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<title>Mapping URLs to Filesystem Locations - Apache HTTP Server</title>
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<p class="apache">Apache HTTP Server Version 2.2</p>
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<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="./">Version 2.2</a></div><div id="page-content"><div id="preamble"><h1>Mapping URLs to Filesystem Locations</h1>
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    <p>This document explains how Apache uses the URL of a request
    to determine the filesystem location from which to serve a
    file.</p>
  </div>
<div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#related">Related Modules and Directives</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#documentroot">DocumentRoot</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#outside">Files Outside the DocumentRoot</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#user">User Directories</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#redirect">URL Redirection</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#proxy">Reverse Proxy</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#rewrite">Rewriting Engine</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#notfound">File Not Found</a></li>
</ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="related" id="related">Related Modules and Directives</a></h2>

<table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_alias.html">mod_alias</a></code></li><li><code class="module"><a href="./mod/mod_proxy.html">mod_proxy</a></code></li><li><code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code></li><li><code class="module"><a href="./mod/mod_userdir.html">mod_userdir</a></code></li><li><code class="module"><a href="./mod/mod_speling.html">mod_speling</a></code></li><li><code class="module"><a href="./mod/mod_vhost_alias.html">mod_vhost_alias</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_alias.html#alias">Alias</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#aliasmatch">AliasMatch</a></code></li><li><code class="directive"><a href="./mod/mod_speling.html#checkspelling">CheckSpelling</a></code></li><li><code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code></li><li><code class="directive"><a href="./mod/core.html#errordocument">ErrorDocument</a></code></li><li><code class="directive"><a href="./mod/core.html#options">Options</a></code></li><li><code class="directive"><a href="./mod/mod_proxy.html#proxypass">ProxyPass</a></code></li><li><code class="directive"><a href="./mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a></code></li><li><code class="directive"><a href="./mod/mod_proxy.html#proxypassreversecookiedomain">ProxyPassReverseCookieDomain</a></code></li><li><code class="directive"><a href="./mod/mod_proxy.html#proxypassreversecookiepath">ProxyPassReverseCookiePath</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#redirect">Redirect</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#redirectmatch">RedirectMatch</a></code></li><li><code class="directive"><a href="./mod/mod_rewrite.html#rewritecond">RewriteCond</a></code></li><li><code class="directive"><a href="./mod/mod_rewrite.html#rewriterule">RewriteRule</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#scriptalias">ScriptAlias</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#scriptaliasmatch">ScriptAliasMatch</a></code></li><li><code class="directive"><a href="./mod/mod_userdir.html#userdir">UserDir</a></code></li></ul></td></tr></table>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="documentroot" id="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 <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code> specified
    in your configuration files. Therefore, the files and directories
    underneath the <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code>
    make up the basic document tree which will be visible from the
    web.</p>

    <p>For example, if <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code>
    were set to <code>/var/www/html</code> then a request for
    <code>http://www.example.com/fish/guppies.html</code> would result
    in the file <code>/var/www/html/fish/guppies.html</code> being
    served to the requesting client.</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 class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code> can be specified for each
    virtual host, or alternatively, the directives provided by the
    module <code class="module"><a href="./mod/mod_vhost_alias.html">mod_vhost_alias</a></code> can
    be used to dynamically determine the appropriate place from which
    to serve content based on the requested IP address or
    hostname.</p>

    <p>The <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code> directive
    is set in your main server configuration file
    (<code>httpd.conf</code>) and, possibly, once per additional <a href="vhosts/">Virtual Host</a> you create.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="outside" id="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 <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code>. Apache offers several
    different ways to accomplish this. On Unix systems, symbolic links
    can bring other parts of the filesystem under the <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code>. For security reasons,
    Apache will follow symbolic links only if the <code class="directive"><a href="./mod/core.html#options">Options</a></code> setting for the relevant
    directory includes <code>FollowSymLinks</code> or
    <code>SymLinksIfOwnerMatch</code>.</p>

