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8 <title>Mapping URLs to Filesystem Locations - Apache HTTP Server</title>
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14 <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>
15 <p class="apache">Apache HTTP Server Version 2.1</p>
16 <img alt="" src="./images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="./images/left.gif" /></a></div>
19 <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>Mapping URLs to Filesystem Locations</h1>
20 <p>This document explains how Apache uses the URL of a request
21 to determine the filesystem location from which to serve a
24 <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#related">Related Modules and Directives</a></li>
25 <li><img alt="" src="./images/down.gif" /> <a href="#documentroot">DocumentRoot</a></li>
26 <li><img alt="" src="./images/down.gif" /> <a href="#outside">Files Outside the DocumentRoot</a></li>
27 <li><img alt="" src="./images/down.gif" /> <a href="#user">User Directories</a></li>
28 <li><img alt="" src="./images/down.gif" /> <a href="#redirect">URL Redirection</a></li>
29 <li><img alt="" src="./images/down.gif" /> <a href="#proxy">Reverse Proxy</a></li>
30 <li><img alt="" src="./images/down.gif" /> <a href="#rewrite">Rewriting Engine</a></li>
31 <li><img alt="" src="./images/down.gif" /> <a href="#notfound">File Not Found</a></li>
33 <div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
35 <h2><a name="related" id="related">Related Modules and Directives</a></h2>
37 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="./mod/mod_alias.html">mod_alias</a></code></li><li><code class="module"><a href="./mod/mod_proxy.html">mod_proxy</a></code></li><li><code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code></li><li><code class="module"><a href="./mod/mod_userdir.html">mod_userdir</a></code></li><li><code class="module"><a href="./mod/mod_speling.html">mod_speling</a></code></li><li><code class="module"><a href="./mod/mod_vhost_alias.html">mod_vhost_alias</a></code></li></ul></td><td><ul><li><code class="directive"><a href="./mod/mod_alias.html#alias">Alias</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#aliasmatch">AliasMatch</a></code></li><li><code class="directive"><a href="./mod/mod_speling.html#checkspelling">CheckSpelling</a></code></li><li><code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code></li><li><code class="directive"><a href="./mod/core.html#errordocument">ErrorDocument</a></code></li><li><code class="directive"><a href="./mod/core.html#options">Options</a></code></li><li><code class="directive"><a href="./mod/mod_proxy.html#proxypass">ProxyPass</a></code></li><li><code class="directive"><a href="./mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#redirect">Redirect</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#redirectmatch">RedirectMatch</a></code></li><li><code class="directive"><a href="./mod/mod_rewrite.html#rewritecond">RewriteCond</a></code></li><li><code class="directive"><a href="./mod/mod_rewrite.html#rewritematch">RewriteMatch</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#scriptalias">ScriptAlias</a></code></li><li><code class="directive"><a href="./mod/mod_alias.html#scriptaliasmatch">ScriptAliasMatch</a></code></li><li><code class="directive"><a href="./mod/mod_userdir.html#userdir">UserDir</a></code></li></ul></td></tr></table>
38 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
40 <h2><a name="documentroot" id="documentroot">DocumentRoot</a></h2>
42 <p>In deciding what file to serve for a given request, Apache's
43 default behavior is to take the URL-Path for the request (the part
44 of the URL following the hostname and port) and add it to the end
45 of the <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code> specified
46 in your configuration files. Therefore, the files and directories
47 underneath the <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code>
48 make up the basic document tree which will be visible from the
51 <p>Apache is also capable of <a href="vhosts/">Virtual
52 Hosting</a>, where the server receives requests for more than one
53 host. In this case, a different <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code> can be specified for each
54 virtual host, or alternatively, the directives provided by the
55 module <code class="module"><a href="./mod/mod_vhost_alias.html">mod_vhost_alias</a></code> can
56 be used to dynamically determine the appropriate place from which
57 to serve content based on the requested IP address or
59 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
61 <h2><a name="outside" id="outside">Files Outside the DocumentRoot</a></h2>
63 <p>There are frequently circumstances where it is necessary to
64 allow web access to parts of the filesystem that are not strictly
65 underneath the <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code>. Apache offers several
66 different ways to accomplish this. On Unix systems, symbolic links
67 can bring other parts of the filesystem under the <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code>. For security reasons,
68 Apache will follow symbolic links only if the <code class="directive"><a href="./mod/core.html#options">Options</a></code> setting for the relevant
