How to solve "Address already in use" error on ...

啓動nova-api報錯：CRITICAL nova [-] [Errno 98] Address already in use....
解決方法：

You can safely ignore this error, if doing a ps aux | grep nova-api tells that nova-api is running. If not, this is probably because someone else is already using the port(8777, by default) and nova-api is not able to grab it. To make nova-api run, kill the other process(if not needed using kill <pid>), ensure that the port is listening(using netstat -ntlp | grep <port_no>) and then doing a sudo service nova-api start.