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

<div class="example"><p><code>Alias /docs /var/web</code></p></div>

    <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
    <code class="directive"><a href="./mod/mod_alias.html#scriptalias">ScriptAlias</a></code> directive
    works the same way, with the additional effect that all content
    located at the target path is treated as <a class="glossarylink" href="./glossary.html#cgi" title="see glossary">CGI</a> scripts.</p>

    <p>For situations where you require additional flexibility, you
    can use the <code class="directive"><a href="./mod/mod_alias.html#aliasmatch">AliasMatch</a></code>
    and <code class="directive"><a href="./mod/mod_alias.html#scriptaliasmatch">ScriptAliasMatch</a></code>
    directives to do powerful <a class="glossarylink" href="./glossary.html#regex" title="see glossary">regular
    expression</a> based matching and substitution. For
    example,</p>

<div class="example"><p><code>ScriptAliasMatch ^/~([a-zA-Z0-9]+)/cgi-bin/(.+)
      /home/$1/cgi-bin/$2</code></p></div>

    <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>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="user" id="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 <code class="module"><a href="./mod/mod_userdir.html">mod_userdir</a></code>
    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>

<div class="example"><p><code>http://www.example.com/~user/file.html</code></p></div>

    <p>For security reasons, it is inappropriate to give direct
    access to a user's home directory from the web. Therefore, the
    <code class="directive"><a href="./mod/mod_userdir.html#userdir">UserDir</a></code> 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 <code class="directive"><a href="./mod/mod_alias.html#aliasmatch">AliasMatch</a></code>
    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>

<div class="example"><p><code>AliasMatch ^/upages/([a-zA-Z0-9]+)/?(.*)
      /home/$1/public_html/$2</code></p></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="redirect" id="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 <code class="directive"><a href="./mod/mod_alias.html#redirect">Redirect</a></code> directive. For example, if
    the contents of the directory <code>/foo/</code> under the
    <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></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>

<div class="example"><p><code>Redirect permanent /foo/
      http://www.example.com/bar/</code></p></div>

    <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 <code class="directive"><a href="./mod/mod_alias.html#redirectmatch">RedirectMatch</a></code> 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>

<div class="example"><p><code>RedirectMatch permanent ^/$
      http://www.example.com/startpage.html</code></p></div>

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

<div class="example"><p><code>RedirectMatch temp .*
      http://othersite.example.com/startpage.html</code></p></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="proxy" id="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>

<div class="example"><p><code>
ProxyPass /foo/ http://internal.example.com/bar/<br />
ProxyPassReverse /foo/ http://internal.example.com/bar/<br />
ProxyPassReverseCookieDomain internal.example.com public.example.com<br />
ProxyPassReverseCookiePath /foo/ /bar/
</code></p></div>

<p>The <code class="directive"><a href="./mod/mod_proxy.html#proxypass">ProxyPass</a></code> configures
the server to fetch the appropriate documents, while the
<code class="directive"><a href="./mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a></code>
directive rewrites redirects originating at
<code>internal.example.com</code> so that they target the appropriate
directory on the local server.  Similarly, the
<code class="directive"><a href="./mod/mod_proxy.html#proxypassreversecookiedomain">ProxyPassReverseCookieDomain</a></code>
and <code class="directive"><a href="./mod/mod_proxy.html#proxypassreversecookiepath">ProxyPassReverseCookiePath</a></code>
rewrite cookies set by the backend server.</p>
<p>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>.  A third-party module
<a href="http://apache.webthing.com/mod_proxy_html/">mod_proxy_html</a>
is available to rewrite links in HTML and XHTML.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="rewrite" id="rewrite">Rewriting Engine</a></h2>

    <p>When even more powerful substitution is required, the rewriting
    engine provided by <code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code>
    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="rewrite/">detailed mod_rewrite documentation</a>.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="notfound" id="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
    <code class="module"><a href="./mod/mod_speling.html">mod_speling</a></code> (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
    <code class="directive"><a href="./mod/core.html#errordocument">ErrorDocument</a></code> directive
    and can be customized in a flexible manner as discussed in the
    <a href="custom-error.html">Custom error responses</a>
    document.</p>
</div></div>
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