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15 <p class="apache">Apache HTTP Server Version 2.3</p>
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28 <p>In order to effectively manage a web server, it is necessary
29 to get feedback about the activity and performance of the
30 server as well as any problems that may be occurring. The Apache HTTP Server
31 provides very comprehensive and flexible logging
32 capabilities. This document describes how to configure its
33 logging capabilities, and how to understand what the logs
36 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#overview">Overview</a></li>
37 <li><img alt="" src="./images/down.gif" /> <a href="#security">Security Warning</a></li>
38 <li><img alt="" src="./images/down.gif" /> <a href="#errorlog">Error Log</a></li>
39 <li><img alt="" src="./images/down.gif" /> <a href="#permodule">Per-module logging</a></li>
40 <li><img alt="" src="./images/down.gif" /> <a href="#accesslog">Access Log</a></li>
41 <li><img alt="" src="./images/down.gif" /> <a href="#rotation">Log Rotation</a></li>
42 <li><img alt="" src="./images/down.gif" /> <a href="#piped">Piped Logs</a></li>
43 <li><img alt="" src="./images/down.gif" /> <a href="#virtualhost">Virtual Hosts</a></li>
44 <li><img alt="" src="./images/down.gif" /> <a href="#other">Other Log Files</a></li>
46 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
48 <h2><a name="overview" id="overview">Overview</a></h2>
51 <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>
54 The Apache HTTP Server provides a variety of different mechanisms for
55 logging everything that happens on your server, from the initial
56 request, through the URL mapping process, to the final resolution of
57 the connection, including any errors that may have occurred in the
58 process. In addition to this, third-party modules may provide logging
59 capabilities, or inject entries into the existing log files, and
60 applications such as CGI programs, or PHP scripts, or other handlers,
61 may send messages to the server error log.
65 In this document we discuss the logging modules that are a standard
66 part of the http server.
69 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
71 <h2><a name="security" id="security">Security Warning</a></h2>
74 <p>Anyone who can write to the directory where Apache httpd is
75 writing a log file can almost certainly gain access to the uid
76 that the server is started as, which is normally root. Do
77 <em>NOT</em> give people write access to the directory the logs
78 are stored in without being aware of the consequences; see the
79 <a href="misc/security_tips.html">security tips</a> document
82 <p>In addition, log files may contain information supplied
83 directly by the client, without escaping. Therefore, it is
84 possible for malicious clients to insert control-characters in
85 the log files, so care must be taken in dealing with raw
87 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
89 <h2><a name="errorlog" id="errorlog">Error Log</a></h2>
92 <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>
94 <p>The server error log, whose name and location is set by the
95 <code class="directive"><a href="./mod/core.html#errorlog">ErrorLog</a></code> directive, is the
96 most important log file. This is the place where Apache httpd
97 will send diagnostic information and record any errors that it
98 encounters in processing requests. It is the first place to
99 look when a problem occurs with starting the server or with the
100 operation of the server, since it will often contain details of
101 what went wrong and how to fix it.</p>
103 <p>The error log is usually written to a file (typically
104 <code>error_log</code> on Unix systems and
105 <code>error.log</code> on Windows and OS/2). On Unix systems it
106 is also possible to have the server send errors to
107 <code>syslog</code> or <a href="#piped">pipe them to a
110 <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
111 can customize what values are logged. A default is format defined
112 if you don't specify one. A typical log message follows:</p>
114 <div class="example"><p><code>
115 [Fri Sep 09 10:42:29.902022 2011] [core:error] [pid 35708:tid 4328636416]
116 [client 72.15.99.187] File does not exist: /usr/local/apache2/htdocs/favicon.ico