69 directory includes <code>FollowSymLinks</code> or
70 <code>SymLinksIfOwnerMatch</code>.</p>
72 <p>Alternatively, the <code class="directive"><a href="./mod/mod_alias.html#alias">Alias</a></code> directive will map any part
73 of the filesystem into the web space. For example, with</p>
75 <div class="example"><p><code>Alias /docs /var/web</code></p></div>
77 <p>the URL <code>http://www.example.com/docs/dir/file.html</code>
78 will be served from <code>/var/web/dir/file.html</code>. The
79 <code class="directive"><a href="./mod/mod_alias.html#scriptalias">ScriptAlias</a></code> directive
80 works the same way, with the additional effect that all content
81 located at the target path is treated as CGI scripts.</p>
83 <p>For situations where you require additional flexibility, you
84 can use the <code class="directive"><a href="./mod/mod_alias.html#aliasmatch">AliasMatch</a></code> and
85 <code class="directive"><a href="./mod/mod_alias.html#scriptaliasmatch">ScriptAliasMatch</a></code>
86 directives to do powerful regular-expression based matching and
87 substitution. For example,</p>
89 <div class="example"><p><code>ScriptAliasMatch ^/~([a-zA-Z0-9]*)/cgi-bin/(.*)
90 /home/$1/cgi-bin/$2</code></p></div>
92 <p>will map a request to
93 <code>http://example.com/~user/cgi-bin/script.cgi</code> to the
94 path <code>/home/user/cgi-bin/script.cgi</code> and will treat
95 the resulting file as a CGI script.</p>
96 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
98 <h2><a name="user" id="user">User Directories</a></h2>
100 <p>Traditionally on Unix systems, the home directory of a
101 particular <em>user</em> can be referred to as
102 <code>~user/</code>. The module <code class="module"><a href="./mod/mod_userdir.html">mod_userdir</a></code>
103 extends this idea to the web by allowing files under each user's
104 home directory to be accessed using URLs such as the
107 <div class="example"><p><code>http://www.example.com/~user/file.html</code></p></div>
109 <p>For security reasons, it is inappropriate to give direct
110 access to a user's home directory from the web. Therefore, the
111 <code class="directive"><a href="./mod/mod_userdir.html#userdir">UserDir</a></code> directive
112 specifies a directory underneath the user's home directory
113 where web files are located. Using the default setting of
114 <code>Userdir public_html</code>, the above URL maps to a file
116 <code>/home/user/public_html/file.html</code> where
117 <code>/home/user/</code> is the user's home directory as
118 specified in <code>/etc/passwd</code>.</p>
120 <p>There are also several other forms of the
121 <code>Userdir</code> directive which you can use on systems
122 where <code>/etc/passwd</code> does not contain the location of
123 the home directory.</p>
125 <p>Some people find the "~" symbol (which is often encoded on the
126 web as <code>%7e</code>) to be awkward and prefer to use an
127 alternate string to represent user directories. This functionality
128 is not supported by mod_userdir. However, if users' home
129 directories are structured in a regular way, then it is possible
130 to use the <code class="directive"><a href="./mod/mod_alias.html#aliasmatch">AliasMatch</a></code>
131 directive to achieve the desired effect. For example, to make
132 <code>http://www.example.com/upages/user/file.html</code> map to
133 <code>/home/user/public_html/file.html</code>, use the following
134 <code>AliasMatch</code> directive:</p>
136 <div class="example"><p><code>AliasMatch ^/upages/([a-zA-Z0-9]*)/?(.*)
137 /home/$1/public_html/$2</code></p></div>
138 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
139 <div class="section">
140 <h2><a name="redirect" id="redirect">URL Redirection</a></h2>
142 <p>The configuration directives discussed in the above sections
143 tell Apache to get content from a specific place in the filesystem
144 and return it to the client. Sometimes, it is desirable instead to
145 inform the client that the requested content is located at a
146 different URL, and instruct the client to make a new request with
147 the new URL. This is called <em>redirection</em> and is
148 implemented by the <code class="directive"><a href="./mod/mod_alias.html#redirect">Redirect</a></code> directive. For example, if
149 the contents of the directory <code>/foo/</code> under the
150 <code class="directive"><a href="./mod/core.html#documentroot">DocumentRoot</a></code> are moved
151 to the new directory <code>/bar/</code>, you can instruct clients
152 to request the content at the new location as follows:</p>
154 <div class="example"><p><code>Redirect permanent /foo/
155 http://www.example.com/bar/</code></p></div>
157 <p>This will redirect any URL-Path starting in
158 <code>/foo/</code> to the same URL path on the
159 <code>www.example.com</code> server with <code>/bar/</code>
160 substituted for <code>/foo/</code>. You can redirect clients to
161 any server, not only the origin server.</p>
163 <p>Apache also provides a <code class="directive"><a href="./mod/mod_alias.html#redirectmatch">RedirectMatch</a></code> directive for more
164 complicated rewriting problems. For example, to redirect requests
165 for the site home page to a different site, but leave all other
166 requests alone, use the following configuration:</p>
