The PHP encoding in openserver has failed, what should I do?

Question

linux

The file is saved in utf-8 encoding in php format.
The encoding crashed after executing this script (the strtoupper and strtolower methods also do not work for me, in an attempt to fix this problem I created another one)

<?php 
  $text = mb_strtoupper('ПРИВЕТ');
  print $text;
?>

After that, all the scripts were with a broken coding! The entire Internet has been rummaged!
Here is the code:

<?php 
  $text = strtoupper('ПРИВЕТ');
  print $text;
?>

Outputs:
ЏРИВЕС
Further, even with a normal encoding, the strtoupper and strtolower methods do not work.

Answer 1

tar + cron, the classic of all classics.
You can rsync + cron.
Google is full of manov.

Answer 2

set_charset('utf8') or something like this should be there

Answer 3

You can also write in .htaccess: AddDefaultCharset UTF-8.