Strange issue with mysql php pdo

Well, when i open pdo connection and close setting variable of connection as NULL it close the connection, but if i run some query then try to close and make the script sleep a bit, in show full processlist show as connection opened NULL, part of code: conexao::OpenCon(); $output = self::$link->query('select count(id) from tb01')->fetchColumn(); conexao::CloseCon(); sleep(50); echo $output; These methods: public static function CloseCon() { self::$link = NULL; } protected static function OpenCon() { try { self::$link = new PDO('mysql:host='.DB_HOST.';dbname='.DB_NAME.';charset=utf8', DB_USER, DB_PASS); self::$link->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); self::$link->exec('SET NAMES utf8'); } catch (PDOException $e) { die($e->getMessage()); } } Very strange cuz it only happens in my CentOs Linux Server, in Ubuntu it works fine, could it be some mysql configs? Please someone help me, thanks.