pcntl_signal — Installs a signal handler
pcntl_fork — The pcntl_fork() function creates a child process that differs from the parent process only in its PID and PPID. Please see your system's fork(2) man page for specific details as to how fork works on your system.
https://www.baidufe.com/item/9565cec0004cb49d25fd.html
http://www.ruanyifeng.com/blog/2016/02/linux-daemon.html