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20 <p class="apache">Apache HTTP Server Version 2.5</p>
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33 <p>In order to effectively manage a web server, it is necessary
34 to get feedback about the activity and performance of the
35 server as well as any problems that may be occurring. The Apache HTTP Server
36 provides very comprehensive and flexible logging
37 capabilities. This document describes how to configure its
38 logging capabilities, and how to understand what the logs
41 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#overview">Overview</a></li>
42 <li><img alt="" src="./images/down.gif" /> <a href="#security">Security Warning</a></li>
43 <li><img alt="" src="./images/down.gif" /> <a href="#errorlog">Error Log</a></li>
44 <li><img alt="" src="./images/down.gif" /> <a href="#permodule">Per-module logging</a></li>
45 <li><img alt="" src="./images/down.gif" /> <a href="#accesslog">Access Log</a></li>
46 <li><img alt="" src="./images/down.gif" /> <a href="#rotation">Log Rotation</a></li>
47 <li><img alt="" src="./images/down.gif" /> <a href="#piped">Piped Logs</a></li>
48 <li><img alt="" src="./images/down.gif" /> <a href="#virtualhost">Virtual Hosts</a></li>
49 <li><img alt="" src="./images/down.gif" /> <a href="#other">Other Log Files</a></li>
50 </ul><h3>See also</h3><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
51 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
53 <h2><a name="overview" id="overview">Overview</a> <a title="Permanent link" href="#overview" class="permalink">¶</a></h2>
56 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_log_config.html">mod_log_config</a></code></li><li><code class="module"><a href="./mod/mod_log_forensic.html">mod_log_forensic</a></code></li><li><code class="module"><a href="./mod/mod_logio.html">mod_logio</a></code></li><li><code class="module"><a href="./mod/mod_cgi.html">mod_cgi</a></code></li></ul></td><td /></tr></table>
59 The Apache HTTP Server provides a variety of different mechanisms for
60 logging everything that happens on your server, from the initial
61 request, through the URL mapping process, to the final resolution of
62 the connection, including any errors that may have occurred in the
63 process. In addition to this, third-party modules may provide logging
64 capabilities, or inject entries into the existing log files, and
65 applications such as CGI programs, or PHP scripts, or other handlers,
66 may send messages to the server error log.
70 In this document we discuss the logging modules that are a standard
71 part of the http server.
74 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
76 <h2><a name="security" id="security">Security Warning</a> <a title="Permanent link" href="#security" class="permalink">¶</a></h2>
79 <p>Anyone who can write to the directory where Apache httpd is
80 writing a log file can almost certainly gain access to the uid
81 that the server is started as, which is normally root. Do
82 <em>NOT</em> give people write access to the directory the logs
83 are stored in without being aware of the consequences; see the
84 <a href="misc/security_tips.html">security tips</a> document
87 <p>In addition, log files may contain information supplied
88 directly by the client, without escaping. Therefore, it is
89 possible for malicious clients to insert control-characters in
90 the log files, so care must be taken in dealing with raw
92 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
94 <h2><a name="errorlog" id="errorlog">Error Log</a> <a title="Permanent link" href="#errorlog" class="permalink">¶</a></h2>
97 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/core.html">core</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/core.html#errorlog">ErrorLog</a></code></li><li><code class="directive"><a href="./mod/core.html#errorlogformat">ErrorLogFormat</a></code></li><li><code class="directive"><a href="./mod/core.html#loglevel">LogLevel</a></code></li></ul></td></tr></table>
99 <p>The server error log, whose name and location is set by the
100 <code class="directive"><a href="./mod/core.html#errorlog">ErrorLog</a></code> directive, is the
101 most important log file. This is the place where Apache httpd
102 will send diagnostic information and record any errors that it
103 encounters in processing requests. It is the first place to
104 look when a problem occurs with starting the server or with the
105 operation of the server, since it will often contain details of
106 what went wrong and how to fix it.</p>
108 <p>The error log is usually written to a file (typically
