docs/manual/mod/mod_expires.html - httpd - Git at Google

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  <HEAD>
   <TITLE>Apache module mod_expires</TITLE>
  </HEAD>
  <BODY>
   <!--#include virtual="header.html" -->
   <H1>Module mod_expires</H1>
   <P>
   This module is contained in the <CODE>mod_expires.c</CODE> file, and
   is <STRONG>not</STRONG> compiled in by default.  It provides for the
   generation of <CODE>Expires</CODE> headers according to user-specified
   criteria.
   </P>
   <H2>Summary</H2>
   <P>
   This module controls the setting of the <CODE>Expires</CODE> HTTP
   header in server responses.  The expiration date can set to be
   relative to either the time the source file was last modified, or to
   the time of the client access.
   </P>
   <P>
   The <CODE>Expires</CODE> HTTP header is an instruction to the client
   about the document's validity and persistence.  If cached, the document
   may be fetched from the cache rather than from the source until this
   time has passed.  After that, the cache copy is considered
   &quot;expired&quot; and invalid, and a new copy must be obtained from
   the source.
   </P>
   <H2>Directives</H2>
   <P>
   <MENU>
    <LI><A
         HREF="#expiresactive"
        >ExpiresActive</A>
    </LI>
    <LI><A
         HREF="#expiresbytype"
        >ExpiresByType</A>
    </LI>
    <LI><A
         HREF="#expiresdefault"
        >ExpiresDefault</A>
    </LI>
   </MENU>
   <HR>
   <A NAME="expiresactive">
    <H2>ExpiresActive directive</H2>
   </A>
   <!--%plaintext &lt;?INDEX {\tt ExpiresActive} directive&gt; -->
   <P>
   <STRONG>Syntax:</STRONG> ExpiresActive <EM>boolean</EM>
   <BR>
   <STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
   <br>
   <STRONG>Override:</STRONG> Indexes
   <br>
   <STRONG>Status:</STRONG> Extension
   <br>
   <STRONG>Module:</STRONG> mod_expires
   </P>
   <P>
   This directive enables or disables the generation of the
   <CODE>Expires</CODE> header for the document realm in question.  (That
   is, if found in an <CODE>.htaccess</CODE> file, for instance, it
   applies only to documents generated from that directory.)  If set to
   <EM><CODE>Off</CODE></EM>, no <CODE>Expires</CODE> header will be
   generated for any document in the realm (unless overridden at a lower
   level, such as an <CODE>.htaccess</CODE> file overriding a server
   config file).  If set to <EM><CODE>On</CODE></EM>, the header will be
   added to served documents according to the criteria defined by the
   <A
    HREF="expiresbytype"
   >ExpiresByType</A>
   and
   <A
    HREF="#expiresdefault"
   >ExpiresDefault</A>
   directives (<EM>q.v.</EM>).
   </P>
   <P>
   Note that this directive does not guarantee that an
   <CODE>Expires</CODE> header will be generated.  If the criteria aren't
   met, no header will be sent, and the effect will be as though this
   directive wasn't even specified.
   </P>
   <HR>
   <A NAME="expiresbytype">
    <H2>ExpiresByType directive</H2>
   </A>
   <!--%plaintext &lt;?INDEX {\tt ExpiresByType} directive&gt; -->
   <P>
   <STRONG>Syntax:</STRONG> ExpiresByType <EM>mime-type &lt;code&gt;seconds</EM>
   <BR>
   <STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
   <br>
   <STRONG>Override:</STRONG> Indexes
   <br>
   <STRONG>Status:</STRONG> Extension
   <br>
   <STRONG>Module:</STRONG> mod_expires
   </P>
   <P>
   This directive defines the value of the <CODE>Expires</CODE> header
   generated for documents of the specified type (<EM>e.g.</EM>,
   <CODE>text/html</CODE>).  The second argument sets the number of
   seconds that will be added to a base time to construct the expiration
   date.
   </P>
   <P>
   The base time is either the last modification time of the file, or the
   time of the client's access to the document.  Which should be used is
   specified by the <CODE><EM>&lt;code&gt;</EM></CODE> field;
   <STRONG>M</STRONG> means that the file's last modification time should
   be used as the base time, and <STRONG>A</STRONG> means the client's
   access time should be used.
