How to make a site written in php5 also work on php7?

Question

Zend Framework

I had to install php7 on the local machine, since ubuntu 16.04 does not allow installing php5, and they also say that php5 will be removed from the official repositories for Linux soon.
Is it possible to make php7 work with a project written in php5 with the help of some settings?
Now on php7 immediately this error occurs:

session_write_close(): Failed to write session data (user). Please verify that the current setting of session.save_path is correct (/var/lib/php/sessions) in <b>/var/www/like2go/library/Zend/Session.php</b> on line 732

Answer 1

Look at what was removed in php 7 (usually something that was already deprecated in 5.6) and just don't use these features.