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- <h1 align="center">Log Files</h1>
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+ --><title>Log Files- Apache HTTP Server</title><link href="./style/manual.css" type="text/css" rel="stylesheet"/></head><body><blockquote><div align="center"><img src="./images/sub.gif" alt="[APACHE DOCUMENTATION]"/><h3>Apache HTTP Server Version 2.0</h3></div><h1 align="center">Log Files</h1>
<p>In order to effectively manage a web server, it is necessary
to get feedback about the activity and performance of the
server as well as any problems that may be occuring. The Apache
capabilities. This document describes how to configure its
logging capabilities, and how to understand what the logs
contain.</p>
-
- <ul>
- <li><a href="#security">Security Warning</a></li>
-
- <li><a href="#errorlog">Error Log</a></li>
-
- <li>
- <a href="#accesslog">Access Log</a>
-
- <ul>
- <li><a href="#common">Common Log Format</a></li>
-
- <li><a href="#combined">Combined Log Format</a></li>
-
- <li><a href="#multiple">Multiple Access Logs</a></li>
-
- <li><a href="#conditional">Conditional Logging</a></li>
- </ul>
- </li>
-
- <li><a href="#rotation">Log Rotation</a></li>
-
- <li><a href="#piped">Piped Logs</a></li>
-
- <li><a href="#virtualhosts">Virtual Hosts</a></li>
-
- <li>
- <a href="#other">Other Log Files</a>
-
- <ul>
- <li><a href="#pidfile">PID File</a></li>
-
- <li><a href="#scriptlog">Script Log</a></li>
-
- <li><a href="#rewritelog">Rewrite Log</a></li>
- </ul>
- </li>
- </ul>
- <hr />
-
- <h2><a id="security" name="security">Security Warning</a></h2>
-
+ <ul><li><a href="#security">Security Warning</a></li><li><a href="#errorlog">Error Log</a></li><li><a href="#accesslog">Access Log</a><ul><li><a href="#common">Common Log Format</a></li><li><a href="#combined">Combined Log Format</a></li><li><a href="#multiple">Multiple Access Logs</a></li><li><a href="#conditional">Conditional Logs</a></li></ul></li><li><a href="#rotation">Rotation Logs</a></li><li><a href="#piped">Piped Logs</a></li><li><a href="#virtualhost">Virtual Hosts</a></li><li><a href="#other">Other Log Files</a><ul><li><a href="#pidfile">PID File</a></li><li><a href="#scriptlog">Script Log</a></li><li><a href="#rewritelog">Rewrite Log</a></li></ul></li></ul><hr/><h2><a name="security">Security Warning</a></h2>
+
+
<p>Anyone who can write to the directory where Apache is
writing a log file can almost certainly gain access to the uid
that the server is started as, which is normally root. Do
possible for malicious clients to insert control-characters in
the log files, so care must be taken in dealing with raw
logs.</p>
- <hr />
-
- <h2><a id="errorlog" name="errorlog">Error Log</a></h2>
-
- <table border="1">
- <tr>
- <td valign="top"><strong>Related Directives</strong><br />
- <br />
- <a href="mod/core.html#errorlog">ErrorLog</a><br />
- <a href="mod/core.html#loglevel">LogLevel</a> </td>
- </tr>
- </table>
-
+ <h2><a name="errorlog">Error Log</a></h2>
+
+
+ <table border="1"><tr><td valign="top"><strong>Related Modules</strong><br/><br/></td><td valign="top"><strong>Related Directives</strong><br/><br/><a href="./mod/mod_core.html#errorlog" class="directive"><code class="directive">ErrorLog</code></a><br/><a href="./mod/mod_core.html#loglevel" class="directive"><code class="directive">LogLevel</code></a><br/></td></tr></table>
+
<p>The server error log, whose name and location is set by the
- <a href="mod/core.html#errorlog">ErrorLog</a> directive, is the
+ <a href="./mod/core.html#errorlog" class="directive"><code class="directive">ErrorLog</code></a> directive, is the
most important log file. This is the place where Apache httpd
will send diagnostic information and record any errors that it
encounters in processing requests. It is the first place to
is also possible to have the server send errors to
<code>syslog</code> or <a href="#piped">pipe them to a
program</a>.</p>
-
+
<p>The format of the error log is relatively free-form and
descriptive. But there is certain information that is contained
in most error log entries. For example, here is a typical
message.</p>
-
- <blockquote>
- <code>[Wed Oct 11 14:32:52 2000] [error] [client 127.0.0.1]
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ [Wed Oct 11 14:32:52 2000] [error] [client 127.0.0.1]
client denied by server configuration:
- /export/home/live/ap/htdocs/test</code>
- </blockquote>
-
+ /export/home/live/ap/htdocs/test
+ </code></td></tr></table></blockquote>
+
<p>The first item in the log entry is the date and time of the
message. The second entry lists the severity of the error being
- reported. The <a href="mod/core.html#loglevel">LogLevel</a>
+ reported. The <a href="./mod/core.html#loglevel" class="directive"><code class="directive">LogLevel</code></a>
directive is used to control the types of errors that are sent
to the error log by restricting the severity level. The third
entry gives the IP address of the client that generated the
<p>It is not possible to customize the error log by adding or
removing information. However, error log entries dealing with
- particular requests have corresponding entries in the <a
- href="#accesslog">access log</a>. For example, the above example
+ particular requests have corresponding entries in the <a href="#accesslog">access log</a>. For example, the above example
entry corresponds to an access log entry with status code 403.
Since it is possible to customize the access log, you can
obtain more information about error conditions using that log
file.</p>
-
+
<p>During testing, it is often useful to continuously monitor
the error log for any problems. On unix systems, you can
accomplish this using:</p>
-
- <blockquote>
- <code>tail -f error_log</code>
- </blockquote>
- <hr />
-
- <h2><a id="accesslog" name="accesslog">Access Log</a></h2>
-
- <table border="1">
- <tr>
- <td valign="top"><strong>Related Modules</strong><br />
- <br />
- <a href="mod/mod_log_config.html">mod_log_config</a><br />
- </td>
-
- <td valign="top"><strong>Related Directives</strong><br />
- <br />
- <a
- href="mod/mod_log_config.html#customlog">CustomLog</a><br />
- <a
- href="mod/mod_log_config.html#logformat">LogFormat</a><br />
- <a href="mod/mod_setenvif.html#setenvif">SetEnvIf</a>
- </td>
- </tr>
- </table>
-
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ tail -f error_log
+ </code></td></tr></table></blockquote>
+ <h2><a name="accesslog">Access Log</a></h2>
+
+
+ <table border="1"><tr><td valign="top"><strong>Related Modules</strong><br/><br/><code><a href="./mod/mod_log_config.html">mod_log_config</a></code>, <br/><code><a href="./mod/mod_setenvif.html">mod_setenvif</a></code><br/></td><td valign="top"><strong>Related Directives</strong><br/><br/><a href="./mod/mod_log_config.html#customlog" class="directive"><code class="directive">CustomLog</code></a><br/><a href="./mod/mod_log_config.html#logformat" class="directive"><code class="directive">LogFormat</code></a><br/><a href="./mod/mod_setenvif.html#setenvif" class="directive"><code class="directive">SetEnvIf</code></a><br/></td></tr></table>
+
<p>The server access log records all requests processed by the
server. The location and content of the access log are
- controlled by the <a
- href="mod/mod_log_config.html#customlog">CustomLog</a>
- directive. The <a
- href="mod/mod_log_config.html#logformat">LogFormat</a>
- directive can be used to simplify the selection of the contents
- of the logs. This section describes how to configure the server
+ controlled by the <a href="./mod/mod_log_config.html#
+ customlog" class="directive"><code class="directive">
+ CustomLog</code></a> directive. The <a href="./mod/mod_log_config.html#
+ logformat" class="directive"><code class="directive">
+ LogFormat</code></a> directive can be used to simplify the selection of
+ the contents of the logs. This section describes how to configure the server
to record information in the access log.</p>
<p>Of course, storing the information in the access log is only
general is beyond the scope of this document, and not really
