docs/manual/mod/mod_log_config.xml

<?xml version="1.0"?>
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.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.
-->

<modulesynopsis metafile="mod_log_config.xml.meta">

<name>mod_log_config</name>
<description>Logging of the requests made to the server</description>
<status>Base</status>
<sourcefile>mod_log_config.c</sourcefile>
<identifier>log_config_module</identifier>

<summary>
    <p>This module provides for flexible logging of client
    requests. Logs are written in a customizable format, and may be
    written directly to a file, or to an external program.
    Conditional logging is provided so that individual requests may
    be included or excluded from the logs based on characteristics
    of the request.</p>

    <p>Three directives are provided by this module:
    <directive module="mod_log_config">TransferLog</directive> to create
    a log file, <directive module="mod_log_config">LogFormat</directive>
    to set a custom format, and <directive module="mod_log_config"
    >CustomLog</directive> to define a log file and format in one
    step. The <directive>TransferLog</directive> and <directive
    >CustomLog</directive> directives can be used multiple times in each
    server to cause each request to be logged to multiple files.</p>
</summary>
<seealso><a href="../logs.html">Apache Log Files</a></seealso>

<section id="formats"><title>Custom Log Formats</title>

    <p>The format argument to the <directive module="mod_log_config"
    >LogFormat</directive> and <directive module="mod_log_config"
    >CustomLog</directive> directives is a string. This string is
    used to log each request to the log file. It can contain literal
    characters copied into the log files and the C-style control
    characters "\n" and "\t" to represent new-lines and tabs.
    Literal quotes and backslashes should be escaped with
    backslashes.</p>

    <p>The characteristics of the request itself are logged by
    placing "<code>%</code>" directives in the format string, which are
    replaced in the log file by the values as follows:</p>

    <table border="1" style="zebra">
    <columnspec><column width=".2"/><column width=".8"/></columnspec>
    <tr><th>Format&nbsp;String</th>
        <th>Description</th></tr>

    <tr><td><code>%%</code></td>
        <td>The percent sign.</td></tr>

    <tr><td><code>%a</code></td>
        <td>Client IP address of the request (see the
        <module>mod_remoteip</module> module).</td></tr>

    <tr><td><code>%{c}a</code></td>
        <td>Underlying peer IP address of the connection (see the
        <module>mod_remoteip</module> module).</td></tr>

    <tr><td><code>%A</code></td>
        <td>Local IP-address.</td></tr>

    <tr><td><code>%B</code></td>
        <td>Size of response in bytes, excluding HTTP headers.</td></tr>

    <tr><td><code>%b</code></td>
        <td>Size of response in bytes, excluding HTTP headers. In CLF format, <em>i.e.</em>
        a '<code>-</code>' rather than a 0 when no bytes are sent.</td></tr>

    <tr><td><code>%{<var>VARNAME</var>}C</code></td>
        <td>The contents of cookie <var>VARNAME</var> in the request sent
        to the server. Only version 0 cookies are fully supported.</td></tr>

    <tr><td><code>%D</code></td>
        <td>The time taken to serve the request, in microseconds. See %T for details.</td></tr>

    <tr><td><code>%{<var>VARNAME</var>}e</code></td>
        <td>The contents of the environment variable
        <var>VARNAME</var>.</td></tr>

    <tr><td><code>%f</code></td>
        <td>Filename.</td></tr>

    <tr><td><code>%h</code></td>
        <td>Remote hostname. Will log the IP address if <directive
        module="core">HostnameLookups</directive> is set to
        <code>Off</code>, which is the default. If it logs the hostname
        for only a few hosts, you probably have access control
        directives mentioning them by name. See <a
        href="mod_authz_host.html#reqhost">the Require host
        documentation</a>. This format is affected by modifications to the 
        remote hostname by modules like <module>mod_remoteip</module>.</td></tr>

    <tr><td><code>%{c}h</code></td>
        <td>Like <code>%h</code>, but always reports on the hostname of the
        underlying TCP connection and not any modifications to the 
        remote hostname by modules like <module>mod_remoteip</module>.</td></tr>