168 <div class="example"><p><code>RedirectMatch permanent ^/$
169 http://www.example.com/startpage.html</code></p></div>
171 <p>Alternatively, to temporarily redirect all pages on one site
172 to a particular page on another site, use the following:</p>
174 <div class="example"><p><code>RedirectMatch temp .*
175 http://othersite.example.com/startpage.html</code></p></div>
176 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
177 <div class="section">
178 <h2><a name="proxy" id="proxy">Reverse Proxy</a></h2>
180 <p>Apache also allows you to bring remote documents into the URL space
181 of the local server. This technique is called <em>reverse
182 proxying</em> because the web server acts like a proxy server by
183 fetching the documents from a remote server and returning them to the
184 client. It is different from normal proxying because, to the client,
185 it appears the documents originate at the reverse proxy server.</p>
187 <p>In the following example, when clients request documents under the
188 <code>/foo/</code> directory, the server fetches those documents from
189 the <code>/bar/</code> directory on <code>internal.example.com</code>
190 and returns them to the client as if they were from the local
193 <div class="example"><p><code>
194 ProxyPass /foo/ http://internal.example.com/bar/<br />
195 ProxyPassReverse /foo/ http://internal.example.com/bar/
198 <p>The <code class="directive"><a href="./mod/mod_proxy.html#proxypass">ProxyPass</a></code> configures
199 the server to fetch the appropriate documents, while the
200 <code class="directive"><a href="./mod/mod_proxy.html#proxypassreverse">ProxyPassReverse</a></code>
201 directive rewrites redirects originating at
202 <code>internal.example.com</code> so that they target the appropriate
203 directory on the local server. It is important to note, however, that
204 links inside the documents will not be rewritten. So any absolute
205 links on <code>internal.example.com</code> will result in the client
206 breaking out of the proxy server and requesting directly from
207 <code>internal.example.com</code>.</p>
208 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
209 <div class="section">
210 <h2><a name="rewrite" id="rewrite">Rewriting Engine</a></h2>
212 <p>When even more powerful substitution is required, the rewriting
213 engine provided by <code class="module"><a href="./mod/mod_rewrite.html">mod_rewrite</a></code>
214 can be useful. The directives provided by this module use
215 characteristics of the request such as browser type or source IP
216 address in deciding from where to serve content. In addition,
217 mod_rewrite can use external database files or programs to
218 determine how to handle a request. The rewriting engine is capable
219 of performing all three types of mappings discussed above:
220 internal redirects (aliases), external redirects, and proxying.
221 Many practical examples employing mod_rewrite are discussed in the
222 <a href="misc/rewriteguide.html">URL Rewriting Guide</a>.</p>
223 </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div>
224 <div class="section">
225 <h2><a name="notfound" id="notfound">File Not Found</a></h2>
227 <p>Inevitably, URLs will be requested for which no matching
228 file can be found in the filesystem. This can happen for
229 several reasons. In some cases, it can be a result of moving
230 documents from one location to another. In this case, it is
231 best to use <a href="#redirect">URL redirection</a> to inform
232 clients of the new location of the resource. In this way, you
233 can assure that old bookmarks and links will continue to work,
234 even though the resource is at a new location.</p>
236 <p>Another common cause of "File Not Found" errors is
237 accidental mistyping of URLs, either directly in the browser,
238 or in HTML links. Apache provides the module
239 <code class="module"><a href="./mod/mod_speling.html">mod_speling</a></code> (sic) to help with
240 this problem. When this module is activated, it will intercept
241 "File Not Found" errors and look for a resource with a similar
242 filename. If one such file is found, mod_speling will send an
243 HTTP redirect to the client informing it of the correct
244 location. If several "close" files are found, a list of
245 available alternatives will be presented to the client.</p>
247 <p>An especially useful feature of mod_speling, is that it will
248 compare filenames without respect to case. This can help
249 systems where users are unaware of the case-sensitive nature of
250 URLs and the unix filesystem. But using mod_speling for
251 anything more than the occasional URL correction can place
252 additional load on the server, since each "incorrect" request
253 is followed by a URL redirection and a new request from the
256 <p>If all attempts to locate the content fail, Apache returns
257 an error page with HTTP status code 404 (file not found). The
258 appearance of this page is controlled with the
259 <code class="directive"><a href="./mod/core.html#errordocument">ErrorDocument</a></code> directive
260 and can be customized in a flexible manner as discussed in the
261 <a href="custom-error.html">Custom error responses</a>
265 <p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p>
266 <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></div>