   </P>
   <P>
   The difference in effect is subtle.  If <EM>M</EM> is used, all current
   copies of the document in all caches will expire at the same time,
   which can be good for something like a weekly notice that's always
   found at the same URL.  If <EM>A</EM> is used, the date of expiration
   is different for each client; this can be good for image files that
   don't change very often, particularly for a set of related documents
   that all refer to the same images (<EM>i.e.</EM>, the images will be
   accessed repeatedly within a relatively short timespan).
   </P>
   <P>
   <STRONG>Example:</STRONG>
   </P>
   <P>
   <PRE>
    ExpiresActive On                  # enable expirations
    ExpiresByType image/gif A2592000  # expire GIF images after a month
                                      #  in the client's cache
    ExpiresByType text/html M604800   # HTML documents are good for a
                                      #  week from the time they were
                                      #  changed, period
   </PRE>
   </P>
   <P>
   Note that this directive only has effect if <CODE>ExpiresActive
   On</CODE> has been specified.  It overrides, for the specified MIME
   type <EM>only</EM>, any expiration date set by the
   <A
    HREF="#expiresdefault"
   >ExpiresDefault</A>
   directive.
   </P>
   <HR>
   <A NAME="expiresdefault">
    <H2>ExpiresDefault directive</H2>
   </A>
   <!--%plaintext &lt;?INDEX {\tt ExpiresDefault} directive&gt; -->
   <P>
   <STRONG>Syntax:</STRONG> ExpiresDefault <EM>&lt;code&gt;seconds</EM>
   <BR>
   <STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
   <br>
   <STRONG>Override:</STRONG> Indexes
   <br>
   <STRONG>Status:</STRONG> Extension
   <br>
   <STRONG>Module:</STRONG> mod_expires
   </P>
   <P>
   This directive sets the default algorithm for calculating the
   expiration time for all documents in the affected realm.  It can be
   overridden on a type-by-type basis by the
   <A
    HREF="#expiresbytype"
   >ExpiresByType</A>
   directive.  See the description of that directive for details about
   the syntax of the argument.
   </P>
   <!--#include virtual="footer.html" -->
  </BODY>
 </HTML>
	<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
	<HTML>
	<HEAD>
	<TITLE>Apache module mod_expires</TITLE>
	</HEAD>
	<BODY>
	<!--#include virtual="header.html" -->
	<H1>Module mod_expires</H1>
	<P>
	This module is contained in the <CODE>mod_expires.c</CODE> file, and
	is <STRONG>not</STRONG> compiled in by default. It provides for the
	generation of <CODE>Expires</CODE> headers according to user-specified
	criteria.
	</P>
	<H2>Summary</H2>
	<P>
	This module controls the setting of the <CODE>Expires</CODE> HTTP
	header in server responses. The expiration date can set to be
	relative to either the time the source file was last modified, or to
	the time of the client access.
	</P>
	<P>
	The <CODE>Expires</CODE> HTTP header is an instruction to the client
	about the document's validity and persistence. If cached, the document
	may be fetched from the cache rather than from the source until this
	time has passed. After that, the cache copy is considered
	"expired" and invalid, and a new copy must be obtained from
	the source.
	</P>
	<H2>Directives</H2>
	<P>
	<MENU>
	<LI><A
	HREF="#expiresactive"
	>ExpiresActive</A>
	</LI>
	<LI><A
	HREF="#expiresbytype"
	>ExpiresByType</A>
	</LI>
	<LI><A
	HREF="#expiresdefault"
	>ExpiresDefault</A>
	</LI>
	</MENU>
	<HR>
	<A NAME="expiresactive">
	<H2>ExpiresActive directive</H2>
	</A>
	<!--%plaintext <?INDEX {\tt ExpiresActive} directive> -->
	<P>
	<STRONG>Syntax:</STRONG> ExpiresActive <EM>boolean</EM>
	<BR>
	<STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
	<br>
	<STRONG>Override:</STRONG> Indexes
	<br>
	<STRONG>Status:</STRONG> Extension
	<br>
	<STRONG>Module:</STRONG> mod_expires
	</P>
	<P>
	This directive enables or disables the generation of the
	<CODE>Expires</CODE> header for the document realm in question. (That
	is, if found in an <CODE>.htaccess</CODE> file, for instance, it
	applies only to documents generated from that directory.) If set to
	<EM><CODE>Off</CODE></EM>, no <CODE>Expires</CODE> header will be
	generated for any document in the realm (unless overridden at a lower
	level, such as an <CODE>.htaccess</CODE> file overriding a server
	config file). If set to <EM><CODE>On</CODE></EM>, the header will be
	added to served documents according to the criteria defined by the
	<A
	HREF="expiresbytype"
	>ExpiresByType</A>
	and
	<A
	HREF="#expiresdefault"
	>ExpiresDefault</A>
	directives (<EM>q.v.</EM>).
