Fix IO Error: The Network Adapter Could not Establish the Connection on Oracle SQL

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Oracle SQL is an integrated development environment designed to work with Oracle databases using SQL. This product is developed and provided free of charge by Oracle Corporation and is based on the Java Development Kit. Recently, there have been many reports of an “I/O error: the network adapter could connect” when testing a database connection.

What is the cause of this error?

Whenever you see that a network adapter could not connect, you either have the wrong SQL Developer URL or you have a basic SQL*Net connection problem! This error is most likely caused by one of these factors:

  • You are using the wrong URL
  • The wrong port number or IP address (or DNS host name) was used.
  • The earpiece is not configured correctly.
  • The listening process (service) is not in progress. You can launch it with the “lsnrctl start” command or restart it on Windows by starting the Listener service.

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Make sure your entries are correct.

To fix the “The network adapter could not establish the connection” error, first check that you have entered the correct user name and password, as well as the correct host name and port number. Although these are small things, we cannot avoid them. “It’s the little things in a relationship that matter most.”

For the valid host name and port number, you can check the file Listener.ora if you have access to your server, because the Listener is a server process. If you do not have access to the listener.ora file, you can check the tnsnames.ora file.

In the case of the Listener.ora file, check the host and port entry in the Listener label to ensure that the host names and port numbers are valid.

And if you use the TNSnames.ora file to check the host name and port number, look for the entry that has the same name as your SID, then look for the host and port number entry in that particular tag.

Now, try to connect. If this solves your problem, you can avoid the next step. But if the error “The network adapter couldn’t connect” is still present, then don’t worry, just follow the next step.

Starting Listener Service

It is possible that the service to the auditor has not been started. This service is required by the application to establish a connection. Therefore, in this step, we will start the service by typing a command in the command prompt. For that:

  • Press “Windows” + “R” to open the Run command prompt.
  • Type “Cmd” and press “Shift” + “Ctrl” + “Enter” to assign administrator rights.
  • Type the following command to check that the service has started.

lsnrctl Status

  • If the result is similar to the image below, it means that the service has not been launched.
  • Type the following command to start the service manually.

lsnrctl start

  • After starting the listening service, open the application and check if a new connection can be established.

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