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session_status> <session_set_save_handler
[edit] Last updated: Sat, 12 May 2012

view this page in

session_start

(PHP 4, PHP 5)

session_startStart new or resume existing session

Description

bool session_start ( void )

session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.

When session_start() is called or when a session auto starts, PHP will call the open and read session save handlers. These will either be a built-in save handler provided by default or by PHP extensions (such as SQLite or Memcached); or can be custom handler as defined by session_set_save_handler(). The read callback will retrieve any existing session data (stored in a special serialized format) and will be unserialized and used to automatically populate the $_SESSION superglobal when the read callback returns the saved session data back to PHP session handling.

To use a named session, call session_name() before calling session_start().

When session.use_trans_sid is enabled, the session_start() function will register an internal output handler for URL rewriting.

If a user uses ob_gzhandler or similar with ob_start(), the function order is important for proper output. For example, ob_gzhandler must be registered before starting the session.

Return Values

This function returns TRUE if a session was successfully started, otherwise FALSE.

Changelog

Version Description
5.3.0 If a session fails to start, then FALSE is returned. Previously TRUE was returned.
4.3.3 As of PHP 4.3.3, calling session_start() after the session was previously started will result in an error of level E_NOTICE. Also, the second session start will simply be ignored.

Examples

Example #1 A session example: page1.php

<?php
// page1.php

session_start();

echo 
'Welcome to page #1';

$_SESSION['favcolor'] = 'green';
$_SESSION['animal']   = 'cat';
$_SESSION['time']     = time();

// Works if session cookie was accepted
echo '<br /><a href="page2.php">page 2</a>';

// Or maybe pass along the session id, if needed
echo '<br /><a href="page2.php?' SID '">page 2</a>';
?>

After viewing page1.php, the second page page2.php will magically contain the session data. Read the session reference for information on propagating session ids as it, for example, explains what the constant SID is all about.

Example #2 A session example: page2.php

<?php
// page2.php

session_start();

echo 
'Welcome to page #2<br />';

echo 
$_SESSION['favcolor']; // green
echo $_SESSION['animal'];   // cat
echo date('Y m d H:i:s'$_SESSION['time']);

// You may want to use SID here, like we did in page1.php
echo '<br /><a href="page1.php">page 1</a>';
?>

Notes

Note:

To use cookie-based sessions, session_start() must be called before outputing anything to the browser.

Note:

Use of zlib.output_compression is recommended instead of ob_gzhandler()

Note:

This function sends out several HTTP headers depending on the configuration. See session_cache_limiter() to customize these headers.

See Also



session_status> <session_set_save_handler
[edit] Last updated: Sat, 12 May 2012
 
add a note add a note User Contributed Notes session_start
cesar at anui dot org 13-Apr-2012 09:52
To share a session between domains on the same server, you can do:

session_write_close();
session_id($_GET['sessionid']);
session_start();

But if you have Suhosin patch and the domains are on different document_root, $_SESSION is reset on session_start(), and you lose any user data that was on the passed session.

Solution is to set in php.ini:
suhosin.session.encrypt=off

Or, maybe more secure:
suhosin.session.cryptdocroot=off
Doug__fernandes at hotmail dot com 02-Apr-2012 04:48
ERROR Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at

<?php

if (!isset($_SESSION)) {
 
session_start();
}

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset(
$_GET['accesscheck'])) {
 
$_SESSION['PrevUrl'] = $_GET['accesscheck'];
}

if (isset(
$_POST['usuario'])) {
 
$loginUsername=$_POST['usuario'];
 
$password=md5($_POST['senha']);
 
$MM_fldUserAuthorization = "usuarioNivel";
 
$MM_redirectLoginSuccess = "admin/painel.php";
 
$MM_redirectLoginFailed = "admin/erro.php";
 
$MM_redirecttoReferrer = false;
 
mysql_select_db($database_painel_config, $painel_config);
     
 
$LoginRS__query=sprintf("SELECT email, senha, usuarioNivel FROM up_clientes WHERE email=%s AND senha=%s",
 
GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text"));
  
 
$LoginRS = mysql_query($LoginRS__query, $painel_config) or die(mysql_error());
 
$loginFoundUser = mysql_num_rows($LoginRS);
  if (
$loginFoundUser) {
   
   
$loginStrGroup  = mysql_result($LoginRS,0,'usuarioNivel');
   
    if (
PHP_VERSION >= 5.1) {session_regenerate_id(true);} else {session_regenerate_id();}
   
//declare two session variables and assign them
   
$_SESSION['MM_Username'] = $loginUsername;
   
$_SESSION['MM_UserGroup'] = $loginStrGroup;         

    if (isset(
$_SESSION['PrevUrl']) && false) {
     
$MM_redirectLoginSuccess = $_SESSION['PrevUrl'];   
    }
   
header("Location: " . $MM_redirectLoginSuccess );
  }
  else {
   
header("Location: ". $MM_redirectLoginFailed );
  }
}
?>
will dot joi at hotmail dot com 07-Mar-2012 12:54
I had a problem with the session_start(); like this: "Warning: session_start(); [function.session-start]: Cannot send session cache limiter - headers already sent".

This is my php code:

<?php
session_start
();

if (
$_SESSION['nome'] == ""){
die(
'Você não pode acessar essa pagina!');
} else {
}

?>

The problem is the "" that we need to chango to ''.

Correct code:

<?php
session_start
();

if (
$_SESSION['nome'] == ''){
die(
'Você não pode acessar essa pagina!');
} else {
}

?>
LaKing at D250 dot hu 02-Mar-2012 03:13
I had a warning complaining about session_start() after adding an include file.

- It broke the functionality of my php code in a very strange manner.
- The included tree did not contain any additional session_start calls.
- it produced this warning only with with php -l from my development environment, and didn't produce any errors in the error_log.
- the warning pointed into a non-existing line, 1 line after last line of the file.

I use gedit on CentOS 6.1 with UTF-8 as current locale.
- Switching encoding back and forth didn't help.
- Commented out all the included content, only the php tags left, the error wa still there. ..

The solution was to clear out everything, and re-writing the php tags and posting back the content.

As it seems "hidden" unsupported characters produce errors and warnings falsely pointing to this function.
Martin 03-Feb-2012 04:51
Using session_start(); after the <html> tags is generating and  error:

"Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\wamp\www\fol\index.php:1) in C:\wamp\www\fol\index.php on line 2".

 Moving it before <html> tag fixed the problem though. I hope this is helpful for others with same problem.
Andrewgerm 11-Jan-2012 02:10
On the 'cannot start session, session already sent' a small note further to the advice already posted.

As I develop jointly on Windows and Linux, often on the same sites, I do use UTF-8. If you see the session error, try changing the file encoding (perhaps from UTF-8 to US-ASCII, and back again).

Then, to be certain, save-as and overwrite the existing file.

Solved the issue for me.
james at ustelcom dot net 15-Nov-2011 02:52
I had the infamous "Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent ..." error, and I was convinced it was because I was trying to open a session AND send a cookie.  I tried everything that was suggested, uploaded in ANSI, uploaded in UTF 8, etc.  I tried opening the session first, then sending the cookie first.  Turns out my problem was quite simple:

" <?php
session_start
();

?>"

Do you see the problem with my code?  I finally did:

" <?php"
^^------ There is an accidental space!

I'm sure I'm not the only one who encounters this problem.  Hopefully this helps others!
max_bilyk at yahoo dot com 04-Nov-2011 06:53
An interesting bug/misfunction was discovered when using Flash-based file uploader (in my case jQuery plugin Uploadify, but also found similar problem reports about SWFupload).

Problem occurs with PHP 5.2 (and probably later as well) when it is compiled with Suhosin patch.

The problem is that session_start() does not load session data into $_SESSION variable when it gets request from Flash, and in this case $_SESSION variable becomes empty and at the end  of script execution erases session data when script execution ends (PHP saves this empty $_SESSION to file).

The fact that Flash is using its own session management is solved by passing via POST/GET correct session ID, but erasing session data is definitely a problem.

The reason for the problem is method of session data encryption - Suhosin uses user-agent data as a part of encryption key.

And in case client machine makes requests from two different user-agents (browser + flash) Suhosin generates different session decryption key which is unable to decrypt session data (and notice that there's no message about this fact in any log-file).

So the solution for such case may be either by disabling encryption of session data by putting such directive in php.ini:

suhosin.session.encrypt=Off

or, alternatively, still keep session data encrypted but exclude user-agent data from encryption key by using this directive in php.ini:

suhosin.session.cryptua=Off
Dark Angel 16-Oct-2011 07:49
I had script which should under CLI restore session set by web interface.

Spent like few hours understanding why script with session_id($sid) and session_start() is not restoring session, but generating new one. No any notices or anything helping to resolve.

