Although the Apache HTTP Server provides generic error responses in the event of 4xx or 5xx HTTP status codes, these responses are rather stark, uninformative, and can be intimidating to site users. You may wish to provide custom error responses which are either friendlier, or in some language other than English, or perhaps which are styled more in line with your site layout.
Customized error responses can be defined for any HTTP status code designated as an error condition - that is, any 4xx or 5xx status.
Additionally, a set of values are provided, so that the error document can be customized further based on the values of these variables, using Server Side Includes. Or, you can have error conditions handled by a cgi program, or other dynamic handler (PHP, mod_perl, etc) which makes use of these variables.
Custom error documents are configured using the
The syntax of the ErrorDocument directive is:
where the action will be treated as:
When redirecting to a local URL, additional environment variables are set so that the response can be further customized. They are not sent to external URLs.
Redirecting to another URL can be useful, but only if some information can be passed which can then be used to explain or log the error condition more clearly.
To achieve this, when the error redirect is sent, additional environment variables will be set, which will be generated from the headers provided to the original request by prepending 'REDIRECT_' onto the original header name. This provides the error document the context of the original request.
For example, you might receive, in addition to more usual environment variables, the following.
REDIRECT_ environment variables are created from
the environment variables which existed prior to the
redirect. They are renamed with a REDIRECT_
prefix, i.e., HTTP_USER_AGENT becomes
REDIRECT_HTTP_USER_AGENT.
REDIRECT_URL, REDIRECT_STATUS, and
REDIRECT_QUERY_STRING are guaranteed to be set, and
the other headers will be set only if they existed prior to the
error condition.
None of these will be
set if the http:, even if it refers to the same host
as the server).
If you point your ErrorDocument to some variety of
dynamic handler such as a server-side include document, CGI
script, or some variety of other handler, you may wish to use the
available custom environment variables to customize this
response.
If the ErrorDocument specifies a local redirect to a CGI
script, the script should include a "Status:"
header field in its output in order to ensure the propagation
all the way back to the client of the error condition that
caused it to be invoked. For instance, a Perl ErrorDocument
script might include the following:
If the script is dedicated to handling a particular error
condition, such as 404 Not Found, it can
use the specific code and error text instead.
Note that if the response contains Location:
header (in order to issue a client-side redirect), the script
must emit an appropriate Status: header
(such as 302 Found). Otherwise the
Location: header may have no effect.
Provided with your installation of the Apache HTTP Server is a
directory of custom error documents translated into 16 different
languages. There's also a configuration file in the
conf/extra configuration directory that can be included
to enable this feature.
In your server configuration file, you'll see a line such as:
Uncommenting this Include line will enable this
feature, and provide language-negotiated error messages, based on
the language preference set in the client browser.
Additionally, these documents contain various of the
REDIRECT_ variables, so that additional information can
be provided to the end-user about what happened, and what they can
do now.
These documents can be customized to whatever degree you wish to provide more useful information to users about your site, and what they can expect to find there.