part of the job of the web server itself. For more information
about this topic, and for applications which perform log
- analysis, check the <a
- href="http://dmoz.org/Computers/Software/Internet/Site_Management/Log_analysis/">
- Open Directory</a> or <a
- href="http://dir.yahoo.com/Computers_and_Internet/Software/Internet/World_Wide_Web/Servers/Log_Analysis_Tools/">
+ analysis, check the <a href="http://dmoz.org/Computers/Software/Internet/Site_Management/Log_analysis/">
+ Open Directory</a> or <a href="http://dir.yahoo.com/Computers_and_Internet/Software/Internet/World_Wide_Web/Servers/Log_Analysis_Tools/">
Yahoo</a>.</p>
-
+
<p>Various versions of Apache httpd have used other modules and
directives to control access logging, including
mod_log_referer, mod_log_agent, and the
directives.</p>
<p>The format of the access log is highly configurable. The
- format is specified using a <a
- href="mod/mod_log_config.html#format">format string</a> that
+ format is specified using a <a href="./mod/mod_log_config.html#
+ customlog" class="directive"><code class="directive">
+ CustomLog</code></a> that
looks much like a C-style printf(1) format string. Some
examples are presented in the next sections. For a complete
- list of the possible contents of the format string, see the <a
- href="mod/mod_log_config.html">mod_log_config
+ list of the possible contents of the format string, see the <a href="mod/mod_log_config.html">mod_log_config
documentation</a>.</p>
-
- <h3><a id="common" name="common">Common Log Format</a></h3>
-
- <p>A typical configuration for the access log might look as
- follows.</p>
-
- <blockquote>
- <code>LogFormat "%h %l %u %t \"%r\" %>s %b" common<br />
- CustomLog logs/access_log common</code>
- </blockquote>
-
- <p>This defines the <em>nickname</em> <code>common</code> and
- associates it with a particular log format string. The format
- string consists of percent directives, each of which tell the
- server to log a particular piece of information. Literal
- characters may also be placed in the format string and will be
- copied directly into the log output. The quote character
- (<code>"</code>) must be escaped by placing a back-slash before
- it to prevent it from being interpreted as the end of the
- format string. The format string may also contain the special
- control characters "<code>\n</code>" for new-line and
- "<code>\t</code>" for tab.</p>
-
- <p>The <code>CustomLog</code> directive sets up a new log file
- using the defined <em>nickname</em>. The filename for the
- access log is relative to the <a
- href="mod/core.html#serverroot">ServerRoot</a> unless it begins
- with a slash.</p>
-
- <p>The above configuration will write log entries in a format
- known as the Common Log Format (CLF). This standard format can
- be produced by many different web servers and read by many log
- analysis programs. The log file entries produced in CLF will
- look something like this:</p>
-
- <blockquote>
- <code>127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
- /apache_pb.gif HTTP/1.0" 200 2326</code>
- </blockquote>
-
- <p>Each part of this log entry is described below.</p>
-
- <dl>
- <dt><code>127.0.0.1</code> (<code>%h</code>)</dt>
-
- <dd>This is the IP address of the client (remote host) which
- made the request to the server. If <a
- href="mod/core.html#hostnamelookups">HostnameLookups</a> is
- set to <code>On</code>, then the server will try to determine
- the hostname and log it in place of the IP address. However,
- this configuration is not recommended since it can
- significantly slow the server. Instead, it is best to use a
- log post-processor such as <a
- href="programs/logresolve.html">logresolve</a> to determine
- the hostnames. The IP address reported here is not
- necessarily the address of the machine at which the user is
- sitting. If a proxy server exists between the user and the
- server, this address will be the address of the proxy, rather
- than the originating machine.</dd>
-
- <dt><code>-</code> (<code>%l</code>)</dt>
-
- <dd>The "hyphen" in the output indicates that the requested
- piece of information is not available. In this case, the
- information that is not available is the RFC 1413 identity of
- the client determined by <code>identd</code> on the clients
- machine. This information is highly unreliable and should
- almost never be used except on tightly controlled internal
- networks. Apache httpd will not even attempt to determine
- this information unless <a
- href="mod/core.html#identitycheck">IdentityCheck</a> is set
- to <code>On</code>.</dd>
-
- <dt><code>frank</code> (<code>%u</code>)</dt>
-
- <dd>This is the userid of the person requesting the document
- as determined by HTTP authentication. The same value is
- typically provided to CGI scripts in the
- <code>REMOTE_USER</code> environment variable. If the status
- code for the request (see below) is 401, then this value
- should not be trusted because the user is not yet
- authenticated. If the document is not password protected,
- this entry will be "<code>-</code>" just like the previous
- one.</dd>
-
- <dt><code>[10/Oct/2000:13:55:36 -0700]</code>
- (<code>%t</code>)</dt>
-
- <dd>
- The time that the server finished processing the request.
- The format is:
-
- <blockquote>
- <code>[day/month/year:hour:minute:second zone]<br />
- day = 2*digit<br />
- month = 3*letter<br />
- year = 4*digit<br />
- hour = 2*digit<br />
- minute = 2*digit<br />
- second = 2*digit<br />
- zone = (`+' | `-') 4*digit</code>
- </blockquote>
- It is possible to have the time displayed in another format
- by specifying <code>%{format}t</code> in the log format
- string, where <code>format</code> is as in
- <code>strftime(3)</code> from the C standard library.
- </dd>
-
- <dt><code>"GET /apache_pb.gif HTTP/1.0"</code>
- (<code>\"%r\"</code>)</dt>
-
- <dd>The request line from the client is given in double
- quotes. The request line contains a great deal of useful
- information. First, the method used by the client is
- <code>GET</code>. Second, the client requested the resource
- <code>/apache_pb.gif</code>, and third, the client used the
- protocol <code>HTTP/1.0</code>. It is also possible to log
- one or more parts of the request line independently. For
- example, the format string "<code>%m %U%q %H</code>" will log
- the method, path, query-string, and protocol, resulting in
- exactly the same output as "<code>%r</code>".</dd>
-
- <dt><code>200</code> (<code>%>s</code>)</dt>
-
- <dd>This is the status code that the server sends back to the
- client. This information is very valuable, because it reveals
- whether the request resulted in a successful response (codes
- beginning in 2), a redirection (codes beginning in 3), an
- error caused by the client (codes beginning in 4), or an
- error in the server (codes beginning in 5). The full list of
- possible status codes can be found in the <a
- href="http://www.w3.org/Protocols/rfc2616/rfc2616.txt">HTTP
- specification</a> (RFC2616 section 10).</dd>
-
- <dt><code>2326</code> (<code>%b</code>)</dt>
-
- <dd>The last entry indicates the size of the object returned
- to the client, not including the response headers. If no
- content was returned to the client, this value will be
- "<code>-</code>". To log "<code>0</code>" for no content, use
- <code>%B</code> instead.</dd>
- </dl>
-
- <h4><a id="combined" name="combined">Combined Log
- Format</a></h4>
-
- <p>Another commonly used format string is called the Combined
- Log Format. It can be used as follows.</p>
-
- <blockquote>
- <code>LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\"
- \"%{User-agent}i\"" combined<br />
- CustomLog log/acces_log combined</code>
- </blockquote>
-
- <p>This format is exactly the same as the Common Log Format,
- with the addition of two more fields. Each of the additional
- fields uses the percent-directive
- <code>%{<em>header</em>}i</code>, where <em>header</em> can be
- any HTTP request header. The access log under this format will
- look like:</p>
-