$sid was read from STDIN. Issue was that value from STDIN contained '\n' character at the end, which is invalid for session identifier. Discovered by stracing CLI script.

Hope this will save you a lot of time.
sanjuro at 1up-games dot com 18-Aug-2011 11:56
The problem with SID is that if on occasions you don't start a session, instead of outputting an empty string for transparent integration it will return the regular undefined constant notice. So you might want to test the constant with defined() beforehand.
Quick Tipson 13-Aug-2011 09:33
Start session only if not already started:

<?php
 
if (!isset ($_COOKIE[ini_get('session.name')])) {
   
session_start();
  }
?>
egonrp 19-Jul-2011 06:59
SOLVED: Session data lost

My session data lost problem was resolved by using a short name for session key.
This error happens with PHP version 5.2.6 (Debian Lenny), others versions works fine without any modification.

Before:
$_SESSION['current_user_search_filter'] = serialize($myArray);
$value = unserialize($_SESSION['current_user_search_filter']);

After (short key name):
$_SESSION['usearchfilter'] = serialize($myArray);
$value = unserialize($_SESSION['usearchfilter']);

Good Luck! :)
gkemaldag at gmail dot com 20-Apr-2011 12:37
For the error:

Warning: session_start(): Cannot send session cache limiter - headers already sent ...

this kind of errors would occur, when the encoding of your script file needs to send some headers just after your script starts to execute,

this happens mostly with the scripts using normal utf8 encoding.

To overcome the issue, use utf8(without BOM) encoding provided by notepad++ and most modern editors. Using utf8 encoding and cookie based sessions, will result in headers already sent by error.
tbali0524 at gmail dot com 08-Apr-2011 02:25
I spent several hours in debuggging a strange session problem.

My website that uses sessions for login and language selection worked perfectly with Firefox or Chrome but not with IE9. (I did not tried with earlier versions.)
Even more strange was that it also worked with IE9 at localhost using XAMPP but not at the hosted site.

Finally it turned out that the problem was I used underscore (_) in the subdomain name.
(e.g.   "test_mysite.example.com" )
It turned out that underscore is not standard in domain name and IE seems to be more strict in this than the other.
alakys 03-Mar-2011 08:26
Sorry for the noob comment but for those having the error :

Warning: session_start(): Cannot send session cache limiter - headers already sent ...

And before trying all the solutions added by the experts, simply ensure to have your php code before even the DOCTYPE tag like this (and not between the doctype and html tags as I was doing):

<?php session_start(); ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Test Page</title>
</head>

<body>
etc ....

It might sound funny but I am sure this post will save time to some others noobs like me ... !
linblow at hotmail dot fr 16-Feb-2011 05:06
If you want to handle sessions with a class, I wrote this little class:

<?php

/*
    Use the static method getInstance to get the object.
*/

class Session
{
    const
SESSION_STARTED = TRUE;
    const
SESSION_NOT_STARTED = FALSE;
   
   
// The state of the session
   
private $sessionState = self::SESSION_NOT_STARTED;
   
   
// THE only instance of the class
   
private static $instance;
   
   
    private function
__construct() {}
   
   
   
/**
    *    Returns THE instance of 'Session'.
    *    The session is automatically initialized if it wasn't.
    *   
    *    @return    object
    **/
   
   
public static function getInstance()
    {
        if ( !isset(
self::$instance))
        {
           
self::$instance = new self;
        }
       
       
self::$instance->startSession();
       
        return
self::$instance;
    }
   
   
   
/**
    *    (Re)starts the session.
    *   
    *    @return    bool    TRUE if the session has been initialized, else FALSE.
    **/
   
   
public function startSession()
    {
        if (
$this->sessionState == self::SESSION_NOT_STARTED )
        {
           
$this->sessionState = session_start();
        }
       
        return
$this->sessionState;
    }
   
   
   
/**
    *    Stores datas in the session.
    *    Example: $instance->foo = 'bar';
    *   
    *    @param    name    Name of the datas.
    *    @param    value    Your datas.
    *    @return    void
    **/
   
   
public function __set( $name , $value )
    {
       
$_SESSION[$name] = $value;
    }
   
   
   
/**
    *    Gets datas from the session.
    *    Example: echo $instance->foo;
    *   
    *    @param    name    Name of the datas to get.
    *    @return    mixed    Datas stored in session.
    **/
   
   
public function __get( $name )
    {
        if ( isset(
$_SESSION[$name]))
        {
            return
$_SESSION[$name];
        }
    }
   
   
    public function
__isset( $name )
    {
        return isset(
$_SESSION[$name]);
    }
   
   
    public function
__unset( $name )
    {
        unset(
$_SESSION[$name] );
    }
   
   
   
/**
    *    Destroys the current session.
    *   
    *    @return    bool    TRUE is session has been deleted, else FALSE.
    **/
   
   
public function destroy()
    {
        if (
$this->sessionState == self::SESSION_STARTED )
        {
           
$this->sessionState = !session_destroy();
            unset(
$_SESSION );
           
            return !
$this->sessionState;
        }
       
        return
FALSE;
    }
}

/*
    Examples:
*/

// We get the instance
$data = Session::getInstance();

// Let's store datas in the session
$data->nickname = 'Someone';
$data->age = 18;

// Let's display datas
printf( '<p>My name is %s and I\'m %d years old.</p>' , $data->nickname , $data->age );

/*
    It will display:
   
    Array
    (
        [nickname] => Someone
        [age] => 18
    )
*/

printf( '<pre>%s</pre>' , print_r( $_SESSION , TRUE ));

// TRUE
var_dump( isset( $data->nickname ));

// We destroy the session
$data->destroy();

// FALSE
var_dump( isset( $data->nickname ));

?>

I prefer using this class instead of using directly the array $_SESSION.
math[dot]lechat[at-at]gmail[dot]com 14-Feb-2011 01:08
"Cannot send session cookie - headers already sent" comes most often when the file is encoded in UTF-8 WITH BOM under Windows.
When transfered on an UNIX server the BOM is considered as text and sent before any header you can define.
anon at ymous dot com 04-Feb-2011 01:51
I am trying to get a session created by a browser call to be used by a command line cli->curl php call (in this case, both calls to the same server and php.ini), for a set of flexible media import routines,

but the cli->curl call always starts a new session despite me putting PHPSESSID=validID as the first parameter for the url called by curl.

I was able to fix it by calling session_id($_GET['PHPSESSID']) before calling session_start() in the script called via curl.
nizamgok at gmail dot com 16-Jan-2011 11:59
Be aware that when you deliver your flash file through php, you cannot access the session vars that are set from the parent page in Opera, Safari and IE9. I didn't test it with IE6-8. Chrome and Firefox are OK. I don't know the real reason but guessing some of the header data are missing.

swf.php:
<?php

session_start
();

//$_SESSION['test'] --> doesn't exist!
//session_id() --> != 'hey123'

header('Content-type: application/x-shockwave-flash');

readfile('/path/to/flash.swf');

?>

index.php"
<?php

session_id
('hey123');
session_start();
$_SESSION['test'] = 'test';

?>
<object width="550" height="400">
<param name="movie" value="http://example.com/swf/">
</object>

* swf directory has an .htaccess file which points to swf.php
dave1010 at gmail dot com 17-Dec-2010 01:35
PHP locks the session file until it is closed. If you have 2 scripts using the same session (i.e. from the same user) then the 2nd script will not finish its call to session_start() until the first script finishes execution.

If you have scripts that run for more than a second and users may be making more than 1 request at a time then it is worth calling session_write_close() as soon as you've finished writing session data.

<?php
// a lock is places on the session, so other scripts will have to wait
session_start();

// do all your writing to $_SESSION
$_SESSION['a'] = 1;

// $_SESSION can still be read, but writing will not update the session.
// the lock is removed and other scripts can now read the session
session_write_close();

do_something_slow();
?>

Found this out from http://konrness.com/php5/how-to-prevent-blocking-php-requests/
chong at completemr dot com 08-Dec-2010 07:11
We are facing a problem and getting an error when loading a php page

Warning: session_start() [<a href='function.session-start'>function.session-start</a>]: Cannot send session cookie - headers already sent by (output started at /www/http/example/zh_CN/unsubscribe.php:1) in /www/http/example/inc/common.php on line 4

We had google and browse through some helps file and found some suggestion as below.

1. Use ob_start to cache any output before session_start function.

2. Make sure the session.save_path in php.ini is set and point to a valid path

We had tried the above but still having some the same problem.

We are using notepad ++ for the coding.

And we notice that this file is somehow being encoded to UTF-8 by one of my colleague because he though that this will help to display the result in the correct languages.

Solution:
Change the encode to use ANSI and make sure the EOL conversion is set to UNIX.
Bingo. Things are back to normal as expected.

