Nginx, like any other Unix background service, is controlled by signals. Signals are asynchronous events that interrupt normal execution of a process and activate certain functions. The following table lists all signals that Nginx supports and the functions that they trigger:

All signals must be sent to the master process of an instance. The master process of an instance can be located by looking it up in the process list:

# ps -C nginx -f
UID        PID  PPID  C STIME TTY          TIME CMD
root      4754  3201  0 11:10 ?        00:00:00 nginx: master process /usr/sbin/nginx
www-data  4755  4754  0 11:10 ?        00:00:00 nginx: worker process
www-data  4756  4754  0 11:10 ?        00:00:00 nginx: worker process
www-data  4757  4754  0 11:10 ?        00:00:00 nginx: worker...