apache/docs/manual/howto/htaccess.xml

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<manualpage metafile="htaccess.xml.meta">
<parentdocument href="./">How-To / Tutorials</parentdocument>

<title>Apache HTTP Server Tutorial: .htaccess files</title>

<summary>
<p><code>.htaccess</code> files provide a way to make configuration
changes on a per-directory basis.</p>
</summary>

<section id="related"><title>.htaccess files</title>
    <related>
        <modulelist>
            <module>core</module>
            <module>mod_authn_file</module>
            <module>mod_authz_groupfile</module>
            <module>mod_cgi</module>
            <module>mod_include</module>
            <module>mod_mime</module>
        </modulelist>

        <directivelist>
            <directive module="core">AccessFileName</directive>
            <directive module="core">AllowOverride</directive>
            <directive module="core">Options</directive>
            <directive module="mod_mime">AddHandler</directive>
            <directive module="core">SetHandler</directive>
            <directive module="mod_authn_core">AuthType</directive>
            <directive module="mod_authn_core">AuthName</directive>
            <directive module="mod_authn_file">AuthUserFile</directive>
            <directive module="mod_authz_groupfile">AuthGroupFile</directive>
            <directive module="mod_authz_core">Require</directive>
        </directivelist>

    </related>

    <note>You should avoid using <code>.htaccess</code> files completely if you have access to
    httpd main server config file. Using <code>.htaccess</code> files slows down your Apache http server.
    Any directive that you can include in a <code>.htaccess</code> file is better set in a <directive module="core">Directory</directive> block, as it will have the same effect with better performance.</note>
</section>

<section id="what">
<title>What they are/How to use them</title>

    <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>

    <note><title>Note:</title>
      <p>If you want to call your <code>.htaccess</code> file something
      else, you can change the name of the file using the <directive
      module="core">AccessFileName</directive> 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>

      <highlight language="config">AccessFileName .config</highlight>
    </note>

    <p>In general, <code>.htaccess</code> files use the same syntax as
    the <a href="../configuring.html#syntax">main configuration
    files</a>. What you can put in these files is determined by the
    <directive module="core">AllowOverride</directive> 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 <directive
    module="core">AllowOverride</directive> in order for that
    directive to be permitted.</p>

    <p>For example, if you look at the documentation for the <directive
    module="core">AddDefaultCharset</directive>
    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>

    <example><title>Example:</title>
      <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>
    </example>

    <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>
    </section>

    <section id="when"><title>When (not) to use .htaccess files</title>

    <p>In general, you should only use <code>.htaccess</code> files when
    you don't have access to the main server configuration file. There is,
    for example, a common misconception that user authentication should
    always be done in <code>.htaccess</code> files, and, in more recent years,
    another miscomception that <module>mod_rewrite</module> directives
    must go 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. Likewise, <code>mod_rewrite</code> directives work better,
    in many respects, in the main server configuration.</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 <directive module="core"
    type="section">Directory</directive> 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 <directive
    module="core">AllowOverride</directive>
    is set to allow the use of <code>.htaccess</code> files, httpd 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 httpd 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>, httpd must look for the
    following files:</p>

    <example>
      /.htaccess<br />
      /www/.htaccess<br />
      /www/htdocs/.htaccess<br />
      /www/htdocs/example/.htaccess
    </example>

    <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
    <code>.htaccess</code> files were enabled for <code>/</code>, which
    is not usually the case.)</p>

    <p>In the case of <directive
    module="mod_rewrite">RewriteRule</directive> directives, in
    <code>.htaccess</code> context these regular expressions must be
    re-compiled with every request to the directory, whereas in main
    server configuration context they are compiled once and cached.
    Additionally, the rules themselves are more complicated, as one must
    work around the restrictions that come with per-directory context
    and <code>mod_rewrite</code>. Consult the <a
    href="../rewrite/intro.html#htaccess">Rewrite Guide</a> for more
    detail on this subject.</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. Note also that giving users less
    privileges than they need will lead to additional technical support
    requests. Make sure you clearly tell your users what level of
    privileges you have given them. Specifying exactly what you have set
    <directive module="core">AllowOverride</directive> to, and pointing them
    to the relevant documentation, will save yourself a lot of confusion
    later.</p>