Note:
The encode might cause this problem in certain machine but not others. So i had no clue on this. We had no problem running the php code with UTF-8 encode in a 64bits Linux Enterprise but hit the problem running in a 32 bits Linux slackware.

Hope this helps.
user at annon dot org 08-Aug-2010 04:48
I recently stumbled upon a problem in my download script where a download link would be clicked but then no other links would work until that download had finished. Other instances/windows would not work either.

This is because session_start() locks the session data until the script finishes. In my case, until the script had finished sending the file data (which in a throttling script can take a while).

The solution is to use session_write_close();
This writes the current session data back to the session and closes the session so that other instances/windows can access the script using the same session.

Since adding it to my script my site can now have several files downloading at once from the same session and still serve pages.
milanzivanovic at gmail dot com 05-Aug-2010 01:48
Resolve for:

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at

is in changing text editor encoding to ANSI or UTF-8 without BOM.

Thanks God I found the answer!
aladinfajr at gmail dot com 31-May-2010 09:18
my problem was in
session_start();
when i include this term in my first code it show me Warning Message: Cannot Modfie cache limiter
i had tryed many solves and dosn't work

finally

i write my code in other encode
and it sccussfully worked

i hope that help
gultron at hotmail dot com 30-Mar-2010 08:02
Hi,

I just had this error saying that there is something wrong with session_start(); even if session_start(); is the only command in the script.

Warning: session_start() [function.session-start]: Node no longer exists in C:\xampp\htdocs\soui\index.php on line 3

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\xampp\htdocs\soui\index.php:3) in C:\xampp\htdocs\soui\index.php on line 3

I corrected this problem by deleting all the files in the tmp directory of the webserver, C:\xampp\tmp
info.at.merchandisinginteractive.sk 01-Mar-2010 06:46
A handy script that checks fot the presence of uft-8 byte order mark (BOM) in all files in all directories starting on current dir. Combined from the work of other people here...

<?php
function fopen_utf8 ($filename) {
   
$file = @fopen($filename, "r");
   
$bom = fread($file, 3);
    if (
$bom != b"\xEF\xBB\xBF")
    {
        return
false;
    }
    else
    {
        return
true;
    }
}

function
file_array($path, $exclude = ".|..|design", $recursive = true) {
   
$path = rtrim($path, "/") . "/";
   
$folder_handle = opendir($path);
   
$exclude_array = explode("|", $exclude);
   
$result = array();
    while(
false !== ($filename = readdir($folder_handle))) {
        if(!
in_array(strtolower($filename), $exclude_array)) {
            if(
is_dir($path . $filename . "/")) {
                               
// Need to include full "path" or it's an infinite loop
               
if($recursive) $result[] = file_array($path . $filename . "/", $exclude, true);
            } else {
                if (
fopen_utf8($path . $filename) )
                {
                   
//$result[] = $filename;
                   
echo ($path . $filename . "<br>");
                }
            }
        }
    }
    return
$result;
}

$files = file_array(".");
?>
augomat at gmail dot com 01-Feb-2010 11:55
There are some posts around about session_start() beeing terribly slow on ntfs. for me the problem occured from one day to another, system was already running fine for 2 years.
to get around it implementing a custom session_set_save_handler could be an option, although for me it worked just to put a session_write_close() somewhere near the end of my script. (maybe IIS didn't kill the php-threads fast enough?!)
info at nospam dot mmfilm dot sk 29-Dec-2009 07:58
For those of you running in problems with UTF-8 encoded files:

I was getting an error because of the BOM, although i set Dreamweaver to "save as" the without the BOM. It appears that DW will not change this setting in already existing files. After creating a new file withou the BOM, everything worked well.

I also recommend http://people.w3.org/rishida/utils/bomtester/index.php - a utility that remote checks for the presence of BOM.
jamestrowbridge at gmail dot com 29-Dec-2009 09:57
Unfortunately, after pulling my hair out trying to figure out why my application was working fine in every browser other than IE ( Internet Explorer) (Opera, Chrome, Firefox, Safari are what I've tested this in) - when using a DNS CNAME record (like a vanity name that is different from the DNS A record, which is the hostname of the server) sessions do not work correctly.

If you store a session var while on the CNAME:
vanity.example.com and the hostname of the server is hosname.example.com
Then try to call the variable from a different page, it will not find it because of the CNAME (I guess it store the variable under the hostname, then when trying to read it it's still looking under the CNAME) the same application works fine when accessing it under the hostname directly.  Keep in mind that I was testing this on an internal network.
falkon303 at gmail dot com 03-Dec-2009 12:49
I have found that you can use arrays with session variables in a very convenient manner.  Be sure to unset the array afterwards!

The following is an example.

<?php

session_start
();

$sessionvars['name'] = "John";
$sessionvars['age'] = "43";
$sessionvars['gender'] = "Male";
$sessionvars['email'] = "john.doe@example.com";

$_SESSION['arvars'] = $sessionvars;
unset(
$sessionvars);

echo
$_SESSION['arvars']['name']."<br>";
echo
$_SESSION['arvars']['age']."<br>";
echo
$_SESSION['arvars']['gender']."<br>";
echo
$_SESSION['arvars']['email']."<br>";

?>
eugene at ultimatecms dot co dot za 24-Nov-2009 10:39
Ever get an error like this:

Warning: Unknown: open(/tmp/sess_lLFJ,tk9eFs5PGtWKKf559oKFM3, O_RDWR) failed: Permission denied (13) ?

Don't ask me how, but I managed to fix it by calling
session_id() before session_start(), at the top of the page.

Try it. Hopefully it'll help someone else.
myemail gerolf at pictureparking dot com 08-Oct-2009 04:12
please note that at least in php 5.3.0 the setting session.use_only_cookies (in php.ini) defaults to "on". This means that using trans_id, and passing the PHPSESSID via the url does not work untill you change that setting.
Charlie at NOSPAM dot example dot com 22-Sep-2009 07:04
Be warned that depending on end of script to close the session will effectively serialize concurrent session requests.   Concurrent background "data retrieval" (e.g. applications such as AJAX or amfphp/Flex) expecting to retrieve data in parallel can fall into this trap easily.

Holding the session_write_close until after an expensive operation is likewise problematic.

To minimize effects, call session_write_close (aka session_commit) as early as practical (e.g. without introducing race conditions) or otherwise avoid the serialization bottleneck.
schlang 26-Jul-2009 10:44
if you store your sessions in a database, always ensure that the type of the database column is large enough for your session values
emre@yazici 23-Jul-2009 02:46
PHP Manual specifically denotes this common mistake:

Depending on the session handler, not all characters are allowed within the session id. For example, the file session handler only allows characters in the range a-z A-Z 0-9 , (comma) and - (minus)!

See session_id() manual page for more details.
dstuff at brainsware dot org 21-Jul-2009 05:53
It seems like spaces in the name don't work either - got a new session id generated each time
abiusx at gmail dot com 12-Jul-2009 03:03
Working with Comet, or any other parallel or simultaneous requests from a single browser (a single session) would lock the application if it uses a centralized session management.

To fix this, you should add session_commit() (Alias of session_write_close() ) after ALL session management, i.e using any session_* functions except session_start() is forbidden after that an causes an error.
hperrin at gmail dot com 24-Jun-2009 01:41
When using session_start() multiple times in one script, it seems to only maintain $_SESSION variables with string keys.

<?php
session_start
();
$_SESSION[0] = 'this is a test';
$_SESSION[1] = 'this is also a test';
$_SESSION['test0'] = 'this is a test';
$_SESSION['test1'] = 'this is also a test';
session_write_close();

session_start();
echo
"Session var 0 = ".$_SESSION[0]."<br />";
echo
"Session var 1 = ".$_SESSION[1]."<br />";
echo
"Session var 'test0' = ".$_SESSION['test0']."<br />";
echo
"Session var 'test1' = ".$_SESSION['test1'];

?>

Outputs:
Session var 0 =
Session var 1 =
Session var 'test0' = this is a test
Session var 'test1' = this is also a test
gilthans NOSPAN at gmail dot com 04-Jun-2009 05:55
If two different files don't access the same session, it can only mean one thing: they aren't on the same directory level.
Examples:
a) One is under https, and one is under http. (very common and annoying error)
b) One is under /, another is under /dir1, and /dir1 was first to run. The cookie created by the session is for /dir1 and deeper only, so the other script can't read it; it sees no session so it starts a new one.

Solutions:
1) Session start should always happen at root dir. If one of your scripts discovers user is not logged in, for example, use session_destroy() and send him to the login in the root dir. Scripts that use session without requiring login needs more creative solutions, like redirecting to the root dir, setting the session, and redirecting back.
2) Use SID from page to page, instead of cookies. The upside is that this also works with http/https. The downside is very ugly URL codes and more difficult maintainability ('which pages links to gallery.php without using SID?!').
kavih7 at yahoo dot com 18-May-2009 04:52
I ran into a problem that has a solution that may not be quite intuitive to people (well, atleast it wasn't for me). I had one script that called session_start() and that script would run for an indefinite amount of time. I had a second script that would also call session_start(), but would only run for a few seconds each time it is called.

