Apache Log Files ExplainedConfigure Web Logs in ApacheAuthor's Note: While most of this piece discusses configuration options for any operating system Apache supports, some of the content will be Unix/Linux (*nix) specific, which now includes Macintosh OS X and its underlying Unix kernel. One of the many pieces of the Website puzzle is Web logs. Traffic analysis is central to most Websites, and the key to getting the most out of your traffic analysis revolves around how you configure your Web logs. Apache is one of the most -- if not the most -- powerful open source solutions for Website operations. You will find that Apache's Web logging features are flexible for the single Website or for managing numerous domains requiring Web log analysis. For the single site, Apache is pretty much configured for logging in the default install. The initial httpd.conf file (found in /etc/httpd/conf/httpd.conf in most cases) should have a section on logs that looks similar to this (Apache 2.0.x), with descriptive comments for each item. Your default logs folder will be found in /etc/httpd/logs . This location can be changed when dealing with multiple Websites, as we'll see later. For now, let's review this section of log configuration. ErrorLog logs/error_log Error LogsThe error log contains messages sent from Apache for errors encountered during the course of operation. This log is very useful for troubleshooting Apache issues on the server side. Apache Log Tip: If you are monitoring errors or testing your server, you can use the command line to interactively watch log entries. Open a shell session and type "tail –f /path/to/error_log" . This will show you the last few entries in the file and also continue to show new entries as they occur. There are no real customization options available, other than telling Apache where to establish the file, and what level of error logging you seek to capture. First, let's look at the error log configuration code from httpd.conf. ErrorLog logs/error_log You may wish to store all error-related information in one error log. If so, the above is fine, even for multiple domains. However, you can specify an error log file for each individual domain you have. This is done in the <VirtualHost> container with an entry like this: <VirtualHost 10.0.0.2> If you are responsible for reviewing error log files as a server administrator, it is recommended that you maintain a single error log. If you're hosting for clients, and they are responsible for monitoring the error logs, it's more convenient to specify individual error logs they can access at their own convenience. The setting that controls the level of error logging to capture follows below. LogLevel warn Apache's definitions for their error log levels are as follows:
Tracking Website ActivityOften by default, Apache will generate three activity logs: access, agent and referrer. These track the accesses to your Website, the browsers being used to access the site and referring urls that your site visitors have arrived from. It is commonplace now to utilize Apache's "combined" log format, which compiles all three of these logs into one logfile. This is very convenient when using traffic analysis software as a majority of these third-party programs are easiest to configure and schedule when only dealing with one log file per domain. Let's break down the code in the combined log format and see what it all means. LogFormat "%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"" combined LogFormat starts the line and simply tells Apache you are defining a log file type (or nickname), in this case, combined. Now let's look at the cryptic symbols that make up this log file definition.
To review all of the available configuration codes for generating a custom log, see Apache's [1] docs on the module_log_config , which powers log files in Apache. Apache Log Tip: You could capture more from the HTTP header if you so desired. A full listing and definition of data in the header is found at the World Wide Web Consortium [2] . For a single Website, the default entry would suffice: CustomLog logs/access_log combined However, for logging multiple sites, you have a few options. The most common is to identify individual log files for each domain. This is seen in the example below, again using the log directive within the <VirtualHost> container for each domain. <VirtualHost 10.0.0.2> This method works well for most hosts. However, there may be situations where this could become unmanageable. Apache recommends a special single log file for large virtual host environments and provides a tool for generating individual logs per individual domain. We will call this log type the cvh format, standing for "common virtual host." Simply by adding a %v (which stands for virtual host) to the beginning of the combined log format defined earlier and giving it a new nickname of cvh, we can compile all domains into one log file, then automatically split them into individual log files for processing by a traffic analysis package. LogFormat "%v %h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"" cvh In this case, we do not make any CustomLog entries in the <VirtualHost> containers and simply have one log file generated by Apache. A program created by Apache called split_logfile is included in the src/support directory of your Apache sources. If you did not compile from source or do not have the sources, you can get the Perl script [3] . The individual log files created from your master log file will be named for each domain (virtual host) and look like: virtualhost.log. |
