In order for nginx to re-read the configuration file, a HUP signal should be sent to the master process. The master process first checks the syntax validity, then tries to apply new configuration, that is, to open log files and new listen sockets. If this fails, it rolls back changes and continues to work with old configuration. If this succeeds, it starts new worker processes, and sends messages
![Controlling nginx](https://cdn-ak-scissors.b.st-hatena.com/image/square/d623c1882630da83f7f83a37660867287869ec1f/height=288;version=1;width=512/http%3A%2F%2Fnginx.org%2Fnginx.png)