Here is where the problem occurs: Once session_start is called from the long living script, no other script can call session_start until that long running script calls session_commit() (session_write_close()) or ends.

In any case, this may have seem very intuitive to others, but having an abstracted system in place, I never see the session management at the script level, so it was hard to figure out what was locking any other requests.

Hope this helps others.
suporte2 at sosdominios dot net 07-May-2009 06:39
I found myself in trouble when using $_SESSION['varname']. The value from varname was not shown with echo $_SESSION['varname'] in the page where I'd like to use that value.
After many tries I found that session_start() was missing in the page where I'd like to use the value from varname. When I put de session_start() in that page the problem was solved.

--

Tive problemas utilizando $_SESSION['variavel']. A variavel não aparecia na página que deveria utiliza-la.
Após muitas tentativas pude verificar que não estava usando session_start() na página que receberia o valor da variável.
Inseri session_start() nessa pagina tambem e funcionou perfeitamente!
Gravis 01-Apr-2009 11:04
If you want to check if a session has already been activated, you can check $_COOKIE["PHPSESSID"] for a value before reactivating that session.

Example code:

== login.php ==
<?php
  session_start
();
 
$_SESSION["data"] = "you have an active session!";
  echo
"<a href=\"page.php\">go</a>";
?>

== page.php ==
<?php
 
if(isset($_COOKIE["PHPSESSID"]))
  {
   
session_start();
    echo
$_SESSION["data"];
  }
  else
  {
    echo
"no cookies required!";
  }
?>

This can prevent forcing a cookie on someone (very annoying in lynx) that doesnt intend to login on your site.
LaurenceJ44 at Hotmail dot com 01-Apr-2009 12:36
I kept getting:
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at myfile.php:2)

Only when I had uploaded my pages from my home development server to my hosted website.  the same page worked fine in development, so there must be a difference in the php setup, but since this is a site that hosts many different clients web sites, I can't get them to change thier config.

After a little bit of research and trial and error, I found the cure was to move the line:
<?php session_start(); ?>

to be the very 1st line in any .php file.

orginally I had:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<?php session_start(); ?>
<html>
<head>
...etc

so I changed it to :
<?php session_start(); ?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
...etc

and all is well...

The clue is in the warning message, it ends :2)  which means the session_start() call is not on line 1 of the file!

Hope this helps & good Luck

Loz
microvalen at NOSPAM dot microvalen dot com 22-Mar-2009 10:09
I have tried many times a lot of login scripts but sometimes when you have a lot of traffic you can note the "overloading" of the server tring to deal with all sessions specialy with the long, long scripts and classes ... checking all stuffs (ids, ips, usernames, etc) the loading page increase ...specialy when you have a "home" server with a small blog..

if you open the folder "/tmp" you will thousands of files that do nothing else that increasing the size of the folder.
Sessions are good and I just offer an alternative.
.. and for that I just created in about 20 min a simple script that can handle a simple login.

<b>(Be aware !! this is just an example .. it not make use of any check of xss atacks or other scripts !!!</b>

and make use of cookies [today all moderns browsers use cookies])

<?php

$mysqli
= new mysqli('localhost', 'root', 'pass', 'nameofDB');

if (
mysqli_connect_errno()) {
   
printf("Connect failed: %s\n", mysqli_connect_error());
    exit(); }

$cookie = (isset($_COOKIE['vuid'])) ? $_COOKIE['vuid'] : '';

if(!
$cookie) {
   
$user_level = 0;
   
setcookie('vuid', '0.' . md5('anonymous')); }
else {
   
$part = explode('.', $cookie);
   
$user_level = (int) $part[0];
   
$user_name = (string) $part[1];

    if(
$user_level != 0) {
       
$is_logged = check_login($user_level, $user_name); }
    else {
       
$is_logged = false; } }

if(isset(
$_GET['login'])) {
      
// here you MUST make a form and a function that realy check the login ...
       
if($YourFunctionCheckIsOk) {
   
setcookie('vuid', /*levels betwen 1-9*/ '9.' . md5('PutTheUserNameHere'));
    echo
'<meta http-equiv="refresh" content="1;URL=index.php">
    Correct Login<br>
    You will be redirected to the main page'
; } }
elseif(isset(
$_GET['logout'])) {
   
setcookie('vuid', '0.' . md5('anonymous'));
    echo
'<meta http-equiv="refresh" content="1;URL=index.php">
    You are out now ... see you soon<br>
    You will be redirected to the main page'
; }
else {
    if(
$is_logged) {
        echo
'Welcome ' . USERNAME . ' <a href="?logout">LOGOUT</a>'; }
    else {
        echo
'You are a Anonymous. LOGIN <a href="?login">HERE</a>'; } }

function
check_login($user_level, $user_name) {
    global
$mysqli;

   
$is_logged = false;

   
$result = $mysqli->query('SELECT nick FROM accounts WHERE user_level = ' . $user_level);
   
$row = $result->fetch_array();
   
$result->close();
    if(
$user_name === md5($row['nick'])) {
       
define('USERNAME', $row['nick']);
        return
$is_logged = true; }
    return
$is_logged = false; }

$mysqli->close();

?>

PS: you can change the nick with the ip or better use both !
like:
 "level.md5(sha1(nick)).sha1(md5(ip)) etc ...
 "0.4aea7c7d495676.4aea7c7d495676"
and check them separetly by <a href="http://php.net/explode">"exploding"</a> them ..
play arround ...
tchalvakspam at gmail dot com 23-Feb-2009 01:25
Be aware that if a browser isn't accepting cookies, it can cause the session to invisibly not save between two pages.

So for example, in Firefox 3.0.6 there is a bug where "localhost" addresses are currently not saving cookies.  This will kill any attempts to use session code in development where localhost is used.

One workaround for this is to use a different synonym for the localhost address, i.e. http://127.0.0.1/, or set up a virtualhost, e.g. http://localdevelopment/

Overall, pay close attention if you see to different, unexpected session behavior in two different browsers, it may be a result of the cookies being handled differently or being dropped.
yesmarklapointe at hotmail dot com 04-Feb-2009 04:32
Here is some info about how to use SID with session_start().
Experiment run on WAMPserver, PHP version 5.2.6.
Using FireFox 3.0.

The definition found at http://www.php.net/manual/en/session.constants.php 
describes SID is a “pre-defined constant” containing either:
1). the session name and session ID in the form of "name=ID" .
This is the same name as would be returned by session_name(), and the same id as would be returned
by session_id(). 

2).  Or an empty string,  if the session ID was set in an appropriate session cookie.

Example code:
<?php
session_start
();
echo
'<a href="page2.php?' . SID . '">page2</a>';
?>

This code will yield in the browser one of the following:
a).   “page 2”      (as a hyperlink, but mouseover shows the link is to something in the form of
http://www.example.com/page2.php?PHPSESSID=e2bd7072....  )

b).   “page 2”     (as a hyperlink, but mouseover shows http://www.example.com/page2.php? )

Which result is determined by whether or not the browser is sending a matching session cookie back to the script. Result “a” above always appears at least initially since the script hasn’t yet set a cookie and neither has it been done automatically yet by the php.ini setting session.use_cookies. However, after refreshing or using the back button, the form in "b" will appear because then the cookie exists (either you set it or session.use_cookies did it automatically).
info at vanylla dot it 30-Jan-2009 04:06
If while testing locally on your Windows machine you get many warnigns like:

Warning: session_start()... failed: No such file or directory
Warning: session_start()...: Cannot send session cache limiter - headers already sent
etc.

you need to configure properly the session.save_path in your php.ini file.

Set session.save_path to an existing folder on your PC.
For example: session.save_path="C:\Temp";
Jessycormier at gmail dot com 24-Jan-2009 03:14
I found i was getting a lot of
"Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent "

Warnings, on some pages, where as on other pages it worked just fine.

After some time looking around and trying things like ob_start() and session_write_close()... nothing seemed to work.

Then i realized the encoding of the page. I checked the encoding of the page and it was set to UTF-8, so I changed it to ANSI and now the Warnings went away.