- <blockquote>
- <code>127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
- /apache_pb.gif HTTP/1.0" 200 2326
- "http://www.example.com/start.html" "Mozilla/4.08 [en]
- (Win98; I ;Nav)"</code>
- </blockquote>
-
- <p>The additional fields are:</p>
-
- <dl>
- <dt><code>"http://www.example.com/start.html"</code>
- (<code>\"%{Referer}i\"</code>)</dt>
-
- <dd>The "Referer" (sic) HTTP request header. This gives the
- site that the client reports having been referred from. (This
- should be the page that links to or includes
- <code>/apache_pb.gif</code>).</dd>
-
- <dt><code>"Mozilla/4.08 [en] (Win98; I ;Nav)"</code>
- (<code>\"%{User-agent}i\"</code>)</dt>
-
- <dd>The User-Agent HTTP request header. This is the
- identifying information that the client browser reports about
- itself.</dd>
- </dl>
-
- <h3><a id="multiple" name="multiple">Multiple Access
- Logs</a></h3>
-
- <p>Multiple access logs can be created simply by specifying
- multiple <code>CustomLog</code> directives in the configuration
- file. For example, the following directives will create three
- access logs. The first contains the basic CLF information,
- while the second and third contain referer and browser
- information. The last two <code>CustomLog</code> lines show how
- to mimic the effects of the <code>ReferLog</code> and
- <code>AgentLog</code> directives.</p>
-
- <blockquote>
- <code>LogFormat "%h %l %u %t \"%r\" %>s %b" common<br />
- CustomLog logs/access_log common<br />
- CustomLog logs/referer_log "%{Referer}i -> %U"<br />
- CustomLog logs/agent_log "%{User-agent}i"</code>
- </blockquote>
-
- <p>This example also shows that it is not necessary to define a
- nickname with the <code>LogFormat</code> directive. Instead,
- the log format can be specified directly in the
- <code>CustomLog</code> directive.</p>
-
- <h3><a id="conditional" name="conditional">Conditional
- Logging</a></h3>
-
- <p>There are times when it is convenient to exclude certain
- entries from the access logs based on characteristics of the
- client request. This is easily accomplished with the help of <a
- href="env.html">environment variables</a>. First, an
- environment variable must be set to indicate that the request
- meets certain conditions. This is usually accomplished with <a
- href="mod/mod_setenvif.html#setenvif">SetEnvIf</a>. Then the
- <code>env=</code> clause of the <code>CustomLog</code>
- directive is used to include or exclude requests where the
- environment variable is set. Some examples:</p>
-
- <blockquote>
- <code># Mark requests from the loop-back interface<br />
- SetEnvIf Remote_Addr "127\.0\.0\.1" dontlog<br />
- # Mark requests for the robots.txt file<br />
- SetEnvIf Request_URI "^/robots\.txt$" dontlog<br />
- # Log what remains<br />
- CustomLog logs/access_log common env=!dontlog</code>
- </blockquote>
-
- <p>As another example, consider logging requests from
- english-speakers to one log file, and non-english speakers to a
- different log file.</p>
-
- <blockquote>
- <code>SetEnvIf Accept-Language "en" english<br />
- CustomLog logs/english_log common env=english<br />
- CustomLog logs/non_english_log common env=!english</code>
- </blockquote>
-
- <p>Although we have just shown that conditional logging is very
- powerful and flexibly, it is not the only way to control the
- contents of the logs. Log files are more useful when they
- contain a complete record of server activity. It is often
- easier to simply post-process the log files to remove requests
- that you do not want to consider.</p>
- <hr />
-
- <h2><a id="rotation" name="rotation">Log Rotation</a></h2>
-
+
+ <h3><a name="common">Common Log Format</a></h3>
+
+
+ <p>A typical configuration for the access log might look as
+ follows.</p>
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ LogFormat "%h %l %u %t \"%r\" %>s %b" common<br>
+ CustomLog logs/access_log common
+ </code></td></tr></table></blockquote>
+
+ <p>This defines the <em>nickname</em> <code>common</code> and
+ associates it with a particular log format string. The format
+ string consists of percent directives, each of which tell the
+ server to log a particular piece of information. Literal
+ characters may also be placed in the format string and will be
+ copied directly into the log output. The quote character
+ (<code>"</code>) must be escaped by placing a back-slash before
+ it to prevent it from being interpreted as the end of the
+ format string. The format string may also contain the special
+ control characters "<code>\n</code>" for new-line and
+ "<code>\t</code>" for tab.</p>
+
+ <p>The <code>CustomLog</code> directive sets up a new log file
+ using the defined <em>nickname</em>. The filename for the
+ access log is relative to the <a href="./mod/core.html#
+ serverroot" class="directive"><code class="directive">
+ ServerRoot</code></a> unless it begins
+ with a slash.</p>
+
+ <p>The above configuration will write log entries in a format
+ known as the Common Log Format (CLF). This standard format can
+ be produced by many different web servers and read by many log
+ analysis programs. The log file entries produced in CLF will
+ look something like this:</p>
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
+ /apache_pb.gif HTTP/1.0" 200 2326
+ </code></td></tr></table></blockquote>
+
+ <p>Each part of this log entry is described below.</p>
+
+ <dl>
+ <dt><code>127.0.0.1</code> (<code>%h</code>)</dt>
+
+ <dd>This is the IP address of the client (remote host) which
+ made the request to the server. If <a href="./mod/core.html#
+ hostnamelookups" class="directive"><code class="directive">
+ HostnameLookups</code></a> is
+ set to <code>On</code>, then the server will try to determine
+ the hostname and log it in place of the IP address. However,
+ this configuration is not recommended since it can
+ significantly slow the server. Instead, it is best to use a
+ log post-processor such as <a href="programs/logresolve.html">logresolve</a> to determine
+ the hostnames. The IP address reported here is not
+ necessarily the address of the machine at which the user is
+ sitting. If a proxy server exists between the user and the
+ server, this address will be the address of the proxy, rather
+ than the originating machine.</dd>
+
+ <dt><code>-</code> (<code>%l</code>)</dt>
+
+ <dd>The "hyphen" in the output indicates that the requested
+ piece of information is not available. In this case, the
+ information that is not available is the RFC 1413 identity of
+ the client determined by <code>identd</code> on the clients
+ machine. This information is highly unreliable and should
+ almost never be used except on tightly controlled internal
+ networks. Apache httpd will not even attempt to determine
+ this information unless <a href="./mod/core.html#
+ identitycheck" class="directive"><code class="directive">
+ IdentityCheck</code></a> is set
+ to <code>On</code>.</dd>
+
+ <dt><code>frank</code> (<code>%u</code>)</dt>
+
+ <dd>This is the userid of the person requesting the document
+ as determined by HTTP authentication. The same value is
+ typically provided to CGI scripts in the
+ <code>REMOTE_USER</code> environment variable. If the status
+ code for the request (see below) is 401, then this value
+ should not be trusted because the user is not yet
+ authenticated. If the document is not password protected,
+ this entry will be "<code>-</code>" just like the previous
+ one.</dd>
+
+ <dt><code>[10/Oct/2000:13:55:36 -0700]</code>
+ (<code>%t</code>)</dt>
+
+ <dd>
+ The time that the server finished processing the request.
+ The format is:
+
+ <blockquote>
+ <code>[day/month/year:hour:minute:second zone]<br>
+ day = 2*digit<br>
+ month = 3*letter<br>
+ year = 4*digit<br>
+ hour = 2*digit<br>
+ minute = 2*digit<br>
+ second = 2*digit<br>
+ zone = (`+' | `-') 4*digit</code>
+ </blockquote>
+ It is possible to have the time displayed in another format
+ by specifying <code>%{format}t</code> in the log format
+ string, where <code>format</code> is as in
+ <code>strftime(3)</code> from the C standard library.
