asg13.htm

apache技术手册

<FONT SIZE=5 COLOR="#FF0000"><B>The </B><B>mod_log_config</B><B> Module</B></FONT></CENTER></H3>

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<P>The mod_log_config module is not built into Apache by default. In order to use any of its directives, you need to reconfigure Apache to include this module and comment out the standard mod_log_common from the list, and recompile the server.

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<P>This module allows the logging of server requests using a user-specified format. It is considered experimental; however, in my experience it works great. As previously mentioned, this will be the default logging module for Apache 1.2 and beyond. mod_log_config implements the TransferLog directive (same as the common log module) and an additional directive, LogFormat. Because both the mod_log_common and mod_log_config implement the TransferLog directive, I would consider it wise to only compile one or the other into Apache. Otherwise, your results may be unexpected.

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<P>The log format is flexible; you can specify it with the LogFormat directive. The argument to the LogFormat is a string, which can include literal characters copied into the log files and percent sign (%) directives like the following:

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%h

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Remote host.

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%l

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<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Remote logname (from identd, if supplied).

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%u

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<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

Remote user (from auth; may be bogus if return status (%s) is 401).

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<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

%t

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Time of the request using the time format used by the Common Log Format.

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%r

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<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

First line of request.

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%s

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Status. For requests that got internally redirected, this is the status of the original request; %&gt;s for the last.

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%b

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Bytes sent.

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%{<I>Header</I>}i

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The contents of <I>Header</I>: header line(s) in the request sent to the client.

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%{<I>Header</I>}o

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<TD VALIGN=top  BGCOLOR=#80FFFF ><FONT COLOR=#000080>

The contents of <I>Header</I>: header line(s) in the reply.</FONT>

</TABLE><P>One of the better features this module produces is conditional logging. Conditional logging can include the information depending on a HTTP response code. You can specify the conditions for inclusion of a particular field by specifying the HTTP status code between the % and letter code for the field. You may specify more than one HTTP status code by separating them with a comma (,). In addition, you can specify to log any of the environment variables, such as the User-Agent or the Referer, received by the server by specifying its name between braces ({<I>variable</I>}). Here are a few examples:

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<FONT COLOR="#000080">%400,500{User-agent}i</FONT></PRE>

<P>The preceding example logs User-agent headers only on Bad Request or Not Implemented errors.

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<P>You can also specify that a field be logged. If a certain HTTP code is not returned by adding an exclamation symbol (!) in front of the code, you want to check for

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<FONT COLOR="#000080">%!200,304,302{Referer}i</FONT></PRE>

<P>This example logs the Referer header information on all requests not returning a normal return code. When a condition is not met, the field is null. As with the common log format, a null field is indicated by a dash (-) character.

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<P>Virtual hosts can have their own LogFormat and/or TransferLog. If no LogFormat is specified, it is inherited from the main server process. If the virtual hosts don't have their own TransferLog, entries are written to the main server's log. To differentiate between virtual hosts writing to a common log file, you can prepend a label to the log format string:

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<FONT COLOR="#000080">&lt;VirtualHost xxx.com&gt;

LogFormat &quot;xxx <I>formatstring</I>&quot;

...

&lt;/VirtualHost&gt;

&lt;VirtualHost yyy.com&gt;

LogFormat &quot;yyy formatstring&quot;

...

<A NAME="I3"></A><A NAME="I4"></A><A NAME="I5"></A><A NAME="I6"></A><A NAME="I7"></A><A NAME="I8"></A>&lt;/VirtualHost&gt;</FONT></PRE>

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<FONT SIZE=4 COLOR="#FF0000"><B>LogFormat</B></FONT></CENTER></H4>

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<P>The format of the log is specified as a string of characters:

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Syntax:

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LogFormat <I>string</I>

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Default:

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LogFormat &quot;%h %l %u %t \&quot;%r\&quot; %s %b&quot; (same as the CLF)</FONT>

