In my local machine and online server, i have a folder 'test' and three files in it (one.php,two.php,three.php) .

one.php

<?php
ob_start();
session_start();
$_SESSION['one'] = 1;
header('Location:two.php');
exit();
?>

two.php

<?php
ob_start();
session_start();
$_SESSION['two'] = 2;
header('Location:three.php');
exit();
?>

three.php

<?php
ob_start();
session_start();
echo '<pre>';print_r($_SESSION);
?>

while i take one.php in browser i getting an output

//Local machine

array[one] =1  
array[two] =2

this is correct

// Online Server

array[one] =1

this is not correct

What is wrong with this? i donot getting any warning,

Anyone please tell me, what is the problem?

I got the reason for this issue.

It was related to the session.save_path of php.ini file .

Make sure that the session save path directory is setup in php.ini, exists and is writable.

try calling session_write_close(); before sending the header.

You should always add *session_start();* in the first line of your code. There is a problem in php 5.2.11 that have been fixed with version 5.2.17.

This code does not work:

<?php 
     session_start();
?>

This code works fine:

<?php session_start();?>

So if you check your php host version and the version is 5.2.11 or previous to that one, that could be the problem!