Warning: require_once(/opt/magento2/app/autoload.php): Failed to open stream: No such file or directory in /opt/magento2/app/bootstrap.php on line 43

Fatal error: Uncaught Error: Failed opening required '/opt/magento2/app/autoload.php' (include_path='.:/usr/share/php') in /opt/magento2/app/bootstrap.php:43 Stack trace: #0 /opt/magento2/pub/index.php(15): require() #1 {main} thrown in /opt/magento2/app/bootstrap.php on line 43