    <tr><td><code>%H</code></td>
        <td>The request protocol.</td></tr>

    <tr><td><code>%{<var>VARNAME</var>}i</code></td>
        <td>The contents of <code><var>VARNAME</var>:</code> header line(s)
        in the request sent to the server. Changes made by other
        modules (e.g. <module>mod_headers</module>) affect this.  If you're
        interested in what the request header was prior to when most
        modules would have modified it, use <module>mod_setenvif</module>
        to copy the header into an internal environment variable and log
        that value with the <code>%{<var>VARNAME</var>}e</code> described
        above.
        </td></tr>

    <tr><td><code>%k</code></td>
        <td>Number of keepalive requests handled on this connection.  Interesting if
          <directive module="core">KeepAlive</directive> is being used, so that,
          for example, a '1' means the first keepalive request after the initial
          one, '2' the second, etc...;
          otherwise this is always 0 (indicating the initial request).</td></tr>

    <tr><td><code>%l</code></td>
        <td>Remote logname (from identd, if supplied). This will return a
        dash unless <module>mod_ident</module> is present and <directive
        module="mod_ident">IdentityCheck</directive> is set
        <code>On</code>.</td></tr>

    <tr><td><code>%L</code></td>
        <td>The request log ID from the error log (or '-' if nothing has been
            logged to the error log for this request). Look for the
            matching error log line to see what request caused what error.</td></tr>

    <tr><td><code>%{c}L</code></td>
        <td>The connection log ID from the error log (or '-' if nothing has been
            logged to the error log for this request). Look for the
            matching error log line to see what request caused what error.</td></tr>

    <tr><td><code>%m</code></td>
        <td>The request method.</td></tr>

    <tr><td><code>%{<var>VARNAME</var>}n</code></td>
        <td>The contents of note <var>VARNAME</var> from another
        module.</td></tr>

    <tr><td><code>%{<var>VARNAME</var>}o</code></td>
        <td>The contents of <code><var>VARNAME</var>:</code> header line(s)
        in the reply.</td></tr>

    <tr><td><code>%p</code></td>
        <td>The canonical port of the server serving the request.</td></tr>

    <tr><td><code>%{<var>format</var>}p</code></td>
        <td>The canonical port of the server serving the request, or the
        server's actual port, or the client's actual port. Valid formats
        are <code>canonical</code>, <code>local</code>, or <code>remote</code>.
        </td></tr>

    <tr><td><code>%P</code></td>
        <td>The process ID of the child that serviced the request.</td></tr>

    <tr><td><code>%{<var>format</var>}P</code></td>
        <td>The process ID or thread ID of the child that serviced the
        request.  Valid formats are <code>pid</code>, <code>tid</code>,
        and <code>hextid</code>.
        </td></tr>

    <tr><td><code>%q</code></td>
        <td>The query string (prepended with a <code>?</code> if a query
        string exists, otherwise an empty string).</td></tr>

    <tr><td><code>%r</code></td>
        <td>First line of request. Does not adhere to 
        <directive module="core">MergeSlashes</directive>. (i.e. no merging
        even if ON)</td></tr>

    <tr><td><code>%R</code></td>
        <td>The handler generating the response (if any).</td></tr>

    <tr><td><code>%s</code></td>
        <td>Status. For requests that have been internally redirected, this is
        the status of the <em>original</em> request. Use <code>%&gt;s</code>
        for the final status.</td></tr>

    <tr><td><code>%t</code></td>
        <td>Time the request was received, in the format <code>[18/Sep/2011:19:18:28 -0400]</code>.
        The last number indicates the timezone offset from GMT</td></tr>