119 <p>The first item in the log entry is the date and time of the
120 message. The next is the module producing the message (core, in this
121 case) and the severity level of that message. This is followed by
122 the process ID and, if appropriate, the thread ID, of the process
123 that experienced the condition. Next, we have the client address
124 that made the request. And finally is the detailed error message,
125 which in this case indicates a request for a file that did not
128 <p>A very wide variety of different messages can appear in the
129 error log. Most look similar to the example above. The error
130 log will also contain debugging output from CGI scripts. Any
131 information written to <code>stderr</code> by a CGI script will
132 be copied directly to the error log.</p>
134 <p>Putting a <code>%L</code> token in both the error log and the access
135 log will produce a log entry ID with which you can correlate the entry
136 in the error log with the entry in the access log. If
137 <code class="module"><a href="./mod/mod_unique_id.html">mod_unique_id</a></code> is loaded, its unique request ID will be
138 used as the log entry ID, too.</p>
140 <p>During testing, it is often useful to continuously monitor
141 the error log for any problems. On Unix systems, you can
142 accomplish this using:</p>
144 <div class="example"><p><code>
147 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
148 <div class="section">
149 <h2><a name="permodule" id="permodule">Per-module logging</a></h2>
152 <p>The <code class="directive"><a href="./mod/core.html#loglevel">LogLevel</a></code> directive
153 allows you to specify a log severity level on a per-module basis. In
154 this way, if you are troubleshooting a problem with just one
155 particular module, you can turn up its logging volume without also
156 getting the details of other modules that you're not interested in.
157 This is particularly useful for modules such as
158 <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
159 want to know details about what it's trying to do.</p>
161 <p>Do this by specifying the name of the module in your
162 <code class="directive">LogLevel</code> directive:</p>
164 <div class="example"><p><code>
165 LogLevel info rewrite:trace5
168 <p>This sets the main <code class="directive">LogLevel</code> to info, but
169 turns it up to <code>trace5</code> for
170 <code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
172 <div class="note">This replaces the per-module logging directives, such as
173 <code>RewriteLog</code>, that were present in earlier versions of
175 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
176 <div class="section">
177 <h2><a name="accesslog" id="accesslog">Access Log</a></h2>
180 <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>
182 <p>The server access log records all requests processed by the
183 server. The location and content of the access log are
184 controlled by the <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code>
185 directive. The <code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code>
186 directive can be used to simplify the selection of
187 the contents of the logs. This section describes how to configure the server
188 to record information in the access log.</p>
190 <p>Of course, storing the information in the access log is only
191 the start of log management. The next step is to analyze this
192 information to produce useful statistics. Log analysis in
193 general is beyond the scope of this document, and not really
194 part of the job of the web server itself. For more information
195 about this topic, and for applications which perform log
196 analysis, check the <a href="http://dmoz.org/Computers/Software/Internet/Site_Management/Log_analysis/">
197 Open Directory</a> or <a href="http://dir.yahoo.com/Computers_and_Internet/Software/Internet/World_Wide_Web/Servers/Log_Analysis_Tools/">
200 <p>Various versions of Apache httpd have used other modules and
201 directives to control access logging, including
202 mod_log_referer, mod_log_agent, and the
203 <code>TransferLog</code> directive. The <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code> directive now subsumes
204 the functionality of all the older directives.</p>
206 <p>The format of the access log is highly configurable. The format
