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417 lines
16 KiB
HTML
Executable File
417 lines
16 KiB
HTML
Executable File
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Apache Tutorial: .htaccess files</title>
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</head>
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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#000080"
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alink="#FF0000">
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<!--#include virtual="header.html" -->
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<h1 align="CENTER"><code>.htaccess</code> files</h1>
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<!-- INDEX BEGIN -->
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<ul>
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<li><a href="#what">What they are/How to use them</a></li>
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<li><a href="#when">When (not) to use <code
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class="file">.htaccess</code></a> files</li>
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<li><a href="#how">How directives are applied</a></li>
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<li><a href="#auth">Authentication example</a></li>
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<li><a href="#ssi">Server side includes example</a></li>
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<li><a href="#cgi">CGI example</a></li>
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<li><a href="#troubleshoot">Troubleshooting</a></li>
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</ul>
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<!-- Index End -->
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<table border="1">
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<tr>
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<td valign="top"><strong>Related Modules</strong><br />
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<br />
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<code><a href="../mod/core.html">core</a></code><br />
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<code><a href="../mod/mod_auth.html">mod_auth</a></code><br />
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<code><a href="../mod/mod_cgi.html">mod_cgi</a></code><br />
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<code><a href="../mod/mod_includes.html">mod_includes</a><br />
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</code> <a href="../mod/mod_mime.html">mod_mine</a><br />
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</td>
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<td valign="top"><strong>Related Directives</strong><br />
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<br />
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<code><a
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href="../mod/core.html#accessfilename">AccessFileName</a></code><br />
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<code><a
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href="../mod/core.html#allowoverride">AllowOverride</a></code><br />
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<code><a href="../mod/core.html#options">Options</a></code><br />
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<code><a
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href="../mod/mod_mime.html#addhandler">AddHandler</a></code><br />
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<code><a
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href="../mod/core.html#sethandler">SetHandler</a></code><br />
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<code><a
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href="../mod/core.html#authtype">AuthType</a></code><br />
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<code><a
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href="../mod/core.html#authname">AuthName</a></code><br />
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<code><a
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href="../mod/mod_auth.html#authuserfile">AuthUserFile</a></code><br />
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<code><a
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href="../mod/mod_auth.html#authuserfile">AuthGroupFile</a></code><br />
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<code><a href="../mod/core.html#require">Require</a></code><br />
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</td>
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</tr>
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</table>
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<hr />
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<h2><a id="what" name="what">What they are/How to use them</a></h2>
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<p><code>.htaccess</code> files (or "distributed configuration files")
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provide a way to make configuration changes on a per-directory basis. A
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file, containing one or more configuration directives, is placed in a
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particular document directory, and the directives apply to that
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directory, and all subdirectories thereof.</p>
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<p>Note: If you want to call your <code>.htaccess</code> file something
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else, you can change the name of the file using the <code><a
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href="../mod/core.html#accessfilename">AccessFileName</a></code>
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directive. For example, if you would rather call the file
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<code>.config</code> then you can put the following in your server
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configuration file:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>AccessFileName .config</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>What you can put in these files is determined by the <code><a
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href="../mod/core.html#allowoverride">AllowOverride</a></code>
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directive. This directive specifies, in categories, what directives
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will be honored if they are found in a <code>.htaccess</code> file. If
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a directive is permitted in a <code>.htaccess</code> file, the
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documentation for that directive will contain an Override section,
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specifying what value must be in <code>AllowOverride</code> in order
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for that directive to be permitted.</p>
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<p>For example, if you look at the documentation for the <a
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href="../mod/core.html#adddefaultcharset">AddDefaultCharset</a>
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directive, you will find that it is permitted in <code>.htaccess</code>
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files. (See the Context line in the directive summary.) The <a
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href="../mod/directive-dict.html#Context">Override</a> line reads
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"<code>FileInfo</code>". Thus, you must have at least
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"<code>AllowOverride FileInfo</code>" in order for this directive to be
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honored in <code>.htaccess</code> files.</p>
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<p>Example:</p>
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<blockquote>
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<table>
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<tr>
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<td><a
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href="../mod/directive-dict.html#Context">Context:</a></td>
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<td>server config, virtual host, directory, .htaccess</td>
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</tr>
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<tr>
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<td><a
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href="../mod/directive-dict.html#Override">Override:</a></td>
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<td>FileInfo</td>
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</tr>
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</table>
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</blockquote>
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<p>If you are unsure whether a particular directive is permitted in a
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<code>.htaccess</code> file, look at the documentation for that
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directive, and check the Context line for ".htaccess."</p>
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<h2><a id="when" name="when">When (not) to use .htaccess files</a></h2>
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<p>In general, you should never use <code>.htaccess</code> files unless
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you don't have access to the main server configuration file. There is,
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for example, a prevailing misconception that user authentication should
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always be done in <code>.htaccess</code> files. This is simply not the
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case. You can put user authentication configurations in the main server
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configuration, and this is, in fact, the preferred way to do
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things.</p>
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<p><code>.htaccess</code> files should be used in a case where the
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content providers need to make configuration changes to the server on a
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per-directory basis, but do not have root access on the server system.
