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261 lines
9.8 KiB
HTML
261 lines
9.8 KiB
HTML
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Apache module mod_expires</title>
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<!--#include virtual="header.html" -->
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<h1 align="CENTER">Module mod_expires</h1>
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<p>This module provides for the generation of
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<code>Expires</code> HTTP headers according to user-specified
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criteria.</p>
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<p><a href="module-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="module-dict.html#SourceFile"
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rel="Help"><strong>Source File:</strong></a>
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mod_expires.c<br />
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<a href="module-dict.html#ModuleIdentifier"
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rel="Help"><strong>Module Identifier:</strong></a>
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expires_module<br />
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<a href="module-dict.html#Compatibility"
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rel="Help"><strong>Compatibility:</strong></a> Available in
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Apache 1.2 and later.</p>
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<h2>Summary</h2>
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<p>This module controls the setting of the <code>Expires</code>
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HTTP header in server responses. The expiration date can set to
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be relative to either the time the source file was last
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modified, or to the time of the client access.</p>
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<p>The <code>Expires</code> HTTP header is an instruction to
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the client about the document's validity and persistence. If
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cached, the document may be fetched from the cache rather than
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from the source until this time has passed. After that, the
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cache copy is considered "expired" and invalid, and a new copy
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must be obtained from the source.</p>
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<h2>Directives</h2>
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<ul>
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<li><a href="#expiresactive">ExpiresActive</a></li>
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<li><a href="#expiresbytype">ExpiresByType</a></li>
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<li><a href="#expiresdefault">ExpiresDefault</a></li>
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</ul>
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<h2><a id="AltSyn" name="AltSyn">Alternate Interval
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Syntax</a></h2>
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<p>The <a
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href="#expiresdefault"><samp>ExpiresDefault</samp></a> and <a
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href="#expiresbytype"><samp>ExpiresByType</samp></a> directives
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can also be defined in a more readable syntax of the form:</p>
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<dl>
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<dd><code>ExpiresDefault "<base> [plus] {<num>
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<type>}*"<br />
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ExpiresByType type/encoding "<base> [plus]
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{<num> <type>}*"</code></dd>
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</dl>
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<p>where <base> is one of:</p>
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<ul>
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<li><samp>access</samp></li>
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<li><samp>now</samp> (equivalent to
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'<samp>access</samp>')</li>
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<li><samp>modification</samp></li>
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</ul>
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<p>The '<samp>plus</samp>' keyword is optional. <num>
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should be an integer value [acceptable to <samp>atoi()</samp>],
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and <type> is one of:</p>
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<ul>
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<li><samp>years</samp></li>
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<li><samp>months</samp></li>
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<li><samp>weeks</samp></li>
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<li><samp>days</samp></li>
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<li><samp>hours</samp></li>
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<li><samp>minutes</samp></li>
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<li><samp>seconds</samp></li>
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</ul>
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<p>For example, any of the following directives can be used to
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make documents expire 1 month after being accessed, by
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default:</p>
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<dl>
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<dd><code>ExpiresDefault "access plus 1 month"<br />
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ExpiresDefault "access plus 4 weeks"<br />
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ExpiresDefault "access plus 30 days"</code></dd>
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</dl>
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<p>The expiry time can be fine-tuned by adding several
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'<num> <type>' clauses:</p>
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<dl>
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<dd><code>ExpiresByType text/html "access plus 1 month 15
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days 2 hours"<br />
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ExpiresByType image/gif "modification plus 5 hours 3
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minutes"</code></dd>
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</dl>
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<p>Note that if you use a modification date based setting, the
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Expires header will <strong>not</strong> be added to content
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that does not come from a file on disk. This is due to the fact
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that there is no modification time for such content.</p>
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<hr />
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<h2><a id="expiresactive" name="expiresactive">ExpiresActive
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directive</a></h2>
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<!--%plaintext <?INDEX {\tt ExpiresActive} directive> -->
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<p><a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> ExpiresActive
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on|off<br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config, virtual
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host, directory, .htaccess<br />
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<a href="directive-dict.html#Override"
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rel="Help"><strong>Override:</strong></a> Indexes<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_expires</p>
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<p>This directive enables or disables the generation of the
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<code>Expires</code> header for the document realm in question.