Good luck any one else.
philippe dot latulippe at xxxxgmail dot com 11-Jan-2009 06:12
When using session_start() with cookies over an encrypted connection (like HTTPS) it is important to set php_ini('session.cookie_secure',true).  This sets a flag in the cookie which will stop browsers from sending this cookie over an unsecured connection.  If this is not done, a Man-In-The-Middle could easily cause the victim's browser to send his session ID in plaintext, gaining access to the account and defeating the goal of the secure connection.

http://fscked.org/blog/fully-automated-active-https-cookie-hijacking
zidaine_38 at yahoo dot com 05-Dec-2008 08:31
<?php
class SESSION
{
   public function
__construct ()
   {
  
self :: commence ();
   }

   public function
commence ()
   {
    if ( !isset(
$_SESSION ['ready'] ) )
     {
     
session_start ();
     
$_SESSION ['ready'] = TRUE;
     }
   }

   public function
set ( $fld , $val )
   {
  
self :: commence ();
  
$_SESSION [ $fld]  = $val;
   }
   public function
un_set ( $fld
   {
  
self :: commence ();
   unset(
$_SESSION [$fld] );
   }
   public function
destroy ()
   {
  
self :: commence ();
   unset (
$_SESSION );
  
session_destroy ();
   }
   public function
get ( $fld )
   {
  
self :: commence ();
   return
$_SESSION [$fld];
   }
   public function
is_set ( $fld ) {
  
self :: commence ();
   return isset(
$_SESSION [$fld] );
   }
}
?>

This Class is handy to all who want easy session handling.
Just include () or require () this to pages where you will have to use session.

example:

<?php
 
include ( "/path/to/sess.inc.php" );
 if( !
SESSION :: is_set ( "number" ) )
  {
  
SESSION :: set ( "number" , 1 );
  }
 else
  {
  
$_SESSION ["number"] ++;
  }
  echo
SESSION :: get ( "number" );
?>
andy_isherwood at hotmail dot com 18-Nov-2008 06:54
A session created with session_start will only be available to pages within the directory tree of the page that first created it.

i.e. If the page that first creates the session is /dir1/dir2/index.php and the user then goes to any page above dir2 (e.g. /dir1/index.php), session_start will create a new session rather than use the existing one.
aban at datahouselibya dot com 17-Jul-2008 08:11
for resolve the problem with session_start()
Cannot send session cache limiter - headers already sent (output started at ..."

write it at first line of the page like

<?php session_start(); ?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<body>
<?php $_SESSION['name']='mohamed'; ?>
</body>
<html>
michael at pythontech dot net dot au 13-Jul-2008 08:17
@ash

Whilst this may prevent session hijacking attempts, it also ruins the user experience, pressing back and forward will result in the 'security' token being out of sync. Also opening new tabs/ windows will also cause issues.

A better method would be to simply check the ip address or ip block of the user. But this is not without problems either.

To access highly sensitive information, the user should be required to enter his/her password again, even tho they are logged in. This ensures that session hijackers can not access this information.

All this goes hand-in-hand with regenerating session ids on login, and good use of https.
ash at atomic-network dot co dot uk 28-May-2008 09:33
@My last post...
the function will generate the session "token" you just need to do a check and regenerate it on each page load...
ash at atomic-network dot co dot uk 28-May-2008 09:29
When developing applications or just creating a general website with the use of sessions, many developers do not think about securing session hijacking attacks. For further information I recommend searching google, however I have produced a small function to be called immediately after session_start().

your_page.php:
<?php
session_start
();
include_once
'session_secure.inc.php';
session_secure();
# Your content here.
?>

session_secure.inc.php :
<?php
function session_secure(){
   
// wrapped for the php entry....
   
$alph =array('A','a','B','b','C','c','D','d','E',
   
'e','F','f','G','g','H','h','I','i','J','K','k',
   
'L','l','M','m','N','n','O','o','P','p','Q','q',
   
'R','r','S','s','T','t','U','u','V','v','W','w',
   
'X','x','Y','y','Z','z');
    for(
$i=0;$i<rand(10,20);$i++){
       
$tmp[] =$alph[rand(0,count($alph))];
       
$tmp[] =rand(0,9);
    }
    return
implode("",shuffle($tmp));
}
?>

There are quicker ways like md5(time()*rand()), however the function above is completely random, and will render an attackers hijacking task almost impossible.
vladimir at pixeltomorrow dot com 14-May-2008 07:31
Kind of ankward it's not mentioned here, but you should also trigger the session_write_close() function as soon as possible so you'll release the lock over the session files.

Cheers,
Vladimir Ghetau
chrismckeeuk at gmail dot com 10-May-2008 12:51
If your sessions are failing to hold the stored data ensure that session.use_only_cookies is set to 1 in your PHP.ini config.

Also using the session auto start saves on a lot of issues and removes the issue of people setting the session_start after the html begins.
Anthony Catel p at NOSPAM dot rabol dot fr 03-May-2008 08:02
session_start() generate a warning if PHPSESSID contains illegal characters

Warning: session_start() [function.session-start]: The session id contains illegal characters, valid characters are a-z, A-Z, 0-9 and '-,' in /home/para/dev/mon_site/header.php on line 17

To avoid i wrote this :

<?php
   
function my_session_start()
    {
        if (isset(
$_COOKIE['PHPSESSID'])) {
           
$sessid = $_COOKIE['PHPSESSID'];
        } else if (isset(
$_GET['PHPSESSID'])) {
           
$sessid = $_GET['PHPSESSID'];
        } else {
           
session_start();
            return
false;
        }
       
        if (!
preg_match('/^[a-z0-9]{32}$/', $sessid)) {
            return
false;
        }
       
session_start();
       
        return
true;
    }
?>
php at hogerheijde dot net 29-Feb-2008 11:53
That's why you shouldn't use register_globals and refer to
$_GET['id']
for the page.php?id=1
or if you don't care if it is GET or POST you can use
$_REQUEST['id']

Those will not be cleared by session_start().

To complete: you should use $_SESSION['id'] to get the content of the session.
jphansen at uga dot edu 25-Feb-2008 11:12
I just wrote that session_start() will erase your querystring variable(s) once called. I want to clarify that it will only do this if a variable by the same subscript is defined in $_SESSION[].
jphansen at uga dot edu 25-Feb-2008 10:55
Warning, calling session_start() will reset your querystring values.

Navigating to page.php?id=1

<?php
echo "id = $id"; // 1
session_start();
echo
"id = $id"; // ""
?>
fixis at nexus dot com 16-Feb-2008 06:42
I also found using session_write_close(); after you send your custom headers sometimes helps on some servers.  This protects any data from being cleared out by some of these errors mentioned.
cbake6807 at comcast dot net 05-Feb-2008 08:20
Having a problem in IE causing your getFile.php script to be pushed to the browser as an empty text file, instead of the intended attachment?

If your php config causes session_start() to output a cookie, or anything funky, IE will not like the filename and will also try and read the file contents inline into the browser window.

Don't use session_start() or USE Output Buffering after the session is started.

<? //session_start();

   
function force_download($file)
    {
        if ((isset(
$file))&&(file_exists($file))) {
          
$fileArray = explode("/", $file);
          
header("Content-type: application/force-download");
          
header("Content-Disposition: attachment; filename=".$fileArray[sizeof($fileArray)-1]);
          
header("Content-Transfer-Encoding: Binary");
          
header("Content-length: ".filesize($file));
          
header('Content-Type: application/octet-stream');
          
header("Content-Disposition: attachment; filename=".$fileArray[sizeof($fileArray)-1]);
          
readfile("$file");
        } else {
           echo
"No file selected";
        }
//end if

   
}//end function

?>
rudylattae at gmail dot com 27-Jan-2008 05:58
File Encoding was causing my session_start() statement to generate an unexpected warning.

Environment:
OS: Windows XP Pro (32bit)
PHP: v5.2.5
Apache: v2.0.61

I was having this warning:
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at ...

I was rather pissed off because I know of this issue and I know how to fix it:

1) Just make sure the session_start() directive is processed before any other statements that modify the content headers.

2) Failing #1 above, you should also make sure that your script files do not have any beginning/trailing space or carriage return characters.

3) As a last stand, you could use output buffering to hold your stuff in memory and then spit it out at the very end. This would essentially allow you to manipulate the headers to your heart's content without getting any crap from php.

Note: with regards to #2 above, I know some devels use the interesting construct of no closing php braces e.g.:

> info.php
<?php
    phpinfo
();

?> (they omit this)

It seems the tag is not required by php (at least php does not puke) so the parser does not treat any trailing spaces as output to be sent to the user agent. I'm not using this loop-hole at the moment.

Anyway the above resolutions *did not* work for me (yer even #3) and I was about to give up and just gag php with good ol "@".

It was then that I thought to check the encoding of my php file. Turns out I had left my editor in UTF-8 encode mode from some previous (i18n) work I had done. I switched to ANSI and that fixed the problem. Suddenly the same file that had caused php to scream in pain was being processed without any issues.

I also noted that I could set the editor to "Encode in UTF-8 without BOM" and that also works. The BOM is the byte order mark which php probably glosses over (or does not understand). I didn't look too far into it.

