3 <TITLE>Ccustom error responses</TITLE>
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8 <H1>Custom error responses</H1>
12 <DD>Additional functionality. Allows webmasters to configure the response of
13 Apache to some error or problem.<BR>
14 <P>Customizable responses can be defined to be activated in the event of a
15 server detected error or problem.<BR>
16 e.g. if a script crashes and produces a "500 Server Error" response, then
17 this response can be replaced with either some friendlier text or by a
18 redirection to another URL (local or external).
20 <DD>NCSA httpd 1.3 would return some boring old error/problem message which
21 would often be meaningless to the user, and would provide no means of logging
22 the symptoms which caused it.<BR><BR>
24 <DD>The server can be asked to;
26 <LI>Display some other text, instead of the NCSA hard coded messages, or
27 <LI>redirect to a local URL, or
28 <LI>redirect to an external URL.
30 <P>Redirecting to another URL can be useful, but only if some information
31 can be passed which can then be used to explain and/or log the error/problem
32 more clearly.<BR>To achieve this, Apache will define new CGI-like environment
35 REDIRECT_HTTP_ACCEPT=*/*, image/gif, image/x-xbitmap, image/jpeg <br>
36 REDIRECT_HTTP_USER_AGENT=Mozilla/1.1b2 (X11; I; HP-UX A.09.05 9000/712) <br>
37 REDIRECT_PATH=.:/bin:/usr/local/bin:/etc <br>
38 REDIRECT_QUERY_STRING= <br>
39 REDIRECT_REMOTE_ADDR=121.345.78.123 <br>
40 REDIRECT_REMOTE_HOST=ooh.ahhh.com <br>
41 REDIRECT_SERVER_NAME=crash.bang.edu <br>
42 REDIRECT_SERVER_PORT=80 <br>
43 REDIRECT_SERVER_SOFTWARE=Apache/0.8.15 <br>
44 REDIRECT_URL=/cgi-bin/buggy.pl <br>
47 note the <code>REDIRECT_</code> prefix. <p>
49 At least <code>REDIRECT_URL</code> and <code>REDIRECT_QUERY_STRING</code> will
50 be passed to the new URL (assuming it's a cgi-script or a cgi-include). The
51 other variables will exist only if they existed prior to the error/problem.<p>
54 <DD><em>file: </em>server configuration<BR>
55 <P>Here are some examples...
57 ErrorDocument 500 /cgi-bin/crash-recover <br>
58 ErrorDocument 500 "Sorry, our script crashed because %s. Oh dear<br>
59 ErrorDocument 500 http://xxx/ <br>
60 ErrorDocument 404 /Lame_excuses/not_found.html <br>
61 ErrorDocument 401 /Subscription/how_to_subscribe.html
64 <code><A HREF="core.html#errordocument">ErrorDocument</A></code>
65 <3-digit-code> action <p>
67 where the action can be,
69 <LI>Text to be displayed.<BR>Prefix the text with a quote ("). Whatever
70 follows the quote is displayed. If the error/problem produced any additional
71 information, it can be specified using <code>%s</code>.
72 <em>Note: the (") prefix isn't displayed.</em>
73 <LI>An external URL to redirect to.
74 <LI>A local URL to redirect to.
76 <P><code>ErrorDocument</code> definitions are sensitive to a
77 <code>SIGHUP</code>, so you can change any of the definitions or add new ones
78 prior to sending a <code>SIGHUP</code> (kill -1) signal.
82 <h2>Custom error responses and redirects</H2>
85 <DD>Apache's behaviour to redirected URLs has been modified so that additional
86 environment variables are available to a script/server-include.<p>
89 <DD>Standard CGI vars were made available to a script which has been
90 redirected to. No indication of where the redirection came from was provided.
93 <DD>A new batch of environment variables will be initialized for use by a
94 script which has been redirected to.<BR>
95 Each new variable will have the prefix <code>REDIRECT_</code>.<BR>
96 REDIRECT_ environment variables are created from the CGI environment
97 variables which existed prior to the redirect, they are renamed with a
98 REDIRECT_ prefix, i.e. HTTP_USER_AGENT -> REDIRECT_HTTP_USER_AGENT.<BR>
99 In addition to these new variables, Apache will define
100 <code>REDIRECT_URL</code> and <code>REDIRECT_STATUS</code> to help the script
101 trace its origin.<BR>
102 Logging: both the original URL and the URL being redirected to, will
103 now be logged correctly in the access log.<p>
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