	</P>
	<P>
	Note that this directive does not guarantee that an
	<CODE>Expires</CODE> header will be generated. If the criteria aren't
	met, no header will be sent, and the effect will be as though this
	directive wasn't even specified.
	</P>
	<HR>
	<A NAME="expiresbytype">
	<H2>ExpiresByType directive</H2>
	</A>
	<!--%plaintext <?INDEX {\tt ExpiresByType} directive> -->
	<P>
	<STRONG>Syntax:</STRONG> ExpiresByType <EM>mime-type <code>seconds</EM>
	<BR>
	<STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
	<br>
	<STRONG>Override:</STRONG> Indexes
	<br>
	<STRONG>Status:</STRONG> Extension
	<br>
	<STRONG>Module:</STRONG> mod_expires
	</P>
	<P>
	This directive defines the value of the <CODE>Expires</CODE> header
	generated for documents of the specified type (<EM>e.g.</EM>,
	<CODE>text/html</CODE>). The second argument sets the number of
	seconds that will be added to a base time to construct the expiration
	date.
	</P>
	<P>
	The base time is either the last modification time of the file, or the
	time of the client's access to the document. Which should be used is
	specified by the <CODE><EM><code></EM></CODE> field;
	<STRONG>M</STRONG> means that the file's last modification time should
	be used as the base time, and <STRONG>A</STRONG> means the client's
	access time should be used.
	</P>
	<P>
	The difference in effect is subtle. If <EM>M</EM> is used, all current
	copies of the document in all caches will expire at the same time,
	which can be good for something like a weekly notice that's always
	found at the same URL. If <EM>A</EM> is used, the date of expiration
	is different for each client; this can be good for image files that
	don't change very often, particularly for a set of related documents
	that all refer to the same images (<EM>i.e.</EM>, the images will be
	accessed repeatedly within a relatively short timespan).
	</P>
	<P>
	<STRONG>Example:</STRONG>
	</P>
	<P>
	<PRE>
	ExpiresActive On # enable expirations
	ExpiresByType image/gif A2592000 # expire GIF images after a month
	# in the client's cache
	ExpiresByType text/html M604800 # HTML documents are good for a
	# week from the time they were
	# changed, period
	</PRE>
	</P>
	<P>
	Note that this directive only has effect if <CODE>ExpiresActive
	On</CODE> has been specified. It overrides, for the specified MIME
	type <EM>only</EM>, any expiration date set by the
	<A
	HREF="#expiresdefault"
	>ExpiresDefault</A>
	directive.
	</P>
	<HR>
	<A NAME="expiresdefault">
	<H2>ExpiresDefault directive</H2>
	</A>
	<!--%plaintext <?INDEX {\tt ExpiresDefault} directive> -->
	<P>
	<STRONG>Syntax:</STRONG> ExpiresDefault <EM><code>seconds</EM>
	<BR>
	<STRONG>Context:</STRONG> server config, virtual host, directory, .htaccess
	<br>
	<STRONG>Override:</STRONG> Indexes
	<br>
	<STRONG>Status:</STRONG> Extension
	<br>
	<STRONG>Module:</STRONG> mod_expires
	</P>
	<P>
	This directive sets the default algorithm for calculating the
	expiration time for all documents in the affected realm. It can be
	overridden on a type-by-type basis by the
	<A
	HREF="#expiresbytype"
	>ExpiresByType</A>
	directive. See the description of that directive for details about
	the syntax of the argument.
	</P>
	<!--#include virtual="footer.html" -->
	</BODY>
	</HTML>