Debian 9 and PHP upgrade to PHP 7.3

Introduction

As mentioned, Debian 9 includes the now unsupported PHP 7.0. The new Debian 10 Buster, probably planned for summer 2019, will include version 7.3. For now, we'll have to fend for ourselves. https://wiki.debian.org/PHP

PHP is now releasing its versions on a yearly cycle http://php.net/supported-versions.php

In addition to this, we have Drupal, which also has its own requirements. https://www.drupal.org/docs/7/system-requirements/php-requirements and https://www.drupal.org/docs/8/system-requirements/php-requirements

And this is the table that applies to Drupal itself, but a given version of PHP must also support any additional modules.

New PHP versions in Debian

As mentioned, only PHP 7.0 is included in Debian 9 https://packages.debian.org/stable/php/php. One of the members of the Debian PHP team is Ondrej Sury https://tracker.debian.org/pkg/php-defaults, https://deb.sury.org/. And it is his repository that offers new versions of PHP for Debian (and Ubuntu), and even different versions of PHP and for several versions of Debian

• http://php.net/releases/7_0_0.php
• http://php.net/releases/7_1_0.php
• http://php.net/releases/7_2_0.php
• http://php.net/releases/7_3_0.php

Warning! You need to choose the right PHP version, your application/code may not work correctly with the latest PHP 7.3 for example, and only version 7.2 would do

The following steps I found on this blog https://computingforgeeks.com/how-to-install-php-7-3-on-debian-9-debian… describe how to install version 7.3

apt -y install lsb-release apt-transport-https ca-certificates
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" | tee /etc/apt/sources.list.d/php7.3.list
apt-get update
apt-get -y install php7.3

And we're done:

But beware - the system now offers us several versions of PHP, so even when installing additional PHP modules you need to specify the correct version.

root@deb9php:~# apt-cache search php-gd
php7.0-gd - GD module for PHP
php-gd - GD module for PHP [default]

php5.6-gd - GD module for PHP
php7.1-gd - GD module for PHP
php7.2-gd - GD module for PHP
php7.3-gd - GD module for PHP

And if you are used to installing some PHP-dependent application using debian packages, such as phpMyAdmin, it may have a dependency on a particular version of PHP.