109 <code>error_log</code> on Unix systems and
110 <code>error.log</code> on Windows and OS/2). On Unix systems it
111 is also possible to have the server send errors to
112 <code>syslog</code> or <a href="#piped">pipe them to a
115 <p>The format of the error log is defined by the <code class="directive"><a href="./mod/core.html#errorlogformat">ErrorLogFormat</a></code> directive, with which you
116 can customize what values are logged. A default is format defined
117 if you don't specify one. A typical log message follows:</p>
119 <div class="example"><p><code>
120 [Fri Sep 09 10:42:29.902022 2011] [core:error] [pid 35708:tid 4328636416]
121 [client 72.15.99.187] File does not exist: /usr/local/apache2/htdocs/favicon.ico
124 <p>The first item in the log entry is the date and time of the
125 message. The next is the module producing the message (core, in this
126 case) and the severity level of that message. This is followed by
127 the process ID and, if appropriate, the thread ID, of the process
128 that experienced the condition. Next, we have the client address
129 that made the request. And finally is the detailed error message,
130 which in this case indicates a request for a file that did not
133 <p>A very wide variety of different messages can appear in the
134 error log. Most look similar to the example above. The error
135 log will also contain debugging output from CGI scripts. Any
136 information written to <code>stderr</code> by a CGI script will
137 be copied directly to the error log.</p>
139 <p>Putting a <code>%L</code> token in both the error log and the access
140 log will produce a log entry ID with which you can correlate the entry
141 in the error log with the entry in the access log. If
142 <code class="module"><a href="./mod/mod_unique_id.html">mod_unique_id</a></code> is loaded, its unique request ID will be
143 used as the log entry ID, too.</p>
145 <p>During testing, it is often useful to continuously monitor
146 the error log for any problems. On Unix systems, you can
147 accomplish this using:</p>
149 <div class="example"><p><code>
152 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
153 <div class="section">
154 <h2><a name="permodule" id="permodule">Per-module logging</a> <a title="Permanent link" href="#permodule" class="permalink">¶</a></h2>
157 <p>The <code class="directive"><a href="./mod/core.html#loglevel">LogLevel</a></code> directive
158 allows you to specify a log severity level on a per-module basis. In
159 this way, if you are troubleshooting a problem with just one
160 particular module, you can turn up its logging volume without also
161 getting the details of other modules that you're not interested in.
162 This is particularly useful for modules such as
163 <code class="module"><a href="./mod/mod_proxy.html">mod_proxy</a></code> or <code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code> where you
164 want to know details about what it's trying to do.</p>
166 <p>Do this by specifying the name of the module in your
167 <code class="directive">LogLevel</code> directive:</p>
169 <pre class="prettyprint lang-config">LogLevel info rewrite:trace5</pre>
172 <p>This sets the main <code class="directive">LogLevel</code> to info, but
173 turns it up to <code>trace5</code> for
174 <code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
176 <div class="note">This replaces the per-module logging directives, such as
177 <code>RewriteLog</code>, that were present in earlier versions of
179 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
180 <div class="section">
181 <h2><a name="accesslog" id="accesslog">Access Log</a> <a title="Permanent link" href="#accesslog" class="permalink">¶</a></h2>
184 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_log_config.html">mod_log_config</a></code></li><li><code class="module"><a href="./mod/mod_setenvif.html">mod_setenvif</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code></li><li><code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code></li><li><code class="directive"><a href="./mod/mod_setenvif.html#setenvif">SetEnvIf</a></code></li></ul></td></tr></table>
186 <p>The server access log records all requests processed by the
187 server. The location and content of the access log are
188 controlled by the <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code>
189 directive. The <code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code>
190 directive can be used to simplify the selection of
191 the contents of the logs. This section describes how to configure the server
