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diff --git a/APACHE_1_3_42/htdocs/manual/env.html.en b/APACHE_1_3_42/htdocs/manual/env.html.en new file mode 100644 index 0000000000..a96e002c01 --- /dev/null +++ b/APACHE_1_3_42/htdocs/manual/env.html.en @@ -0,0 +1,347 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta name="generator" content="HTML Tidy, see www.w3.org" /> + + <title>Environment Variables in Apache</title> + </head> + <!-- Background white, links blue (unvisited), navy (visited), red (active) --> + + <body bgcolor="#FFFFFF" text="#000000" link="#0000FF" + vlink="#000080" alink="#FF0000"> + <!--#include virtual="header.html" --> + + <h1 align="center">Environment Variables in Apache</h1> + + <p>The Apache HTTP Server provides a mechanism for storing + information in named variables that are called <em>environment + variables</em>. This information can be used to control various + operations such as logging or access control. The variables are + also used as a mechanism to communicate with external programs + such as CGI scripts. This document discusses different ways to + manipulate and use these variables.</p> + + <p>Although these variables are referred to as <em>environment + variables</em>, they are not the same as the environment + variables controlled by the underlying operating system. + Instead, these variables are stored and manipulated in an + internal Apache structure. They only become actual operating + system environment variables when they are provided to CGI + scripts and Server Side Include scripts. If you wish to + manipulate the operating system environment under which the + server itself runs, you must use the standard environment + manipulation mechanisms provided by your operating system + shell.</p> + + <ul> + <li><a href="#setting">Setting Environment Variables</a></li> + + <li><a href="#using">Using Environment Variables</a></li> + + <li><a href="#special">Special Purpose Environment + Variables</a></li> + + <li><a href="#examples">Examples</a></li> + </ul> + <hr /> + + <h2><a id="setting" name="setting">Setting Environment + Variables</a></h2> + + <table border="1"> + <tr> + <td valign="top"><strong>Related Modules</strong><br /> + <br /> + <a href="mod/mod_env.html">mod_env</a><br /> + <a href="mod/mod_rewrite.html">mod_rewrite</a><br /> + <a href="mod/mod_setenvif.html">mod_setenvif</a><br /> + <a href="mod/mod_unique_id.html">mod_unique_id</a><br /> + </td> + + <td valign="top"><strong>Related Directives</strong><br /> + <br /> + <a + href="mod/mod_setenvif.html#browsermatch">BrowserMatch</a><br /> + <a + href="mod/mod_setenvif.html#browsermatchnocase">BrowserMatchNoCase</a><br /> + <a href="mod/mod_env.html#passenv">PassEnv</a><br /> + <a + href="mod/mod_rewrite.html#RewriteRule">RewriteRule</a><br /> + <a href="mod/mod_env.html#setenv">SetEnv</a><br /> + <a + href="mod/mod_setenvif.html#setenvif">SetEnvIf</a><br /> + <a + href="mod/mod_setenvif.html#setenvifnocase">SetEnvIfNoCase</a><br /> + <a href="mod/mod_env.html#unsetenv">UnsetEnv</a><br /> + </td> + </tr> + </table> + + <h3>Basic Environment Manipulation</h3> + + <p>The most basic way to set an environment variable in Apache + is using the unconditional <code>SetEnv</code> directive. + Variables may also be passed from the environment of the shell + which started the server using the <code>PassEnv</code> + directive.</p> + + <h3>Conditional Per-Request Settings</h3> + + <p>For additional flexibility, the directives provided by + mod_setenvif allow environment variables to be set on a + per-request basis, conditional on characteristics of particular + requests. For example, a variable could be set only when a + specific browser (User-Agent) is making a request, or only when + a specific Referer [sic] header is found. Even more flexibility + is available through the mod_rewrite's <code>RewriteRule</code> + which uses the <code>[E=...]</code> option to set environment + variables.</p> + + <h3>Unique Identifiers</h3> + + <p>Finally, mod_unique_id sets the environment variable + <code>UNIQUE_ID</code> for each request to a value which is + guaranteed to be unique across "all" requests under very + specific conditions.</p> + + <h3>Standard CGI Variables</h3> + + <p>In addition to all environment variables set within the + Apache configuration and passed from the shell, CGI scripts and + SSI pages are provided with a set of environment variables + containing meta-information about the request as required by + the <a href="misc/FAQ.html#cgi-spec">CGI specification</a>.