+ </dd>
+
+ <dt><code>"GET /apache_pb.gif HTTP/1.0"</code>
+ (<code>\"%r\"</code>)</dt>
+
+ <dd>The request line from the client is given in double
+ quotes. The request line contains a great deal of useful
+ information. First, the method used by the client is
+ <code>GET</code>. Second, the client requested the resource
+ <code>/apache_pb.gif</code>, and third, the client used the
+ protocol <code>HTTP/1.0</code>. It is also possible to log
+ one or more parts of the request line independently. For
+ example, the format string "<code>%m %U%q %H</code>" will log
+ the method, path, query-string, and protocol, resulting in
+ exactly the same output as "<code>%r</code>".</dd>
+
+ <dt><code>200</code> (<code>%>s</code>)</dt>
+
+ <dd>This is the status code that the server sends back to the
+ client. This information is very valuable, because it reveals
+ whether the request resulted in a successful response (codes
+ beginning in 2), a redirection (codes beginning in 3), an
+ error caused by the client (codes beginning in 4), or an
+ error in the server (codes beginning in 5). The full list of
+ possible status codes can be found in the <a href="http://www.w3.org/Protocols/rfc2616/rfc2616.txt">HTTP
+ specification</a> (RFC2616 section 10).</dd>
+
+ <dt><code>2326</code> (<code>%b</code>)</dt>
+
+ <dd>The last entry indicates the size of the object returned
+ to the client, not including the response headers. If no
+ content was returned to the client, this value will be
+ "<code>-</code>". To log "<code>0</code>" for no content, use
+ <code>%B</code> instead.</dd>
+ </dl>
+
+
+ <h3><a name="combined">Combined Log Format</a></h3>
+
+
+ <p>Another commonly used format string is called the Combined
+ Log Format. It can be used as follows.</p>
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\"
+ \"%{User-agent}i\"" combined<br>
+ CustomLog log/acces_log combined
+ </code></td></tr></table></blockquote>
+
+ <p>This format is exactly the same as the Common Log Format,
+ with the addition of two more fields. Each of the additional
+ fields uses the percent-directive
+ <code>%{<em>header</em>}i</code>, where <em>header</em> can be
+ any HTTP request header. The access log under this format will
+ look like:</p>
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
+ /apache_pb.gif HTTP/1.0" 200 2326
+ "http://www.example.com/start.html" "Mozilla/4.08 [en]
+ (Win98; I ;Nav)"
+ </code></td></tr></table></blockquote>
+
+ <p>The additional fields are:</p>
+
+ <dl>
+ <dt><code>"http://www.example.com/start.html"</code>
+ (<code>\"%{Referer}i\"</code>)</dt>
+
+ <dd>The "Referer" (sic) HTTP request header. This gives the
+ site that the client reports having been referred from. (This
+ should be the page that links to or includes
+ <code>/apache_pb.gif</code>).</dd>
+
+ <dt><code>"Mozilla/4.08 [en] (Win98; I ;Nav)"</code>
+ (<code>\"%{User-agent}i\"</code>)</dt>
+
+ <dd>The User-Agent HTTP request header. This is the
+ identifying information that the client browser reports about
+ itself.</dd>
+ </dl>
+
+
+ <h3><a name="multiple">Multiple Access Logs</a></h3>
+
+
+ <p>Multiple access logs can be created simply by specifying
+ multiple <a href="./mod/core.html#customlog" class="directive"><code class="directive">CustomLog</code></a>
+ directives in the configuration
+ file. For example, the following directives will create three
+ access logs. The first contains the basic CLF information,
+ while the second and third contain referer and browser
+ information. The last two <a href="./mod/core.html#
+ customlog" class="directive"><code class="directive">
+ CustomLog</code></a> lines show how
+ to mimic the effects of the <a href="./mod/core.html#referlog" class="directive"><code class="directive">ReferLog</code></a>
+ and <a href="./mod/core.html#agentlog" class="directive"><code class="directive">AgentLog</code></a> directives.</p>
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ LogFormat "%h %l %u %t \"%r\" %>s %b" common<br>
+ CustomLog logs/access_log common<br>
+ CustomLog logs/referer_log "%{Referer}i -> %U"<br>
+ CustomLog logs/agent_log "%{User-agent}i"
+ </code></td></tr></table></blockquote>
+
+ <p>This example also shows that it is not necessary to define a
+ nickname with the <code>LogFormat</code> directive. Instead,
+ the log format can be specified directly in the
+ <a href="./mod/core.html#customlog" class="directive"><code class="directive">CustomLog</code></a> directive.</p>
+
+
+ <h3><a name="conditional">Conditional Logs</a></h3>
+
+
+ <p>There are times when it is convenient to exclude certain
+ entries from the access logs based on characteristics of the
+ client request. This is easily accomplished with the help of <a href="env.html">environment variables</a>. First, an
+ environment variable must be set to indicate that the request
+ meets certain conditions. This is usually accomplished with
+ <a href="./mod/mod_setenvif.html#setenvif" class="directive"><code class="directive">SetEnvIf</code></a>. Then the
+ <code>env=</code> clause of the <code>CustomLog</code>
+ directive is used to include or exclude requests where the
+ environment variable is set. Some examples:</p>
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ # Mark requests from the loop-back interface<br>
+ SetEnvIf Remote_Addr "127\.0\.0\.1" dontlog<br>
+ # Mark requests for the robots.txt file<br>
+ SetEnvIf Request_URI "^/robots\.txt$" dontlog<br>
+ # Log what remains<br>
+ CustomLog logs/access_log common env=!dontlog
+ </code></td></tr></table></blockquote>
+
+ <p>As another example, consider logging requests from
+ english-speakers to one log file, and non-english speakers to a
+ different log file.</p>
+
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ SetEnvIf Accept-Language "en" english<br>
+ CustomLog logs/english_log common env=english<br>
+ CustomLog logs/non_english_log common env=!english
+ </code></td></tr></table></blockquote>
+
+ <p>Although we have just shown that conditional logging is very
+ powerful and flexibly, it is not the only way to control the
+ contents of the logs. Log files are more useful when they
+ contain a complete record of server activity. It is often
+ easier to simply post-process the log files to remove requests
+ that you do not want to consider.</p>
+
+ <h2><a name="rotation">Rotation Logs</a></h2>
+
+
<p>On even a moderately busy server, the quantity of
information stored in the log files is very large. The access
log file typically grows 1 MB or more per 10,000 requests. It
files by moving or deleting the existing logs. This cannot be
done while the server is running, because Apache will continue
writing to the old log file as long as it holds the file open.
