how to install php 5.6 on ubuntu 16.04 running Virtualmin Control Panel - ubuntu-16.04

Question

i have tried a number of times to get php 5.6 working on ubuntu 16.04
I keep getting a server error 500 when trying to browse http:/domain.com/phpinfo.php to check which version of php is active (server also has 7.0, 7.1, & 7.2)
I also have same error when attempting to run php 7.1 (7.0 & 7.2 are working no problems and i have websites running on the virtualmin server.
I have looked at various answers about this kind of thing here but in all honesty, the answers are often so broken and different i cant find a single procedure that is reliable and works.
Anyone help with this?
For example, will the following ispconfig 3 tutorial, which installs php5.6 in /opt directory, work with virtualmin? ( https://www.howtoforge.com/tutorial/how-to-install-php-5-6-on-ubuntu-16-04/ )
My assumption is that the above tutorial will work and i just need to tell virtualmin where the php 5.6 binaries are located in /opt/? ( see this thread... https://www.virtualmin.com/node/40004 )

Answer 1

By default, Ubuntu 16.04 server assigns the PHP 7.07 or higher version. If you want to allow/assign PHP 5.6 on your server then you will have to install it manually from the following command:
Step 1: Step 1: Update Apt-Get
Linux command: apt-get update && apt-get upgrade.
Step 2: Install PHP 5.6
Install the PHP5.6 repository with these two commands.
Linux command:
apt-get install -y software-properties-common
add-apt-repository ppa:ondrej/php
apt-get update
apt-get install -y php5.6
Step 3: Switch PHP 7.0 to PHP 5.6
Switch from PHP 7.0 to PHP 5.6 while restarting Apache to recognize the change:
a2dismod php7.0 ; a2enmod php5.6 ; service apache2 restart
Verify that PHP 5.6 is running on Apache by putting up a PHP info page. To do so, use the code below in a file named as infopage.php and upload it to the /var/www/html directory.
<? phpinfo(); ?>

Answer 2

First add the ppa:ondrej/php repository:
sudo -s
apt-get update
apt-get install -y software-properties-common
add-apt-repository ppa:ondrej/php
If at this point it throws a CPG error like:
Reading package lists... Done
W: GPG error: http://ppa.launchpad.net/ondrej/php/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY <THE_KEY>
W: The repository 'http://ppa.launchpad.net/ondrej/php/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
..pay attention in the 2nd line showing THE_KEY, then solve with:
apt-key adv --keyserver keyserver.ubuntu.com --recv-keys <THE_KEY>
Finally:
apt-get update
apt-get install -y php5.6
php -v