Description:
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Debian9 stretch
PHP 7.0.27-0+deb9u1 (cli) (built: Jan  5 2018 13:51:52) ( NTS )
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
rsyslogd 8.24.0,

When I change the parameter 'log_level' in php-fpm  configuration file : 'php-fpm.conf' from notice to something else PHP no returns error in PHP-FPM logs.

apache error log ok
error in screen ok with 'display_errors = On' in 'php.ini'


Test script:
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'php-fpm.conf':
log_level = warning # or error ...

'test.php':
<?php
toto( );



Expected result:
----------------
Apr 18 13:18:52 debian9-php php7.0-fpm[2171]: [WARNING] [pool fpm-www] child 2172 said into stderr: "NOTICE: PHP message: PHP Fatal error:  Uncaught Error: Call to undefined function treu() in /var/www/localhost/public_html/test.php:10"
Apr 18 13:18:52 debian9-php php7.0-fpm[2171]: [WARNING] [pool fpm-www] child 2172 said into stderr: "Stack trace:"
Apr 18 13:18:52 debian9-php php7.0-fpm[2171]: [WARNING] [pool fpm-www] child 2172 said into stderr: "#0 {main}"
Apr 18 13:18:52 debian9-php php7.0-fpm[2171]: [WARNING] [pool fpm-www] child 2172 said into stderr: "  thrown in /var/www/localhost/public_html/test.php on line 10"


Actual result:
--------------
Nothing returned