</TABLE><P>You are free to specify the fields in any order you want. But for compatibility with the CLF, you may want to observe the order of the standard elements (as in the CLF specification):

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<FONT COLOR="#000080"><I>host ident authuser date request status bytes</I></FONT></PRE>

<P>I like the following format, which provides a lot of useful information:

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<FONT COLOR="#000080">&quot;%h %l %u %t \&quot;%r\&quot; %s %b %{Cookie}i %{User-agent}i %400,401,403,404{Referer}i&quot;</FONT></PRE>

<P>In order to enable the Cookie header, we compiled in the mod_cookies. We also disabled the CookieLog by pointing it to /dev/null. There is no need to have a separate Cookie log when you can include this information in the main log.

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<P><A NAME="I9"></A><A NAME="I10"></A><A NAME="I11"></A><A NAME="I12"></A><A NAME="I13"></A><A NAME="I14"></A>To enable logging, you need to use the TransferLog directive:

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Syntax:

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TransferLog [<I>filename</I>] | [|<I>program</I>]

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Default:

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TransferLog logs/transfer_log</FONT>

</TABLE><P><I>filename</I> is the name of a file relative of ServerRoot.

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<P>|<I>program</I> is the pipe symbol (|) followed by a path to a program capable of receiving the log information on stdin.

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<P>As with any program started by the server, the program is run with the UID and GID of the user that started the httpd daemon. If the user starting the program is root, be sure that the User directive demotes the server privileges to those of an unprivileged user such as nobody. Also, make sure the program is secure.

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<FONT SIZE=5 COLOR="#FF0000"><B>The Error Log</B></FONT></CENTER></H3>

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<P>In addition to the transfer (or access) logs, you'll want to keep a close watch on the error log. The location of the error is defined with the ErrorLog directive, which defaults to logs/error_log. The format of this log is rather simple, it lists the date and time of the error, along with a message. Usually you'll want to look for messages that report a failed access because that could mean that there is a broken link somewhere.

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<P>If you are debugging CGI, you will want to be aware that information sent by a CGI to the standard error stream (stderr) is logged to the error log file, which makes the contents of this file invaluable while debugging your CGI.

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<P>Apache 1.2 introduces the ScriptLog directive, which will send all stderr messages to the log file specified with it. However, at the time of this writing, I could not obtain additional information to fully document this directive. Please check the Apache site for the latest information on Apache 1.2.

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<P>If you want to keep a watch on any of your log files as the entries are added, you can use the UNIX tail command. The tail command delivers the last part of a file. tail has an option that allows it to remain listening in for new text to be appended to a file. You can specify this functionality by specifying the -f switch:

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<FONT COLOR="#000080">tail -f /usr/local/etc/httpd/logs/error_log</FONT></PRE>

<P>This will display any error entries as they happen. You can also use this command on the transfer log and have up-to-the-second information regarding any activity on your Web server. (For an even better activity report, take a look at <A HREF="asg11.htm" tppabs="http://docs.rinet.ru:8080/Apachu/asg11.htm">Chapter 11</A>, &quot;Basic System Administration,&quot; for information on the Status module.)

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<FONT SIZE=5 COLOR="#FF0000"><B>Searching and Gathering</B></FONT></CENTER></H3>

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<P>Now that you have your logs accumulating data, you may want to be able to quickly search them. UNIX comes with a wide range of tools that can easily search a large file for a pattern. Our examples use our richer log files. I used a CLF-file format that had extra information at the end. I used the mod_log_config module and specified a log format of

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<FONT COLOR="#000080">LogFormat &quot;%h %l %u %t \&quot;%r\&quot; %s %b %{Cookie}i %{User-agent}i %400,401,403,404{Referer}i&quot;</FONT></PRE>

<P>This log format adds the Cookie header (a number) associated with each request. It also logs the browser the visitor was using and the Referer header information if the request was bad.

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<P>This format allows you to pack a lot of useful information into a single log file while still remaining compatible with most, if not all, of the standard logging tools available. (The order of the first seven fields is the same as the CLF.)

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