192 to record information in the access log.</p>
194 <p>Of course, storing the information in the access log is only
195 the start of log management. The next step is to analyze this
196 information to produce useful statistics. Log analysis in
197 general is beyond the scope of this document, and not really
198 part of the job of the web server itself. For more information
199 about this topic, and for applications which perform log
200 analysis, check the <a href="http://dmoz.org/Computers/Software/Internet/Site_Management/Log_Analysis/">
204 <p>Various versions of Apache httpd have used other modules and
205 directives to control access logging, including
206 mod_log_referer, mod_log_agent, and the
207 <code>TransferLog</code> directive. The <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code> directive now subsumes
208 the functionality of all the older directives.</p>
210 <p>The format of the access log is highly configurable. The format
211 is specified using a format string that looks much like a C-style
212 printf(1) format string. Some examples are presented in the next
213 sections. For a complete list of the possible contents of the
214 format string, see the <code class="module"><a href="./mod/mod_log_config.html">mod_log_config</a></code> <a href="mod/mod_log_config.html#formats">format strings</a>.</p>
216 <h3><a name="common" id="common">Common Log Format</a></h3>
219 <p>A typical configuration for the access log might look as
222 <pre class="prettyprint lang-config">LogFormat "%h %l %u %t \"%r\" %>s %b" common
223 CustomLog "logs/access_log" common</pre>
226 <p>This defines the <em>nickname</em> <code>common</code> and
227 associates it with a particular log format string. The format
228 string consists of percent directives, each of which tell the
229 server to log a particular piece of information. Literal
230 characters may also be placed in the format string and will be
231 copied directly into the log output. The quote character
232 (<code>"</code>) must be escaped by placing a backslash before
233 it to prevent it from being interpreted as the end of the
234 format string. The format string may also contain the special
235 control characters "<code>\n</code>" for new-line and
236 "<code>\t</code>" for tab.</p>
238 <p>The <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code>
239 directive sets up a new log file using the defined
240 <em>nickname</em>. The filename for the access log is relative to
241 the <code class="directive"><a href="./mod/core.html#serverroot">ServerRoot</a></code> unless it
242 begins with a slash.</p>
244 <p>The above configuration will write log entries in a format
245 known as the Common Log Format (CLF). This standard format can
246 be produced by many different web servers and read by many log
247 analysis programs. The log file entries produced in CLF will
248 look something like this:</p>
250 <div class="example"><p><code>
251 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
252 /apache_pb.gif HTTP/1.0" 200 2326
255 <p>Each part of this log entry is described below.</p>
258 <dt><code>127.0.0.1</code> (<code>%h</code>)</dt>
260 <dd>This is the IP address of the client (remote host) which
261 made the request to the server. If <code class="directive"><a href="./mod/core.html#hostnamelookups">HostnameLookups</a></code> is
262 set to <code>On</code>, then the server will try to determine
263 the hostname and log it in place of the IP address. However,
264 this configuration is not recommended since it can
265 significantly slow the server. Instead, it is best to use a
266 log post-processor such as <code class="program"><a href="./programs/logresolve.html">logresolve</a></code> to determine
267 the hostnames. The IP address reported here is not
268 necessarily the address of the machine at which the user is
269 sitting. If a proxy server exists between the user and the
270 server, this address will be the address of the proxy, rather
271 than the originating machine.</dd>
273 <dt><code>-</code> (<code>%l</code>)</dt>
275 <dd>The "hyphen" in the output indicates that the requested
276 piece of information is not available. In this case, the
277 information that is not available is the RFC 1413 identity of
278 the client determined by <code>identd</code> on the clients
279 machine. This information is highly unreliable and should
280 almost never be used except on tightly controlled internal
281 networks. Apache httpd will not even attempt to determine
282 this information unless <code class="directive"><a href="./mod/mod_ident.html#identitycheck">IdentityCheck</a></code> is set
