Call to undefined function mysqli_init()

Hello, I have a new installation on linux mint with apache2, mysql, php7 and CodeIgniter3.0.4 - latest
when I want to access db, there is this error coming. Then I controlled phpini() but there is no mysqli
only mysqlnd (native driver) ... is there anybody who is developing with php7 and knows how to install
php7 with mysqli ? Sorry my bad english, this is not my native language.

Error:


An uncaught Exception was encountered

Type: Error

Message: Call to undefined function mysqli_init()

Filename: /var/www/html/codeigniter/sys304/database/drivers/mysqli/mysqli_driver.php

Line Number: 136

Backtrace:

File: /var/www/html/codeigniter/app304/models/Welcome.php
Line: 12
Function: database

File: /var/www/html/codeigniter/app304/controllers/Mfw.php
Line: 24
Function: model

File: /var/www/html/codeigniter/index.php
Line: 292
Function: require_once