After many hours of searching the net, and forums to upgrade to PHP 7.1 on Debian Jessie (8) while using virtualmin, i thought i'd post an easy how to that works with Virtualmin 6.03.gpl and Webmin 1.881.. which is all in one place and lets you choose PHP versions for each Vhost.
i have done this on 3 different production systems after first testing them on clones, and i can confirm this works perfectly if you're using FCGId. Follow this step by step (please backup your server/servers first! i cannot be held responsible if things go wrong!)
Update and upgrade OS using APT:
Install Sury Repository for PHP7.1:
apt-get install apt-transport-https lsb-release ca-certificate
wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg
echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" > /etc/apt/sources.list.d/php.list
Update APT, and install PHP7.1:
apt-get install php7.1 php7.1-mysql php7.1-cgi
Update Virtualmin Config:
Update Vhost with new PHP version:
At this point, your site should be working with PHP 7.1. Your php.ini file will now be located in /etc/php/7.1/cgi/php.ini
If you need to install PHP modules such as cURL etc, you can do this using:
I have read about issues where sometimes after doing this, you will see an error 500. i have found that many people have not installed "apt-get install php7.1-cgi" .this needs to be there to avoid this issue. generally, you will find within /home/site/fcgi-bin/php7.1.fcgi that it does specify "exec /usr/bin/php-cgi7.1". so without php7.1-cgi package, you will see error 500's.
If for any reason you cannot get this to work, you can revert to PHP 5.6 by:
Revert Vhost to older PHP 5 version