    <tr><td><code>%{<var>format</var>}t</code></td>
        <td>The time, in the form given by format, which should be in
        an extended <code>strftime(3)</code> format (potentially localized).
        If the format starts with <code>begin:</code> (default) the time is taken
        at the beginning of the request processing. If it starts with
        <code>end:</code> it is the time when the log entry gets written,
        close to the end of the request processing. In addition to the formats
        supported by <code>strftime(3)</code>, the following format tokens are
        supported:
        <table>
        <tr><td><code>sec</code></td><td>number of seconds since the Epoch</td></tr>
        <tr><td><code>msec</code></td><td>number of milliseconds since the Epoch</td></tr>
        <tr><td><code>usec</code></td><td>number of microseconds since the Epoch</td></tr>
        <tr><td><code>msec_frac</code></td><td>millisecond fraction</td></tr>
        <tr><td><code>usec_frac</code></td><td>microsecond fraction</td></tr>
        </table>
        These tokens can not be combined with each other or <code>strftime(3)</code>
        formatting in the same format string. You can use multiple
        <code>%{<var>format</var>}t</code> tokens instead.
        </td></tr>

    <tr><td><code>%T</code></td>
        <td><p>The time taken to serve the request, in seconds. The time measured
        begins when the first line of the HTTP request is read from the host
        operating system by the HTTP server and ends when the last byte of
        the response is written by the HTTP server to the host operating system.</p>
        <p>The time measured does <em>not</em> include any of the following:</p>
        <ul>
         <li> Time spent in TCP or TLS handshakes.</li>
         <li> The time before a webserver thread is able to read the first 
              line of the request.</li>
         <li> Delays in the operating system putting the response data out 
              onto the network.</li>
         <li> Time taken for the response to arrive at the client host.</li>
         <li> Time taken for the useragent to read and process the 
              response.</li>
       </ul>
    </td></tr>

    <tr><td><code>%{<var>UNIT</var>}T</code></td>
        <td>The time taken to serve the request, in a time unit given by
        <code>UNIT</code>. Valid units are <code>ms</code> for milliseconds,
        <code>us</code> for microseconds, and <code>s</code> for seconds.
        Using <code>s</code> gives the same result as <code>%T</code>
        without any format; using <code>us</code> gives the same result
        as <code>%D</code>. Combining <code>%T</code> with a unit is
        available in 2.4.13 and later.</td></tr>

    <tr><td><code>%u</code></td>
        <td>Remote user if the request was authenticated. May be bogus if return status
        (<code>%s</code>) is 401 (unauthorized).</td></tr>

    <tr><td><code>%U</code></td>
        <td>The URL path requested, not including any query string. 
        Adheres to <directive module="core">MergeSlashes</directive>.
        (i.e. slashes are merged if <code>ON</code>)</td></tr>

    <tr><td><code>%v</code></td>
        <td>The canonical <directive module="core">ServerName</directive>
        of the server serving the request.</td></tr>

    <tr><td><code>%V</code></td>
        <td>The server name according to the <directive module="core"
        >UseCanonicalName</directive> setting.</td></tr>

    <tr><td><code>%X</code></td>
        <td>Connection status when response is completed:

        <table>
        <columnspec><column width=".2"/><column width=".6"/></columnspec>
        <tr><td><code>X</code> =</td>
            <td>Connection aborted before the response completed.</td></tr>
        <tr><td><code>+</code> =</td>
            <td>Connection may be kept alive after the response is
            sent.</td></tr>
        <tr><td><code>-</code> = </td>
            <td>Connection will be closed after the response is
            sent.</td></tr>
        </table>

        </td></tr>

    <tr><td><code>%I</code></td>
        <td>Bytes received, including request and headers. Cannot be zero.
        You need to enable <module>mod_logio</module> to use this.</td></tr>

    <tr><td><code>%O</code></td>
        <td>Bytes sent, including headers. May be zero in rare cases
        such as when a request is aborted before a response is sent.
        You need to enable <module>mod_logio</module> to use this.</td></tr>

    <tr><td><code>%S</code></td>
        <td>Bytes transferred (received and sent), including request and headers,
        cannot be zero. This is the combination of %I and %O. You need to
        enable <module>mod_logio</module> to use this.</td></tr>

    <tr><td><code>%{<var>VARNAME</var>}^ti</code></td>
        <td>The contents of <code><var>VARNAME</var>:</code> trailer line(s)
        in the request sent to the server.  </td></tr>

    <tr><td><code>%{<var>VARNAME</var>}^to</code></td>
        <td>The contents of <code><var>VARNAME</var>:</code> trailer line(s)
        in the response sent from the server.  </td></tr>