- Instead, the server must be <a
- href="stopping.html">restarted</a> after the log files are
+ Instead, the server must be <a href="stopping.html">restarted</a> after the log files are
moved or deleted so that it will open new log files.</p>
<p>By using a <em>graceful</em> restart, the server can be
scenario that simply rotates the logs and compresses the old
logs to save space is:</p>
- <blockquote>
- <code>mv access_log access_log.old<br />
- mv error_log error_log.old<br />
- apachectl graceful<br />
- sleep 600<br />
- gzip access_log.old error_log.old</code>
- </blockquote>
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ mv access_log access_log.old<br>
+ mv error_log error_log.old<br>
+ apachectl graceful<br>
+ sleep 600<br>
+ gzip access_log.old error_log.old
+ </code></td></tr></table></blockquote>
- <p>Another way to perform log rotation is using <a
- href="#piped">piped logs</a> as discussed in the next
+ <p>Another way to perform log rotation is using <a href="#piped">piped logs</a> as discussed in the next
section.</p>
- <hr />
-
- <h2><a id="piped" name="piped">Piped Logs</a></h2>
-
+ <h2><a name="piped">Piped Logs</a></h2>
+
+
<p>Apache httpd is capable of writing error and access log
files through a pipe to another process, rather than directly
to a file. This capability dramatically increases the
<p>Some simple examples using piped logs:</p>
- <blockquote>
- <code># compressed logs<br />
- CustomLog "|/usr/bin/gzip -c >>
- /var/log/access_log.gz" common<br />
- # almost-real-time name resolution<br />
- CustomLog "|/usr/local/apache/bin/logresolve >>
- /var/log/access_log" common</code>
- </blockquote>
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ # compressed logs<br>
+ CustomLog "|/usr/bin/gzip -c >>
+ /var/log/access_log.gz" common<br>
+ # almost-real-time name resolution<br>
+ CustomLog "|/usr/local/apache/bin/logresolve >>
+ /var/log/access_log" common
+ </code></td></tr></table></blockquote>
<p>Notice that quotes are used to enclose the entire command
that will be called for the pipe. Although these examples are
<p>One important use of piped logs is to allow log rotation
without having to restart the server. The Apache HTTP Server
- includes a simple program called <a
- href="programs/rotatelogs.html">rotatelogs</a> for this
+ includes a simple program called <a href="programs/rotatelogs.html">rotatelogs</a> for this
purpose. For example, to rotate the logs every 24 hours, you
can use:</p>
- <blockquote>
- <code>CustomLog "|/usr/local/apache/bin/rotatelogs
- /var/log/access_log 86400" common</code>
- </blockquote>
-
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ CustomLog "|/usr/local/apache/bin/rotatelogs
+ /var/log/access_log 86400" common
+ </code></td></tr></table></blockquote>
+
<p>A similar, but much more flexible log rotation program
called <a href="http://www.cronolog.org/">cronolog</a>
is available at an external site.</p>
<p>As with conditional logging, piped logs are a very powerful
tool, but they should not be used where a simpler solution like
off-line post-processing is available.</p>
- <hr />
-
- <h2><a id="virtualhosts" name="virtualhosts">Virtual
- Hosts</a></h2>
-
+ <h2><a name="virtualhost">Virtual Hosts</a></h2>
+
+
<p>When running a server with many <a href="vhosts/">virtual
hosts</a>, there are several options for dealing with log
files. First, it is possible to use logs exactly as in a
for easy collection of statistics on individual virtual
hosts.</p>
- <p>If <code>CustomLog</code> or <code>ErrorLog</code>
- directives are placed inside a <code><VirtualHost></code>
+ <p>If <a href="./mod/mod_log_config.html#customlog" class="directive"><code class="directive">CustomLog</code></a>
+ or <a href="./mod/mod_log_config.html#errorlog" class="directive"><code class="directive">ErrorLog</code></a>
+ directives are placed inside a <a href="./mod/core.html#
+ <virtualhost>" class="directive"><code class="directive">
+ <VirtualHost></code></a>
section, all requests or errors for that virtual host will be
logged only to the specified file. Any virtual host which does
not have logging directives will still have its requests sent
to the main server logs. This technique is very useful for a
small number of virtual hosts, but if the number of hosts is
very large, it can be complicated to manage. In addition, it
- can often create problems with <a
- href="vhosts/fd-limits.html">insufficient file
+ can often create problems with <a href="vhosts/fd-limits.html">insufficient file
descriptors</a>.</p>
<p>For the access log, there is a very good compromise. By
later split the log into individual files. For example,
consider the following directives.</p>
- <blockquote>
- <code>LogFormat "%v %l %u %t \"%r\" %>s %b"
- comonvhost<br />
- CustomLog logs/access_log comonvhost</code>
- </blockquote>
+ <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
+ LogFormat "%v %l %u %t \"%r\" %>s %b"
+ comonvhost<br>
+ CustomLog logs/access_log comonvhost
+ </code></td></tr></table></blockquote>
<p>The <code>%v</code> is used to log the name of the virtual
- host that is serving the request. Then a program like <a
- href="programs/other.html">split-logfile</a> can be used to
+ host that is serving the request. Then a program like <a href="programs/other.html">split-logfile</a> can be used to
post-process the access log in order to split it into one file
per virtual host.</p>
-
- <p>Unfortunately, no similar technique is available for the
- error log, so you must choose between mixing all virtual hosts
- in the same error log and using one error log per virtual
- host.</p>
- <hr />
-
- <h2><a id="other" name="other">Other Log Files</a></h2>
-
- <table border="1">
- <tr>
- <td valign="top"><strong>Related Modules</strong><br />
- <br />
- <a href="mod/mod_cgi.html">mod_cgi</a><br />
- <a href="mod/mod_rewrite.html">mod_rewrite</a> </td>
-
- <td valign="top"><strong>Related Directives</strong><br />
- <br />
- <a href="mod/core.html#pidfile">PidFile</a><br />
- <a
- href="mod/mod_rewrite.html#RewriteLog">RewriteLog</a><br />
- <a
- href="mod/mod_rewrite.html#RewriteLogLevel">RewriteLogLevel</a><br />
- <a href="mod/mod_cgi.html#scriptlog">ScriptLog</a><br />
- <a
- href="mod/mod_cgi.html#scriptloglength">ScriptLogLength</a><br />
- <a
- href="mod/mod_cgi.html#scriptlogbuffer">ScriptLogBuffer</a>
- </td>
- </tr>
- </table>
-
- <h3><a id="pidfile" name="pidfile">PID File</a></h3>
-
- <p>On startup, Apache httpd saves the process id of the parent
- httpd process to the file <code>logs/httpd.pid</code>. This
- filename can be changed with the <a
- href="mod/core.html#pidfile">PidFile</a> directive. The
- process-id is for use by the administrator in restarting and
- terminating the daemon by sending signals to the parent
- process; on Windows, use the -k command line option instead.
- For more information see the <a href="stopping.html">Stopping
- and Restarting</a> page.</p>
-
- <h3><a id="scriptlog" name="scriptlog">Script Log</a></h3>
-
- <p>In order to aid in debugging, the <a
- href="mod/mod_cgi.html#scriptlog">ScriptLog</a> directive
- allows you to record the input to and output from CGI scripts.
- This should only be used in testing - not for live servers.
- More information is available in the <a
- href="mod/mod_cgi.html">mod_cgi documentation</a>.</p>
-
- <h3><a id="rewritelog" name="rewritelog">Rewrite Log</a></h3>
-
- <p>When using the powerful and complex features of <a
- href="mod/mod_rewrite.html">mod_rewrite</a>, it is almost
- always necessary to use the <a
- href="mod/mod_rewrite.html#RewriteLog">RewriteLog</a> to help
- in debugging. This log file produces a detailed analysis of how
- the rewriting engine transforms requests. The level of detail
- is controlled by the <a
- href="mod/mod_rewrite.html#RewriteLogLevel">RewriteLogLevel</a>
- directive.</p>
- <!--#include virtual="footer.html" -->
- </body>
-</html>
-
+ <h2><a name="other">Other Log Files</a></h2>
+
+
+ <table border="1"><tr><td valign="top"><strong>Related Modules</strong><br/><br/><code><a href="./mod/mod_cgi.html">mod_cgi</a></code>, <br/><code><a href="./mod/mod_rewrite.html">mod_rewrite</a></code><br/></td><td valign="top"><strong>Related Directives</strong><br/><br/><a href="./mod/core.html#pidfile" class="directive"><code class="directive">PidFile</code></a><br/><a href="./mod/mod_rewrite.html#rewritelog" class="directive"><code class="directive">RewriteLog</code></a><br/><a href="./mod/mod_rewrite.html#rewriteloglevel" class="directive"><code class="directive">RewriteLogLevel</code></a><br/><a href="./mod/mod_cgi.html#scriptlog" class="directive"><code class="directive">ScriptLog</code></a><br/><a href="./mod/mod_cgi.html#scriptloglength" class="directive"><code class="directive">ScriptLogLength</code></a><br/><a href="./mod/mod_cgi.html#scriptbuffer" class="directive"><code class="directive">ScriptBuffer</code></a><br/></td></tr></table>
+
+ <h3><a name="pidfile">PID File</a></h3>
+
+
+ <p>On startup, Apache httpd saves the process id of the parent
+ httpd process to the file <code>logs/httpd.pid</code>. This
+ filename can be changed with the <a href="./mod/core.html#pidfile
+ " class="directive"><code class="directive">PidFile
+ </code></a> directive. The
+ process-id is for use by the administrator in restarting and
+ terminating the daemon by sending signals to the parent
+ process; on Windows, use the -k command line option instead.
+ For more information see the <a href="stopping.html">Stopping
+ and Restarting</a> page.</p>
+
+
+ <h3><a name="scriptlog">Script Log</a></h3>
+
+
+ <p>In order to aid in debugging, the <a href="./mod/mod_cgi.html#
+ scriptlog" class="directive"><code class="directive">
+ ScriptLog</code></a> directive
+ allows you to record the input to and output from CGI scripts.
+ This should only be used in testing - not for live servers.
