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