    </table>

    <section id="modifiers"><title>Modifiers</title>

      <p>Particular items can be restricted to print only for
      responses with specific HTTP status codes by placing a
      comma-separated list of status codes immediately following the
      "%". The status code list may be preceded by a "<code>!</code>" to
      indicate negation.</p>

    <table border="1" style="zebra">
    <columnspec><column width=".2"/><column width=".8"/></columnspec>

    <tr><th>Format String</th>
    <th>Meaning</th></tr>

    <tr>
    <td><code>%400,501{User-agent}i</code></td>
    <td>Logs <code>User-agent</code> on 400 errors and 501 errors only. For
      other status codes, the literal string <code>"-"</code> will be
      logged.</td></tr>

    <tr><td><code>%!200,304,302{Referer}i</code></td>
    <td>Logs <code>Referer</code> on all requests that do
    <em>not</em> return one of the three specified codes,
    "<code>-</code>" otherwise.
    </td></tr>

    </table>

      <p>The modifiers "&lt;" and "&gt;" can be used for requests that
      have been internally redirected to choose whether the original
      or final (respectively) request should be consulted.  By
      default, the <code>%</code> directives <code>%s, %U, %T,
      %D,</code> and <code>%r</code> look at the original request
      while all others look at the final request.  So for example,
      <code>%&gt;s</code> can be used to record the final status of
      the request and <code>%&lt;u</code> can be used to record the
      original authenticated user on a request that is internally
      redirected to an unauthenticated resource.</p>

    </section>

    <section id="format-notes"><title>Format Notes</title>

      <p>For security reasons, starting with version 2.0.46,
      non-printable and other special characters in format strings
      that may contain arbitrary string data are escaped using
      <code>\x<var>hh</var></code> sequences, where <var>hh</var>
      stands for the hexadecimal representation of the raw
      byte. Exceptions from this rule are <code>"</code> and
      <code>\</code>, which are escaped by prepending a backslash, and
      all whitespace characters, which are written in their C-style
      notation (<code>\n</code>, <code>\t</code>, etc).  In versions
      prior to 2.0.46, no escaping was performed on these strings so
      you had to be quite careful when dealing with raw log files.</p>

      <table>
      <columnspec><column width=".1"/><column width=".45"/><column width=".45"/></columnspec>
      <tr><th>Format</th><th>Description</th><th>Escaped</th></tr>
      <tr><td><code>%c</code></td><td>SSL variable (shortcut)</td><td>Yes</td></tr>
      <tr><td><code>%C</code></td><td>Cookie value</td><td>Yes</td></tr>
      <tr><td><code>%e</code></td><td>Environment variable</td><td>Yes</td></tr>
      <tr><td><code>%f</code></td><td>Request filename</td><td>Yes</td></tr>
      <tr><td><code>%h</code></td><td>Remote hostname</td><td>Yes</td></tr>
      <tr><td><code>%H</code></td><td>Request protocol</td><td>Yes</td></tr>
      <tr><td><code>%i</code></td><td>Request header</td><td>Yes</td></tr>
      <tr><td><code>%l</code></td><td>Remote logname</td><td>Yes</td></tr>
      <tr><td><code>%m</code></td><td>Request method</td><td>Yes</td></tr>
      <tr><td><code>%n</code></td><td>Note</td><td>Yes</td></tr>
      <tr><td><code>%o</code></td><td>Response header</td><td>Yes</td></tr>
      <tr><td><code>%q</code></td><td>Query string</td><td>Yes</td></tr>
      <tr><td><code>%r</code></td><td>Request line</td><td>Yes</td></tr>
      <tr><td><code>%R</code></td><td>Handler</td><td>Yes</td></tr>
      <tr><td><code>%u</code></td><td>Remote user</td><td>Yes</td></tr>
      <tr><td><code>%U</code></td><td>Request URI</td><td>Yes</td></tr>
      <tr><td><code>%v</code></td><td>Server hostname</td><td>Yes</td></tr>
      <tr><td><code>%V</code></td><td>Canonical server name</td><td>Yes</td></tr>
      <tr><td><code>%x</code></td><td>SSL variable</td><td>Yes</td></tr>
      <tr><td><code>%^ti</code></td><td>Request trailer</td><td>Yes</td></tr>
      <tr><td><code>%^to</code></td><td>Response trailer</td><td>Yes</td></tr>
      <tr><td><code>%a</code></td><td>Remote IP address</td><td>No (IP address)</td></tr>
      <tr><td><code>%A</code></td><td>Local IP address</td><td>No (IP address)</td></tr>
      <tr><td><code>%b</code>, <code>%B</code></td><td>Bytes sent</td><td>No (numeric)</td></tr>
      <tr><td><code>%D</code></td><td>Request duration (microseconds)</td><td>No (numeric)</td></tr>
      <tr><td><code>%F</code></td><td>Request flushed</td><td>No (single character)</td></tr>
      <tr><td><code>%k</code></td><td>Requests on connection</td><td>No (numeric)</td></tr>
      <tr><td><code>%L</code></td><td>Log ID</td><td>No (internally generated)</td></tr>
      <tr><td><code>%p</code></td><td>Server port</td><td>No (numeric)</td></tr>
      <tr><td><code>%P</code></td><td>PID/TID</td><td>No (numeric)</td></tr>
      <tr><td><code>%s</code></td><td>Status code</td><td>No (numeric)</td></tr>
      <tr><td><code>%t</code></td><td>Request time</td><td>No (formatted time)</td></tr>
      <tr><td><code>%T</code></td><td>Request duration (seconds)</td><td>No (numeric)</td></tr>
      <tr><td><code>%X</code></td><td>Connection status</td><td>No (single character)</td></tr>
      </table>