</p> + + <h3>Some Caveats</h3> + + <ul> + <li>It is not possible to override or change the standard CGI + variables using the environment manipulation directives.</li> + + <li>When <a href="suexec.html">suexec</a> is used to launch + CGI scripts, the environment will be cleaned down to a set of + <em>safe</em> variables before CGI scripts are launched. The + list of <em>safe</em> variables is defined at compile-time in + <code>suexec.c</code>.</li> + + <li>For portability reasons, the names of environment + variables may contain only letters, numbers, and the + underscore character. In addition, the first character may + not be a number. Characters which do not match this + restriction will be replaced by an underscore when passed to + CGI scripts and SSI pages.</li> + </ul> + <hr /> + + <h2><a id="using" name="using">Using Environment + Variables</a></h2> + + <table border="1"> + <tr> + <td valign="top"><strong>Related Modules</strong><br /> + <br /> + <a href="mod/mod_access.html">mod_access</a><br /> + <a href="mod/mod_cgi.html">mod_cgi</a><br /> + <a href="mod/mod_include.html">mod_include</a><br /> + <a href="mod/mod_log_config.html">mod_log_config</a><br /> + <a href="mod/mod_rewrite.html">mod_rewrite</a><br /> + </td> + + <td valign="top"><strong>Related Directives</strong><br /> + <br /> + <a href="mod/mod_access.html#allow">Allow</a><br /> + <a + href="mod/mod_log_config.html#customlog">CustomLog</a><br /> + <a href="mod/mod_access.html#deny">Deny</a><br /> + <a + href="mod/mod_log_config.html#logformat">LogFormat</a><br /> + <a + href="mod/mod_rewrite.html#RewriteCond">RewriteCond</a><br /> + <a + href="mod/mod_rewrite.html#RewriteRule">RewriteRule</a><br /> + </td> + </tr> + </table> + + <h3>CGI Scripts</h3> + + <p>One of the primary uses of environment variables is to + communicate information to CGI scripts. As discussed above, the + environment passed to CGI scripts includes standard + meta-information about the request in addition to any variables + set within the Apache configuration. For more details, see the + <a href="howto/cgi.html">CGI tutorial</a>.</p> + + <h3>SSI Pages</h3> + + <p>Server-parsed (SSI) documents processed by mod_include's + <code>server-parsed</code> handler can print environment + variables using the <code>echo</code> element, and can use + environment variables in flow control elements to makes parts + of a page conditional on characteristics of a request. Apache + also provides SSI pages with the standard CGI environment + variables as discussed above. For more details, see the <a + href="howto/ssi.html">SSI tutorial</a>.</p> + + <h3>Access Control</h3> + + <p>Access to the server can be controlled based on the value of + environment variables using the <code>allow from env=</code> + and <code>deny from env=</code> directives. In combination with + <code>SetEnvIf</code>, this allows for flexible control of + access to the server based on characteristics of the client. + For example, you can use these directives to deny access to a + particular browser (User-Agent).</p> + + <h3>Conditional Logging</h3> + + <p>Environment variables can be logged in the access log using + the <code>LogFormat</code> option <code>%e</code>. In addition, + the decision on whether or not to log requests can be made + based on the status of environment variables using the + conditional form of the <code>CustomLog</code> directive. In + combination with <code>SetEnvIf</code> this allows for flexible + control of which requests are logged. For example, you can + choose not to log requests for filenames ending in + <code>gif</code>, or you can choose to only log requests from + clients which are outside your subnet.</p> + + <h3>URL Rewriting</h3> + + <p>The <code>%{ENV:...}</code> form of <em>TestString</em> in + the <code>RewriteCond</code> allows mod_rewrite's rewrite + engine to make decisions conditional on environment variables. + Note that the variables accessible in mod_rewrite without the + <code>ENV:</code> prefix are not actually environment + variables. Rather, they are variables special to mod_rewrite + which cannot be accessed from other modules.</p> + <hr /> + + <h2><a id="special" name="special">Special Purpose Environment + Variables</a></h2> + + <p>Interoperability problems have led to the introduction of + mechanisms to modify the way Apache behaves when talking to + particular clients. To make these mechanisms as flexible as + possible, they are invoked by defining environment variables, + typically with <a + href="mod/mod_browser.html#browsermatch">BrowserMatch</a>, + though <a href="mod/mod_env.html#setenv">SetEnv</a> and <a + href="mod/mod_env.html#passenv">PassEnv</a> could also be used, + for example.