I have a git repo with an expressionengine 2 site we are trying to test on newer versions of php so as to upgrade it. My colleague tried to set up letsencrypt on it last night and made some change to apache, and probably not to any code: I came in after him and restored from git so all the files are as before, but the apache config has changed, and possibly other things relating to ssl. Can anyone explain how I can step through the code to see where the error is happening, or if it's something else? I managed to step through until I got to codeigniter/core/CodeIgniter but from there I am not sure what is happening.. If you know what files are run in succession each time EE 2 loads, it'd save me a lot of time debugging and I'd be really grateful!
The first thing I would do is disable extensions in the config.php file. Then force on error reporting in the index.php . What version of php are you running? v2+ will fail on later versions pf php, primarily v7+ If the page loads with extensions disabled, then an extension is causing this. then disable each extension in the CP, remove the config variable, then turn them back on one by one until you get the WSOD, then you'll know which extension to address. To upgrade all the way to v5, you need to upgrade to v3 on a php5.3+ server, then move to a server with php7+ to finish the upgrade. It's not an easy process by any stretch.