      <p>The <code>%b</code> and
      <code>%B</code> format strings do not represent the number of
      bytes sent to the client, but simply the size in bytes of the
      HTTP response (which will differ, for instance, if the
      connection is aborted, or if SSL is used).  The <code>%O</code>
      format provided by <module>mod_logio</module> will log the
      actual number of bytes sent over the network.</p>

      <note>
      <p>Note: <module>mod_cache</module> is implemented as a
      quick-handler and not as a standard handler. Therefore, the
      <code>%R</code> format string will not return any handler
      information when content caching is involved.</p>
      </note>

      <note>
      <p>Note: The '^' character at the start of three-character formats
      has no significance, but it must be the first character of any newly
      added three-character format to avoid potential conflicts with log
      formats that use literals adjacent to a format specifier, such as
      "%Dus".</p>
      </note>

    </section>

    <section id="examples"><title>Examples</title>

      <p>Some commonly used log format strings are:</p>

      <dl>
        <dt>Common Log Format (CLF)</dt>
        <dd><code>"%h %l %u %t \"%r\" %&gt;s %b"</code></dd>

        <dt>Common Log Format with Virtual Host</dt>
        <dd><code>"%v %h %l %u %t \"%r\" %&gt;s %b"</code></dd>

        <dt>NCSA extended/combined log format</dt>
        <dd><code>"%h %l %u %t \"%r\" %&gt;s %b \"%{Referer}i\"
        \"%{User-agent}i\""</code></dd>

        <dt>Referer log format</dt>
        <dd><code>"%{Referer}i -&gt; %U"</code></dd>

        <dt>Agent (Browser) log format</dt>
        <dd><code>"%{User-agent}i"</code></dd>
      </dl>

      <p>You can use the <code>%{format}t</code> directive multiple
      times to build up a time format using the extended format tokens
      like <code>msec_frac</code>:</p>
      <dl>
<dt>Timestamp including milliseconds</dt>
<dd><code>"%{%d/%b/%Y %T}t.%{msec_frac}t %{%z}t"</code></dd>

      </dl>

    </section>
</section>

<section id="security"><title>Security Considerations</title>
    <p>See the <a
    href="../misc/security_tips.html#serverroot">security tips</a>
    document for details on why your security could be compromised
    if the directory where logfiles are stored is writable by
    anyone other than the user that starts the server.</p>
</section>

