Installation guide

196 Chapter 14. Apache HTTP Server
14.5.32. CacheNegotiatedDocs
By default, your Web server asks proxy servers not to cache any documents which were negotiated on
the basis of content (that is, they may change over time or because of the input from the requester).
If you set CacheNegotiatedDocs to on, you are disabling that function and proxy servers will be
allowed to cache documents.
14.5.33. UseCanonicalName
UseCanonicalName is set by default to on. UseCanonicalName allows the server to construct an
URL that references itself, using ServerName and Port. When the server refers to itself in response
to requests from clients, it uses this URL. If you set UseCanonicalName to off, the server will
instead use the value that came in the request from the client to refer to itself.
14.5.34. TypesConfig
TypesConfig names the file which sets the default list of MIME type mappings (filename exten-
sions to content types). The default TypesConfig file is /etc/mime.types. Instead of editing
/etc/mime.types, the recommended way to add MIME type mappings is to use the AddType
directive.
For more information about AddType, refer to Section 14.5.58.
14.5.35. DefaultType
DefaultType sets a default content type for the Web server to use for documents whose MIME types
can not be determined. Your Web server defaults to assume a plain text content type for any file with
an indeterminate content type.
14.5.36. IfModule
IfModule and /IfModule tags surround directives that are conditional. The directives con-
tained within the IfModule tags are processed under one of two conditions. The directives are pro-
cessed if the module contained within the starting IfModule tag is loaded in to httpd. Or, if an
"!" (an exclamation point) is included before the module name, the directives are processed only if the
module in the starting IfModule tag is not compiled in.
The mod_mime_magic.c file is included in these IfModule tags. The mod_mime_magic module
can be compared to the UNIX file command, which looks at a few bytes of a file’s contents, then
uses "magic numbers" and other hints in order to figure out the MIME type of the file.
If the mod_mime_magic module is compiled in to the Apache HTTP Server, these IfModule tags
tell the mod_mime_magic module where the hints definition file is: /usr/share/magic in this case.
The mod_mime_magic module is not compiled in by default. If you would like to use it, see Section
14.7, for instructions on how to add modules to your server.
14.5.37. HostnameLookups
HostnameLookups can be set to on, off or double. If you allow HostnameLookups (by setting
it to on), 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 set HostnameLookups to double, your server will perform a double-reverse DNS. In