Understanding PHP Session Side-Effect Warning

When attempting to host a PHP website, you may encounter the warning, "Your script possibly relies on a session side-effect which existed until PHP 4.2.3." This issue stems from the session extension not considering global variables as a data source, unless the register_globals configuration is enabled.

Causes of the Warning

The warning typically occurs due to the presence of global variables with names identical to session variables. For instance:

$_SESSION['var1'] = null;
$var1 = 'something';

In such cases, PHP tries to automatically populate the session data from the global variable.

Troubleshooting the Issue

To troubleshoot the issue, examine your code for global variables with names that match session variables. If such variables are present, disable the session side effect warning by adding the following lines to your script:

ini_set('session.bug_compat_warn', 0);
ini_set('session.bug_compat_42', 0);

You can also set these values in your php.ini or .htaccess configuration files.

Important Note

It is not recommended to rely on this warning to identify and fix issues with your code. Instead, ensure that your code intentionally populates session data from global variables and consider using the register_globals configuration if necessary.