admin/environment/moodle

Displays the current Moodle version in the source code folder, and the oldest version of Moodle required to upgrade to that current version.

If error like this is displayed:

You must solve all the environmental problems (errors) found above before proceeding to install this Moodle version!

That's mean moodle has no read permissions for

./admin/environment.xml

and you need to fix this problem.