Why might data not be written to a file when executing a script using KRON?

Question

PHP

I'm trying to write data to a file:

$fd = fopen("check_game.txt", 'w+') or die("не удалось создать файл");
$str = "pm";
fwrite($fd, $str);
fclose($fd);

When executing the script manually (using the browser's address bar), everything works fine.
But if I put this script on CRON, then these lines are not executed at all. For some reason the data is not being written to the file.

Answer 1

Relative to the file does not work. Need complete (/home/user/www/site/public/check.txt)