+ More information is available in the <a href="mod/mod_cgi.html">mod_cgi documentation</a>.</p>
+
+
+ <h3><a name="rewritelog">Rewrite Log</a></h3>
+
+
+ <p>When using the powerful and complex features of <a href="mod/mod_rewrite.html">mod_rewrite</a>, it is almost
+ always necessary to use the <a href="./mod/mod_rewrite.html#
+ rewritelog" class="directive"><code class="directive">
+ RewriteLog</code></a> to help
+ in debugging. This log file produces a detailed analysis of how
+ the rewriting engine transforms requests. The level of detail
+ is controlled by the <a href="./mod/mod_rewrite.html#
+ rewriteloglevel" class="directive"><code class="directive">
+ RewriteLogLevel</code></a> directive.</p>
+
+ </blockquote><hr/><h3 align="center">Apache HTTP Server Version 2.0</h3><a href="./"><img src="./images/index.gif" alt="Index"/></a><a href="./"><img src="./images/home.gif" alt="Home"/></a></body></html>
\ No newline at end of file
--- /dev/null
+<?xml version="1.0" encoding="UTF-8" ?>
+<!DOCTYPE manualpage SYSTEM "./style/manualpage.dtd">
+<?xml-stylesheet type="text/xsl" href="./style/manual.en.xsl"?>
+
+<manualpage>
+ <relativepath href="."/>
+
+ <title>Log Files</title>
+
+ <summary>
+ <p>In order to effectively manage a web server, it is necessary
+ to get feedback about the activity and performance of the
+ server as well as any problems that may be occuring. The Apache
+ HTTP Server provides very comprehensive and flexible logging
+ capabilities. This document describes how to configure its
+ logging capabilities, and how to understand what the logs
+ contain.</p>
+ </summary>
+
+ <section id="security">
+ <title>Security Warning</title>
+
+ <p>Anyone who can write to the directory where Apache is
+ writing a log file can almost certainly gain access to the uid
+ that the server is started as, which is normally root. Do
+ <em>NOT</em> give people write access to the directory the logs
+ are stored in without being aware of the consequences; see the
+ <a href="misc/security_tips.html">security tips</a> document
+ for details.</p>
+
+ <p>In addition, log files may contain information supplied
+ directly by the client, without escaping. Therefore, it is
+ possible for malicious clients to insert control-characters in
+ the log files, so care must be taken in dealing with raw
+ logs.</p>
+ </section>
+
+ <section id="errorlog">
+ <title>Error Log</title>
+
+ <related>
+ <directivelist>
+ <directive module="mod_core">ErrorLog</directive>
+ <directive module="mod_core">LogLevel</directive>
+ </directivelist>
+ </related>
+
+ <p>The server error log, whose name and location is set by the
+ <directive module="core">ErrorLog</directive> directive, is the
+ most important log file. This is the place where Apache httpd
+ will send diagnostic information and record any errors that it
+ encounters in processing requests. It is the first place to
+ look when a problem occurs with starting the server or with the
+ operation of the server, since it will often contain details of
+ what went wrong and how to fix it.</p>
+
+ <p>The error log is usually written to a file (typically
+ <code>error_log</code> on unix systems and
+ <code>error.log</code> on Windows and OS/2). On unix systems it
+ is also possible to have the server send errors to
+ <code>syslog</code> or <a href="#piped">pipe them to a
+ program</a>.</p>
+
+ <p>The format of the error log is relatively free-form and
+ descriptive. But there is certain information that is contained
+ in most error log entries. For example, here is a typical
+ message.</p>
+
+ <example>
+ [Wed Oct 11 14:32:52 2000] [error] [client 127.0.0.1]
+ client denied by server configuration:
+ /export/home/live/ap/htdocs/test
+ </example>
+
+ <p>The first item in the log entry is the date and time of the
+ message. The second entry lists the severity of the error being
+ reported. The <directive module="core">LogLevel</directive>
+ directive is used to control the types of errors that are sent
+ to the error log by restricting the severity level. The third
+ entry gives the IP address of the client that generated the
+ error. Beyond that is the message itself, which in this case
+ indicates that the server has been configured to deny the
+ client access. The server reports the file-system path (as
+ opposed to the web path) of the requested document.</p>
+
+ <p>A very wide variety of different messages can appear in the
+ error log. Most look similar to the example above. The error
+ log will also contain debugging output from CGI scripts. Any
+ information written to <code>stderr</code> by a CGI script will
+ be copied directly to the error log.</p>
+
+ <p>It is not possible to customize the error log by adding or
+ removing information. However, error log entries dealing with
+ particular requests have corresponding entries in the <a
+ href="#accesslog">access log</a>. For example, the above example
+ entry corresponds to an access log entry with status code 403.
+ Since it is possible to customize the access log, you can
+ obtain more information about error conditions using that log
+ file.</p>
+
+ <p>During testing, it is often useful to continuously monitor
+ the error log for any problems. On unix systems, you can
+ accomplish this using:</p>
+
+ <example>
+ tail -f error_log
+ </example>
+ </section>
+
+ <section id="accesslog">
+ <title>Access Log</title>
+
+ <related>
+ <modulelist>
+ <module>mod_log_config</module>
+ <module>mod_setenvif</module>
+ </modulelist>
+ <directivelist>
+ <directive module="mod_log_config">CustomLog</directive>
+ <directive module="mod_log_config">LogFormat</directive>
+ <directive module="mod_setenvif">SetEnvIf</directive>
+ </directivelist>
+ </related>
+
+ <p>The server access log records all requests processed by the
+ server. The location and content of the access log are
+ controlled by the <directive module="mod_log_config">
+ CustomLog</directive> directive. The <directive module="mod_log_config">
+ LogFormat</directive> directive can be used to simplify the selection of
+ the contents of the logs. This section describes how to configure the server
+ to record information in the access log.</p>
+
+ <p>Of course, storing the information in the access log is only
+ the start of log management. The next step is to analyze this
+ information to produce useful statistics. Log analysis in
+ general is beyond the scope of this document, and not really
+ part of the job of the web server itself. For more information
+ about this topic, and for applications which perform log
+ analysis, check the <a
+ href="http://dmoz.org/Computers/Software/Internet/Site_Management/Log_analysis/">
+ Open Directory</a> or <a
+ href="http://dir.yahoo.com/Computers_and_Internet/Software/Internet/World_Wide_Web/Servers/Log_Analysis_Tools/">
+ Yahoo</a>.</p>
+
+ <p>Various versions of Apache httpd have used other modules and
+ directives to control access logging, including
+ mod_log_referer, mod_log_agent, and the
+ <code>TransferLog</code> directive. The <code>CustomLog</code>
+ directive now subsumes the functionality of all the older
+ directives.</p>
+
+ <p>The format of the access log is highly configurable. The
+ format is specified using a <directive module="mod_log_config">
+ CustomLog</directive> that
+ looks much like a C-style printf(1) format string. Some
+ examples are presented in the next sections. For a complete
+ list of the possible contents of the format string, see the <a
+ href="mod/mod_log_config.html">mod_log_config
+ documentation</a>.</p>
+
+ <section id="common">
+ <title>Common Log Format</title>
+
+ <p>A typical configuration for the access log might look as
+ follows.</p>
+
+ <example>
+ LogFormat "%h %l %u %t \"%r\" %>s %b" common<br />
+ CustomLog logs/access_log common
+ </example>
+
+ <p>This defines the <em>nickname</em> <code>common</code> and
+ associates it with a particular log format string. The format
+ string consists of percent directives, each of which tell the
+ server to log a particular piece of information. Literal
+ characters may also be placed in the format string and will be
+ copied directly into the log output. The quote character
+ (<code>"</code>) must be escaped by placing a back-slash before
+ it to prevent it from being interpreted as the end of the
+ format string. The format string may also contain the special
+ control characters "<code>\n</code>" for new-line and
+ "<code>\t</code>" for tab.</p>
+
+ <p>The <code>CustomLog</code> directive sets up a new log file
+ using the defined <em>nickname</em>. The filename for the
+ access log is relative to the <directive module="core">
+ ServerRoot</directive> unless it begins
+ with a slash.</p>
+
+ <p>The above configuration will write log entries in a format
+ known as the Common Log Format (CLF). This standard format can
+ be produced by many different web servers and read by many log
+ analysis programs. The log file entries produced in CLF will
+ look something like this:</p>
+
+ <example>
+ 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
+ /apache_pb.gif HTTP/1.0" 200 2326
+ </example>
+
+ <p>Each part of this log entry is described below.</p>
+
+ <dl>
+ <dt><code>127.0.0.1</code> (<code>%h</code>)</dt>
+
+ <dd>This is the IP address of the client (remote host) which
+ made the request to the server. If <directive module="core">
+ HostnameLookups</directive> is
+ set to <code>On</code>, then the server will try to determine
+ the hostname and log it in place of the IP address. However,
+ this configuration is not recommended since it can
+ significantly slow the server. Instead, it is best to use a
+ log post-processor such as <a
+ href="programs/logresolve.html">logresolve</a> to determine
+ the hostnames. The IP address reported here is not
+ necessarily the address of the machine at which the user is
+ sitting. If a proxy server exists between the user and the
+ server, this address will be the address of the proxy, rather
+ than the originating machine.</dd>
+
+ <dt><code>-</code> (<code>%l</code>)</dt>
+
+ <dd>The "hyphen" in the output indicates that the requested
+ piece of information is not available. In this case, the
+ information that is not available is the RFC 1413 identity of
+ the client determined by <code>identd</code> on the clients
+ machine. This information is highly unreliable and should
+ almost never be used except on tightly controlled internal
+ networks. Apache httpd will not even attempt to determine
+ this information unless <directive module="core">
+ IdentityCheck</directive> is set
+ to <code>On</code>.</dd>
+
+ <dt><code>frank</code> (<code>%u</code>)</dt>
+
+ <dd>This is the userid of the person requesting the document
+ as determined by HTTP authentication. The same value is
+ typically provided to CGI scripts in the
+ <code>REMOTE_USER</code> environment variable. If the status
+ code for the request (see below) is 401, then this value
+ should not be trusted because the user is not yet
+ authenticated. If the document is not password protected,
+ this entry will be "<code>-</code>" just like the previous
+ one.</dd>
+
+ <dt><code>[10/Oct/2000:13:55:36 -0700]</code>
+ (<code>%t</code>)</dt>
+
+ <dd>
+ The time that the server finished processing the request.