207 is specified using a format string that looks much like a C-style
208 printf(1) format string. Some examples are presented in the next
209 sections. For a complete list of the possible contents of the
210 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>
212 <h3><a name="common" id="common">Common Log Format</a></h3>
215 <p>A typical configuration for the access log might look as
218 <div class="example"><p><code>
219 LogFormat "%h %l %u %t \"%r\" %>s %b" common<br />
220 CustomLog logs/access_log common
223 <p>This defines the <em>nickname</em> <code>common</code> and
224 associates it with a particular log format string. The format
225 string consists of percent directives, each of which tell the
226 server to log a particular piece of information. Literal
227 characters may also be placed in the format string and will be
228 copied directly into the log output. The quote character
229 (<code>"</code>) must be escaped by placing a backslash before
230 it to prevent it from being interpreted as the end of the
231 format string. The format string may also contain the special
232 control characters "<code>\n</code>" for new-line and
233 "<code>\t</code>" for tab.</p>
235 <p>The <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code>
236 directive sets up a new log file using the defined
237 <em>nickname</em>. The filename for the access log is relative to
238 the <code class="directive"><a href="./mod/core.html#serverroot">ServerRoot</a></code> unless it
239 begins with a slash.</p>
241 <p>The above configuration will write log entries in a format
242 known as the Common Log Format (CLF). This standard format can
243 be produced by many different web servers and read by many log
244 analysis programs. The log file entries produced in CLF will
245 look something like this:</p>
247 <div class="example"><p><code>
248 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
249 /apache_pb.gif HTTP/1.0" 200 2326
252 <p>Each part of this log entry is described below.</p>
255 <dt><code>127.0.0.1</code> (<code>%h</code>)</dt>
257 <dd>This is the IP address of the client (remote host) which
258 made the request to the server. If <code class="directive"><a href="./mod/core.html#hostnamelookups">HostnameLookups</a></code> is
259 set to <code>On</code>, then the server will try to determine
260 the hostname and log it in place of the IP address. However,
261 this configuration is not recommended since it can
262 significantly slow the server. Instead, it is best to use a
263 log post-processor such as <code class="program"><a href="./programs/logresolve.html">logresolve</a></code> to determine
264 the hostnames. The IP address reported here is not
265 necessarily the address of the machine at which the user is
266 sitting. If a proxy server exists between the user and the
267 server, this address will be the address of the proxy, rather
268 than the originating machine.</dd>
270 <dt><code>-</code> (<code>%l</code>)</dt>
272 <dd>The "hyphen" in the output indicates that the requested
273 piece of information is not available. In this case, the
274 information that is not available is the RFC 1413 identity of
275 the client determined by <code>identd</code> on the clients
276 machine. This information is highly unreliable and should
277 almost never be used except on tightly controlled internal
278 networks. Apache httpd will not even attempt to determine
279 this information unless <code class="directive"><a href="./mod/core.html#identitycheck">IdentityCheck</a></code> is set
280 to <code>On</code>.</dd>
282 <dt><code>frank</code> (<code>%u</code>)</dt>
284 <dd>This is the userid of the person requesting the document
285 as determined by HTTP authentication. The same value is
286 typically provided to CGI scripts in the
287 <code>REMOTE_USER</code> environment variable. If the status
288 code for the request (see below) is 401, then this value
289 should not be trusted because the user is not yet
290 authenticated. If the document is not password protected,
291 this part will be "<code>-</code>" just like the previous
294 <dt><code>[10/Oct/2000:13:55:36 -0700]</code>
295 (<code>%t</code>)</dt>
298 The time that the request was received.
302 <code>[day/month/year:hour:minute:second zone]<br />
304 month = 3*letter<br />
307 minute = 2*digit<br />
308 second = 2*digit<br />
