How to install mysqli module in Ubuntu
The MySQLi Extension (MySQL Improved) is a relational database driver used in the PHP programming language to provide an interface with MySQL databases.
From Ubuntu Hardy (8.04), mysqli is part of the php5-mysql package along with the standard mysql library and pdo - see http://packages.ubuntu.com/hardy/php5-mysql for more info.
So we just need to install the package php5-mysql only.
#apt-get install php5-mysql
That's all......