apachectl 调用 $httpd -k
1. kill - TERM `cat /usr/local/apache/logs/http.pid`
2. /bin/httpd -k stop/start/restart/graceful/graceful-stop
3. apachectl -k stop
发送停止信号给parent， 然后kill off its children, 花几秒时间
4. apachectl -k graceful
parent advis children to exit or exit immediatly if they‘re not serving anyting
5 apachectl -k restart
kill all of chidren