I've installed "PHP PECL EXTENSION/MODULE ON UBUNTU". At the end, I was asked to add some configuration lines in the a file called php_ini that can be found in this path:
For accessing the system files you need root permission.So you would need to use
sudo command.it would be like
sudo vim /etc/php5/apache2/php.ini(if u are using vim editor) as
user2075215 mentioned in comment.