Installation guide

124 Chapter 13. Apache Configuration
Use the Log Level menu to set how verbose the error messages in the error logs will be. It
can be set (from least verbose to most verbose) to emerg, alert, crit, error, warn, notice, info
or debug. This option corresponds to the LogLevel directive.
The value chosen with the Reverse DNS Lookup menu defines the HostnameLookups direc-
tive. Choosing No Reverse Lookup sets the value to off. Choosing Reverse Lookup sets the
value to on. Choosing Double Reverse Lookup sets the value to double.
If you choose Reverse Lookup, your server will automatically resolve the IP address for
each connection which requests a document from your Web server. Resolving the IP address
means that your server will make one or more connections to the DNS in order to find out
the hostname that corresponds to a particular IP address.
If you choose Double Reverse Lookup, your server will perform a double-reverse DNS.
In other words, after a reverse lookup is performed, a forward lookup is performed on the
result. At least one of the IP addresses in the forward lookup must match the address from
the first reverse lookup.
Generally, you should leave this option set to No Reverse Lookup, because the DNS requests
add a load to your server and may slow it down. If your server is busy, the effects of trying
to perform these reverse lookups or double reverse lookups may be quite noticeable.
Reverse lookups and double reverse lookups are also an issue for the Internet as a whole. All
of the individual connections made to look up each hostname add up. Therefore, for your
own Web server’s benefit, as well as for the Internet’s benefit, you should leave this option
set to No Reverse Lookup.
13.2.3. Environment Variables
Apache can use the mod_env module to configure the environment variables which are
passed to CGI scripts and SSI pages. Use the Environment Variables page to configure the
directives for this Apache module.