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<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.</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>.</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>%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>. <code>hextid</code> requires APR 1.2.0 or

higher.

</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.</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>The time taken to serve the request, in seconds.</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.</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. Cannot be zero. 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 <code>%r</code>,

<code>%i</code> and <code>%o</code> 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>

<p>Since httpd 2.0, unlike 1.3, 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>

</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>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>

</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>

</modulesynopsis>