503 Service Unavailable : PHP-FPM issue

Error: 503 Service Unavailable The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

Solution: 

systemctl start php80-php-fpm (if face the error follow the next command )

systemctl status php80-php-fpm.service

ERROR: unable to bind listening socket for address '127.0.0.1:9000': Address already in use (98)

netstat -tulpn | grep -w 9000 

tcp        0      0 127.0.0.1:9000          0.0.0.0:*               LISTEN      884/php-fpm: master 

kill 884

systemctl start php80-php-fpm

Note: Use your PHP version, PID and Port in the command. if netstat not works install net-tools first: yum install net-tools