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Apache官方在今天放出产品系列2.2的最新版本2.2.11的源码包 最流行的HTTP服务器软件之一

    path from the requested URL to the document root to make the
    path to the document. Example:</p>

    <div class="example"><p><code>
      DocumentRoot /usr/web
    </code></p></div>

    <p>then an access to
    <code>http://www.my.host.com/index.html</code> refers to
    <code>/usr/web/index.html</code>. If the <var>directory-path</var> is 
    not absolute then it is assumed to be relative to the <code class="directive"><a href="#serverroot">ServerRoot</a></code>.</p>

    <p>The <code class="directive">DocumentRoot</code> should be specified without
    a trailing slash.</p>

<h3>See also</h3>
<ul>
<li><a href="../urlmapping.html#documentroot">Mapping URLs to Filesystem
Locations</a></li>
</ul>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="EnableMMAP" id="EnableMMAP">EnableMMAP</a> <a name="enablemmap" id="enablemmap">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Use memory-mapping to read files during delivery</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>EnableMMAP On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>EnableMMAP On</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Core</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>core</td></tr>
</table>
    <p>This directive controls whether the <code class="program"><a href="../programs/httpd.html">httpd</a></code> may use
    memory-mapping if it needs to read the contents of a file during
    delivery.  By default, when the handling of a request requires
    access to the data within a file -- for example, when delivering a
    server-parsed file using <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> -- Apache
    memory-maps the file if the OS supports it.</p>

    <p>This memory-mapping sometimes yields a performance improvement.
    But in some environments, it is better to disable the memory-mapping
    to prevent operational problems:</p>

    <ul>
    <li>On some multiprocessor systems, memory-mapping can reduce the
    performance of the <code class="program"><a href="../programs/httpd.html">httpd</a></code>.</li>
    <li>With an NFS-mounted <code class="directive"><a href="#documentroot">DocumentRoot</a></code>,
    the <code class="program"><a href="../programs/httpd.html">httpd</a></code> may crash due to a segmentation fault if a file
    is deleted or truncated while the <code class="program"><a href="../programs/httpd.html">httpd</a></code> has it
    memory-mapped.</li>
    </ul>

    <p>For server configurations that are vulnerable to these problems,
    you should disable memory-mapping of delivered files by specifying:</p>

    <div class="example"><p><code>
      EnableMMAP Off
    </code></p></div>

    <p>For NFS mounted files, this feature may be disabled explicitly for
    the offending files by specifying:</p>

    <div class="example"><p><code>
      &lt;Directory "/path-to-nfs-files"&gt;
      <span class="indent">
        EnableMMAP Off
      </span>
      &lt;/Directory&gt;
    </code></p></div>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="EnableSendfile" id="EnableSendfile">EnableSendfile</a> <a name="enablesendfile" id="enablesendfile">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Use the kernel sendfile support to deliver files to the client</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>EnableSendfile On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>EnableSendfile On</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Core</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>core</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.0.44 and later</td></tr>
</table>
    <p>This directive controls whether <code class="program"><a href="../programs/httpd.html">httpd</a></code> may use the
    sendfile support from the kernel to transmit file contents to the client.
    By default, when the handling of a request requires no access
    to the data within a file -- for example, when delivering a
    static file -- Apache uses sendfile to deliver the file contents
    without ever reading the file if the OS supports it.</p>

    <p>This sendfile mechanism avoids separate read and send operations,
    and buffer allocations. But on some platforms or within some
    filesystems, it is better to disable this feature to avoid
    operational problems:</p>

    <ul>
    <li>Some platforms may have broken sendfile support that the build
    system did not detect, especially if the binaries were built on
    another box and moved to such a machine with broken sendfile
    support.</li>
    <li>On Linux the use of sendfile triggers TCP-checksum
    offloading bugs on certain networking cards when using IPv6.</li>
    <li>On Linux on Itanium, sendfile may be unable to handle files
    over 2GB in size.</li>
    <li>With a network-mounted <code class="directive"><a href="#documentroot">DocumentRoot</a></code> (e.g., NFS or SMB),
    the kernel may be unable to serve the network file through
    its own cache.</li>
    </ul>