309 zone = (`+' | `-') 4*digit</code>
311 <p>It is possible to have the time displayed in another format
312 by specifying <code>%{format}t</code> in the log format
313 string, where <code>format</code> is either as in
314 <code>strftime(3)</code> from the C standard library,
315 or one of the supported special tokens. For details see
316 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>
319 <dt><code>"GET /apache_pb.gif HTTP/1.0"</code>
320 (<code>\"%r\"</code>)</dt>
322 <dd>The request line from the client is given in double
323 quotes. The request line contains a great deal of useful
324 information. First, the method used by the client is
325 <code>GET</code>. Second, the client requested the resource
326 <code>/apache_pb.gif</code>, and third, the client used the
327 protocol <code>HTTP/1.0</code>. It is also possible to log
328 one or more parts of the request line independently. For
329 example, the format string "<code>%m %U%q %H</code>" will log
330 the method, path, query-string, and protocol, resulting in
331 exactly the same output as "<code>%r</code>".</dd>
333 <dt><code>200</code> (<code>%>s</code>)</dt>
335 <dd>This is the status code that the server sends back to the
336 client. This information is very valuable, because it reveals
337 whether the request resulted in a successful response (codes
338 beginning in 2), a redirection (codes beginning in 3), an
339 error caused by the client (codes beginning in 4), or an
340 error in the server (codes beginning in 5). The full list of
341 possible status codes can be found in the <a href="http://www.w3.org/Protocols/rfc2616/rfc2616.txt">HTTP
342 specification</a> (RFC2616 section 10).</dd>
344 <dt><code>2326</code> (<code>%b</code>)</dt>
346 <dd>The last part indicates the size of the object returned
347 to the client, not including the response headers. If no
348 content was returned to the client, this value will be
349 "<code>-</code>". To log "<code>0</code>" for no content, use
350 <code>%B</code> instead.</dd>
354 <h3><a name="combined" id="combined">Combined Log Format</a></h3>
357 <p>Another commonly used format string is called the Combined
358 Log Format. It can be used as follows.</p>
360 <div class="example"><p><code>
361 LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\"
362 \"%{User-agent}i\"" combined<br />
363 CustomLog log/access_log combined
366 <p>This format is exactly the same as the Common Log Format,
367 with the addition of two more fields. Each of the additional
368 fields uses the percent-directive
369 <code>%{<em>header</em>}i</code>, where <em>header</em> can be
370 any HTTP request header. The access log under this format will
373 <div class="example"><p><code>
374 127.0.0.1 - frank [10/Oct/2000:13:55:36 -0700] "GET
375 /apache_pb.gif HTTP/1.0" 200 2326
376 "http://www.example.com/start.html" "Mozilla/4.08 [en]
380 <p>The additional fields are:</p>
383 <dt><code>"http://www.example.com/start.html"</code>
384 (<code>\"%{Referer}i\"</code>)</dt>
386 <dd>The "Referer" (sic) HTTP request header. This gives the
387 site that the client reports having been referred from. (This
388 should be the page that links to or includes
389 <code>/apache_pb.gif</code>).</dd>
391 <dt><code>"Mozilla/4.08 [en] (Win98; I ;Nav)"</code>
392 (<code>\"%{User-agent}i\"</code>)</dt>
394 <dd>The User-Agent HTTP request header. This is the
395 identifying information that the client browser reports about
400 <h3><a name="multiple" id="multiple">Multiple Access Logs</a></h3>
403 <p>Multiple access logs can be created simply by specifying
404 multiple <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code>
405 directives in the configuration
406 file. For example, the following directives will create three
407 access logs. The first contains the basic CLF information,
408 while the second and third contain referer and browser
409 information. The last two <code class="directive"><a href="./mod/mod_log_config.html#customlog">CustomLog</a></code> lines show how
410 to mimic the effects of the <code>ReferLog</code> and <code>AgentLog</code> directives.</p>
412 <div class="example"><p><code>
413 LogFormat "%h %l %u %t \"%r\" %>s %b" common<br />
414 CustomLog logs/access_log common<br />
415 CustomLog logs/referer_log "%{Referer}i -> %U"<br />
416 CustomLog logs/agent_log "%{User-agent}i"
