nginx: [error] invalid PID numbe

报错：

nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
nginx -s reload
nginx: [error] invalid PID number "" in "/run/nginx.pid"

原因：
nginx还没有启动，所有没有PID

解决：

nginx -c /etc/nginx/nginx.conf
nginx -s reload