283 to <code>On</code>.</dd>
285 <dt><code>frank</code> (<code>%u</code>)</dt>
287 <dd>This is the userid of the person requesting the document
288 as determined by HTTP authentication. The same value is
289 typically provided to CGI scripts in the
290 <code>REMOTE_USER</code> environment variable. If the status
291 code for the request (see below) is 401, then this value
292 should not be trusted because the user is not yet
293 authenticated. If the document is not password protected,
294 this part will be "<code>-</code>" just like the previous
297 <dt><code>[10/Oct/2000:13:55:36 -0700]</code>
298 (<code>%t</code>)</dt>
301 The time that the request was received.
305 <code>[day/month/year:hour:minute:second zone]<br />
307 month = 3*letter<br />
310 minute = 2*digit<br />
311 second = 2*digit<br />
312 zone = (`+' | `-') 4*digit</code>
314 <p>It is possible to have the time displayed in another format
315 by specifying <code>%{format}t</code> in the log format
316 string, where <code>format</code> is either as in
317 <code>strftime(3)</code> from the C standard library,
318 or one of the supported special tokens. For details see
319 the <code class="module"><a href="./mod/mod_log_config.html">mod_log_config</a></code> <a href="mod/mod_log_config.html#formats">format strings</a>.</p>
322 <dt><code>"GET /apache_pb.gif HTTP/1.0"</code>
323 (<code>\"%r\"</code>)</dt>
325 <dd>The request line from the client is given in double
326 quotes. The request line contains a great deal of useful
327 information. First, the method used by the client is
328 <code>GET</code>. Second, the client requested the resource
329 <code>/apache_pb.gif</code>, and third, the client used the
330 protocol <code>HTTP/1.0</code>. It is also possible to log
331 one or more parts of the request line independently. For
332 example, the format string "<code>%m %U%q %H</code>" will log
333 the method, path, query-string, and protocol, resulting in
334 exactly the same output as "<code>%r</code>".</dd>
336 <dt><code>200</code> (<code>%>s</code>)</dt>
338 <dd>This is the status code that the server sends back to the
339 client. This information is very valuable, because it reveals
340 whether the request resulted in a successful response (codes
341 beginning in 2), a redirection (codes beginning in 3), an
342 error caused by the client (codes beginning in 4), or an
343 error in the server (codes beginning in 5). The full list of
344 possible status codes can be found in the <a href="http://www.w3.org/Protocols/rfc2616/rfc2616.txt">HTTP
345 specification</a> (RFC2616 section 10).</dd>
347 <dt><code>2326</code> (<code>%b</code>)</dt>
349 <dd>The last part indicates the size of the object returned
350 to the client, not including the response headers. If no
351 content was returned to the client, this value will be
352 "<code>-</code>". To log "<code>0</code>" for no content, use
353 <code>%B</code> instead.</dd>
357 <h3><a name="combined" id="combined">Combined Log Format</a></h3>
360 <p>Another commonly used format string is called the Combined
361 Log Format. It can be used as follows.</p>
363 <pre class="prettyprint lang-config">LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\"" combined
364 CustomLog "log/access_log" combined</pre>
367 <p>This format is exactly the same as the Common Log Format,
368 with the addition of two more fields. Each of the additional
369 fields uses the percent-directive
370 <code>%{<em>header</em>}i</code>, where <em>header</em> can be
371 any HTTP request header. The access log under this format will
374 <div class="example"><p><code>
375 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
376 /apache_pb.gif HTTP/1.0" 200 2326
377 "http://www.example.com/start.html" "Mozilla/4.08 [en]
381 <p>The additional fields are:</p>
384 <dt><code>"http://www.example.com/start.html"</code>
385 (<code>\"%{Referer}i\"</code>)</dt>
387 <dd>The "Referer" (sic) HTTP request header. This gives the
388 site that the client reports having been referred from. (This
389 should be the page that links to or includes
390 <code>/apache_pb.gif</code>).</dd>
392 <dt><code>"Mozilla/4.08 [en] (Win98; I ;Nav)"</code>
393 (<code>\"%{User-agent}i\"</code>)</dt>
395 <dd>The User-Agent HTTP request header. This is the
396 identifying information that the client browser reports about
401 <h3><a name="multiple" id="multiple">Multiple Access Logs</a></h3>
404 <p>Multiple access logs can be created simply by specifying
405 multiple <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code>
406 directives in the configuration
407 file. For example, the following directives will create three