I hope this helps someone else.

Cheers!
omnibus at omnibus dot edu dot pl 07-Jan-2008 03:29
You probably know it but in case somebody did not:
session_start() must be called BEFORE any explicit operations on the $_SESSION variable; otherwise $_SESSION will be treated as an ordinary variable and not stored for future use.
k dot dafalias at ist dot eduhi dot at 14-Nov-2007 04:25
If you encounter "The session id contains illegal characters" error, find out, if you get an empty session id.
If so, the problem ist fixed easily:

if(!session_id()) session_regenerate_id();
bulk at janoszen dot hu 09-Oct-2007 11:13
Don't *ever* use /dev/random as a session entropy file, because session_handler will hang for a *long* time after open(). This configuration will be *the* overkill:

<?php
ini_set
("session.entropy_file", "/dev/random");
ini_set("session.entropy_length", "512");
?>

Use /dev/urandom instead. The reason for this is (from Wikipedia):

A counterpart to /dev/random is /dev/urandom ("unlimited" random source) which reuses the internal pool to produce more pseudo-random bits. This means that the call will not block, but the output may contain less entropy than the corresponding read from /dev/random.

We spent 2 days on figuring this out. You have been warned.
ehassler at synapsestudios dot com 19-Sep-2007 04:32
At work we had an odd warning, "Cannot send session cache limiter - headers already sent". In the following:

header('meta:1');
session_start();

the first header went across fine, but the session_start died with the warning. 

What was happening was that the session contained an object which fired __autoload() when it was unserialized. The __autoload() then included the file with the class definition, but that file also output non-header text.  This caused session_start() to be unable to add the session_id to the headers.

This was difficult to find because we weren't able to see the text that was output from the file that was __autoload()ed, only the warning.
(zero)luke(zero)(at)gmail(dot)com 06-Jul-2007 03:55
Regarding the posts discussing ways of checking if a session is active, I've found that this is the best way, aslong as you dont assign any variables to the $_SESSION superglobal before calling the function.

The Function:

<?php

function session_started(){

    if(isset(
$_SESSION)){ return true; }else{ return false; }

}

?>

An Example:

<?php

function session_started(){
    if(isset(
$_SESSION)){ return true; }else{ return false; }
}

//Start the output buffer so we dont create any errors with headers
ob_start();

//Check to see if it has been started
if(session_started()){
    echo
'The session has been started.<br />';
}else{
    echo
'The session has not been started.<br />';
}

//Start the session
echo 'Starting Session...<br />';
session_start();

//Check again
if(session_started()){
    echo
'The session has been started.<br />';
}else{
    echo
'The session has not been started.<br />';
}

//Flush the buffer to screen
ob_end_flush();

?>

Hope this helps some people.
Steffen dot Pietsch at berlinonline dot de 15-May-2007 03:05
Beware to use $_SESSION as parameter to a function.
(here: php5  5.1.2)

Use:
    $s=array(); foreach($_SESSION as $k => $v) $s[$k]=$v;
    $result = VeranstaltungTermin::search($s, $quellen, $KatCount);

otherwise the garbage-collection of php5 will destroy at end of script Your $_SESSION array before writing to disk
Chris Brown 24-Apr-2007 04:17
Here's another session tip for you, relevant to IE6:

If you find that your session is unexpectedly lost when your application opens a page in a pop-up window, try closing down any other copies of IE running on your machine.

The problem is that IE doesn't always use the same IE process to host a new pop-up window - it chooses one (using some mysterious strategy) from the pool of running IE processes! Since session information (cookies) is not preserved across processes, the pop-up may loose the session (and probably redirect the user to your log-in page.)

I don't know a work-around for this, except for close all other IE windows. Microsoft state that they do not guarantee that sessions will be preserved across multiple windows: http://support.microsoft.com/default.aspx/kb/196383
leandroico---at---gmail---dot---com 17-Mar-2007 04:21
TAGS: session_start headers output errors include_once require_once php tag new line

Errors with output headers related to *session_start()* being called inside include files.

If you are starting your session inside an include file you must be aware of the presence of undesired characters after php end tag.

Let's take an example:
> page.php
<?php
include_once 'i_have_php_end_tag.inc.php';
include_once
'init_session.inc.php';

echo
"Damn! Why I'm having these output header errors?";
?>

> i_have_php_end_tag.inc.php
<?php
$_JUST_A_GLOBAL_VAR
= 'Yes, a global var, indeed';
?>

> init_session.inc.php
<?php
session_start
();
$_SESSION['blabla'] = 123;
?>

With all this stuff we will get an error, something like:
"... Cannot send session cache limiter - headers already sent (output started at ...", right?

To solve this problem we have to ignore all output sent by include files. To ensure that we need to use the couple of functions: *ob_start()* and *ob_end_clean()* to suppress the output. So, all we have to do is changing the *page.php* to this:

<?php
ob_start
();
include_once
'i_have_php_end_tag.inc.php';
include_once
'init_session.inc.php';
ob_end_clean();

echo
"Woo hoo! All right! Die you undesired outputs!!!";
?>
iam1981 26-Feb-2007 05:45
I had the same "session data lost" issue. I couldn't solve it with a single session_start(). Instead I had to include session_start() in each page.

Another X File archived...
design at ericcorriel dot com 15-Feb-2007 08:08
For those encoding their pages in UTF-8 but running into problems with BOM data (Byte Order Marks) being outputted before anything else - such as $_SESSION data - but wish to use UTF-8 encoding, and who do NOT wish to use UTF-8 No BOM encoding because the latter produces weird results when using foreign language accented characters, try the following :

- Save your document with UTF-8 No BOM encoding (on a mac, using BBEdit, this is normally found on the very bottom left corner of the window).  This will produce a document that will not output BOM data.
- then, in your scripts, include the following: 

header('Content-Type: text/html; charset=UTF-8');

before your call to session_start()

hope that helps someone.
r dot s dot goldsmith at far-blue dot co dot uk 24-Jan-2007 03:22
If you ever want to know whether a session is open or has already been closed (e.g. with session_write_close()) when you need to open one (in my case, writing a framework and, therefore, not controlling the session directly), I have been unable to find an official check. However, I did notice that session_start() has the following behaviour:

* If the session has been open before but is now closed, when you call session_start() the $_SESSION array is reset to the content of the session.

* If the session is already open, the $_SESSION array is left totally untouched.

Therefore, I came up with the following (obviously assuming you have already tested $_SESSION exists):

<?php
$_SESSION
['testMe']='test';
@
session_start();

if(isset(
$_SESSION['testMe']))
{
    echo
"Session was open\n";
    unset(
$_SESSION['testMe']);
}
else
    echo
"Session was closed\n";
?>

Until someone can tell me the 'official' way to do it, this seems to work.

Just to save some confusion, $_SESSION, session_id() and the SID define all maintain their values after a session_write_close() so are of no use in identifying if a session is currently open or not. Hence this trick.
Devour 18-Jan-2007 02:51
How many times you've seen this error when actually your code is perfect:

Warning: session_start(): The session id contains invalid characters,
valid characters are only a-z, A-Z and 0-9 in

Usually there are MANY reasons why such an error can appear into your logs, page, etc. (one way to generate it, is to send PHPSESSID='').

But it wasn't our case. We checked everything, and we even logged the entire request ($_GET, $_POST) that was generating the error.
Still no luck. Until one point, when we checked what the session cookie contains.
It seems there are few bots that are trying to buffer overflow (?) a page, using session cookies manually changed to contain something else than session id (strlen == 32 and  hex number) The bot in our case was trying to mass submit spam on pages.
So we needed to check and destroy any session id that do not comply.

After adding this code:
$sn=session_name();
if(isset($_GET[$sn])) if(strlen($_GET[$sn])!=32) unset($_GET[$sn]);
if(isset($_POST[$sn])) if(strlen($_POST[$sn])!=32) unset($_POST[$sn]);
if(isset($_COOKIE[$sn])) if(strlen($_COOKIE[$sn])!=32) unset($_COOKIE[$sn]);
if(isset($PHPSESSID)) if(strlen($PHPSESSID)!=32) unset($PHPSESSID);
session_start();
we got rid of that.

