html</code>. The <a
    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 use the <a
    href="mod/mod_alias.html#aliasmatch">AliasMatch</a> and <a
    href="mod/mod_alias.html#scriptaliasmatch">ScriptAliasMatch</a>
    directives to do powerful regular-expression based matching and
    substitution. For example,</p>

    <blockquote>
      <code>ScriptAliasMatch ^/~([a-zA-Z0-9]*)/cgi-bin/(.*)
      /home/$1/cgi-bin/$2</code>
    </blockquote>

    <p>will map a request to
    <code>http://example.com/~user/cgi-bin/script.cgi</code> to the
    path <code>/home/user/cgi-bin/script.cgi</code> and will treat
    the resulting file as a CGI script.</p>

    <h2><a id="user" 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 <a
    href="mod/mod_userdir.html">mod_userdir</a> extends this idea
    to the web by allowing files under each user's home directory
    to be accessed using URLs such as the following.</p>

    <blockquote>
      <code>http://www.example.com/~user/file.html</code>
    </blockquote>

    <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 like
    <code>/home/user/public_html/file.html</code> where
    <code>/home/user/</code> is the user's home directory as
    specified in <code>/etc/passwd</code>.</p>

    <p>There are also several other forms of the
    <code>Userdir</code> directive which you can use on systems
    where <code>/etc/passwd</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>http://www.example.com/upages/user/file.html</code> map
    to <code>/home/user/public_html/file.html</code>, use the
    following <code>AliasMatch</code> directive:</p>

    <blockquote>
      <code>AliasMatch ^/upages/([a-zA-Z0-9]*)/?(.*)
      /home/$1/public_html/$2</code>
    </blockquote>

    <h2><a id="redirect" 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 <a
    href="mod/mod_alias.html#redirect">Redirect</a> directive. For
    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 /foo/
      http://www.example.com/bar/</code>
    </blockquote>

    <p>This will redirect any URL-Path starting in
    <code>/foo/</code> to the same URL path on the
    <code>www.example.com</code> server with <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 id="proxy" name="proxy">Reverse Proxy</a></h2>

<p>Apache also allows you to bring remote documents into the URL space
of the local server.  This technique is called <em>reverse
proxying</em> 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 proxying because, to the client,
it appears the documents originate at the reverse proxy server.</p>

<p>In the following example, when clients request documents under the
<code>/foo/</code> directory, the server fetches those documents from
the <code>/bar/</code> directory on <code>internal.example.com</code>
and returns them to the client as if they were from the local
server.</p>

<blockquote>
ProxyPass /foo/ http://internal.example.com/bar/<br />
ProxyPassReverse /foo/ http://internal.example.com/bar/
</blockquote>

<p>The <a href="mod/mod_proxy.html#proxypass">ProxyPass</a> configures
the server to fetch the appropriate documents, while the <a
href="mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a>
directive rewrites redirects originating at
<code>internal.examle.com</code> so that they target the appropriate
directory on the local server.  It is important to note, however, that
links inside the documents will not be rewritten.  So any absolute
links on <code>internal.example.com</code> will result in the client
breaking out of the proxy server and requesting directly from
<code>internal.example.com</code>.</p>


    <h2><a id="rewrite" name="rewrite">Rewriting Engine</a></h2>

    <p>When even more powerful substitution is required, the rewriting
    engine provided by <a href="mod/mod_rewrite.html">mod_rewrite</a>
    can 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. 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 mod_rewrite are discussed in the
    <a href="misc/rewriteguide.html">URL Rewriting Guide</a>.</p>

    <h2><a id="notfound" 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. Apache provides the module <a
    href="mod/mod_speling.html">mod_speling</a> (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
    href="mod/core.html#errordocument">ErrorDocument</a> directive
    and can be customized in a flexible manner as discussed in the
    <a href="custom-error.html">Custom error responses</a> and <a
    href="misc/custom_errordocs.html">International Server Error
    Responses</a> documents.</p>
        <hr />

    <h3 align="center">Apache HTTP Server Version 2.0</h3>
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