Fatal error: Uncaught Error: Undefined constant "db_servername" in /var/www/travel/main/session.php:14 Stack trace: #0 [internal function]: SysSession->open() #1 /var/www/travel/main/main.php(20): session_start() #2 /var/www/travel/smnh.ir/public_html/main.php(8): include('...') #3 /var/www/travel/smnh.ir/public_html/index.php(2): include('...') #4 {main} thrown in /var/www/travel/main/session.php on line 14