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 <div class="example"><p><code>
438 # Mark requests from the loop-back interface<br />
439 SetEnvIf Remote_Addr "127\.0\.0\.1" dontlog<br />
440 # Mark requests for the robots.txt file<br />
441 SetEnvIf Request_URI "^/robots\.txt$" dontlog<br />
442 # Log what remains<br />
443 CustomLog logs/access_log common env=!dontlog
446 <p>As another example, consider logging requests from
447 english-speakers to one log file, and non-english speakers to a
448 different log file.</p>
450 <div class="example"><p><code>
451 SetEnvIf Accept-Language "en" english<br />
452 CustomLog logs/english_log common env=english<br />
453 CustomLog logs/non_english_log common env=!english
456 <p>In a caching scenario one would want to know about
457 the efficiency of the cache. A very simple method to
458 find this out would be:</p>
460 <div class="example"><p><code>
461 SetEnv CACHE_MISS 1<br />
462 LogFormat "%h %l %u %t "%r " %>s %b %{CACHE_MISS}e" common-cache<br />
463 CustomLog logs/access_log common-cache
466 <p><code class="module"><a href="./mod/mod_cache.html">mod_cache</a></code> will run before
467 <code class="module"><a href="./mod/mod_env.html">mod_env</a></code> and when successfull will deliver the
468 content without it. In that case a cache hit will log
469 <code>-</code>, while a cache miss will log <code>1</code>.</p>
471 <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
472 conditional upon the HTTP response code:</p>
474 <div class="example"><p><code>
475 LogFormat "%400,501{User-agent}i" browserlog<br />
476 LogFormat "%!200,304,302{Referer}i" refererlog
479 <p>In the first example, the <code>User-agent</code> will be
480 logged if the HTTP status code is 400 or 501. In other cases, a
481 literal "-" will be logged instead. Likewise, in the second
482 example, the <code>Referer</code> will be logged if the HTTP
483 status code is <strong>not</strong> 200, 204, or 302. (Note the
484 "!" before the status codes.</p>
486 <p>Although we have just shown that conditional logging is very
487 powerful and flexible, it is not the only way to control the
488 contents of the logs. Log files are more useful when they
489 contain a complete record of server activity. It is often
490 easier to simply post-process the log files to remove requests
491 that you do not want to consider.</p>
493 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
494 <div class="section">
495 <h2><a name="rotation" id="rotation">Log Rotation</a></h2>
498 <p>On even a moderately busy server, the quantity of
499 information stored in the log files is very large. The access
500 log file typically grows 1 MB or more per 10,000 requests. It
501 will consequently be necessary to periodically rotate the log
502 files by moving or deleting the existing logs. This cannot be
503 done while the server is running, because Apache httpd will continue
504 writing to the old log file as long as it holds the file open.
505 Instead, the server must be <a href="stopping.html">restarted</a> after the log files are
506 moved or deleted so that it will open new log files.</p>
508 <p>By using a <em>graceful</em> restart, the server can be
509 instructed to open new log files without losing any existing or
510 pending connections from clients. However, in order to
511 accomplish this, the server must continue to write to the old
512 log files while it finishes serving old requests. It is
513 therefore necessary to wait for some time after the restart
514 before doing any processing on the log files. A typical
515 scenario that simply rotates the logs and compresses the old
516 logs to save space is:</p>
518 <div class="example"><p><code>
519 mv access_log access_log.old<br />
520 mv error_log error_log.old<br />
521 apachectl graceful<br />
523 gzip access_log.old error_log.old
526 <p>Another way to perform log rotation is using <a href="#piped">piped logs</a> as discussed in the next
528 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
529 <div class="section">
530 <h2><a name="piped" id="piped">Piped Logs</a></h2>
533 <p>Apache httpd is capable of writing error and access log
534 files through a pipe to another process, rather than directly
535 to a file. This capability dramatically increases the
536 flexibility of logging, without adding code to the main server.
