docs/manual/configuring.xml

<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
<?xml-stylesheet type="text/xsl" href="./style/manual.en.xsl"?>
<!-- $LastChangedRevision$ -->

<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->

<manualpage metafile="configuring.xml.meta">

  <title>Configuration Files</title>

<summary>
<p>This document describes the files used to configure Apache HTTP
Server.</p>
</summary>

  <section id="main">
    <title>Main Configuration Files</title>
    <related>
      <modulelist>
        <module>mod_mime</module>
      </modulelist>
      <directivelist>
        <directive module="core" type="section">IfDefine</directive>
        <directive module="core">Include</directive>
        <directive module="mod_mime">TypesConfig</directive>
      </directivelist>
    </related>

    <p>Apache HTTP Server is configured by placing <a
    href="mod/directives.html">directives</a> in plain text
    configuration files. The main configuration file is usually called
    <code>httpd.conf</code>. The location of this file is set at
    compile-time, but may be overridden with the <code>-f</code>
    command line flag. In addition, other configuration files may be
    added using the <directive module="core">Include</directive>
    directive, and wildcards can be used to include many configuration
    files. Any directive may be placed in any of these configuration
    files. Changes to the main configuration files are only
    recognized by httpd when it is started or restarted.</p>

    <p>The server also reads a file containing mime document types;
    the filename is set by the <directive
    module="mod_mime">TypesConfig</directive> directive,
    and is <code>mime.types</code> by default.</p>
  </section>

  <section id="syntax">
    <title>Syntax of the Configuration Files</title>

    <p>httpd configuration files contain one directive per line.
    The backslash "\" may be used as the last character on a line
    to indicate that the directive continues onto the next line.
    To be interpreted as such a continuation, there must be no
    other characters or white space between the backslash and the
    end of the line. </p>

    <p>Lines that begin with the hash character "#" are considered
    comments, and are ignored. Comments may <strong>not</strong> be
    included on the same line as a configuration directive, including
    at the start of a line that has been continued as described in the
    preceding paragraph. Commented lines may also be continued, meaning
    the next physical line is also interpreted as a comment because the
    logical line begins with a hash character.
    </p>

    <p> White space occurring before a directive is ignored, so
    you may indent directives for clarity. Blank lines are also ignored.
    Arguments to directives are separated by whitespace. If an
    argument contains spaces, you must enclose that argument in
    quotes.</p>

    <section id="quotes"><title>Quoting and Escaping</title>

    <p>Either double quotes (<code>"</code>) or single quotes
    (<code>'</code>) can be used to enclose an argument that contains
    spaces.  The quotes themselves are not part of the argument.</p>

    <p>Inside a quoted string, only two escape sequences are
    recognized: <code>\\</code> produces a literal backslash, and
    <code>\"</code> (or <code>\'</code> if the string is
    single-quoted) produces a literal quote character without ending
    the string.  All other backslash sequences are passed through
    unchanged — for example, <code>\n</code> is the literal two
    characters <code>\n</code>, not a newline.</p>

    <p>Outside of quotes, backslashes have no special meaning and
    are treated as literal characters.  The only exception is the
    line-continuation backslash at the very end of a line, as
    described above.</p>

    <p>Note that adjacent quoted strings with no whitespace between
    them are <strong>not</strong> concatenated — they are parsed as
    separate arguments.  For example:</p>

    <example>
    # This is TWO arguments, not one:<br />
    Header set X-Foo "bar""baz"
    </example>

    <p>Some directives accept arguments that contain sub-expressions
    with their own syntax, such as
    <directive module="mod_rewrite">RewriteRule</directive> flags or
    <a href="expr.html">ap_expr</a> expressions.  In those cases, the
    config file parser first removes the enclosing quotes and processes
    backslash escapes as described above, then the directive's own
    parser processes the result.  When in doubt, using single quotes
    around an argument that contains backslashes can avoid unexpected
    double-processing of escape sequences.</p>

    </section>

    <p>Directives in the configuration files are case-insensitive,
    but arguments to directives are often case sensitive. </p>

    <p>The values of variables defined with the <directive
    module="core">Define</directive> or of shell environment variables can
    be used in configuration file lines using the syntax
    <code>${VAR}</code>.<br />
    If "VAR" is the name of a valid variable, the value of that variable is
    substituted into that spot in the configuration file line, and processing
    continues as if that text were found directly in the configuration
    file.<br />
    Variables defined with <directive module="core">Define</directive> take
    precedence over shell environment variables.<br />
    If the "VAR" variable is not defined, the characters <code>${VAR}</code>
    are left unchanged, and a warning is logged. If instead a default value
    should be substituted, the conditional form
    <code>${VAR?=some default value}</code> can be used. Note that a
    <strong>defined</strong> empty variable will <strong>not</strong> be
    substituted with the default value, and that an empty default value like
    in <code>${VAR?=}</code> is a valid substitution (which produces an empty
    value if "VAR" is not defined, but no warning).<br />
    Variable names may not contain colon ":" characters, to avoid clashes with
    <directive module="mod_rewrite">RewriteMap</directive>'s syntax.</p>

    <p>Only shell environment variables defined before the server is started
    can be used in expansions. Environment variables defined in the
    configuration file itself, for example with <directive
    module="mod_env">SetEnv</directive>, take effect too late to be used for
    expansions in the configuration file.</p>

