Delicious Bookmark this on Delicious Share on Facebook SlashdotSlashdot It! Digg! Digg

PHP : Function Reference : Session Handling Functions : session_cache_limiter


Get and/or set the current cache limiter (PHP 4 >= 4.0.3, PHP 5)
string session_cache_limiter ( [string cache_limiter] )

Example 2223. session_cache_limiter() example


/* set the cache limiter to 'private' */

$cache_limiter = session_cache_limiter();

"The cache limiter is now set to $cache_limiter<br />";

Code Examples / Notes » session_cache_limiter


You can find more information about to control the cache in PHP at
If you have a dinamic website and want to allow your visitors to use the back button after they sent a form with the post method, the best combination I found was:
header("Expires: Sat, 01 Jan 2000 00:00:00 GMT");
header("Last-Modified: ".gmdate("D, d M Y H:i:s")." GMT");
header("Cache-Control: post-check=0, pre-check=0",false);
// and after you start the session
I try some combinations using header("Cache-Control: no-cache, must-revalidate"), but when clicking the back button, the last changes in the form back to their previous states. The combination above works fine with IE 6.x. I didn't test this with other browsers.
When I try something like session_cache_limiter("nocache, must-revalidate") it doesn't work. The page only updates when I used the browser's refresh button. In dynamic web sites this is not good. The content must be fresh after each click.
I didn't find these combinations like "private, must-revalidate" documented in the manual and I guess that something different from "none, nocache, private, public and private_no_expire" are resolved to "none" or something like that. One thing I notice is that in session_cache_limiter() it is "nocache", but in header() it is "no-cache". This may give us some clues about how session_cache_limiter() function works.
About caching, the perfect solution I think is to give the correct expiration date and time and also the right last-modified header for each element in the web site, when they are really updated. This means a lot of extra controls of course, but may worth in web sites with high overload.
The "public" option means that all available cache in proxies and clientes will be used, so this improves the speed of the web site and also reduces the used bandwidth. But without the right expiration and last-modified headers, you can use it only in static web sites.
The "private" option means that only the cache in clients will be used. This is good for a more sensitive data that can be stored locally in the browser cache. It have some benefits of the public option, but the same restrictions too.
The "nocache" (or no-cache?) option means that the HTML portion will not be cached, but the images, CSS and JS files will. This is good for dynamic websites because you still can use the power of cache without loose the refreshness after each click. These files can be updated when you open the web site or use the browser's refresh button.
I don't know why, but flash files are never updated when you click the refresh button. A common solution for this is to change the file name when you update the flash file.
The "no-store" option means that all the content will not be cached anyway, including images, CSS or JS files. I don't know if this applyes to flash files too, but is possible. This option must be used with very sensitive data. I think the SSL uses this by default.


We had a strange problem with zip file downloads (not using SSL) under IE5.  If the user chose the option to "save to disk", then everything worked fine, but if they chose "open", then winzip was launched okay - but the displayed zip archive was empty.
We eventually tracked this down to the Cache-Control header and the php script was fixed by adding
before the first call to session_register()


There is a bug(?) in Internet Explorer v5.5 to do with file downloads over a secure (https) web connection when using sessions. If you have a php script which delivers files for downloading by setting headers for the content-type etc. from a URL like this:
- or -
and that script uses sessions, then you must explicitly set
*before* you use
otherwise you will get one of the following errors from IE when it attmpts to download the file:
Internet Explorer cannot download filename.ext from name.of.your.webserver
Internet Explorer was not able to open this site. The requested site is either unavailable or cannot be found. Please try again later.
Mmm, this is useful error message isn't it! The other error you will see when right clicking and choosing 'Save Target As...' gives the error
Internet Explorer cannot download filename.ext from name.of.your.webserver
The file could not be written to the cache.
This problem does not occur over unsecure (http) links and files download OK. I don't know why this should be the case, but PHP seems to send an extra no-cache header when using sessions which breaks IE when it is using SSL. Setting the session_cache_limiter turns off this behaviour.