( Note: The code is before session_start() )

Strange, kinda paranoid, but effective.
cppforlife at yahoo dot com 18-Dec-2006 10:12
If you are getting headers sent error check what is the encoding of your file. In my case i had utf-8, so i changed it to ansi, and everything worked.

hope it helps!
mike at mikebird dot co dot uk 10-Dec-2006 02:34
It seems that the session file is opened exclusively.
On some occasions (Windows) I have found that the file lock is not released properly for whatever reason, therefore causing session_start() to hang infinitely on any future script executions.
My way round this problem was to use session_set_save_handler() and make sure the write function used fopen($file, 'w') instead of fopen($file, 'x')
evil dot 2000 at web dot de 07-Oct-2006 04:06
I had a problem accessing a session which is open in another frame at the same time.
I had a frame, which is displaying a live text like a chat. It has an opend and locked session. I tried to add data to this session with another frame, but this wouldn't work.
In the first frame i had a loop which is looking for fresh data in the session and prints it out like this:
<?php
 session_start
();

 [...]

 while (
true) {
  echo
$_SESSION["input"]."\n";
 
sleep(1);
 }
?>
But this locks the session, and no other frame can access the session data at the same time.
So i modified this loop a bit like this:
<?php
 session_start
();

 [...]

 
session_commit();
 while (
true) {
 
ob_start(); session_start(); ob_end_clean();
  echo
$_SESSION["input"]."\n";
 
session_commit();
 
sleep(1);
 }
?>
Now the second frame is able to access the session.
The ob_start() and ob_end_clean() is just for surpressing the cookie output to the browser.
Dino 30-Sep-2006 06:36
With IE and FF, session_start() appears to stop form values being preserved when the user browses 'back' to a page (I'm using SBS2K3 IIS6 PHP5.1.1).

For example if you set some hidden form values from javascript in one page, then navigate to another page and come back using the browsers back button, the form values should be preserved. But this does not happen when your your form page uses session_start().

The following seems to sort this out nicely:

session_cache_limiter('public');
session_start();
double at dumpit dot de 29-Sep-2006 07:35
A bedder way to check wether the session is started including ip logging, so it will be a little saver. in 4 small lines.

<?php

   
if( !isset( $_SESSION ) ) { session_start(); }
    if( isset(
$_SESSION['REMOTE_ADDR'] ) && $_SESSION['REMOTE_ADDR'] != $_SERVER['REMOTE_ADDR'] )
    {
session_regenerate_id(); $_SESSION['REMOTE_ADDR'] = $_SERVER['REMOTE_ADDR']; }
    if( !isset(
$_SESSION['REMOTE_ADDR'] ) ) { $_SESSION['REMOTE_ADDR'] = $_SERVER['REMOTE_ADDR']; }
   
?>

Yes, the code is a little bit self-willed ;)
ben dot morin at spaboom dot com 29-Sep-2006 09:49
James at skinsupport dot com raises a good point (warning) about additional requests from the browser.  The request for favicon.ico, depending on how it is handled, can have unintended results on your sessions. 

For example, suppose you have ErrorDocument 404 /signin.php, no favicon.ico file and all pages in your site where the user signs in are also redirected to /signin.php if they're not already signed in. 

If signin.php does any clean up or reassigning of session_id (as all good signin.php pages should) then the additional request from the browser for favicon.ico could potentially corrupt the session as set by the actual request. 

Kudos to James for pointing it out and shame on me for skimming past it and not seeing how it applied to my problem.  Thanks too to the Firefox Live HTTP Headers extension for showing the additional request. 

Don't waste days or even hours on this if your session cookies are not being sent or if the session data isn't what you expect it to be.  At a minimum, eliminate this case and see if any additional requests could be at fault.
truthhunter 25-Sep-2006 05:57
Another one bitten by the "a different domain name gives you a new session" in IE...

My site uses interactive PDF documents.  A user saves data from them into FDF documents, and when this happens, the site also includes the URL of the PDF in the FDF data (using the FDF "/F" tag).

This URL is generated using the $_SERVER["HTTP_HOST"] value from PHP.  For some as-yet-undetermined reason, when my hosting provider updated PHP (I believe to 4.4.1), for a time the $_SERVER["HTTP_HOST"] value apparently dropped the "www." from my domain name.  So, some FDF files were saved with this different URL value.  Needless to say, when one of these FDFs loaded the corresponding PDF, although the load and display of the PDF worked, any subsequent save operation (which relies on current session information for validating the user, etc.) initiated from within the PDF failed.  The original session had been established for the "www.example.com", but because the PDF URL lacked the "www.", PHP/IE had established a new, essentially empty, session.

I scratched my head over this problem for months and only recently happened upon this fix.  In my case, manually patching the failing (binary) FDF files to include the "www." in the URL for the PDF did fix it.

Hopefully someone else finds this helpful...!
mjr-php at ranney dot com 14-Sep-2006 09:55
For some reason, MSIE gets confused when session_start() is called and the Content-disposition has been set to "attachment".  The only solution I've found is this:

<?php
if(strpos($_SERVER['HTTP_USER_AGENT'],"MSIE")) {
 
session_cache_limiter('public');
}
session_start();
?>
kyzer at 4u dot net 13-Sep-2006 05:42
Recursive session usage isn't possible. By that I mean fetching (via curl or such) another page on the site which uses sessions, as part of a page which itself uses sessions.

For example:
page1.php:
<?php
session_start
();
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, "http://example.com/backend.php");
curl_exec($curl);
?>

backend.php:
<?php
session_start
();
print
$_SESSION['foo'];
?>

In this case, requesting page1.php will hang the request indefinitely. backend.php is waiting to open the session data for reading/writing, but it's still locked by page1.php, which is waiting for backend.php to finish.

Because there's no session_end(), you can't get PHP to relinquish the lock on the session data after session_start() has occured. The solution is just to include backend.php or its functionality directly, e.g.:

require './backend.php';
roope dot luhtalaNOSPAM at iki dot fi 07-Sep-2006 10:36
If your session_start() does not set a cookie, but instead just generates a new session_id on every request, you should check if your script is echoing something before the function call. Even a line change in the code before the session_start() function prevents the cookie to be set.
colemanc at colemanesolutions dot com 28-Aug-2006 03:30
In reference to the "Cannot send session cache limiter..." error message, I have tried a number of ways to supress the error. An If/Then block will work only if you store the flag in a session variable, cookie, or other method. Or, you can obviously supress error messages by the error level. However, the simplest way to do it is a simple:

@session_start();

This will hide all error messages resulting from that line of code. I would only recommend this method AFTER you have fully tested your code but it is very effective when that is your only error and you do not want to completely stop code exectution by means of a die() or exit() function.
core58 at mail dot ru 08-Aug-2006 06:36
when you're using session trans sid ENABLED, and you perform redirect such as Header( "Location..." ), redirected client will SURELY loose his session.
to avoid this, you can use a modified version of redirect function, like this:

<?php

function Redirect302( $location )
{
   
$sname = session_name();
   
$sid = session_id();
    if(
strlen( $sid ) < 1 )
    {
       
Header( $location );
        return;
    }
   
    if( isset(
$_COOKIE[ $sname ] ) || strpos( $location, $sname."=".$sid ) !== false )
    {
       
Header( $location );
        return;
    }
    else
    {
        if(
strpos( $location, "?" ) > 0 )
           
$separator = "&";
        else
           
$separator = "?";

       
$fixed = $location . $separator . $sname."=".$sid;
       
Header( $fixed );
        return;
    }
}

?>

expamle:
Redirect302( "Location: /YourPage/index.php" );

the function performs common redirect if no session is active, and appends session "name=sid" to query string when session is already started,  like PHP parser does when outputting your page.

hope, you'll find it useful.
yours:)
devonmitton at gmail dot com 26-Jul-2006 01:35
I ran into the problem of losing the session after i redirect the user with header( location:);

I found that the problem doesn't occur in php5. Atleast for myself. I tested it on IIS as well as Apache and both times using php5 fixed the issue.

Secondly, I found a weird solution: The website i'm building required Cyrillic type, so i encode the pages using UTF-8. The problem that happens is that UTF-8 sends information before the php tags, and therefore before the session_start(); which ultimately renders the session_start(); call ineffective.

The UTF-8 encoding sends a small chunk of information before anything. This is called BOM (byte order marks).

To ensure that they don't show up, you need to save your files with a UTF-8 encoding which bypasses BOM. BBEdit for the Macintosh with allow for this under the file encoding options.

To recap: In this instance and for my situation, UTF-8, no BOM will allow sessions to pass through the header( location:); redirect, or using PHP5.

Hope this helps someone! [i will also repeat this comment under the header() function]
James 13-Jul-2006 04:22
To avoid the notice commited by PHP since 4.3.3 when you start a session twice, check session_id() first:

if (session_id() == "")
  session_start();
saykyo (mail at gmail dot com) 12-Jul-2006 08:23
Watch out for using UTF-8 encoding in your php scripts!

I don't know about other enviroments, but in Windows XP, if you edit a document and set it to be UTF-8, the editor (notepad for exapmle) inserts two invisible bytes at the beginning of the file (they read FF FE in hex for me). I suppose this happens so Windows can identify the file as UTF-8.

Since these two bytes are placed before anything else in the file, including <? ?> tags, when you execute the php script, they get outputed to the browser (even tough they won't be shown in the source of the result document, they're there!) before your php code gets a chance to run anything. This effectively cripples functions like session_start() ($_COOKIE to be exact).

