Php - Your PHP installation appears to be missing the MySQL extension which is required by WordPress

in the end i found a solution First, make sure MySQL server is running. Type the following command at a shell prompt:

/etc/init.d/mysql status

If MySQL is not running, enter:

/etc/init.d/mysql start

If MySQL is not installed, type the following command to install MySQL server:

apt-get install mysql-server

Make sure MySQL module for php5 is installed:

dpkg --list | grep php5-mysql

To install php5-mysql module enter:

apt-get install php5-mysql

Next, restart the Apache2 web server:

/etc/init.d/apache2 restart

The php mysql api is deprecated. It's kaput --- going away -- not to be used, finito.

If you have a modern version of PHP (> 5.6) then Wordpress should automatically switch to make use of mysqli. That should be your first attempt.

If you can not update your php, rather than attempting to resurrect something that php no longer supports, just patch your wordpress: http://wordpress.org/plugins/mysqli/

This MySQL library worked for me:

sudo apt-get install php5-mysqlnd-ms