408 access logs. The first contains the basic CLF information,
409 while the second and third contain referer and browser
410 information. The last two <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code> lines show how
411 to mimic the effects of the <code>ReferLog</code> and <code>AgentLog</code> directives.</p>
413 <pre class="prettyprint lang-config">LogFormat "%h %l %u %t \"%r\" %>s %b" common
414 CustomLog "logs/access_log" common
415 CustomLog "logs/referer_log" "%{Referer}i -> %U"
416 CustomLog "logs/agent_log" "%{User-agent}i"</pre>
419 <p>This example also shows that it is not necessary to define a
420 nickname with the <code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code> directive. Instead,
421 the log format can be specified directly in the <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code> directive.</p>
424 <h3><a name="conditional" id="conditional">Conditional Logs</a></h3>
427 <p>There are times when it is convenient to exclude certain
428 entries from the access logs based on characteristics of the
429 client request. This is easily accomplished with the help of <a href="env.html">environment variables</a>. First, an
430 environment variable must be set to indicate that the request
431 meets certain conditions. This is usually accomplished with
432 <code class="directive"><a href="./mod/mod_setenvif.html#setenvif">SetEnvIf</a></code>. Then the
433 <code>env=</code> clause of the <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code> directive is used to
434 include or exclude requests where the environment variable is
435 set. Some examples:</p>
437 <pre class="prettyprint lang-config"># Mark requests from the loop-back interface
438 SetEnvIf Remote_Addr "127\.0\.0\.1" dontlog
439 # Mark requests for the robots.txt file
440 SetEnvIf Request_URI "^/robots\.txt$" dontlog
442 CustomLog "logs/access_log" common env=!dontlog</pre>
445 <p>As another example, consider logging requests from
446 english-speakers to one log file, and non-english speakers to a
447 different log file.</p>
449 <pre class="prettyprint lang-config">SetEnvIf Accept-Language "en" english
450 CustomLog "logs/english_log" common env=english
451 CustomLog "logs/non_english_log" common env=!english</pre>
454 <p>In a caching scenario one would want to know about
455 the efficiency of the cache. A very simple method to
456 find this out would be:</p>
458 <pre class="prettyprint lang-config">SetEnv CACHE_MISS 1
459 LogFormat "%h %l %u %t "%r " %>s %b %{CACHE_MISS}e" common-cache
460 CustomLog "logs/access_log" common-cache</pre>
463 <p><code class="module"><a href="./mod/mod_cache.html">mod_cache</a></code> will run before
464 <code class="module"><a href="./mod/mod_env.html">mod_env</a></code> and, when successful, will deliver the
465 content without it. In that case a cache hit will log
466 <code>-</code>, while a cache miss will log <code>1</code>.</p>
468 <p>In addition to the <code>env=</code> syntax, <code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code> supports logging values
469 conditional upon the HTTP response code:</p>
471 <pre class="prettyprint lang-config">LogFormat "%400,501{User-agent}i" browserlog
472 LogFormat "%!200,304,302{Referer}i" refererlog</pre>
475 <p>In the first example, the <code>User-agent</code> will be
476 logged if the HTTP status code is 400 or 501. In other cases, a
477 literal "-" will be logged instead. Likewise, in the second
478 example, the <code>Referer</code> will be logged if the HTTP
479 status code is <strong>not</strong> 200, 204, or 302. (Note the
480 "!" before the status codes.</p>
482 <p>Although we have just shown that conditional logging is very
483 powerful and flexible, it is not the only way to control the
484 contents of the logs. Log files are more useful when they
485 contain a complete record of server activity. It is often
486 easier to simply post-process the log files to remove requests
487 that you do not want to consider.</p>
489 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
490 <div class="section">
491 <h2><a name="rotation" id="rotation">Log Rotation</a> <a title="Permanent link" href="#rotation" class="permalink">¶</a></h2>
494 <p>On even a moderately busy server, the quantity of
495 information stored in the log files is very large. The access
496 log file typically grows 1 MB or more per 10,000 requests. It
497 will consequently be necessary to periodically rotate the log
498 files by moving or deleting the existing logs. This cannot be
499 done while the server is running, because Apache httpd will continue
500 writing to the old log file as long as it holds the file open.
