Getting PHP errors to log in Nginx/PHP-FPM Under Nginx/PHP-FPM, I can't get PHP errors logged to craft/storage/runtime/logs/phperrors.log as they should be.

Initially, errors weren't logging anywhere, but I discovered I needed:
catch_workers_output = yes in our PHP-FPM config.

Errors are now logging to /var/log/php7.0-fpm.log, but not to Craft's custom location.
I'm only 80% confident in this answer, but I'm pretty sure that runtime PHP ini_set calls won't work with nginx running with FastCGI (which is what Craft uses to change the error_log path.

Try setting that path directly in your /etc/php5/fpm/php.ini file.