+ The format is:
+
+ <blockquote>
+ <code>[day/month/year:hour:minute:second zone]<br />
+ day = 2*digit<br />
+ month = 3*letter<br />
+ year = 4*digit<br />
+ hour = 2*digit<br />
+ minute = 2*digit<br />
+ second = 2*digit<br />
+ zone = (`+' | `-') 4*digit</code>
+ </blockquote>
+ It is possible to have the time displayed in another format
+ by specifying <code>%{format}t</code> in the log format
+ string, where <code>format</code> is as in
+ <code>strftime(3)</code> from the C standard library.
+ </dd>
+
+ <dt><code>"GET /apache_pb.gif HTTP/1.0"</code>
+ (<code>\"%r\"</code>)</dt>
+
+ <dd>The request line from the client is given in double
+ quotes. The request line contains a great deal of useful
+ information. First, the method used by the client is
+ <code>GET</code>. Second, the client requested the resource
+ <code>/apache_pb.gif</code>, and third, the client used the
+ protocol <code>HTTP/1.0</code>. It is also possible to log
+ one or more parts of the request line independently. For
+ example, the format string "<code>%m %U%q %H</code>" will log
+ the method, path, query-string, and protocol, resulting in
+ exactly the same output as "<code>%r</code>".</dd>
+
+ <dt><code>200</code> (<code>%>s</code>)</dt>
+
+ <dd>This is the status code that the server sends back to the
+ client. This information is very valuable, because it reveals
+ whether the request resulted in a successful response (codes
+ beginning in 2), a redirection (codes beginning in 3), an
+ error caused by the client (codes beginning in 4), or an
+ error in the server (codes beginning in 5). The full list of
+ possible status codes can be found in the <a
+ href="http://www.w3.org/Protocols/rfc2616/rfc2616.txt">HTTP
+ specification</a> (RFC2616 section 10).</dd>
+
+ <dt><code>2326</code> (<code>%b</code>)</dt>
+
+ <dd>The last entry indicates the size of the object returned
+ to the client, not including the response headers. If no
+ content was returned to the client, this value will be
+ "<code>-</code>". To log "<code>0</code>" for no content, use
+ <code>%B</code> instead.</dd>
+ </dl>
+ </section>
+
+ <section id="combined">
+ <title>Combined Log Format</title>
+
+ <p>Another commonly used format string is called the Combined
+ Log Format. It can be used as follows.</p>
+
+ <example>
+ LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\"
+ \"%{User-agent}i\"" combined<br />
+ CustomLog log/acces_log combined
+ </example>
+
+ <p>This format is exactly the same as the Common Log Format,
+ with the addition of two more fields. Each of the additional
+ fields uses the percent-directive
+ <code>%{<em>header</em>}i</code>, where <em>header</em> can be
+ any HTTP request header. The access log under this format will
+ look like:</p>
+
+ <example>
+ 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
+ /apache_pb.gif HTTP/1.0" 200 2326
+ "http://www.example.com/start.html" "Mozilla/4.08 [en]
+ (Win98; I ;Nav)"
+ </example>
+
+ <p>The additional fields are:</p>
+
+ <dl>
+ <dt><code>"http://www.example.com/start.html"</code>
+ (<code>\"%{Referer}i\"</code>)</dt>
+
+ <dd>The "Referer" (sic) HTTP request header. This gives the
+ site that the client reports having been referred from. (This
+ should be the page that links to or includes
+ <code>/apache_pb.gif</code>).</dd>
+
+ <dt><code>"Mozilla/4.08 [en] (Win98; I ;Nav)"</code>
+ (<code>\"%{User-agent}i\"</code>)</dt>
+
+ <dd>The User-Agent HTTP request header. This is the
+ identifying information that the client browser reports about
+ itself.</dd>
+ </dl>
+ </section>
+
+ <section id="multiple">
+ <title>Multiple Access Logs</title>
+
+ <p>Multiple access logs can be created simply by specifying
+ multiple <directive module="core">CustomLog</directive>
+ directives in the configuration
+ file. For example, the following directives will create three
+ access logs. The first contains the basic CLF information,
+ while the second and third contain referer and browser
+ information. The last two <directive module="core">
+ CustomLog</directive> lines show how
+ to mimic the effects of the <directive module="core">ReferLog</directive>
+ and <directive module="core">AgentLog</directive> directives.</p>
+
+ <example>
+ LogFormat "%h %l %u %t \"%r\" %>s %b" common<br />
+ CustomLog logs/access_log common<br />
+ CustomLog logs/referer_log "%{Referer}i -> %U"<br />
+ CustomLog logs/agent_log "%{User-agent}i"
+ </example>
+
+ <p>This example also shows that it is not necessary to define a
+ nickname with the <code>LogFormat</code> directive. Instead,
+ the log format can be specified directly in the
+ <directive module="core">CustomLog</directive> directive.</p>
+ </section>
+
+ <section id="conditional">
+ <title>Conditional Logs</title>
+
+ <p>There are times when it is convenient to exclude certain
+ entries from the access logs based on characteristics of the
+ client request. This is easily accomplished with the help of <a
+ href="env.html">environment variables</a>. First, an
+ environment variable must be set to indicate that the request
+ meets certain conditions. This is usually accomplished with
+ <directive module="mod_setenvif">SetEnvIf</directive>. Then the
+ <code>env=</code> clause of the <code>CustomLog</code>
+ directive is used to include or exclude requests where the
+ environment variable is set. Some examples:</p>
+
+ <example>
+ # Mark requests from the loop-back interface<br />
+ SetEnvIf Remote_Addr "127\.0\.0\.1" dontlog<br />
+ # Mark requests for the robots.txt file<br />
+ SetEnvIf Request_URI "^/robots\.txt$" dontlog<br />
+ # Log what remains<br />
+ CustomLog logs/access_log common env=!dontlog
+ </example>
+
+ <p>As another example, consider logging requests from
+ english-speakers to one log file, and non-english speakers to a
+ different log file.</p>
+
+ <example>
+ SetEnvIf Accept-Language "en" english<br />
+ CustomLog logs/english_log common env=english<br />
+ CustomLog logs/non_english_log common env=!english
+ </example>
+
+ <p>Although we have just shown that conditional logging is very
+ powerful and flexibly, it is not the only way to control the
+ contents of the logs. Log files are more useful when they
+ contain a complete record of server activity. It is often
+ easier to simply post-process the log files to remove requests
+ that you do not want to consider.</p>
+ </section>
+ </section>
+
+ <section id="rotation">
+ <title>Rotation Logs</title>
+
+ <p>On even a moderately busy server, the quantity of
+ information stored in the log files is very large. The access
+ log file typically grows 1 MB or more per 10,000 requests. It
+ will consequently be necessary to periodically rotate the log
+ files by moving or deleting the existing logs. This cannot be
+ done while the server is running, because Apache will continue
+ writing to the old log file as long as it holds the file open.
