Unable to Connect to MySQL Database: Troubleshooting Error Message

When attempting to switch from the MySQL driver to the MySQLi driver in CodeIgniter, users may encounter the error message "Unable to connect to your database server using the provided settings." This error can arise from incorrect PHP configurations.

To debug the issue, it is recommended to add the following code to the end of the file ./config/database.php and review the output:

...
echo '
';
print_r($db['default']);
echo '
';

echo 'Connecting to database: ' .$db['default']['database'];
$dbh = mysql_connect(
    $db['default']['hostname'],
    $db['default']['username'],
    $db['default']['password']
) or die('Cannot connect to the database because: ' . mysql_error());
mysql_select_db($db['default']['database']);

echo '
';

echo 'Connecting to database: ' .$db['default']['database'];
$dbh = mysql_connect(
    $db['default']['hostname'],
    $db['default']['username'],
    $db['default']['password']
) or die('Cannot connect to the database because: ' . mysql_error());
mysql_select_db($db['default']['database']);

echo '
   Connected OK:'  ;
die( 'file: ' .__FILE__ . ' Line: ' .__LINE__); 

This code prints the database settings and attempts to connect to the database using the MySQL driver. If the connection is successful, "Connected OK:" will be displayed. Otherwise, the error message will provide specific information on the cause of the connection failure.

Reviewing the output from this code will help identify the source of the error and enable you to resolve it appropriately. Common causes for this error include incorrect credentials, firewall restrictions, or network issues.