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In the event that the server administrator is not willing to make
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frequent configuration changes, it might be desirable to permit
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individual users to make these changes in <code>.htaccess</code> files
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for themselves. This is particularly true, for example, in cases where
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ISPs are hosting multiple user sites on a single machine, and want
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their users to be able to alter their configuration.</p>
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<p>However, in general, use of <code>.htaccess</code> files should be
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avoided when possible. Any configuration that you would consider
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putting in a <code>.htaccess</code> file, can just as effectively be
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made in a <a href="../mod/core.html#Directory"><Directory></a>
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section in your main server configuration file.</p>
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<p>There are two main reasons to avoid the use of
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<code>.htaccess</code> files.</p>
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<p>The first of these is performance. When <code>AllowOverride</code>
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is set to allow the use of <code>.htaccess</code> files, Apache will
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look in every directory for <code>.htaccess</code> files. Thus,
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permitting <code>.htaccess</code> files causes a performance hit,
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whether or not you actually even use them! Also, the
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<code>.htaccess</code> file is loaded every time a document is
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requested.</p>
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<p>Further note that Apache must look for <code>.htaccess</code> files
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in all higher-level directories, in order to have a full complement of
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directives that it must apply. (See section on <a href="#how">how
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directives are applied</a>.) Thus, if a file is requested out of a
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directory <code>/www/htdocs/example</code>, Apache must look for the
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following files:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>/.htaccess<br />
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/www/.htaccess<br />
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/www/htdocs/.htaccess<br />
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/www/htdocs/example/.htaccess</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>And so, for each file access out of that directory, there are 4
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additional file-system accesses, even if none of those files are
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present. (Note that this would only be the case if .htaccess files were
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enabled for /, which is not usually the case.)</p>
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<p>The second consideration is one of security. You are permitting
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users to modify server configuration, which may result in changes over
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which you have no control. Carefully consider whether you want to give
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your users this privilege.</p>
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<p>Note that it is completely equivalent to put a .htaccess file in a
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directory <code>/www/htdocs/example</code> containing a directive, and
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to put that same directive in a Directory section <code><Directory
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/www/htdocs/example></code> in your main server configuration:</p>
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<p><code>.htaccess</code> file in <code>/www/htdocs/example</code>:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>AddType text/example .exm</code>
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</td>
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</tr>
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</table>
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</blockquote>
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<p><code>httpd.conf</code></p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code><Directory
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/www/htdocs/example><br />
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AddType text/example .exm<br />
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</Directory></code> </td>
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</tr>
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</table>
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</blockquote>
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<p>However, putting this configuration in your server configuration
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file will result in less of a performance hit, as the configuration is
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loaded once when Apache starts, rather than every time a file is
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requested.</p>
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<p>The use of <code>.htaccess</code> files can be disabled completely
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by setting the <code>AllowOverride</code> directive to "none"</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>AllowOverride None</code> </td>
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</tr>
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</table>
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</blockquote>
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<h2><a id="how" name="how">How directives are applied</a></h2>
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<p>The configuration directives found in a <code>.htaccess</code> file
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are applied to the directory in which the <code>.htaccess</code> file
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is found, and to all subdirectories thereof. However, it is important
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to also remember that there may have been <code>.htaccess</code> files
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in directories higher up. Directives are applied in the order that they
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are found. Therefore, a <code>.htaccess</code> file in a particular
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directory may override directives found in <code>.htaccess</code> files
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found higher up in the directory tree. And those, in turn, may have
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overridden directives found yet higher up, or in the main server
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configuration file itself.</p>
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<p>Example:</p>
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<p>In the directory <code>/www/htdocs/example1</code> we have a
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<code>.htaccess</code> file containing the following:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>Options +ExecCGI</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>(Note: you must have "<code>AllowOverride Options</code>" in effect
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to permit the use of the "<code><a
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href="../mod/core.html#options">Options</a></code>" directive in
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<code>.htaccess</code> files.)</p>
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<p>In the directory <code>/www/htdocs/example1/example2</code> we have
