How to solve ORA-12505, Listener does not currently know of SID This is very common error and really it will suck your blood if you are not right path. I will try to explain you about this error. As you can see this error is showing itself that listener is up and running but not serving the SID that it is meant for. And yes 1st you need to check where you are facing this error. Is it on client side or on server side. So what is the SID this listener looking for? SID is name for your database or you can say service identifier, That is help to to identify the the service like we use PROD for production UAT for testing server. SID of Database should be identical to avoid the confusion. It's length is 8 character only that means you can not extend it more then 8 character. Now how listener works ? As we all know its like a car, That drop us from airport to hotel, hahah sorry I am not good in examples. So let me explain technically, whenever you try to make connection from ...