How to debug "FastCGI sent in stderr: Primary script unknown while reading response header from upstream" and find the actual error message?
To answer your question:
- in php-fpm.d/www.conf file:
set the access.log entry:
access.log = /var/log/$pool.access.log
restart php-fpm service.
try to access your page
cat /var/log/www.access.log, you will see access logs like:
- - 10/Nov/2016:19:02:11 +0000 "GET /app.php" 404
- - 10/Nov/2016:19:02:37 +0000 "GET /app.php" 404
To resolve "Primary script unknown" problem:
if you see "GET /" without a correct php file name, then it's your nginx conf problem.
if you see "GET /app.php" with 404, it means nginx is correctly passing the script file name but php-fpm failed to access this file (user "php-fpm:php-fpm" don't have access to your file, which trapped me for 3 hours)
Hope my answer helps.