by Tim Hunt.
Well, are you prepared to read https://github.com/moodle/moodle/blob/master/admin/environment.xml
It is possible to run Moodle on RHEL5. The OU is doing so. (I suppose we might have upgraded selected packages manually. I don't know.) Anyway, Moodle gives its requirements in terms of PHP version etc. It is up to you which distro you use to satisfy those requirements.