Pagina en blanco al iniciar a configurar mi Server monitor

[dick de avila]

Fatal error: Uncaught RuntimeException: Extension DOM is required. in /var/www/html/phpservermon/vendor/symfony/config/Util/XmlUtils.php:50 Stack trace: #0 /var/www/html/phpservermon/vendor/symfony/config/Util/XmlUtils.php(131): Symfony\Component\Config\Util\XmlUtils::parse() #1 /var/www/html/phpservermon/vendor/symfony/dependency-injection/Loader/XmlFileLoader.php(379): Symfony\Component\Config\Util\XmlUtils::loadFile() #2 /var/www/html/phpservermon/vendor/symfony/dependency-injection/Loader/XmlFileLoader.php(44): Symfony\Component\DependencyInjection\Loader\XmlFileLoader->parseFileToDOM() #3 /var/www/html/phpservermon/src/psm/Router.php(213): Symfony\Component\DependencyInjection\Loader\XmlFileLoader->load() #4 /var/www/html/phpservermon/src/psm/Router.php(58): psm\Router->buildServiceContainer() #5 /var/www/html/phpservermon/src/bootstrap.php(78): psm\Router->__construct() #6 /var/www/html/phpservermon/index.php(29): require('/var/www/html/p...') #7 {main} thrown in /var/www/html/phpservermon/vendor/symfony/config/Util/XmlUtils.php on line 50

Me muestra este error....
Utilizo ubuntu server 20.04