在我的服务器上，phpmyadmin 出现错误消息：
phpMyAdmin - Error The mbstring extension is missing. Please check your PHP configuration.
php7有两个版本：
- cli : 路径 => /etc/php/7.2/cli
- 网络：路径 => /etc/php/7.0/apache2
我知道 Mbstring 模块没有安装在 Apache2 中：
sudo a2enmod mbstring
ERROR: Module mbstring does not exist!
所以我想在php7.0中安装mbstring：
sudo apt-get install php7.0-mbstring
No version of the php7.0-mbstring package is available, but it exists in the database.
This usually means that the package is missing, has become obsolete,
or is only available from another source.
E: The package "php7.0-mbstring" does not have a version that can be installed
所以：
sudo apt-get install php-mbstring
php-mbstring is already the most recent version (1: 7.2 + 60ubuntu1).
但是7.2没用！我想要 7.0 的 mbstring！
我能怎么做 ？