<directivesynopsis>
<name>BufferedLogs</name>
<description>Buffer log entries in memory before writing to disk</description>
<syntax>BufferedLogs On|Off</syntax>
<default>BufferedLogs Off</default>
<contextlist><context>server config</context></contextlist>

<usage>
    <p>The <directive>BufferedLogs</directive> directive causes
    <module>mod_log_config</module> to store several log entries in
    memory and write them together to disk, rather than writing them
    after each request.  On some systems, this may result in more
    efficient disk access and hence higher performance.  It may be
    set only once for the entire server; it cannot be configured
    per virtual-host.</p>

    <note>This directive should be used with caution as a crash might
    cause loss of logging data.</note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>CustomLog</name>
<description>Sets filename and format of log file</description>
<syntax>CustomLog  <var>file</var>|<var>pipe</var>|<var>provider</var>
<var>format</var>|<var>nickname</var>
[env=[!]<var>environment-variable</var>|
expr=<var>expression</var>]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>The <directive>CustomLog</directive> directive is used to
    log requests to the server. A log format is specified, and the
    logging can optionally be made conditional on request
    characteristics using environment variables.</p>

    <p>The first argument, which specifies the location to which
    the logs will be written, can take one of the following two
    types of values:</p>

    <dl>
      <dt><var>file</var></dt>
      <dd>A filename, relative to the <directive module="core"
      >ServerRoot</directive>.</dd>

      <dt><var>pipe</var></dt>
      <dd>The pipe character "<code>|</code>", followed by the path
      to a program to receive the log information on its standard
      input. See the notes on <a href="../logs.html#piped">piped logs</a>
      for more information.

      <note type="warning"><title>Security:</title>
      <p>If a program is used, then it will be run as the user who
      started <program>httpd</program>. This will be root if the server was
      started by root; be sure that the program is secure.</p>
      </note>
      <note type="warning"><title>Note</title>
        <p>When entering a file path on non-Unix platforms, care should be taken
        to make sure that only forward slashed are used even though the platform
        may allow the use of back slashes. In general it is a good idea to always
        use forward slashes throughout the configuration files.</p>
      </note></dd>
      <dt><var>provider</var></dt>
      <dd>Modules implementing ErrorLog providers can also be used as a target
      for CustomLog messages. To use ErrorLog provider as a target,
      "provider:argument" syntax must be used. You can for example use
      <module>mod_journald</module> or <module>mod_syslog</module>
      as a provider:
    <highlight language="config">
# CustomLog logging to journald
CustomLog "journald" "%h %l %u %t \"%r\" %&gt;s %b"

# CustomLog logging to syslog with "user" facility
CustomLog "syslog:user" "%h %l %u %t \"%r\" %&gt;s %b"
    </highlight>
      </dd>
    </dl>

    <p>The second argument specifies what will be written to the
    log file. It can specify either a <var>nickname</var> defined by
    a previous <directive module="mod_log_config">LogFormat</directive>
    directive, or it can be an explicit <var>format</var> string as
    described in the <a href="#formats">log formats</a> section.</p>

    <p>For example, the following two sets of directives have
    exactly the same effect:</p>

    <highlight language="config">
# CustomLog with format nickname
LogFormat "%h %l %u %t \"%r\" %&gt;s %b" common
CustomLog "logs/access_log" common

# CustomLog with explicit format string
CustomLog "logs/access_log" "%h %l %u %t \"%r\" %&gt;s %b"
    </highlight>

    <p>The third argument is optional and controls whether or
    not to log a particular request. The condition can be the
    presence or absence (in the case of a '<code>env=!<var>name</var></code>'
    clause) of a particular variable in the server
    <a href="../env.html">environment</a>. Alternatively, the condition
    can be expressed as arbitrary boolean <a href="../expr.html"
    >expression</a>. If the condition is not satisfied, the request
    will not be logged. References to HTTP headers  in the expression
    will not cause the header names to be added to the Vary header.</p>

    <p>Environment variables can be set on a per-request
    basis using the <module>mod_setenvif</module>
    and/or <module>mod_rewrite</module> modules. For
    example, if you want to record requests for all GIF
    images on your server in a separate logfile but not in your main
    log, you can use:</p>

