The issue looks something like this — errors occur whether you try to restart or stop the service:
[root@123 ~]# service nginx restart
Stoping nginx… nginx: [error] invalid PID number "" in "/usr/local/nginx/logs/nginx.pid"
failed. Use force-quit
Starting nginx… nginx (pid 11124 599) already running.
The cause is likely that nginx has hung or frozen:
ps -ef|grep nginx
kill -9 599 11124 #Kill the master processes
Restart again, and it should work normally:
service nginx start
or
service nginx restart
