使用nginx -s reload的时候出现：
[error]: invalid PID number “” in “/var/run/nginx.pid”
网上找的的解释：
nginx -s reload is only used to tell a running nginx process to reload its config. After a stop, you don’t have a running nginx process to send a signal to. Just run nginx (possibly with a -c /path/to/config/file)
于是我用了这方法，也就是nginx -c /path/to/config/file)
在我机器上是这样的nginx -c /usr/local/nginx/conf/nginx.conf
重启nginx后丢失nginx.pid问题解决