    <highlight language="config">
SetEnvIf Request_URI \.gif$ gif-image
CustomLog "gif-requests.log" common env=gif-image
CustomLog "nongif-requests.log" common env=!gif-image
    </highlight>

    <p>Or, to reproduce the behavior of the old RefererIgnore
    directive, you might use the following:</p>

    <highlight language="config">
SetEnvIf Referer example\.com localreferer
CustomLog "referer.log" referer env=!localreferer
    </highlight>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>LogFormat</name>
<description>Describes a format for use in a log file</description>
<syntax>LogFormat <var>format</var>|<var>nickname</var>
[<var>nickname</var>]</syntax>
<default>LogFormat "%h %l %u %t \"%r\" %>s %b"</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>This directive specifies the format of the access log
    file.</p>

    <p>The <directive>LogFormat</directive> directive can take one of two
    forms. In the first form, where only one argument is specified,
    this directive sets the log format which will be used by logs
    specified in subsequent <directive>TransferLog</directive>
    directives. The single argument can specify an explicit
    <var>format</var> as discussed in the <a href="#formats">custom log
    formats</a> section above. Alternatively, it can use a
    <var>nickname</var> to refer to a log format defined in a
    previous <directive>LogFormat</directive> directive as described
    below.</p>

    <p>The second form of the <directive>LogFormat</directive>
    directive associates an explicit <var>format</var> with a
    <var>nickname</var>. This <var>nickname</var> can then be used in
    subsequent <directive>LogFormat</directive> or
    <directive module="mod_log_config">CustomLog</directive> directives
    rather than repeating the entire format string. A
    <directive>LogFormat</directive> directive that defines a nickname
    <strong>does nothing else</strong> -- that is, it <em>only</em>
    defines the nickname, it doesn't actually apply the format and make
    it the default. Therefore, it will not affect subsequent
    <directive module="mod_log_config">TransferLog</directive> directives.
    In addition, <directive>LogFormat</directive> cannot use one nickname
    to define another nickname. Note that the nickname should not contain
    percent signs (<code>%</code>).</p>

    <example><title>Example</title>
    <highlight language="config">
      LogFormat "%v %h %l %u %t \"%r\" %&gt;s %b" vhost_common
      </highlight>
    </example>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>TransferLog</name>
<description>Specify location of a log file</description>
<syntax>TransferLog <var>file</var>|<var>pipe</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>This directive has exactly the same arguments and effect as
    the <directive module="mod_log_config">CustomLog</directive>
    directive, with the exception that it does not allow the log format
    to be specified explicitly or for conditional logging of requests.
    Instead, the log format is determined by the most recently specified
    <directive module="mod_log_config">LogFormat</directive> directive
    which does not define a nickname. Common Log Format is used if no
    other format has been specified.</p>

    <example><title>Example</title>
    <highlight language="config">
LogFormat "%h %l %u %t \"%r\" %&gt;s %b \"%{Referer}i\" \"%{User-agent}i\""
TransferLog "logs/access_log"
      </highlight>
    </example>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>GlobalLog</name>
<description>Sets filename and format of log file</description>
<syntax>GlobalLog  <var>file</var>|<var>pipe</var>|<var>provider</var>
<var>format</var>|<var>nickname</var>
[env=[!]<var>environment-variable</var>|
expr=<var>expression</var>]</syntax>
<contextlist><context>server config</context>
</contextlist>
<compatibility>Available in Apache HTTP Server 2.4.19 and later</compatibility>

<usage>

    <p>The <directive>GlobalLog</directive> directive defines a log shared
       by the main server configuration and all defined virtual hosts.</p>

    <p>The <directive>GlobalLog</directive> directive is identical to
    the <directive>CustomLog</directive> directive, apart from the following
    differences:</p>
    <ul>
       <li><directive>GlobalLog</directive> is not valid in virtual host
            context.</li>
       <li><directive>GlobalLog</directive> is used by virtual hosts that
           define their own <directive>CustomLog</directive>, unlike a 
           globally specified <directive>CustomLog</directive>.</li>
    </ul>
</usage>
</directivesynopsis>


</modulesynopsis>