PHP5.6 install GD PHP extension

Hi, I need help with installation GD extension for PHP v 5.6.
ISPConfig3 3.1.15p2
I try

apt-get install php5.6-gd
service apache2 restart​

But in phpinfo() I still do not have gd library loaded.
Site use: fast-cgi
I also try edit

/opt/php-5.6/lib/php.ini​

and add

exteinsion=gd.so
​

Could please someone help ?

 

If you are on Ubuntu try this command:
a2enmod php5.6-gd