mysql issue in opencart server vps

i have restored my backup and since my website is not working showing this error "Warning: mysqli::__construct(): (HY000/2002): No such file or directory in /var/www/html/system/library/db/mysqli.php on line 7Warning: DB\MySQLi::__construct(): Couldn't fetch mysqli in /var/www/html/system/library/db/mysqli.php on line 10Warning: DB\MySQLi::__construct(): Couldn't fetch mysqli in /var/www/html/system/library/db/mysqli.php on line 10" help me reinstate my website