The problems people mention about IE are actually a feature!  
Microsoft Knowledge Base Article 316431 says:
In order for Internet Explorer to open documents in Office (or any out-of-process, ActiveX document server), Internet Explorer must save the file to the local cache directory and ask the associated application to load the file by using IPersistFile::Load. If the file is not stored to disk, this operation fails.
When Internet Explorer communicates with a secure Web site through SSL, Internet Explorer enforces any no-cache request. If the header or headers are present, Internet Explorer does not cache the file. Consequently, Office cannot open the file.
They say this applies to:
Microsoft Internet Explorer 5.5 for Windows 2000
Microsoft Internet Explorer 5.01 for Windows 2000
Microsoft Internet Explorer version 6 for Windows 2000
not sure about other versions!

19-oct-2005 04:11

The onLoad method of Actionscript's loadVars class was returning false in IE6 using SSL until I set --> session_cache_limiter("must-revalidate"); <-- on the receiving PHP script.


Setting session.cache_limiter = none; in your php.ini file will avoid the problem in IE in which pressing the back button after using a POST form will result in "Warning: Page Has Expired".


Please note that you DO NOT NEED to specify session_cache_limiter to get downloads work IMHO.
With IE6 (and others I imagine), you might have a problem with the filename attribute of Content-Disposition being recognised. In my experience, IE always believed the filename of the download was the name of the script (ie, the URL generating the file, rather than the header being pushed).
When adding: Header("Pragma: public");   this was solved.
E.g. (Working CSV / opens in Excel in Windows).
header("Cache-control: private");
header("Content-Type: text/plain");
header("Content-Disposition: attachment; filename=\"$filename\"");
header("Pragma: public");
echo "Dogs,Cats,Fish\n";
echo "1,2,3\n";
echo "4,5,6\n";


In addition to the note above regarding SSL/IE bug/Sessions, also make sure you DO NOT SET THE HEADER 'Pragma: no-cache' if you are sending an inline document (e.g., PDF document).
For example:
header("Content-Type: application/pdf");
header("Content-Disposition: inline; filename=foo.pdf");
header("Accept-Ranges: bytes");
header("Content-Length: $len");
header("Expires: 0");
header("Cache-Control: private");
// header("Pragma: no-cache");//don't send this header!!


In addition to the  above, don't forget to check the php.ini file for the setting:   session.cache_limiter = nocache
Since I use xoops and didn't start the session, I had the SSL/download problem until I noticed this.


After spending a long time trying all the above solutions without success, I eventually found a more likely cause for these errors. There are problems with Apache/SSL and Internet Explorer with SSL connections - detailed information and a simple fix is here:,3396,s=201&a=24899,00.asp
and here:
So a simple web server reconfiguration may save you hours of fiddling with cache control headers!


If you are trying to work with dynamic binaries such as videos or images, the new IE 7 appears to require the ETag header.  You will need to make sure that you follow the specifications for how ETag works in order for your cache control to work properly.  Mozilla supports the ETag header as well, but does NOT require it for caching.  If you need to cache a dynamic image, video, or other binary file, then be sure to set your ETag and then check for the If-Not-Modified header on subsequent requests so that you can properly return the 304 Not Modified page.


IE6 'the file could not be written to the cache':
I tried all the other suggestions mentioned here but none of them worked.
I friend suggested header("Pragma: ");
This worked straight away!

radu dot rendec

I've read the other comments and done some "reasearch" on my own. Using php's session mechanism and explicitly setting the "cache-control" header should not be mixed.
When session_start() is called, the "cache-control" and "pragma" headers are automatically set by php (to whatever value had been specified using session_cache_limiter()).
Explicitly setting those headers _before_ session_start() will have no effect, and explicitly setting them _after_ session_start() will overwrite the settings from session_cache_limiter().
If I had to deal with php sessions, I'd go for using session_cache_limiter() and leaving the headers alone.


I solved the problem with pushing downloads to browser's, without needing to play with server/session parameters by using :
header("Content-Disposition: inline; filename=\"$filename\"");
for IE browsers and
header("Content-Disposition: attachment; filename=\"$filename\"");
for all other browsers.

andrei chirila, andrei_chirila

I played about an hour with the download and sessions. yes, to work you'll need session_cache_limiter("must-revalidate"); but this BEFORE session_start() if you want that your download start [IE problem]. Hope someone will need this someday ...


