I'm currently working on upgrading our Moodle 3.2.1 system (on its Debian 8 machine) to Moodle 3.5 (as a stepping stone to try out before going to the latest Moodle version). The first achievement was getting the machine up to Debian 10 which I have now managed. Moodle still works. Oh and it's currently running on PHP 5.6.40.
I cannot seem to upgrade the system successfully. Currently Moodle 3.2.1 is happy running on Debian 10. As soon as I try to upgrade to 3.5 LTS I end up just with an HTTP 500 error when I try and browse the Moodle site again. Nothing works. I'm following the official guide at :
I noticed that the upgrade to Debian 10 had installed the latest PHP version (7.3). But this seems to co-exist on the machine with the original 5.6.40. I can't seem to find a way (to begin with) to get Moodle to recognise the newer PHP version. After some reading I realise I can only go up as far as PHP 7.2 anyway for Moodle 3.5. I uninstalled PHP 7.3 and installed PHP 7.2 but Moodle still doesn't even recognise that this version is installed (I check before upgrading Moodle because I wouldn't be able to check otherwise - see above the HTTP 500 error once upgraded).
Anyone any ideas on this? I'm just extracting the moodle-latest-35.tgz into the right place. Copying back the config.php and the themes folder (and blocks folder which also seems to have been modified at some point in the past) and making sure that www-data has the right permissions on the folders. But I cannot see where this is going wrong.