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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