The solution is to save the php file in a different encoding, or to manually remove them (I prefer the former).

I hope I helped somebody.
info at methodus dot de 18-May-2006 11:42
To avoid the notice commited by PHP since 4.3.3 when you start a session twice use this function:

<?php
function start_session(){
    static
$started=false;
    if(!
$started){
       
session_start();
       
$started = true;
    }
}
?>

This should help you when your error reporting is set to E_ALL
admin at haravikk dot com 10-May-2006 06:00
Just a note for any of you who have the same trouble as I did. $_SESSION appears to break horribly if you attempt to assign information into integer keys.

For example, a result from a MySQL query may look like:

<?php
array(
   
0 => 'haravikk',
   
'username' => 'haravikk',
   
1 => 'fish',
   
'password' => 'fish'
   
);
?>

Attempting to assign that to $_SESSION either as a straight array, or by placing all keys (for example using a foreach) will FAIL and the data will be unavailable when you move to another page. My solution was to do this:

<?php
function storeSessionArray($array) {
    foreach(
$array as $k => $v)
        if (
is_string($k)) $_SESSION[$k] = $v;
}
?>

This worked correctly =)
james at skinsupport dot com 22-Dec-2005 06:17
One thing of note that caused me three days of trouble:

It's important to note that Firefox (for one) makes two calls to the server automatically.  One for the page, and one for favicon.ico.

If you are setting session variables (as I was) to certain values when a page exists, and other values when pages don't exist, the values for non-existent pages will overwrite the values for existing pages if favicon.ico doesn't exist.

I doubt many of you are doing this, but if you are, this is a consideration you need to address or you'll be bald over the course of a three day period!
zackbloom at gmail dot com 03-Dec-2005 11:16
Yes php does not automatically insert the SID in header redirects.  You must use something like:
'<address>?SID='.SID
to manually insert the SID.
jeremygiberson at gmail dot com 17-Oct-2005 11:13
foltscane at yahoo dot com wrote about people losing session information on page redirects.

The problem is some times the redirect may kick you off to the next page before all the session variables have been saved. The true solution to lost session vars on redirect is to simply call session_write_close(); before setting the redirect header. This will insure that php finishes writing the session info before page redirect gets underway.

ie:
<?
    session_start
();
   
$_SESSION['forward'] = "This session data will not be lost!";

   
session_write_close();
   
header('Location: nextpage.php');
?>
erm[at]the[dash]erm[dot]com 27-May-2005 01:04
If you are insane like me, and want to start a session from the cli so other scripts can access the same information.

I don't know how reliable this is.  The most obvious use I can see is setting pids.

// temp.php

#!/usr/bin/php -q
<?php

session_id
("temp");
session_start();

if (
$_SESSION) {
   
print_r ($_SESSION);
}

$_SESSION['test'] = "this is a test if sessions are usable inside scripts";

?>

// Temp 2

#!/usr/bin/php -q
<?php

session_id
("temp");
session_start();

   
print_r ($_SESSION);

?>
corey at eyewantmedia dot com 19-May-2005 07:19
Here is a crazy feature -- you get one concurrent database connection per session, transparent to the programmer!

I am running php 5.0.4 on iis 6 (yeah, I know...). I noticed under stress testing that database connections were my bottleneck. I spent like 5 hours turning this on, that off, etc because I could not get php to create more than one database connection at a time, regardless of how many requests it was servicing. I tried running php as fastcgi, cgi, and isapi module. I tried using mysql and mysqli extensions. Same thing every time. Then I happened to turn off auto-start sessions and commented out my session_start() calls, and all of the sudden I get multiple connections like I expected!

Don't let this happen to you -- don't freak out! Apparently something somewhere tries to make sure your visitors don't get more than their share of your resources, so they get one db connection per session. I can't say it is what I would like to happen, but now that I know, it doesn't bother me much :) Hope this saves someone some time and headache!
Jose Cavieres 12-Apr-2005 10:11
For the problem of session lost after of redirect with header location...

Try with this:
<?
session_start
();
$_SESSION['mySession'] = "hello";

header ("Location: xpage.php");
exit();
//This sentence do the magic
?>
jorrizza at gmail dot com 02-Apr-2005 05:33
If you open a popup window (please no commercial ones!) with javascript window.open it might happen IE blocks the session cookie.
A simple fix for that is opening the new window with the session ID in a GET value. Note I don't use SID for this, because it will not allways be available.

----page.php----
//you must have a session active here
window.open('popup.php?sid=<?php echo session_id(); ?>', '700x500', 'toolbar=no, status=no, scrollbars=yes, location=no, menubar=no, directories=no, width=700, height=500');

----popup.php----
<?php
session_id
(strip_tags($_GET['sid']));
session_start();
//and go on with your session vars
?>
hbertini at sapo dot pt 13-Mar-2005 12:29
workaround when using session variables in a .php file referred by a frame (.html, or other file type) at a different server than the one serving the .php:

Under these conditions IE6 or later silently refuses the session cookie that is attempted to create (either implicitly or explicitly by invoquing session_start()).

As a consequence, your session variable will return an empty value.

According to MS kb, the workaround is to add a header that says your remote .php page will not abuse from the fact that permission has been granted.

Place this header on the .php file that will create/update the session variables you want:

<?php header('P3P: CP="CAO PSA OUR"'); ?>

Regards,
Hugo
raphael at cynage dot com 22-Feb-2005 08:35
Quick point, since this had been going round in circles for days...

IE will not accept sessions from a domain that has an non alpha-numeric character in it. My development site was running under the vhost mos_dev and it was killing me, trying to work out why IE kept dropping my sessions.
lukasl at ackleymedia dot REMOVESPAM dot com 17-Dec-2004 10:18
About the Session not getting saved on a header("Location:") redirect.

Make sure to call session_write_close() before doing the redirect.  This will make sure that the session values get written to the disk.
m dot kuiphuis at hccnet dot nl 24-Jun-2003 03:37
[Editors Note: For more information about this
http://www.zvon.org/tmRFC/RFC882/Output/chapter5.html ]
 
I use name-based virtual hosting on Linux with Apache and PHP 4.3.2.
Every time when I refreshed (by pressing F5 in Internet Explorer) I noticed that I got a new session_id. Simultaneously browsing the same site with Netscape didn't give me that problem. First I thought this was some PHP issue (before I tested it with Netscape), but after searching a lot on the internet I found the problem.
Since I was using name based virtual hosting for my testserver and we have different webshops for different customers I used the syntax webshop_customername.servername.nl as the domain-name.
The _ in the domain name seemed to be the problem. Internet Explorer just denies setting the cookie on the client when there is a special character (like an _ ) in the domain name. For more information regarding this issue: http://support.microsoft.com/default.aspx?scid=kb;EN-US;316112
Stupidly enough, this information was related to asp (yuk :o)
gadgetguy03 at lycos dot com 20-Jun-2003 07:18
SESSION LOST ON HEADER REDIRECT (CGI on IIS 5.0)

I realize there are numerous scattered posts on this issue, but I would like to add my 2 since it took me a whole day and a download of the LiveHTTPHeaders Mozilla plugin to figure it out.

On the **CGI** version of PHP on IIS 5.0/Windows 2000, the following code will not work as expected:

/***** sess1.php *****/
session_start();
$_SESSION["key1"] = "testvalue";
header("Location: sess2.php");

/***** sess2.php *****/
session_start();
echo "key1 = '".$_SESSION["key1"]."'";

PROBLEM:
All session data is lost after a header redirect from the first page on which the session is initialized. The problem is, the PHPSESSID cookie is not being sent to the browser (ANY browser, IE or Mozilla) on the initial session page with the header("Location: ...") redirect. This is unrelated to client cookie settings - the set-cookie: header just isn't sent.

SOLUTION:
I was able to remedy the problem by switching to the ISAPI DLL version. This seems to be an MS/IIS bug, NOT a PHP bug - go figure. I hope this saves you some headaches especially with your user authentication scripts!!

The closest matching "bug" report I found:
http://bugs.php.net/bug.php?id=14636
benja at benja dot be 15-Apr-2003 11:45
Just for info, session_start() blocks if another PHP using the same session is still running in background. It seems it's waiting the other PHP to finish... and sometimes it can be a problem. Create 2 different sessions by setting 2 different names : session_name() solve the problem.

Benja.
mickey at UNSPAMwebsoft dot com 19-Mar-2002 05:00
A note on Windows installations with an NTFS file structure:

Make sure you give your Internet user account (usually IUSR_MACHINENAME) "Modify" access to the session.save_path directory.  Otherwise session_start() will silently - and oh, so slowly - fail.

("Modify" is a Win2k term, but the concept translates to older IIS installs).

 
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