I recently switched my CentOS 7 web server over to Nginx and php-fpm.
From my experience with Apache I assumed that PHP scripts would be executed by the same user the web server is running as — ‘nginx’ in this case. But this could no longer be taken for granted since php-fpm is a separate process from the web server.
In my configuration php-fpm was actually running as the ‘apache’ user. This meant any files that need to be writable by PHP scripts should still be owned by that user or group rather than ‘nginx’.
A common scenario where this matters is if your users need to be able to install WordPress updates, Plugins, or Themes via the browser without entering additional credentials. In order for this to work, the web server (or in this case, php-fpm) must be able to write to the files in question.
If you are wrestling with file permissions, or are unsure of the correct permissions to set in this scenario, be sure to confirm which user and group are specified in /etc/php-fpm.d/www.conf
# grep "^user\|^group" /etc/php-fpm.d/www.conf user = apache group = apache
Or you can check the actual running process with pstree:
$ pstree -ua | grep "nginx\|php" |-nginx | |-nginx,nginx | |-nginx,nginx | |-nginx,nginx | |-nginx,nginx | |-nginx,nginx | |-nginx,nginx | |-nginx,nginx | `-nginx,nginx |-php-fpm | |-php-fpm,apache | |-php-fpm,apache | |-php-fpm,apache | |-php-fpm,apache | |-php-fpm,apache | |-php-fpm,apache | `-php-fpm,apache