    <p>The maximum length of a line in normal configuration files, after
    variable substitution and joining any continued lines, is approximately
    16 MiB. In <a href="configuring.html#htaccess">.htaccess files</a>, the
    maximum length is 8190 characters.</p>

    <p>You can check your configuration files for syntax errors
    without starting the server by using <code>apachectl
    configtest</code> or the <code>-t</code> command line
    option.</p>

    <p>You can use <module>mod_info</module>'s <code>-DDUMP_CONFIG</code> to
    dump the configuration with all included files and environment
    variables resolved and all comments and non-matching
    <directive module="core" type="section">IfDefine</directive> and
    <directive module="core" type="section">IfModule</directive> sections
    removed. However, the output does not reflect the merging or overriding
    that may happen for repeated directives.</p>
  </section>

  <section id="modules">
    <title>Modules</title>

    <related>
      <modulelist>
        <module>mod_so</module>
      </modulelist>
      <directivelist>
        <directive module="core" type="section">IfModule</directive>
        <directive module="mod_so">LoadModule</directive>
      </directivelist>
    </related>

    <p>httpd is a modular server. This implies that only the most
    basic functionality is included in the core server. Extended
    features are available through <a
    href="mod/">modules</a> which can be loaded
    into httpd. By default, a <a
    href="mod/module-dict.html#Status">base</a> set of modules is
    included in the server at compile-time. If the server is
    compiled to use <a href="dso.html">dynamically loaded</a>
    modules, then modules can be compiled separately and added at
    any time using the <directive module="mod_so">LoadModule</directive>
    directive.
    Otherwise, httpd must be recompiled to add or remove modules.
    Configuration directives may be included conditional on a
    presence of a particular module by enclosing them in an <directive
    module="core" type="section">IfModule</directive> block. However,
    <directive type="section">IfModule</directive> blocks are not
    required, and in some cases may mask the fact that you're missing an
    important module.</p>

    <p>To see which modules are currently compiled into the server,
    you can use the <code>-l</code> command line option. You can also
    see what modules are loaded dynamically using the <code>-M</code>
    command line option.</p>
  </section>

  <section id="scope">
    <title>Scope of Directives</title>

    <related>
      <directivelist>
        <directive module="core" type="section">Directory</directive>
        <directive module="core" type="section">DirectoryMatch</directive>
        <directive module="core" type="section">Files</directive>
        <directive module="core" type="section">FilesMatch</directive>
        <directive module="core" type="section">Location</directive>
        <directive module="core" type="section">LocationMatch</directive>
        <directive module="core" type="section">VirtualHost</directive>
      </directivelist>
    </related>

    <p>Directives placed in the main configuration files apply to
    the entire server. If you wish to change the configuration for
    only a part of the server, you can scope your directives by
    placing them in <directive module="core"
    type="section">Directory</directive>, <directive module="core"
    type="section">DirectoryMatch</directive>, <directive module="core"
    type="section">Files</directive>, <directive module="core"
    type="section">FilesMatch</directive>, <directive module="core"
    type="section">Location</directive>, and <directive module="core"
    type="section">LocationMatch</directive>
    sections. These sections limit the application of the
    directives which they enclose to particular filesystem
    locations or URLs. They can also be nested, allowing for very
    fine grained configuration.</p>

    <p>httpd has the capability to serve many different websites
    simultaneously. This is called <a href="vhosts/">Virtual
    Hosting</a>. Directives can also be scoped by placing them
    inside <directive module="core" type="section">VirtualHost</directive>
    sections, so that they will only apply to requests for a
    particular website.</p>

    <p>Although most directives can be placed in any of these
    sections, some directives do not make sense in some contexts.
    For example, directives controlling process creation can only
    be placed in the main server context. To find which directives
    can be placed in which sections, check the <a
    href="mod/directive-dict.html#Context">Context</a> of the
    directive. For further information, we provide details on <a
    href="sections.html">How Directory, Location and Files sections
    work</a>.</p>
  </section>

  <section id="htaccess">
    <title>.htaccess Files</title>

    <related>
      <directivelist>
        <directive module="core">AccessFileName</directive>
        <directive module="core">AllowOverride</directive>
      </directivelist>
    </related>

    <p>httpd allows for decentralized management of configuration
    via special files placed inside the web tree. The special files
    are usually called <code>.htaccess</code>, but any name can be
    specified in the <directive module="core">AccessFileName</directive>
    directive. Directives placed in <code>.htaccess</code> files
    apply to the directory where you place the file, and all
    sub-directories. The <code>.htaccess</code> files follow the
    same syntax as the main configuration files. Since
    <code>.htaccess</code> files are read on every request, changes
    made in these files take immediate effect.</p>

    <p>To find which directives can be placed in
    <code>.htaccess</code> files, check the <a
    href="mod/directive-dict.html#Context">Context</a> of the
    directive. The server administrator further controls what
    directives may be placed in <code>.htaccess</code> files by
    configuring the <directive module="core">AllowOverride</directive>
    directive in the main configuration files.</p>

    <p>For more information on <code>.htaccess</code> files, see
    the <a href="howto/htaccess.html">.htaccess tutorial</a>.</p>
  </section>
</manualpage>