501 Instead, the server must be <a href="stopping.html">restarted</a> after the log files are
502 moved or deleted so that it will open new log files.</p>
504 <p>By using a <em>graceful</em> restart, the server can be
505 instructed to open new log files without losing any existing or
506 pending connections from clients. However, in order to
507 accomplish this, the server must continue to write to the old
508 log files while it finishes serving old requests. It is
509 therefore necessary to wait for some time after the restart
510 before doing any processing on the log files. A typical
511 scenario that simply rotates the logs and compresses the old
512 logs to save space is:</p>
514 <div class="example"><p><code>
515 mv access_log access_log.old<br />
516 mv error_log error_log.old<br />
517 apachectl graceful<br />
519 gzip access_log.old error_log.old
522 <p>Another way to perform log rotation is using <a href="#piped">piped logs</a> as discussed in the next
524 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
525 <div class="section">
526 <h2><a name="piped" id="piped">Piped Logs</a> <a title="Permanent link" href="#piped" class="permalink">¶</a></h2>
529 <p>Apache httpd is capable of writing error and access log
530 files through a pipe to another process, rather than directly
531 to a file. This capability dramatically increases the
532 flexibility of logging, without adding code to the main server.
533 In order to write logs to a pipe, simply replace the filename
534 with the pipe character "<code>|</code>", followed by the name
535 of the executable which should accept log entries on its
536 standard input. The server will start the piped-log process when
537 the server starts, and will restart it if it crashes while the
538 server is running. (This last feature is why we can refer to
539 this technique as "reliable piped logging".)</p>
541 <p>Piped log processes are spawned by the parent Apache httpd
542 process, and inherit the userid of that process. This means
543 that piped log programs usually run as root. It is therefore
544 very important to keep the programs simple and secure.</p>
546 <p>One important use of piped logs is to allow log rotation
547 without having to restart the server. The Apache HTTP Server
548 includes a simple program called <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code>
549 for this purpose. For example, to rotate the logs every 24 hours, you
552 <pre class="prettyprint lang-config">CustomLog "|/usr/local/apache/bin/rotatelogs /var/log/access_log 86400" common</pre>
555 <p>Notice that quotes are used to enclose the entire command
556 that will be called for the pipe. Although these examples are
557 for the access log, the same technique can be used for the
560 <p>As with conditional logging, piped logs are a very powerful
561 tool, but they should not be used where a simpler solution like
562 off-line post-processing is available.</p>
564 <p>By default the piped log process is spawned without invoking
565 a shell. Use "<code>|$</code>" instead of "<code>|</code>"
566 to spawn using a shell (usually with <code>/bin/sh -c</code>):</p>
568 <pre class="prettyprint lang-config"># Invoke "rotatelogs" using a shell
569 CustomLog "|$/usr/local/apache/bin/rotatelogs /var/log/access_log 86400" common</pre>
572 <p>This was the default behaviour for Apache 2.2.
573 Depending on the shell specifics this might lead to
574 an additional shell process for the lifetime of the logging
575 pipe program and signal handling problems during restart.
576 For compatibility reasons with Apache 2.2 the notation
577 "<code>||</code>" is also supported and equivalent to using
578 "<code>|</code>".</p>
580 <div class="note"><h3>Windows note</h3>
581 <p>Note that on Windows, you may run into problems when running many piped
582 logger processes, especially when HTTPD is running as a service. This is
583 caused by running out of desktop heap space. The desktop heap space given
584 to each service is specified by the third argument to the
585 <code>SharedSection</code> parameter in the
586 HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\SessionManager\SubSystems\Windows
587 registry value. <strong>Change this value with care</strong>; the normal
588 caveats for changing the Windows registry apply, but you might also exhaust
589 the desktop heap pool if the number is adjusted too high.</p>
591 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
592 <div class="section">
593 <h2><a name="virtualhost" id="virtualhost">Virtual Hosts</a> <a title="Permanent link" href="#virtualhost" class="permalink">¶</a></h2>
596 <p>When running a server with many <a href="vhosts/">virtual
597 hosts</a>, there are several options for dealing with log
598 files. First, it is possible to use logs exactly as in a
599 single-host server. Simply by placing the logging directives
600 outside the <code class="directive"><a href="./mod/core.html#virtualhost"><VirtualHost></a></code> sections in the
601 main server context, it is possible to log all requests in the