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a <code>.htaccess</code> file containing:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>Options Includes</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>Because of this second <code>.htaccess</code> file, in the directory
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<code>/www/htdocs/example1/example2</code>, CGI execution is not
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permitted, as only <code>Options Includes</code> is in effect, which
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completely overrides any earlier setting that may have been in
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place.</p>
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<h2><a id="auth" name="auth">Authentication example</a></h2>
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<p>If you jumped directly to this part of the document to find out how
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to do authentication, it is important to note one thing. There is a
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common misconception that you are required to use
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<code>.htaccess</code> files in order to implement password
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authentication. This is not the case. Putting authentication directives
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in a <code><Directory></code> section, in your main server
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configuration file, is the preferred way to implement this, and
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<code>.htaccess</code> files should be used only if you don't have
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access to the main server configuration file. See above for a
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discussion of when you should and should not use <code>.htaccess</code>
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files.</p>
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<p>Having said that, if you still think you need to use a
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<code>.htaccess</code> file, you may find that a configuration such as
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what follows may work for you.</p>
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<p>You must have "<code>AllowOverride AuthConfig</code>" in effect for
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these directives to be honored.</p>
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<p><code>.htaccess</code> file contents:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>AuthType Basic<br />
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AuthName "Password Required"<br />
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AuthUserFile /www/passwords/password.file<br />
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AuthGroupFile /www/passwords/group.file<br />
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Require Group admins</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>Note that <code>AllowOverride AuthConfig</code> must be in effect
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for these directives to have any effect.</p>
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<p>Please see the <a href="auth.html">authentication tutorial</a> for a
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more complete discussion of authentication and authorization.</p>
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<h2><a id="ssi" name="ssi">Server side includes example</a></h2>
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<p>Another common use of <code>.htaccess</code> files is to enable
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Server Side Includes for a particular directory. This may be done with
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the following configuration directives, placed in a
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<code>.htaccess</code> file in the desired directory:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>Options +Includes<br />
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AddType text/html shtml<br />
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AddHandler server-parsed shtml</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>Note that <code>AllowOverride Options</code> and <code>AllowOverride
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FileInfo</code> must both be in effect for these directives to have any
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effect.</p>
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<p>Please see the <a href="ssi.html">SSI tutorial</a> for a more
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complete discussion of server-side includes.</p>
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<h2><a id="cgi" name="cgi">CGI example</a></h2>
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<p>Finally, you may wish to use a <code>.htaccess</code> file to permit
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the execution of CGI programs in a particular directory. This may be
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implemented with the following configuration:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>Options +ExecCGI<br />
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AddHandler cgi-script cgi pl</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>Alternately, if you wish to have all files in the given directory be
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considered to be CGI programs, this may be done with the following
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configuration:</p>
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<blockquote>
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<table cellpadding="10">
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<tr>
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<td bgcolor="#eeeeee"><code>Options +ExecCGI<br />
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SetHandler cgi-script</code> </td>
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</tr>
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</table>
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</blockquote>
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<p>Note that <code>AllowOverride Options</code> must be in effect for
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these directives to have any effect.</p>
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<p>Please see the <a href="cgi.html">CGI tutorial</a> for a more
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complete discussion of CGI programming and configuration.</p>
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<h2><a id="troubleshoot" name="troubleshoot">Troubleshooting</a></h2>
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<p>When you put configuration directives in a <code>.htaccess</code>
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file, and you don't get the desired effect, there are a number of
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things that may be going wrong.</p>
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<p>Most commonly, the problem is that <code><a
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href="../mod/core.html#allowoverride">AllowOverride</a></code> is not
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set such that your configuration directives are being honored. Make
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sure that you don't have a <code>AllowOverride None</code> in effect
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for the file scope in question. A good test for this is to put garbage
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in your <code>.htaccess</code> file and reload. If a server error is
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not generated, then you almost certainly have <code>AllowOverride
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None</code> in effect.</p>
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<p>If, on the other hand, you are getting server errors when trying to
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access documents, check your Apache error log. It will likely tell you
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that the directive used in your .htaccess file is not permitted.
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Alternately, it may tell you that you had a syntax error, which you
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will then need to fix.</p>
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</body>
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</html>
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