If for some reason you need to downgrade your PHP version (to PHP 5.6) you can get it done by following this really short tutorial. Naturally you can downgrade from PHP 7 (as in this example), PHP 7.1 or even 7.2 if needed.
First let’s connect to your server and get the basics done (if you haven’t done so already).
# sudo apt-get install python-software-properties
So now we need to add the repository for PHP 5.6:
# sudo add-apt-repository -y ppa:ondrej/php
Then update your APT package list:
# sudo apt-get update
Time to install PHP 5.6 (FPM):
# sudo apt-get install php5.6-fpm
P.S. If you need those standard PHP 5.6 addons here is what you need to add on this step:
# sudo apt-get install libapache2-mod-php5.6 php5.6-curl php5.6-gd php5.6-mbstring php5.6-mcrypt php5.6-mysql php5.6-xml php5.6-xmlrpc
Now let’s see what we are currently running:
# php -v
PHP 7.0.4-7ubuntu2.1 (cli) ( NTS )
Copyright (c) 1997-2016 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2016 Zend Technologies
So as you can see from the example above we are not quite finished yet… But fear not, there are only three more commands to go:
# sudo mv /usr/bin/php /usr/bin/php7
# sudo mv /usr/bin/php5.6 /usr/bin/php
And now you should check your PHP version again:
# php -v
PHP 5.6.23-2+deb.sury.org~xenial+1 (cli)
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies
with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies
There we go! Almost done, now the only thing left to do is to reboot Apache:
# service apache2 restart