How to fix error "Failed to start The PHP FastCGI Process Manager" on Centos7

1. Check your nginx error.log,my log shows:
 

 ERROR: [pool www] cannot get uid for user 'nginx'

 [pool www] please specify user and group other than root

2. So, I know that I made some wrong deployments in my php-fpm file,so I went to my server /etc/php-fpm.d／]www.conf[/url]
 

; RPM: apache Choosed to be able to access some dir as httpd

user = nginx

; RPM: Keep a group allowed to write in log dir.

group = nginx

3.

systemctl restart php-fpm.service