</p> + + <h2>downgrade-1.0</h2> + + <p>This forces the request to be treated as a HTTP/1.0 request + even if it was in a later dialect.</p> + + <h2>force-no-vary</h2> + + <p>This causes any <code>Vary</code> fields to be removed from + the response header before it is sent back to the client. Some + clients don't interpret this field correctly (see the <a + href="misc/known_client_problems.html">known client + problems</a> page); setting this variable can work around this + problem. Setting this variable also implies + <strong>force-response-1.0</strong>.</p> + + <h2>force-response-1.0</h2> + + <p>This forces an HTTP/1.0 response when set. It was originally + implemented as a result of a problem with AOL's proxies. Some + clients may not behave correctly when given an HTTP/1.1 + response, and this can be used to interoperate with them.</p> + + <h2>nokeepalive</h2> + + <p>This disables <a + href="mod/core.html#keepalive">KeepAlive</a> when set.</p> + + <h2>suppress-error-charset</h2> + <p><i>Available in versions after 1.3.26 and 2.0.40</i></p> + <p>When Apache issues a redirect in response to a client request, + the response includes some actual text to be displayed in case + the client can't (or doesn't) automatically follow the redirection. + Apache ordinarily labels this text according to the character set + which it uses, which is ISO-8859-1.</p> + <p> However, if the redirection is to a page that uses a different + character set, some broken browser versions will try to use the + character set from the redirection text rather than the actual page. + This can result in Greek, for instance, being incorrectly rendered.</p> + <p>Setting this environment variable causes Apache to omit the character + set for the redirection text, and these broken browsers will then correctly + use that of the destination page.</p> + <hr /> + + <h2><a id="examples" name="examples">Examples</a></h2> + + <h3>Changing protocol behavior with misbehaving clients</h3> + + <p>We recommend that the following lines be included in + httpd.conf to deal with known client problems.</p> +<pre> +# +# The following directives modify normal HTTP response behavior. +# The first directive disables keepalive for Netscape 2.x and browsers that +# spoof it. There are known problems with these browser implementations. +# The second directive is for Microsoft Internet Explorer 4.0b2 +# which has a broken HTTP/1.1 implementation and does not properly +# support keepalive when it is used on 301 or 302 (redirect) responses. +# +BrowserMatch "Mozilla/2" nokeepalive +BrowserMatch "MSIE 4\.0b2;" nokeepalive downgrade-1.0 force-response-1.0 + +# +# The following directive disables HTTP/1.1 responses to browsers which +# are in violation of the HTTP/1.0 spec by not being able to grok a +# basic 1.1 response. +# +BrowserMatch "RealPlayer 4\.0" force-response-1.0 +BrowserMatch "Java/1\.0" force-response-1.0 +BrowserMatch "JDK/1\.0" force-response-1.0 +</pre> + + <h3>Do not log requests for images in the access log</h3> + + <p>This example keeps requests for images from appearing in the + access log. It can be easily modified to prevent logging of + particular directories, or to prevent logging of requests + coming from particular hosts.</p> +<pre> + SetEnvIf Request_URI \.gif image-request + SetEnvIf Request_URI \.jpg image-request + SetEnvIf Request_URI \.png image-request + CustomLog logs/access_log env=!image-request +</pre> + + <h3>Prevent "Image Theft"</h3> + + <p>This example shows how to keep people not on your server + from using images on your server as inline-images on their + pages. This is not a recommended configuration, but it can work + in limited circumstances. We assume that all your images are in + a directory called /web/images.</p> +<pre> + SetEnvIf Referer "^http://www.example.com/" local_referal + # Allow browsers that do not send Referer info + SetEnvIf Referer "^$" local_referal + <Directory /web/images> + Order Deny,Allow + Deny from all + Allow from env=local_referal + </Directory> +</pre> + + <p><em>Note:</em> spelling of 'referer' and 'referal' is + intentional.</p> + + <p>For more information about this technique, see the + ApacheToday tutorial " <a + href="http://apachetoday.com/news_story.php3?ltsn=2000-06-14-002-01-PS"> + Keeping Your Images from Adorning Other Sites</a>".</p> + <!--#include virtual="footer.html" --> + </body> +</html> + |