    <p>For server configurations that are vulnerable to these problems,
    you should disable this feature by specifying:</p>

    <div class="example"><p><code>
      EnableSendfile Off
    </code></p></div>

    <p>For NFS or SMB mounted files, this feature may be disabled explicitly
    for the offending files by specifying:</p>

    <div class="example"><p><code>
      &lt;Directory "/path-to-nfs-files"&gt;
      <span class="indent">
        EnableSendfile Off
      </span>
      &lt;/Directory&gt;
    </code></p></div>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="ErrorDocument" id="ErrorDocument">ErrorDocument</a> <a name="errordocument" id="errordocument">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>What the server will return to the client
in case of an error</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ErrorDocument <var>error-code</var> <var>document</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Core</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>core</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Quoting syntax for text messages is different in Apache
2.0</td></tr>
</table>
    <p>In the event of a problem or error, Apache can be configured
    to do one of four things,</p>

    <ol>
      <li>output a simple hardcoded error message</li>

      <li>output a customized message</li>

      <li>redirect to a local <var>URL-path</var> to handle the
      problem/error</li>

      <li>redirect to an external <var>URL</var> to handle the
      problem/error</li>
    </ol>

    <p>The first option is the default, while options 2-4 are
    configured using the <code class="directive">ErrorDocument</code>
    directive, which is followed by the HTTP response code and a URL
    or a message. Apache will sometimes offer additional information
    regarding the problem/error.</p>

    <p>URLs can begin with a slash (/) for local web-paths (relative
    to the <code class="directive"><a href="#documentroot">DocumentRoot</a></code>), or be a
    full URL which the client can resolve. Alternatively, a message
    can be provided to be displayed by the browser. Examples:</p>

    <div class="example"><p><code>
      ErrorDocument 500 http://foo.example.com/cgi-bin/tester<br />
      ErrorDocument 404 /cgi-bin/bad_urls.pl<br />
      ErrorDocument 401 /subscription_info.html<br />
      ErrorDocument 403 "Sorry can't allow you access today"
    </code></p></div>

    <p>Additionally, the special value <code>default</code> can be used
    to specify Apache's simple hardcoded message.  While not required
    under normal circumstances, <code>default</code> will restore
    Apache's simple hardcoded message for configurations that would
    otherwise inherit an existing <code class="directive">ErrorDocument</code>.</p>

    <div class="example"><p><code>
      ErrorDocument 404 /cgi-bin/bad_urls.pl<br /><br />
      &lt;Directory /web/docs&gt;<br />
      <span class="indent">
        ErrorDocument 404 default<br />
      </span>
      &lt;/Directory&gt;
    </code></p></div>

    <p>Note that when you specify an <code class="directive">ErrorDocument</code>
    that points to a remote URL (ie. anything with a method such as
    <code>http</code> in front of it), Apache will send a redirect to the
    client to tell it where to find the document, even if the
    document ends up being on the same server. This has several
    implications, the most important being that the client will not
    receive the original error status code, but instead will
    receive a redirect status code. This in turn can confuse web
    robots and other clients which try to determine if a URL is
    valid using the status code. In addition, if you use a remote
    URL in an <code>ErrorDocument 401</code>, the client will not
    know to prompt the user for a password since it will not
    receive the 401 status code. Therefore, <strong>if you use an
    <code>ErrorDocument 401</code> directive then it must refer to a local
    document.</strong></p>

    <p>Microsoft Internet Explorer (MSIE) will by default ignore
    server-generated error messages when they are "too small" and substitute
    its own "friendly" error messages. The size threshold varies depending on
    the type of error, but in general, if you make your error document
    greater than 512 bytes, then MSIE will show the server-generated
    error rather than masking it.  More information is available in
    Microsoft Knowledge Base article <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;Q294807">Q294807</a>.</p>

    <p>Although most error messages can be overriden, there are certain
    circumstances where the internal messages are used regardless of the
    setting of <code class="directive"><a href="#errordocument">ErrorDocument</a></code>.  In