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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
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-->
<title>Custom Error Responses - Apache HTTP Server</title>
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<p class="menu"><a href="./mod/">Modules</a> | <a href="./mod/directives.html">Directives</a> | <a href="./faq/">FAQ</a> | <a href="./glossary.html">Glossary</a> | <a href="./sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.1</p>
<img alt="" src="./images/feather.gif" /></div>
<div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
<div id="path">
<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="./">Version 2.1</a></div><div id="page-content"><div id="preamble"><h1>Custom Error Responses</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="./en/custom-error.html"> en </a> | <a href="./ja/custom-error.html"> ja </a></p>
</div>
<p>Additional functionality allows webmasters to configure the response
of Apache to some error or problem.</p>
<p>Customizable responses can be defined to be activated in the event of
a server detected error or problem.</p>
<p>If a script crashes and produces a "500 Server Error" response,
then this response can be replaced with either some friendlier text or by
a redirection to another URL (local or external).</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#behavior">Behavior</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#configuration">Configuration</a></li>
<li><img alt="" src="./images/down.gif" /> <a href="#custom">Custom Error Responses and Redirects</a></li>
</ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="behavior" id="behavior">Behavior</a></h2>
<h3>Old Behavior</h3>
<p>NCSA httpd 1.3 would return some boring old error/problem message
which would often be meaningless to the user, and would provide no
means of logging the symptoms which caused it.</p>
<h3>New Behavior</h3>
<p>The server can be asked to:</p>
<ol>
<li>Display some other text, instead of the NCSA hard coded
messages, or</li>
<li>redirect to a local URL, or</li>
<li>redirect to an external URL.</li>
</ol>
<p>Redirecting to another URL can be useful, but only if some
information can be passed which can then be used to explain and/or log
the error/problem more clearly.</p>
<p>To achieve this, Apache will define new CGI-like environment
variables:</p>
<div class="example"><p><code>
REDIRECT_HTTP_ACCEPT=*/*, image/gif, image/x-xbitmap,
image/jpeg<br />
REDIRECT_HTTP_USER_AGENT=Mozilla/1.1b2 (X11; I; HP-UX A.09.05
9000/712)<br />
REDIRECT_PATH=.:/bin:/usr/local/bin:/etc<br />
REDIRECT_QUERY_STRING=<br />
REDIRECT_REMOTE_ADDR=121.345.78.123<br />
REDIRECT_REMOTE_HOST=ooh.ahhh.com<br />
REDIRECT_SERVER_NAME=crash.bang.edu<br />
REDIRECT_SERVER_PORT=80<br />
REDIRECT_SERVER_SOFTWARE=Apache/0.8.15<br />
REDIRECT_URL=/cgi-bin/buggy.pl
</code></p></div>
<p>Note the <code>REDIRECT_</code> prefix.</p>
<p>At least <code>REDIRECT_URL</code> and
<code>REDIRECT_QUERY_STRING</code> will be passed to the
new URL (assuming it's a cgi-script or a cgi-include). The
other variables will exist only if they existed prior to
the error/problem. <strong>None</strong> of these will be
set if your <code class="directive"><a href="./mod/core.html#errordocument">ErrorDocument</a></code> is an
<em>external</em> redirect (anything starting with a
scheme name like <code>http:</code>, even if it refers to the same host
as the server).</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="configuration" id="configuration">Configuration</a></h2>
<p>Use of <code class="directive"><a href="./mod/core.html#errordocument">ErrorDocument</a></code> is enabled
for .htaccess files when the
<code class="directive"><a href="./mod/core.html#allowoverride">AllowOverride</a></code> is set accordingly.</p>
<p>Here are some examples...</p>
<div class="example"><p><code>
ErrorDocument 500 /cgi-bin/crash-recover <br />
ErrorDocument 500 "Sorry, our script crashed. Oh dear" <br />
ErrorDocument 500 http://xxx/ <br />
ErrorDocument 404 /Lame_excuses/not_found.html <br />
ErrorDocument 401 /Subscription/how_to_subscribe.html
</code></p></div>
<p>The syntax is,</p>
<div class="example"><p><code>
ErrorDocument <3-digit-code> <action>
</code></p></div>
<p>where the action can be,</p>
<ol>
<li>Text to be displayed. Prefix the text with a quote
("). Whatever follows the quote is displayed. <em>Note:
the (") prefix isn't displayed.</em></li>
<li>An external URL to redirect to.</li>
<li>A local URL to redirect to.</li>
</ol>
</div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
<div class="section">
<h2><a name="custom" id="custom">Custom Error Responses and Redirects</a></h2>
<p>Apache's behavior to redirected URLs has been modified so
that additional environment variables are available to a
script/server-include.</p>
<h3>Old behavior</h3>
<p>Standard CGI vars were made available to a script which
has been redirected to. No indication of where the
redirection came from was provided.</p>
<h3>New behavior</h3>
<p>A new batch of environment variables will be initialized
for use by a script which has been redirected to. Each new
variable will have the prefix <code>REDIRECT_</code>.
<code>REDIRECT_</code> environment variables are created from
the CGI environment variables which existed prior to the
redirect, they are renamed with a <code>REDIRECT_</code>
prefix, <em>i.e.</em>, <code>HTTP_USER_AGENT</code> becomes
<code>REDIRECT_HTTP_USER_AGENT</code>. In addition to these
new variables, Apache will define <code>REDIRECT_URL</code>
and <code>REDIRECT_STATUS</code> to help the script trace its
origin. Both the original URL and the URL being redirected to
can be logged in the access log.</p>
<p>If the ErrorDocument specifies a local redirect to a CGI
script, the script should include a "<code>Status:</code>"
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:</p>
<div class="example"><p><code>
... <br />
print "Content-type: text/html\n"; <br />
printf "Status: %s Condition Intercepted\n", $ENV{"REDIRECT_STATUS"}; <br />
...
</code></p></div>
<p>If the script is dedicated to handling a particular error
condition, such as <code>404 Not Found</code>, it can
use the specific code and error text instead.</p>
<p>Note that the script <em>must</em> emit an appropriate
<code>Status:</code> header (such as <code>302 Found</code>), if the
response contains a <code>Location:</code> header (in order to issue a
client side redirect). Otherwise the <code>Location:</code> header may
have no effect.</p>
</div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="./en/custom-error.html"> en </a> | <a href="./ja/custom-error.html"> ja </a></p>
</div><div id="footer">
<p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p>
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