sudden nginx hang -- restart fails, "98: Address already in use"

[dwirth]

Hello, all. 

About an hour ago, out of the blue, my server stopped responding to webpage
requests. We are using nginx + php-fpm on RHEL6.

# service nginx status
nginx (pid 31600) is running...

# service nginx restart
Stopping nginx:                                            [FAILED]
Starting nginx: nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address
already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (98: Address already in use)
nginx: [emerg] still could not bind()

I killed the process and was able to restart nginx so the immediate crisis
is over, but I need to know: What the hell happened? What would cause nginx
to hang like this? I have googled around and I see several discussions about
what to do when this happens but zilch about how to keep it from happening.

- Dave

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,247223,247223#msg-247223