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(That is, if found in an <code>.htaccess</code> file, for
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instance, it applies only to documents generated from that
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directory.) If set to <em><code>Off</code></em>, no
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<code>Expires</code> header will be generated for any document
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in the realm (unless overridden at a lower level, such as an
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<code>.htaccess</code> file overriding a server config file).
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If set to <em><code>On</code></em>, the header will be added to
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served documents according to the criteria defined by the <a
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href="#expiresbytype">ExpiresByType</a> and <a
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href="#expiresdefault">ExpiresDefault</a> directives
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(<em>q.v.</em>).</p>
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<p>Note that this directive does not guarantee that an
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<code>Expires</code> header will be generated. If the criteria
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aren't met, no header will be sent, and the effect will be as
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though this directive wasn't even specified.</p>
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<hr />
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<h2><a id="expiresbytype" name="expiresbytype">ExpiresByType
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directive</a></h2>
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<!--%plaintext <?INDEX {\tt ExpiresByType} directive> -->
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<p><a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> ExpiresByType
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<em>MIME-type <code>seconds</em><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config, virtual
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host, directory, .htaccess<br />
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<a href="directive-dict.html#Override"
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rel="Help"><strong>Override:</strong></a> Indexes<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_expires</p>
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<p>This directive defines the value of the <code>Expires</code>
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header generated for documents of the specified type
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(<em>e.g.</em>, <code>text/html</code>). The second argument
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sets the number of seconds that will be added to a base time to
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construct the expiration date.</p>
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<p>The base time is either the last modification time of the
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file, or the time of the client's access to the document. Which
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should be used is specified by the
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<code><em><code></em></code> field; <strong>M</strong>
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means that the file's last modification time should be used as
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the base time, and <strong>A</strong> means the client's access
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time should be used.</p>
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<p>The difference in effect is subtle. If <em>M</em> is used,
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all current copies of the document in all caches will expire at
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the same time, which can be good for something like a weekly
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notice that's always found at the same URL. If <em>A</em> is
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used, the date of expiration is different for each client; this
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can be good for image files that don't change very often,
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particularly for a set of related documents that all refer to
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the same images (<em>i.e.</em>, the images will be accessed
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repeatedly within a relatively short timespan).</p>
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<p><strong>Example:</strong></p>
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<pre>
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ExpiresActive On # enable expirations
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ExpiresByType image/gif A2592000 # expire GIF images after a month
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# in the client's cache
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ExpiresByType text/html M604800 # HTML documents are good for a
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# week from the time they were
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# changed, period
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</pre>
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<br />
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<br />
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<p>Note that this directive only has effect if
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<code>ExpiresActive On</code> has been specified. It overrides,
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for the specified MIME type <em>only</em>, any expiration date
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set by the <a href="#expiresdefault">ExpiresDefault</a>
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directive.</p>
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<p>You can also specify the expiration time calculation using
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an <a href="#AltSyn">alternate syntax</a>, described later in
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this document.</p>
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<hr />
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<h2><a id="expiresdefault" name="expiresdefault">ExpiresDefault
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directive</a></h2>
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<!--%plaintext <?INDEX {\tt ExpiresDefault} directive> -->
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<p><a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> ExpiresDefault
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<em><code>seconds</em><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config, virtual
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host, directory, .htaccess<br />
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<a href="directive-dict.html#Override"
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rel="Help"><strong>Override:</strong></a> Indexes<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_expires</p>
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<p>This directive sets the default algorithm for calculating
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the expiration time for all documents in the affected realm. It
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can be overridden on a type-by-type basis by the <a
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href="#expiresbytype">ExpiresByType</a> directive. See the
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description of that directive for details about the syntax of
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the argument, and the <a href="#AltSyn">alternate syntax</a>
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description as well.</p>
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