537 In order to write logs to a pipe, simply replace the filename
538 with the pipe character "<code>|</code>", followed by the name
539 of the executable which should accept log entries on its
540 standard input. The server will start the piped-log process when
541 the server starts, and will restart it if it crashes while the
542 server is running. (This last feature is why we can refer to
543 this technique as "reliable piped logging".)</p>
545 <p>Piped log processes are spawned by the parent Apache httpd
546 process, and inherit the userid of that process. This means
547 that piped log programs usually run as root. It is therefore
548 very important to keep the programs simple and secure.</p>
550 <p>One important use of piped logs is to allow log rotation
551 without having to restart the server. The Apache HTTP Server
552 includes a simple program called <code class="program"><a href="./programs/rotatelogs.html">rotatelogs</a></code>
553 for this purpose. For example, to rotate the logs every 24 hours, you
556 <div class="example"><p><code>
557 CustomLog "|/usr/local/apache/bin/rotatelogs
558 /var/log/access_log 86400" common
561 <p>Notice that quotes are used to enclose the entire command
562 that will be called for the pipe. Although these examples are
563 for the access log, the same technique can be used for the
566 <p>A similar but much more flexible log rotation program
567 called <a href="http://www.cronolog.org/">cronolog</a>
568 is available at an external site.</p>
570 <p>As with conditional logging, piped logs are a very powerful
571 tool, but they should not be used where a simpler solution like
572 off-line post-processing is available.</p>
574 <p>By default the piped log process is spawned without invoking
575 a shell. Use "<code>|$</code>" instead of "<code>|</code>"
576 to spawn using a shell (usually with <code>/bin/sh -c</code>):</p>
578 <div class="example"><p><code>
579 # Invoke "rotatelogs" using a shell<br />
580 CustomLog "|$/usr/local/apache/bin/rotatelogs
581 /var/log/access_log 86400" common
584 <p>This was the default behaviour for Apache 2.2.
585 Depending on the shell specifics this might lead to
586 an additional shell process for the lifetime of the logging
587 pipe program and signal handling problems during restart.
588 For compatibility reasons with Apache 2.2 the notation
589 "<code>||</code>" is also supported and equivalent to using
590 "<code>|</code>".</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></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 <div class="example"><p><code>
626 LogFormat "%v %l %u %t \"%r\" %>s %b"
628 CustomLog logs/access_log comonvhost
631 <p>The <code>%v</code> is used to log the name of the virtual
632 host that is serving the request. Then a program like <a href="programs/other.html">split-logfile</a> can be used to
633 post-process the access log in order to split it into one file
634 per virtual host.</p>
635 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
636 <div class="section">
637 <h2><a name="other" id="other">Other Log Files</a></h2>
640 <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>
642 <h3>Logging actual bytes sent and received</h3>
645 <p><code class="module"><a href="./mod/mod_logio.html">mod_logio</a></code> adds in two additional
646 <code class="directive"><a href="./mod/mod_log_config.html#logformat">LogFormat</a></code> fields
647 (%I and %O) that log the actual number of bytes received and sent
651 <h3>Forensic Logging</h3>
654 <p><code class="module"><a href="./mod/mod_log_forensic.html">mod_log_forensic</a></code> provides for forensic logging of
655 client requests. Logging is done before and after processing a
656 request, so the forensic log contains two log lines for each
657 request. The forensic logger is very strict with no customizations.
658 It can be an invaluable debugging and security tool.</p>
661 <h3><a name="pidfile" id="pidfile">PID File</a></h3>
664 <p>On startup, Apache httpd saves the process id of the parent
665 httpd process to the file <code>logs/httpd.pid</code>. This
666 filename can be changed with the <code class="directive"><a href="./mod/mpm_common.html#pidfile">PidFile</a></code> directive. The
667 process-id is for use by the administrator in restarting and
668 terminating the daemon by sending signals to the parent
669 process; on Windows, use the -k command line option instead.
670 For more information see the <a href="stopping.html">Stopping
671 and Restarting</a> page.</p>
674 <h3><a name="scriptlog" id="scriptlog">Script Log</a></h3>
677 <p>In order to aid in debugging, the
678 <code class="directive"><a href="./mod/mod_cgi.html#scriptlog">ScriptLog</a></code> directive
679 allows you to record the input to and output from CGI scripts.
680 This should only be used in testing - not for live servers.
681 More information is available in the <a href="mod/mod_cgi.html">mod_cgi</a> documentation.</p>
685 <div class="bottomlang">
686 <p><span>Available Languages: </span><a href="./en/logs.html" title="English"> en </a> |
687 <a href="./fr/logs.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
688 <a href="./ja/logs.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
689 <a href="./ko/logs.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
690 <a href="./tr/logs.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
691 </div><div id="footer">
692 <p class="apache">Copyright 2011 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
693 <p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p></div>
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