请检查您是否在系统中安装了多个php版本，其中一个正在为Web服务器运行，另一个正在为php CLI运行，并且对Web和php使用PHP_INFO- -ini在命令行中，如果找到了不同的版本，则升级或降级意味着将其配置为一个版本，并确保在系统中启用了PDO.

Please check you have installed more than one php version in your system, one is running for web server and another for php CLI, using PHP_INFO for web and php --ini in commandline, if different version found then upgrade or downgrade means make it one version configuration, and make sure PDO is enable in your system.

从php5.6到php7.0:

From php5.6 to php7.0:

    Apache:

    sudo a2dismod php5.6 ; sudo a2enmod php7.0 ; sudo service apache2 restart

    CLI:

    sudo update-alternatives --set php /usr/bin/php7.0

From php7.0 to php5.6:

    Apache:

    sudo a2dismod php7.0 ; sudo a2enmod php5.6 ; sudo service apache2 restart

    CLI:

    sudo update-alternatives --set php /usr/bin/php5.6