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23 <manualpage metafile="custom-error.xml.meta">
25 <title>Custom Error Responses</title>
28 <p>Additional functionality allows webmasters to configure the response
29 of Apache to some error or problem.</p>
31 <p>Customizable responses can be defined to be activated in the event of
32 a server detected error or problem.</p>
34 <p>If a script crashes and produces a "500 Server Error" response,
35 then this response can be replaced with either some friendlier text or by
36 a redirection to another URL (local or external).</p>
39 <section id="behavior">
40 <title>Behavior</title>
43 <title>Old Behavior</title>
45 <p>NCSA httpd 1.3 would return some boring old error/problem message
46 which would often be meaningless to the user, and would provide no
47 means of logging the symptoms which caused it.</p>
51 <title>New Behavior</title>
53 <p>The server can be asked to:</p>
56 <li>Display some other text, instead of the NCSA hard coded
59 <li>redirect to a local URL, or</li>
61 <li>redirect to an external URL.</li>
64 <p>Redirecting to another URL can be useful, but only if some
65 information can be passed which can then be used to explain and/or log
66 the error/problem more clearly.</p>
68 <p>To achieve this, Apache will define new CGI-like environment
72 REDIRECT_HTTP_ACCEPT=*/*, image/gif, image/x-xbitmap,
74 REDIRECT_HTTP_USER_AGENT=Mozilla/1.1b2 (X11; I; HP-UX A.09.05
76 REDIRECT_PATH=.:/bin:/usr/local/bin:/etc<br />
77 REDIRECT_QUERY_STRING=<br />
78 REDIRECT_REMOTE_ADDR=121.345.78.123<br />
79 REDIRECT_REMOTE_HOST=ooh.ahhh.com<br />
80 REDIRECT_SERVER_NAME=crash.bang.edu<br />
81 REDIRECT_SERVER_PORT=80<br />
82 REDIRECT_SERVER_SOFTWARE=Apache/0.8.15<br />
83 REDIRECT_URL=/cgi-bin/buggy.pl
86 <p>Note the <code>REDIRECT_</code> prefix.</p>
88 <p>At least <code>REDIRECT_URL</code> and
89 <code>REDIRECT_QUERY_STRING</code> will be passed to the
90 new URL (assuming it's a cgi-script or a cgi-include). The
91 other variables will exist only if they existed prior to
92 the error/problem. <strong>None</strong> of these will be
93 set if your <directive module="core">ErrorDocument</directive> is an
94 <em>external</em> redirect (anything starting with a
95 scheme name like <code>http:</code>, even if it refers to the same host
100 <section id="configuration">
101 <title>Configuration</title>
103 <p>Use of <directive module="core">ErrorDocument</directive> is enabled
104 for .htaccess files when the
105 <directive module="core">AllowOverride</directive> is set accordingly.</p>
107 <p>Here are some examples...</p>
110 ErrorDocument 500 /cgi-bin/crash-recover <br />
111 ErrorDocument 500 "Sorry, our script crashed. Oh dear" <br />
112 ErrorDocument 500 http://xxx/ <br />
113 ErrorDocument 404 /Lame_excuses/not_found.html <br />
114 ErrorDocument 401 /Subscription/how_to_subscribe.html
117 <p>The syntax is,</p>
120 ErrorDocument <3-digit-code> <action>
123 <p>where the action can be,</p>
126 <li>Text to be displayed. Wrap the text with quotes (").</li>
128 <li>An external URL to redirect to.</li>
130 <li>A local URL to redirect to.</li>
134 <section id="custom">
135 <title>Custom Error Responses and Redirects</title>
137 <p>Apache's behavior to redirected URLs has been modified so
138 that additional environment variables are available to a
139 script/server-include.</p>
142 <title>Old behavior</title>
144 <p>Standard CGI vars were made available to a script which
145 has been redirected to. No indication of where the
146 redirection came from was provided.</p>
150 <title>New behavior</title>
152 <p>A new batch of environment variables will be initialized
153 for use by a script which has been redirected to. Each new
154 variable will have the prefix <code>REDIRECT_</code>.
155 <code>REDIRECT_</code> environment variables are created from
156 the CGI environment variables which existed prior to the
157 redirect, they are renamed with a <code>REDIRECT_</code>
158 prefix, <em>i.e.</em>, <code>HTTP_USER_AGENT</code> becomes
159 <code>REDIRECT_HTTP_USER_AGENT</code>. In addition to these
160 new variables, Apache will define <code>REDIRECT_URL</code>
161 and <code>REDIRECT_STATUS</code> to help the script trace its
162 origin. Both the original URL and the URL being redirected to
163 can be logged in the access log.</p>
165 <p>If the ErrorDocument specifies a local redirect to a CGI
166 script, the script should include a "<code>Status:</code>"
167 header field in its output in order to ensure the propagation
168 all the way back to the client of the error condition that
169 caused it to be invoked. For instance, a Perl ErrorDocument
170 script might include the following:</p>
174 print "Content-type: text/html\n"; <br />
175 printf "Status: %s Condition Intercepted\n", $ENV{"REDIRECT_STATUS"}; <br />
179 <p>If the script is dedicated to handling a particular error
180 condition, such as <code>404 Not Found</code>, it can
181 use the specific code and error text instead.</p>
183 <p>Note that the script <em>must</em> emit an appropriate
184 <code>Status:</code> header (such as <code>302 Found</code>), if the
185 response contains a <code>Location:</code> header (in order to issue a
186 client side redirect). Otherwise the <code>Location:</code> header may