+ Instead, the server must be <a
+ href="stopping.html">restarted</a> after the log files are
+ moved or deleted so that it will open new log files.</p>
+
+ <p>By using a <em>graceful</em> restart, the server can be
+ instructed to open new log files without losing any existing or
+ pending connections from clients. However, in order to
+ accomplish this, the server must continue to write to the old
+ log files while it finishes serving old requests. It is
+ therefore necessary to wait for some time after the restart
+ before doing any processing on the log files. A typical
+ scenario that simply rotates the logs and compresses the old
+ logs to save space is:</p>
+
+ <example>
+ mv access_log access_log.old<br />
+ mv error_log error_log.old<br />
+ apachectl graceful<br />
+ sleep 600<br />
+ gzip access_log.old error_log.old
+ </example>
+
+ <p>Another way to perform log rotation is using <a
+ href="#piped">piped logs</a> as discussed in the next
+ section.</p>
+ </section>
+
+ <section id="piped">
+ <title>Piped Logs</title>
+
+ <p>Apache httpd is capable of writing error and access log
+ files through a pipe to another process, rather than directly
+ to a file. This capability dramatically increases the
+ flexibility of logging, without adding code to the main server.
+ In order to write logs to a pipe, simply replace the filename
+ with the pipe character "<code>|</code>", followed by the name
+ of the executable which should accept log entries on its
+ standard input. Apache will start the piped-log process when
+ the server starts, and will restart it if it crashes while the
+ server is running. (This last feature is why we can refer to
+ this technique as "reliable piped logging".)</p>
+
+ <p>Piped log processes are spawned by the parent Apache httpd
+ process, and inherit the userid of that process. This means
+ that piped log programs usually run as root. It is therefore
+ very important to keep the programs simple and secure.</p>
+
+ <p>Some simple examples using piped logs:</p>
+
+ <example>
+ # compressed logs<br />
+ CustomLog "|/usr/bin/gzip -c >>
+ /var/log/access_log.gz" common<br />
+ # almost-real-time name resolution<br />
+ CustomLog "|/usr/local/apache/bin/logresolve >>
+ /var/log/access_log" common
+ </example>
+
+ <p>Notice that quotes are used to enclose the entire command
+ that will be called for the pipe. Although these examples are
+ for the access log, the same technique can be used for the
+ error log.</p>
+
+ <p>One important use of piped logs is to allow log rotation
+ without having to restart the server. The Apache HTTP Server
+ includes a simple program called <a
+ href="programs/rotatelogs.html">rotatelogs</a> for this
+ purpose. For example, to rotate the logs every 24 hours, you
+ can use:</p>
+
+ <example>
+ CustomLog "|/usr/local/apache/bin/rotatelogs
+ /var/log/access_log 86400" common
+ </example>
+
+ <p>A similar, but much more flexible log rotation program
+ called <a href="http://www.cronolog.org/">cronolog</a>
+ is available at an external site.</p>
+
+ <p>As with conditional logging, piped logs are a very powerful
+ tool, but they should not be used where a simpler solution like
+ off-line post-processing is available.</p>
+ </section>
+
+ <section id="virtualhost">
+ <title>Virtual Hosts</title>
+
+ <p>When running a server with many <a href="vhosts/">virtual
+ hosts</a>, there are several options for dealing with log
+ files. First, it is possible to use logs exactly as in a
+ single-host server. Simply by placing the logging directives
+ outside the <code><VirtualHost></code> sections in the
+ main server context, it is possible to log all requests in the
+ same access log and error log. This technique does not allow
+ for easy collection of statistics on individual virtual
+ hosts.</p>
+
+ <p>If <directive module="mod_log_config">CustomLog</directive>
+ or <directive module="mod_log_config">ErrorLog</directive>
+ directives are placed inside a <directive module="core">
+ <VirtualHost></directive>
+ section, all requests or errors for that virtual host will be
+ logged only to the specified file. Any virtual host which does
+ not have logging directives will still have its requests sent
+ to the main server logs. This technique is very useful for a
+ small number of virtual hosts, but if the number of hosts is
+ very large, it can be complicated to manage. In addition, it
+ can often create problems with <a
+ href="vhosts/fd-limits.html">insufficient file
+ descriptors</a>.</p>
+
+ <p>For the access log, there is a very good compromise. By
+ adding information on the virtual host to the log format
+ string, it is possible to log all hosts to the same log, and
+ later split the log into individual files. For example,
+ consider the following directives.</p>
+
+ <example>
+ LogFormat "%v %l %u %t \"%r\" %>s %b"
+ comonvhost<br />
+ CustomLog logs/access_log comonvhost
+ </example>
+
+ <p>The <code>%v</code> is used to log the name of the virtual
+ host that is serving the request. Then a program like <a
+ href="programs/other.html">split-logfile</a> can be used to
+ post-process the access log in order to split it into one file
+ per virtual host.</p>
+ </section>
+
+ <section id="other">
+ <title>Other Log Files</title>
+
+ <related>
+ <modulelist>
+ <module>mod_cgi</module>
+ <module>mod_rewrite</module>
+ </modulelist>
+ <directivelist>
+ <directive module="core">PidFile</directive>
+ <directive module="mod_rewrite">RewriteLog</directive>
+ <directive module="mod_rewrite">RewriteLogLevel</directive>
+ <directive module="mod_cgi">ScriptLog</directive>
+ <directive module="mod_cgi">ScriptLogLength</directive>
+ <directive module="mod_cgi">ScriptBuffer</directive>
+ </directivelist>
+ </related>
+
+ <section id="pidfile">
+ <title>PID File</title>
+
+ <p>On startup, Apache httpd saves the process id of the parent
+ httpd process to the file <code>logs/httpd.pid</code>. This
+ filename can be changed with the <directive module="core">PidFile
+ </directive> directive. The
+ process-id is for use by the administrator in restarting and
+ terminating the daemon by sending signals to the parent
+ process; on Windows, use the -k command line option instead.
+ For more information see the <a href="stopping.html">Stopping
+ and Restarting</a> page.</p>
+ </section>
+
+ <section id="scriptlog">
+ <title>Script Log</title>
+
+ <p>In order to aid in debugging, the <directive module="mod_cgi">
+ ScriptLog</directive> directive
+ allows you to record the input to and output from CGI scripts.
+ This should only be used in testing - not for live servers.
+ More information is available in the <a
+ href="mod/mod_cgi.html">mod_cgi documentation</a>.</p>
+ </section>
+
+ <section id="rewritelog">
+ <title>Rewrite Log</title>
+
+ <p>When using the powerful and complex features of <a
+ href="mod/mod_rewrite.html">mod_rewrite</a>, it is almost
+ always necessary to use the <directive module="mod_rewrite">
+ RewriteLog</directive> to help
+ in debugging. This log file produces a detailed analysis of how
+ the rewriting engine transforms requests. The level of detail
+ is controlled by the <directive module="mod_rewrite">
+ RewriteLogLevel</directive> directive.</p>
+ </section>
+ </section>
+</manualpage>
+
+
+
+
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