Apache Log Files Details

Apache log files are configured in the /etc/httpd/logs directory, they’re actually stored in the /var/log/httpd directory. Standard logging information from Apache is stored in two baseline log files. Custom log files may also be configured. Such log files may have different names, depending on how virtual hosts are configured, how secure web sites are configured, and how logs are rotated.

Based on the standard Apache configuration files, access attempts are logged in the access_log file and errors are recorded in the error_log file. Standard secure log files include ssl_access_log, ssl_error_log, and ssl_request_log.

In general, it’s helpful to set up different sets of log files for different web sites. To that end, you should set up different log files for the secure versions of a web site. The traffic on a web site is important when choosing a log rotation frequency.

There are standard Apache log file formats. Four different formats: combined, common, the referrer (the web page with the link used to get to your site), and the agent (the user’s web browser). The first two LogFormat lines include a number of percent signs followed by lowercase letters. These directives determine what goes into the log.

# LogLevel: Control the number of messages logged to the error log.

# Possible values include: debug, info, notice, warn, error, crit,

# alert, emerg.

#

LogLevel warn

#

# The following directives define some format nicknames for use with

# a CustomLog directive (see below) .

#

LogFormat “%h %l $u %t \ “%r\” %>S %b \ “%{Referer}i\” \” ” combined

LogFormat “%h %l $u %t \ “%r\” %>S %b” common

LogFormat “ %{Referer}i” agent

LogFormat “ %{User-agent}i” agent

# “combinedio” includes actual counts of actual bytes received (%I) and send (%O) ; this

# requires the mod_logio module to be loaded.

# LogFormat “%h %l %u %u %t \  “%r” %?s %b \ “ %{Referer}i\” \ “%{User-Agent}i\” %I %O” combinedio

#

You can then use the CustomLog directive to select a location for the log file, such as logs/special_access_log, and the desired log file format, such as common. For more information on log files and formats, refer to http://localhost/manual/logs.html.

Some web log analyzers have specific requirements for log file formats. For example, the popular open-source tool awstats (advanced Web Stats) requires the combined log format. It will fail to run if you leave the default common format. Awstats is a great tool for graphically displaying site activity. You can download it from a site such as www.sourceforge.net.