I have PHP 4.3 running on a Windows 2003 Server running IIS 6.0 also using SSL encryption for my pages.  I could not (for the life of me) figure out how to get IE 6.0/WinXPPro to recognize a set of HTML tables as an Excel spreadsheet export, and it was due to the header() variables I was using.  Hopefully these are helpful to others who are attempting the same type of export within PHP.
*This example builds on the previously submitted one, adding a few necessary headers.
header("Expires: Sat, 01 Jan 2000 00:00:00 GMT");
header("Last-Modified: ".gmdate("D, d M Y H:i:s")." GMT");
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: public");
header("Content-Description: File Transfer");

header("Content-Type: application/");
header('Content-Disposition: attachment; filename="fileToExport.xls"');
// and after you start the session

mikko hämäläinen

I had a similair problem (browsers couldn't save files coming from my download-script). Only in my case the problem occured with IE 6.0 and Netscape 7.1. Adding the "session_cache_limiter('public');" before "session_start();" helped.


I had a problem using a FORM with POST method when user of my website was using the back button. The page requested a refresh to be able to see again the FORM.
To solve the problem I used :
session_cache_limiter('private, must-revalidate');
*You need to write this line before any output
Hope that will help some of you ;)


I found that session_cache_limiter("none") works for me when I create PDFs  on the fly because session_cache_limiter("private") causes the browser(IE6) to cache the PDF indefinitely.


Hey!  NickyBoy was right!
I looked all over google and his note was the only place that had it right.  But, there's a caveat.
I wrote up my results here:


Here is some magic for you PHP session lovers out there;
it seems that if you use 'nocache' as an argument for this function, PHP will send the following headers automatically for you:
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Which pretty much render any cache ineffective because no proxy or browser that follows the HTTP 1.1 protocol will cache
your request. In short, every page request, whether explicitly through a page reload or not, will go through your server.
Not something good for those of us looking for a bit of security but also for some performance juice.
The only way to override these headers, if you use the 'nocache' as an argument, is to use the header( ) function
after you start your session but before you send any output:
// Above Headers Sent By PHP.
session_cache_limiter( 'nocache' );
// Start Session.
session_start( );
// Override Headers.
header( 'Cache-Control: no-cache, must-revalidate, post-check=3600, pre-check=3600' );


For those people trying to fix IE6's problem of recognizing the filename attribute in Content-Disposition. I thought I'd add that in addition to the fixes mentioned before, you have to take note of invalid and sensitive characters in the file name. For example, having a space or colon in the filename will cause IE6 to use a randomly generated filename.


for more info about how caches work, and how to cache effectivelly scripted pages, check this :


Be careful using session_cache_limiter() with ob_start('ob_gzhandler')
If ob_start('ob_gzhandler') is called after session_cache_limiter() it seems to overwrite cache control headers with 'nocache' equivalent.
So always put ob_start first.


Avoiding caching PHP pages:
After lot of tries and research this is the best combination of headers I've found that seems to work well even with the proxy of visitors that are using satellit connection.
header("ETag: PUB" . time());
header("Last-Modified: " . gmdate("D, d M Y H:i:s", time()-10) . " GMT");
header("Expires: " . gmdate("D, d M Y H:i:s", time() + 5) . " GMT");
header("Pragma: no-cache");
header("Cache-Control: max-age=1, s-maxage=1, no-cache, must-revalidate");

02-sep-2005 11:04

Andrei Chirila, andrei_chirila at yahoo dot com
12-Jan-2005 09:30
I played about an hour with the download and sessions. yes, to work you'll need session_cache_limiter("must-revalidate"); but this BEFORE session_start() if you want that your download start [IE problem]. Hope someone will need this someday
yes, somebody has needed this today :)
situation: trying to make a session based download management system complete with user login system that requries an authorized user to download some files, and hide all such files from non-authorized users. the user login, download center, and content management system of the site are all tied in to each other, making troubleshooting this headering stuff a headache.
problem: files being served are not accessible thru the regular site, since they are above the htdocs folder in apache, and so headering the file is required, and sessions do not work well with files being headered to the browser.
solution: the download center uses ob_start("");, then  session_cache_limiter("must-revalidate");, before the session_start();, then everything works well.
thank you very much! i was resorting to using a cookie to control this before because i could not figure out how to tie in sessions to the system before!

fernando gabrieli fgabrieli

session_cache_limiter ('private, must-revalidate');
$cache_limiter = session_cache_limiter();
session_cache_expire(60); // in minutes
session_start() ;
If i do not set must-revalidate, IE seems to cache session variables without refreshing them
If i post a form then it refreshes the variables
Firefox does not have this problem
So, be sure to use must-revalidate

Change Language

Follow Navioo On Twitter
eXTReMe Tracker