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21 <div id="page-content">
22 <div id="preamble"><h1>Apache Module mod_expires</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
25 <a href="../fr/mod/mod_expires.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
26 <a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
27 <a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
29 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Generation of <code>Expires</code> and
30 <code>Cache-Control</code> HTTP headers according to user-specified
32 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
33 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>expires_module</td></tr>
34 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_expires.c</td></tr></table>
37 <p>This module controls the setting of the <code>Expires</code>
38 HTTP header and the <code>max-age</code> directive of the
39 <code>Cache-Control</code> HTTP header in server responses. The
40 expiration date can set to be relative to either the time the
41 source file was last modified, or to the time of the client
44 <p>These HTTP headers are an instruction to the client about the
45 document's validity and persistence. If cached, the document may
46 be fetched from the cache rather than from the source until this
47 time has passed. After that, the cache copy is considered
48 "expired" and invalid, and a new copy must be obtained from the
51 <p>To modify <code>Cache-Control</code> directives other than
52 <code>max-age</code> (see <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">RFC
53 2616 section 14.9</a>), you can use the <code class="directive"><a href="../mod/mod_headers.html#header">Header</a></code> directive.</p>
56 <div id="quickview"><h3 class="directives">Directives</h3>
58 <li><img alt="" src="../images/down.gif" /> <a href="#expiresactive">ExpiresActive</a></li>
59 <li><img alt="" src="../images/down.gif" /> <a href="#expiresbytype">ExpiresByType</a></li>
60 <li><img alt="" src="../images/down.gif" /> <a href="#expiresdefault">ExpiresDefault</a></li>
64 <li><img alt="" src="../images/down.gif" /> <a href="#AltSyn">Alternate Interval Syntax</a></li>
66 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
68 <h2><a name="AltSyn" id="AltSyn">Alternate Interval Syntax</a></h2>
69 <p>The <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code> and
70 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directives
71 can also be defined in a more readable syntax of the form:</p>
73 <div class="example"><p><code>
74 ExpiresDefault "<base> [plus] {<num>
76 ExpiresByType type/encoding "<base> [plus]
77 {<num> <type>}*"
80 <p>where <base> is one of:</p>
83 <li><code>access</code></li>
85 <li><code>now</code> (equivalent to
86 '<code>access</code>')</li>
88 <li><code>modification</code></li>
91 <p>The <code>plus</code> keyword is optional. <num>
92 should be an integer value [acceptable to <code>atoi()</code>],
93 and <type> is one of:</p>
96 <li><code>years</code></li>
97 <li><code>months</code></li>
98 <li><code>weeks</code></li>
99 <li><code>days</code></li>
100 <li><code>hours</code></li>
101 <li><code>minutes</code></li>
102 <li><code>seconds</code></li>
105 <p>For example, any of the following directives can be used to
106 make documents expire 1 month after being accessed, by
109 <div class="example"><p><code>
110 ExpiresDefault "access plus 1 month"<br />
111 ExpiresDefault "access plus 4 weeks"<br />
112 ExpiresDefault "access plus 30 days"
115 <p>The expiry time can be fine-tuned by adding several
116 '<num> <type>' clauses:</p>
118 <div class="example"><p><code>
119 ExpiresByType text/html "access plus 1 month 15
121 ExpiresByType image/gif "modification plus 5 hours 3
125 <p>Note that if you use a modification date based setting, the
126 Expires header will <strong>not</strong> be added to content
127 that does not come from a file on disk. This is due to the fact
128 that there is no modification time for such content.</p>
130 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
131 <div class="directive-section"><h2><a name="ExpiresActive" id="ExpiresActive">ExpiresActive</a> <a name="expiresactive" id="expiresactive">Directive</a></h2>
132 <table class="directive">
133 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables generation of <code>Expires</code>
135 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresActive On|Off</code></td></tr>
136 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ExpiresActive Off</code></td></tr>
137 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
138 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
139 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
140 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
142 <p>This directive enables or disables the generation of the
143 <code>Expires</code> and <code>Cache-Control</code> headers for
144 the document realm in question. (That is, if found in an
145 <code>.htaccess</code> file, for instance, it applies only to
146 documents generated from that directory.) If set to
147 <code>Off</code>, the headers will not be generated for any
148 document in the realm (unless overridden at a lower level, such as
149 an <code>.htaccess</code> file overriding a server config
