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27 <div id="preamble"><h1>Apache Module mod_expires</h1>
29 <p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
30 <a href="../fr/mod/mod_expires.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
31 <a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
32 <a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
34 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Generation of <code>Expires</code> and
35 <code>Cache-Control</code> HTTP headers according to user-specified
37 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
38 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>expires_module</td></tr>
39 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_expires.c</td></tr></table>
42 <p>This module controls the setting of the <code>Expires</code>
43 HTTP header and the <code>max-age</code> directive of the
44 <code>Cache-Control</code> HTTP header in server responses. The
45 expiration date can set to be relative to either the time the
46 source file was last modified, or to the time of the client
49 <p>These HTTP headers are an instruction to the client about the
50 document's validity and persistence. If cached, the document may
51 be fetched from the cache rather than from the source until this
52 time has passed. After that, the cache copy is considered
53 "expired" and invalid, and a new copy must be obtained from the
56 <p>To modify <code>Cache-Control</code> directives other than
57 <code>max-age</code> (see <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">RFC
58 2616 section 14.9</a>), you can use the <code class="directive"><a href="../mod/mod_headers.html#header">Header</a></code> directive.</p>
60 <p> When the <code>Expires</code> header is already part of the response
61 generated by the server, for example when generated by a CGI script or
62 proxied from an origin server, this module does not change or add
63 an <code>Expires</code> or <code>Cache-Control</code> header.</p>
65 <div id="quickview"><h3>Topics</h3>
67 <li><img alt="" src="../images/down.gif" /> <a href="#AltSyn">Alternate Interval Syntax</a></li>
68 </ul><h3 class="directives">Directives</h3>
70 <li><img alt="" src="../images/down.gif" /> <a href="#expiresactive">ExpiresActive</a></li>
71 <li><img alt="" src="../images/down.gif" /> <a href="#expiresbytype">ExpiresByType</a></li>
72 <li><img alt="" src="../images/down.gif" /> <a href="#expiresdefault">ExpiresDefault</a></li>
74 <ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
75 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
77 <h2><a name="AltSyn" id="AltSyn">Alternate Interval Syntax</a></h2>
78 <p>The <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code> and
79 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directives
80 can also be defined in a more readable syntax of the form:</p>
82 <pre class="prettyprint lang-config">ExpiresDefault "<var>base</var> [plus <var>num</var> <var>type</var>] [<var>num</var> <var>type</var>] ..."
83 ExpiresByType type/encoding "<var>base</var> [plus <var>num</var> <var>type</var>] [<var>num</var> <var>type</var>] ..."</pre>
86 <p>where <var>base</var> is one of:</p>
89 <li><code>access</code></li>
91 <li><code>now</code> (equivalent to
92 '<code>access</code>')</li>
94 <li><code>modification</code></li>
97 <p>The <code>plus</code> keyword is optional. <var>num</var>
98 should be an integer value [acceptable to <code>atoi()</code>],
99 and <var>type</var> is one of:</p>
102 <li><code>years</code></li>
103 <li><code>months</code></li>
104 <li><code>weeks</code></li>
105 <li><code>days</code></li>
106 <li><code>hours</code></li>
107 <li><code>minutes</code></li>
108 <li><code>seconds</code></li>
111 <p>For example, any of the following directives can be used to
112 make documents expire 1 month after being accessed, by
115 <pre class="prettyprint lang-config">ExpiresDefault "access plus 1 month"
116 ExpiresDefault "access plus 4 weeks"
117 ExpiresDefault "access plus 30 days"</pre>
120 <p>The expiry time can be fine-tuned by adding several
121 '<var>num</var> <var>type</var>' clauses:</p>
123 <pre class="prettyprint lang-config">ExpiresByType text/html "access plus 1 month 15 days 2 hours"
124 ExpiresByType image/gif "modification plus 5 hours 3 minutes"</pre>
127 <p>Note that if you use a modification date based setting, the
128 Expires header will <strong>not</strong> be added to content
129 that does not come from a file on disk. This is due to the fact
130 that there is no modification time for such content.</p>
132 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
133 <div class="directive-section"><h2><a name="ExpiresActive" id="ExpiresActive">ExpiresActive</a> <a name="expiresactive" id="expiresactive">Directive</a></h2>
134 <table class="directive">
135 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables generation of <code>Expires</code>
137 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresActive On|Off</code></td></tr>
138 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ExpiresActive Off</code></td></tr>
139 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
140 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
141 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
142 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
144 <p>This directive enables or disables the generation of the
