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Posted to cvs@httpd.apache.org by rb...@apache.org on 2002/07/25 16:35:28 UTC
cvs commit: httpd-2.0/docs/manual/howto htaccess.html
rbowen 2002/07/25 07:35:28
Added: docs/manual/howto htaccess.html
Log:
First draft of .htaccess tutorial-style documentation.
Reviewed by: Several people on docs mailing list, as well as various
folks on IRC.
Revision Changes Path
1.1 httpd-2.0/docs/manual/howto/htaccess.html
Index: htaccess.html
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<h1 align="CENTER">.htaccess files</h1>
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<ul>
<li><a href="#what">What they are/How to use them</a></li>
<li><a href="#when">When (not) to use them</a></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</a></li>
<li><a href="#cgi">CGI</a></li>
<li><a href="#troubleshoot">Troubleshooting</a></li>
</ul>
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<table border="1">
<tr>
<td valign="top"><strong>Related Modules</strong><br />
<br />
<a href="../mod/core.html">core</a><br />
<a href="../mod/mod_auth.html">mod_auth</a><br />
<a href="../mod/mod_cgi.html">mod_cgi</a><br />
<a href="../mod/mod_includes.html">mod_includes</a><br />
<a href="../mod/mod_mime.html">mod_mine</a><br />
</td>
<td valign="top"><strong>Related Directives</strong><br />
<br />
<a href="../mod/core.html#accessfilename">AccessFileName</a><br />
<a href="../mod/core.html#allowoverride">AllowOverride</a><br />
<a href="../mod/core.html#options">Options</a><br />
<a href="../mod/mod_mime.html#addhandler">AddHandler</a><br />
<a href="../mod/core.html#sethandler">SetHandler</a><br />
<a href="../mod/core.html#authtype">AuthType</a><br />
<a href="../mod/core.html#authname">AuthName</a><br />
<a href="../mod/mod_auth.html#authuserfile">AuthUserFile</a><br />
<a href="../mod/mod_auth.html#authuserfile">AuthGroupFile</a><br />
<a href="../mod/core.html#require">Require</a><br />
</td>
</tr>
</table>
<hr />
<h2><a id="what" name="what">What they are/How to use them</a></h2>
<p>.htaccess 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 .htaccess file something else, you can
change the name of the file using the AccessFileName directive. For
example, if you would rather call the file .config 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 AllowOverride
directive. This directive specifies, in categories, what directives will
be honored if they are found in a .htaccess file. If a directive is
permitted in a .htaccess file, the documentation for that directive will
contain an Override section, specifying what value must be in
AllowOverride in order for that directive to be permitted.</p>
<p>For example, if you look at the docs for the AddDefaultCharset
directive, you will find that it is permitted in .htaccess files. (See
the Context line in the directive summary.) The Override line reads
"FileInfo". Thus, you must have at least "AllowOverride FileInfo" in
order for this directive to be honored in .htaccess files.</p>
<p>Example:</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Context: server config, virtual host, directory, .htaccess<br>
Override: FileInfo
</code></td></tr></table></blockquote>
<p>If you are unsure whether a particular diretive is permitted in a
.htaccess 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 .htaccess 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 .htaccess 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>.htaccess 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 .htaccess files for themselves.</p>
<p>However, in general, use of .htaccess files should be avoided when
possible. Any configuration that you would consider putting in a
.htaccess file, can just as effectively be made in a <Directory>
section in your main server configuration file.</p>
<p>There are two main reasons to avoid the use of .htaccess files.</p>
<p>The first of these is performance. When AllowOverride is set to allow
the use of .htaccess files, Apache will look in every directory for
.htaccess files. Thus, permitting .htaccess files causes a performance
hit, whether or not you actually even use them! Also, the .htaccess file
is loaded every time a document is requested.</p>
<p>Further note that Apache must look for .htaccess files in all
higher-level directories, in order to have a full complement of
directives that it must apply. (See section on how directives are
applied, below.) Thus, if a file is requested out of a directory
/www/htdocs/example, 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 /www/htdocs/example containing a directive, and to put that
same directive in a Directory section <Directory
/www/htdocs/example> in your main server configuration:</p>
<p>.htaccess file in /www/htdocs/example:</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
AddType text/example .exm
</code></td></tr></table></blockquote>
<p>httpd.conf</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 .htaccess files can be disabled completely by setting the
AllowOverride 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 .htaccess file are applied to
the directory in which the .htaccess file is found, and to all
subdirectories thereof. However, it is important to also remember that
there may have been .htaccess files in directories higher up. Directives
are applied in the order that they are found. Therefore, a .htaccess file
in a particular directory may override directives found in .htaccess
files found higher up in the directory tree. And those, in turn, may have
overriden directives found yet higher up, or in the main server
configuration file itself.</p>
<p>Example:</p>
<p>In the directory /www/htdocs/example1 we have a .htaccess 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 "AllowOverride Options" in effect to permit the
use of the "Options" directive in .htaccess files.)</p>
<p>In the directory /www/htdocs/example1/example2 we have a .htaccess
file containing:</p>
<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
Options Includes
</code></td></tr></table></blockquote>
<p>Because of this second .htaccess file, in the directory
/www/htdocs/example1/example2, cgi execution is not permitted, as only
Options Includes 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 .htaccess files in order to
implement password authentication. This is not the case. Putting
authentication directives in a <Directory> section, in your main
server configuration file, is the preferred way to implement this, and
.htaccess 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 .htaccess files.</p>
<p>Having said that, if you still think you need to use a .htaccess file,
you may find that a configuration such as what follows may work for
you.</p>
<p>You must have "AllowOverride AuthConfig" in effect for these
directives to be honored.</p>
<p>.htaccess 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 AllowOverride AuthConfig must be in effect for these
directives to have any effect.</p>
<p>Please see the authentication tutorial for a more complete discussion
of authentication and authorization.</p>
<h2><a id="ssi" name="ssi">SSI example</a></h2>
<p>Another common use of .htaccess files is to enable Server Side
Includes for a particular directory. This may be done with the following
configuration directives, placed in a .htaccess 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 AllowOverride Options and AllowOverride FileInfo must both
be in effect for these directives to have any effect.</p>
<h2><a id="cgi" name="cgi">CGI example</a></h2>
<p>Finally, you may wish to use a .htaccess 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 AllowOverride Options must be in effect for these directives
to have any effect.</p>
<h2><a id="troubleshoot" name="troubleshoot">Troubleshooting</a></h2>
<p>When you put configuration directives in a .htaccess 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 AllowOverride is not set such that
your configuration directives are being honored. Make sure that you don't
have a AllowOverride None in effect for the file scope in question. A
good test for this is to put garbage in your .htaccess file and reload.
If a server error is not generated, then you almost certainly have
AllowOverride None 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>
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