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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 <h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_expires">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_expires">Report a bug</a></li></ul><h3>See also</h3>
76 <li><a href="#comments_section">Comments</a></li></ul></div>
77 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
79 <h2><a name="AltSyn" id="AltSyn">Alternate Interval Syntax</a> <a title="Permanent link" href="#AltSyn" class="permalink">¶</a></h2>
80 <p>The <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code> and
81 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directives
82 can also be defined in a more readable syntax of the form:</p>
84 <pre class="prettyprint lang-config">ExpiresDefault "<var>base</var> [plus <var>num</var> <var>type</var>] [<var>num</var> <var>type</var>] ..."
85 ExpiresByType type/encoding "<var>base</var> [plus <var>num</var> <var>type</var>] [<var>num</var> <var>type</var>] ..."</pre>
88 <p>where <var>base</var> is one of:</p>
91 <li><code>access</code></li>
93 <li><code>now</code> (equivalent to
94 '<code>access</code>')</li>
96 <li><code>modification</code></li>
99 <p>The <code>plus</code> keyword is optional. <var>num</var>
100 should be an integer value [acceptable to <code>atoi()</code>],
101 and <var>type</var> is one of:</p>
104 <li><code>years</code></li>
105 <li><code>months</code></li>
106 <li><code>weeks</code></li>
107 <li><code>days</code></li>
108 <li><code>hours</code></li>
109 <li><code>minutes</code></li>
110 <li><code>seconds</code></li>
113 <p>For example, any of the following directives can be used to
114 make documents expire 1 month after being accessed, by
117 <pre class="prettyprint lang-config">ExpiresDefault "access plus 1 month"
118 ExpiresDefault "access plus 4 weeks"
119 ExpiresDefault "access plus 30 days"</pre>
122 <p>The expiry time can be fine-tuned by adding several
123 '<var>num</var> <var>type</var>' clauses:</p>
125 <pre class="prettyprint lang-config">ExpiresByType text/html "access plus 1 month 15 days 2 hours"
126 ExpiresByType image/gif "modification plus 5 hours 3 minutes"</pre>
129 <p>Note that if you use a modification date based setting, the
130 Expires header will <strong>not</strong> be added to content
131 that does not come from a file on disk. This is due to the fact
132 that there is no modification time for such content.</p>
134 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
135 <div class="directive-section"><h2><a name="ExpiresActive" id="ExpiresActive">ExpiresActive</a> <a name="expiresactive" id="expiresactive">Directive</a> <a title="Permanent link" href="#expiresactive" class="permalink">¶</a></h2>
136 <table class="directive">
137 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables generation of <code>Expires</code>
139 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresActive On|Off</code></td></tr>
140 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>ExpiresActive Off</code></td></tr>
141 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
142 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
143 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
144 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
146 <p>This directive enables or disables the generation of the
147 <code>Expires</code> and <code>Cache-Control</code> headers for
148 the document realm in question. (That is, if found in an
149 <code>.htaccess</code> file, for instance, it applies only to
150 documents generated from that directory.) If set to
151 <code>Off</code>, the headers will not be generated for any
152 document in the realm (unless overridden at a lower level, such as
153 an <code>.htaccess</code> file overriding a server config
154 file). If set to <code>On</code>, the headers will be added to
155 served documents according to the criteria defined by the
156 <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> and
157 <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
158 directives (<em>q.v.</em>).</p>
160 <p>Note that this directive does not guarantee that an
161 <code>Expires</code> or <code>Cache-Control</code> header will be
162 generated. If the criteria aren't met, no header will be sent, and
163 the effect will be as though this directive wasn't even
167 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
168 <div class="directive-section"><h2><a name="ExpiresByType" id="ExpiresByType">ExpiresByType</a> <a name="expiresbytype" id="expiresbytype">Directive</a> <a title="Permanent link" href="#expiresbytype" class="permalink">¶</a></h2>
169 <table class="directive">
170 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Value of the <code>Expires</code> header configured
171 by MIME type</td></tr>
172 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresByType <var>MIME-type</var>
173 <var><code>seconds</var></code></td></tr>
174 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
175 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
176 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
177 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
179 <p>This directive defines the value of the <code>Expires</code>
180 header and the <code>max-age</code> directive of the
181 <code>Cache-Control</code> header generated for documents of the
182 specified type (<em>e.g.</em>, <code>text/html</code>). The second
183 argument sets the number of seconds that will be added to a base
184 time to construct the expiration date. The <code>Cache-Control:
185 max-age</code> is calculated by subtracting the request time from
186 the expiration date and expressing the result in seconds.</p>
188 <p>The base time is either the last modification time of the
189 file, or the time of the client's access to the document. Which
190 should be used is specified by the
191 <code><var><code></var></code> field; <code>M</code>
192 means that the file's last modification time should be used as
193 the base time, and <code>A</code> means the client's access
194 time should be used.</p>
196 <p>The difference in effect is subtle. If <code>M</code> is used,
197 all current copies of the document in all caches will expire at
198 the same time, which can be good for something like a weekly
199 notice that's always found at the same URL. If <code>A</code> is
200 used, the date of expiration is different for each client; this
201 can be good for image files that don't change very often,
202 particularly for a set of related documents that all refer to
203 the same images (<em>i.e.</em>, the images will be accessed
204 repeatedly within a relatively short timespan).</p>
206 <div class="example"><h3>Example:</h3><pre class="prettyprint lang-config"># enable expirations
208 # expire GIF images after a month in the client's cache
209 ExpiresByType image/gif A2592000
210 # HTML documents are good for a week from the
211 # time they were changed
212 ExpiresByType text/html M604800</pre>
215 <p>Note that this directive only has effect if
216 <code>ExpiresActive On</code> has been specified. It overrides,
217 for the specified MIME type <em>only</em>, any expiration date
218 set by the <code class="directive"><a href="#expiresdefault">ExpiresDefault</a></code>
221 <p>You can also specify the expiration time calculation using
222 an <a href="#AltSyn">alternate syntax</a>, described earlier in
226 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
227 <div class="directive-section"><h2><a name="ExpiresDefault" id="ExpiresDefault">ExpiresDefault</a> <a name="expiresdefault" id="expiresdefault">Directive</a> <a title="Permanent link" href="#expiresdefault" class="permalink">¶</a></h2>
228 <table class="directive">
229 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Default algorithm for calculating expiration time</td></tr>
230 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>ExpiresDefault <var><code>seconds</var></code></td></tr>
231 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
232 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>Indexes</td></tr>
233 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
234 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_expires</td></tr>
236 <p>This directive sets the default algorithm for calculating the
237 expiration time for all documents in the affected realm. It can be
238 overridden on a type-by-type basis by the <code class="directive"><a href="#expiresbytype">ExpiresByType</a></code> directive. See the
239 description of that directive for details about the syntax of the
240 argument, and the <a href="#AltSyn">alternate syntax</a>
241 description as well.</p>
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249 <a href="../ko/mod/mod_expires.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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