145 <code>Expires</code> and <code>Cache-Control</code> headers for
146 the document realm in question. (That is, if found in an
147 <code>.htaccess</code> file, for instance, it applies only to
148 documents generated from that directory.) If set to
149 <code>Off</code>, the headers will not be generated for any
150 document in the realm (unless overridden at a lower level, such as
151 an <code>.htaccess</code> file overriding a server config
152 file). If set to <code>On</code>, the headers will be added to
153 served documents according to the criteria defined by the
154 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> and
155 <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
156 directives (<em>q.v.</em>).</p>
158 <p>Note that this directive does not guarantee that an
159 <code>Expires</code> or <code>Cache-Control</code> header will be
160 generated. If the criteria aren't met, no header will be sent, and
161 the effect will be as though this directive wasn't even
165 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
166 <div class="directive-section"><h2><a name="ExpiresByType" id="ExpiresByType">ExpiresByType</a> <a name="expiresbytype" id="expiresbytype">Directive</a></h2>
167 <table class="directive">
168 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Value of the <code>Expires</code> header configured
169 by MIME type</td></tr>
170 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresByType <var>MIME-type</var>
171 <var><code>seconds</var></code></td></tr>
172 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
173 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
174 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
175 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
177 <p>This directive defines the value of the <code>Expires</code>
178 header and the <code>max-age</code> directive of the
179 <code>Cache-Control</code> header generated for documents of the
180 specified type (<em>e.g.</em>, <code>text/html</code>). The second
181 argument sets the number of seconds that will be added to a base
182 time to construct the expiration date. The <code>Cache-Control:
183 max-age</code> is calculated by subtracting the request time from
184 the expiration date and expressing the result in seconds.</p>
186 <p>The base time is either the last modification time of the
187 file, or the time of the client's access to the document. Which
188 should be used is specified by the
189 <code><var><code></var></code> field; <code>M</code>
190 means that the file's last modification time should be used as
191 the base time, and <code>A</code> means the client's access
192 time should be used.</p>
194 <p>The difference in effect is subtle. If <code>M</code> is used,
195 all current copies of the document in all caches will expire at
196 the same time, which can be good for something like a weekly
197 notice that's always found at the same URL. If <code>A</code> is
198 used, the date of expiration is different for each client; this
199 can be good for image files that don't change very often,
200 particularly for a set of related documents that all refer to
201 the same images (<em>i.e.</em>, the images will be accessed
202 repeatedly within a relatively short timespan).</p>
204 <div class="example"><h3>Example:</h3><pre class="prettyprint lang-config"># enable expirations
206 # expire GIF images after a month in the client's cache
207 ExpiresByType image/gif A2592000
208 # HTML documents are good for a week from the
209 # time they were changed
210 ExpiresByType text/html M604800</pre>
213 <p>Note that this directive only has effect if
214 <code>ExpiresActive On</code> has been specified. It overrides,
215 for the specified MIME type <em>only</em>, any expiration date
216 set by the <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
219 <p>You can also specify the expiration time calculation using
220 an <a href="#AltSyn">alternate syntax</a>, described earlier in
224 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
225 <div class="directive-section"><h2><a name="ExpiresDefault" id="ExpiresDefault">ExpiresDefault</a> <a name="expiresdefault" id="expiresdefault">Directive</a></h2>
226 <table class="directive">
227 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Default algorithm for calculating expiration time</td></tr>
228 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresDefault <var><code>seconds</var></code></td></tr>
229 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
230 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
231 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
232 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
234 <p>This directive sets the default algorithm for calculating the
235 expiration time for all documents in the affected realm. It can be
236 overridden on a type-by-type basis by the <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directive. See the
237 description of that directive for details about the syntax of the
238 argument, and the <a href="#AltSyn">alternate syntax</a>
239 description as well.</p>
243 <div class="bottomlang">
244 <p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
245 <a href="../fr/mod/mod_expires.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
246 <a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
247 <a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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