602 same access log and error log. This technique does not allow
603 for easy collection of statistics on individual virtual
606 <p>If <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code>
607 or <code class="directive"><a href="./mod/core.html#errorlog">ErrorLog</a></code>
608 directives are placed inside a
609 <code class="directive"><a href="./mod/core.html#virtualhost"><VirtualHost></a></code>
610 section, all requests or errors for that virtual host will be
611 logged only to the specified file. Any virtual host which does
612 not have logging directives will still have its requests sent
613 to the main server logs. This technique is very useful for a
614 small number of virtual hosts, but if the number of hosts is
615 very large, it can be complicated to manage. In addition, it
616 can often create problems with <a href="vhosts/fd-limits.html">insufficient file
619 <p>For the access log, there is a very good compromise. By
620 adding information on the virtual host to the log format
621 string, it is possible to log all hosts to the same log, and
622 later split the log into individual files. For example,
623 consider the following directives.</p>
625 <pre class="prettyprint lang-config">LogFormat "%v %l %u %t \"%r\" %>s %b" comonvhost
626 CustomLog "logs/access_log" comonvhost</pre>
629 <p>The <code>%v</code> is used to log the name of the virtual
630 host that is serving the request. Then a program like <a href="programs/split-logfile.html">split-logfile</a> can be used to
631 post-process the access log in order to split it into one file
632 per virtual host.</p>
633 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
634 <div class="section">
635 <h2><a name="other" id="other">Other Log Files</a> <a title="Permanent link" href="#other" class="permalink">¶</a></h2>
638 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_logio.html">mod_logio</a></code></li><li><code class="module"><a href="./mod/mod_log_config.html">mod_log_config</a></code></li><li><code class="module"><a href="./mod/mod_log_forensic.html">mod_log_forensic</a></code></li><li><code class="module"><a href="./mod/mod_cgi.html">mod_cgi</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code></li><li><code class="directive"><a href="./mod/mod_log_config.html#bufferedlogs">BufferedLogs</a></code></li><li><code class="directive"><a href="./mod/mod_log_forensic.html#forensiclog">ForensicLog</a></code></li><li><code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code></li><li><code class="directive"><a href="./mod/mod_cgi.html#scriptlog">ScriptLog</a></code></li><li><code class="directive"><a href="./mod/mod_cgi.html#scriptlogbuffer">ScriptLogBuffer</a></code></li><li><code class="directive"><a href="./mod/mod_cgi.html#scriptloglength">ScriptLogLength</a></code></li></ul></td></tr></table>
640 <h3>Logging actual bytes sent and received</h3>
643 <p><code class="module"><a href="./mod/mod_logio.html">mod_logio</a></code> adds in two additional
644 <code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code> fields
645 (%I and %O) that log the actual number of bytes received and sent
649 <h3>Forensic Logging</h3>
652 <p><code class="module"><a href="./mod/mod_log_forensic.html">mod_log_forensic</a></code> provides for forensic logging of
653 client requests. Logging is done before and after processing a
654 request, so the forensic log contains two log lines for each
655 request. The forensic logger is very strict with no customizations.
656 It can be an invaluable debugging and security tool.</p>
659 <h3><a name="pidfile" id="pidfile">PID File</a></h3>
662 <p>On startup, Apache httpd saves the process id of the parent
663 httpd process to the file <code>logs/httpd.pid</code>. This
664 filename can be changed with the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> directive. The
665 process-id is for use by the administrator in restarting and
666 terminating the daemon by sending signals to the parent
667 process; on Windows, use the -k command line option instead.
668 For more information see the <a href="stopping.html">Stopping
669 and Restarting</a> page.</p>
672 <h3><a name="scriptlog" id="scriptlog">Script Log</a></h3>
675 <p>In order to aid in debugging, the
676 <code class="directive"><a href="./mod/mod_cgi.html#scriptlog">ScriptLog</a></code> directive
677 allows you to record the input to and output from CGI scripts.
678 This should only be used in testing - not for live servers.
679 More information is available in the <a href="mod/mod_cgi.html">mod_cgi</a> documentation.</p>
683 <div class="bottomlang">
684 <p><span>Available Languages: </span><a href="./en/logs.html" title="English"> en </a> |
685 <a href="./fr/logs.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
686 <a href="./ja/logs.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
687 <a href="./ko/logs.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
688 <a href="./tr/logs.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
689 </div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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