    <p>Note that it is completely equivalent to put a <code>.htaccess</code>
    file in a directory <code>/www/htdocs/example</code> containing a
    directive, and to put that same directive in a Directory section
    <code>&lt;Directory /www/htdocs/example&gt;</code> in your main server
    configuration:</p>

    <p><code>.htaccess</code> file in <code>/www/htdocs/example</code>:</p>

    <example><title>Contents of .htaccess file in
    <code>/www/htdocs/example</code></title>
    <highlight language="config">AddType text/example .exm</highlight>
    </example>

    <example><title>Section from your <code>httpd.conf</code>
    file</title>
    <highlight language="config">
&lt;Directory /www/htdocs/example&gt;<br />
    AddType text/example .exm<br />
&lt;/Directory&gt;
    </highlight>
    </example>

    <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 httpd 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 <directive module="core">AllowOverride</directive>
    directive to <code>none</code>:</p>

    <highlight language="config">AllowOverride None</highlight>
</section>

<section id="how"><title>How directives are applied</title>

    <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>

    <highlight language="config">Options +ExecCGI</highlight>

    <p>(Note: you must have "<code>AllowOverride Options</code>" in effect
    to permit the use of the "<directive
    module="core">Options</directive>" 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>

    <highlight language="config">Options Includes</highlight>

    <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>

    <section id="merge"><title>Merging of .htaccess with the main
    configuration files</title>

    <p>As discussed in the documentation on <a
    href="../sections.html">Configuration Sections</a>,
    <code>.htaccess</code> files can override the <directive
    type="section" module="core">Directory</directive> sections for
    the corresponding directory, but will be overriden by other types
    of configuration sections from the main configuration files. This
    fact can be used to enforce certain configurations, even in the
    presence of a liberal <directive
    module="core">AllowOverride</directive> setting. For example, to
    prevent script execution while allowing anything else to be set in
    <code>.htaccess</code> you can use:</p>

    <highlight language="config">
&lt;Directory /www/htdocs&gt;
    Allowoverride All
&lt;/Directory&gt;

&lt;Location /&gt;
    Options +IncludesNoExec -ExecCGI<br />
&lt;/Location&gt;
    </highlight>

    <note>This example assumes that your <directive
    module="core">DocumentRoot</directive> is <code>/www/htdocs</code>.</note>
</section>

</section>

<section id="auth"><title>Authentication example</title>

    <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 <directive module="core" type="section">Directory</directive>
    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 <a
    href="#when">above</a> 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><code>.htaccess</code> file contents:</p>

    <highlight language="config">
AuthType Basic
AuthName "Password Required"
AuthUserFile /www/passwords/password.file
AuthGroupFile /www/passwords/group.file
Require Group admins
    </highlight>

    <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>
</section>

<section id="ssi"><title>Server Side Includes example</title>

    <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>

    <highlight language="config">
Options +Includes
AddType text/html shtml
AddHandler server-parsed shtml
    </highlight>

    <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>
</section>

<section id="cgi"><title>CGI example</title>

    <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>

    <highlight language="config">
Options +ExecCGI
AddHandler cgi-script cgi pl
    </highlight>

    <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>

    <highlight language="config">
Options +ExecCGI
SetHandler cgi-script
    </highlight>

    <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="cgi.html">CGI tutorial</a> for a more
    complete discussion of CGI programming and configuration.</p>

</section>

<section id="troubleshoot"><title>Troubleshooting</title>

    <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 <directive
    module="core">AllowOverride</directive> 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 the page. 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 httpd error log. It will likely tell you
    that the directive used in your <code>.htaccess</code> file is not
    permitted.</p>

    <example>
    [Fri Sep 17 18:43:16 2010] [alert] [client 192.168.200.51] /var/www/html/.htaccess: DirectoryIndex not allowed here
    </example>

    <p>This will indicate either that you've used a directive that is
    never permitted in <code>.htaccess</code> files, or that you simply
    don't have <directive module="core">AllowOverride</directive> set to
    a level sufficient for the directive you've used. Consult the
    documentation for that particular directive to determine which is
    the case.</p>

    <p>Alternately, it may tell you that you had a syntax error in your
    usage of the directive itself.</p>

    <example>
    [Sat Aug 09 16:22:34 2008] [alert] [client 192.168.200.51] /var/www/html/.htaccess: RewriteCond: bad flag delimiters
    </example>

    <p>In this case, the error message should be specific to the
    particular syntax error that you have committed.</p>

</section>

</manualpage>