150 file). If set to <code>On</code>, the headers will be added to
151 served documents according to the criteria defined by the
152 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> and
153 <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
154 directives (<em>q.v.</em>).</p>
156 <p>Note that this directive does not guarantee that an
157 <code>Expires</code> or <code>Cache-Control</code> header will be
158 generated. If the criteria aren't met, no header will be sent, and
159 the effect will be as though this directive wasn't even
163 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
164 <div class="directive-section"><h2><a name="ExpiresByType" id="ExpiresByType">ExpiresByType</a> <a name="expiresbytype" id="expiresbytype">Directive</a></h2>
165 <table class="directive">
166 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Value of the <code>Expires</code> header configured
167 by MIME type</td></tr>
168 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresByType <var>MIME-type</var>
169 <var><code>seconds</var></code></td></tr>
170 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
171 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
172 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
173 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
175 <p>This directive defines the value of the <code>Expires</code>
176 header and the <code>max-age</code> directive of the
177 <code>Cache-Control</code> header generated for documents of the
178 specified type (<em>e.g.</em>, <code>text/html</code>). The second
179 argument sets the number of seconds that will be added to a base
180 time to construct the expiration date. The <code>Cache-Control:
181 max-age</code> is calculated by subtracting the request time from
182 the expiration date and expressing the result in seconds.</p>
184 <p>The base time is either the last modification time of the
185 file, or the time of the client's access to the document. Which
186 should be used is specified by the
187 <code><var><code></var></code> field; <code>M</code>
188 means that the file's last modification time should be used as
189 the base time, and <code>A</code> means the client's access
190 time should be used.</p>
192 <p>The difference in effect is subtle. If <code>M</code> is used,
193 all current copies of the document in all caches will expire at
194 the same time, which can be good for something like a weekly
195 notice that's always found at the same URL. If <code>A</code> is
196 used, the date of expiration is different for each client; this
197 can be good for image files that don't change very often,
198 particularly for a set of related documents that all refer to
199 the same images (<em>i.e.</em>, the images will be accessed
200 repeatedly within a relatively short timespan).</p>
202 <div class="example"><h3>Example:</h3><p><code>
203 # enable expirations<br />
204 ExpiresActive On<br />
205 # expire GIF images after a month in the client's cache<br />
206 ExpiresByType image/gif A2592000<br />
207 # HTML documents are good for a week from the<br />
208 # time they were changed<br />
209 ExpiresByType text/html M604800
212 <p>Note that this directive only has effect if
213 <code>ExpiresActive On</code> has been specified. It overrides,
214 for the specified MIME type <em>only</em>, any expiration date
215 set by the <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
218 <p>You can also specify the expiration time calculation using
219 an <a href="#AltSyn">alternate syntax</a>, described earlier in
223 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
224 <div class="directive-section"><h2><a name="ExpiresDefault" id="ExpiresDefault">ExpiresDefault</a> <a name="expiresdefault" id="expiresdefault">Directive</a></h2>
225 <table class="directive">
226 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Default algorithm for calculating expiration time</td></tr>
227 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresDefault <var><code>seconds</var></code></td></tr>
228 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
229 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
230 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
231 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
233 <p>This directive sets the default algorithm for calculating the
234 expiration time for all documents in the affected realm. It can be
235 overridden on a type-by-type basis by the <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directive. See the
236 description of that directive for details about the syntax of the
237 argument, and the <a href="#AltSyn">alternate syntax</a>
238 description as well.</p>
242 <div class="bottomlang">
243 <p><span>Available Languages: </span><a href="../en/mod/mod_expires.html" title="English"> en </a> |
244 <a href="../fr/mod/mod_expires.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
245 <a href="../ja/mod/mod_expires.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
246 <a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
247 </div><div id="footer">
248 <p class="apache">Copyright 2011 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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