Why is Oracle not listening to the server?

The reasons why oracle does not have a listening server: 1. Default configuration, for security reasons to prevent any unauthorized access; 2. Configuration error, an error may occur when configuring the listening server, causing it to not work properly Or cannot be started; 3. The service stops due to system crash, hardware failure, operating system update or other unknown reasons.

The operating environment of this tutorial: Windows 10 system, Oracle version 19c, DELL G3 computer.

The listening server in the Oracle database is an important component used to establish a communication connection between the client and the database. But in fact, the Oracle database does have a listening server, but it may not be enabled by default.

First, let us understand the architecture of the Oracle database. Oracle Database uses a client/server architecture, where the client refers to the application or user interface, and the server refers to the database instance. The listening server acts as an intermediary, accepting connection requests from clients and forwarding them to the database instance, while also sending responses from the database instance back to the client.

So why do we sometimes think that Oracle does not listen to the server?

Default configuration: When installing the Oracle database, the listening server is not enabled by default. This is for security reasons to prevent any unauthorized access. Therefore, if the listening server is not manually configured and enabled, it will not run in the system.

Configuration Error: Sometimes, administrators may make errors when configuring the listening server, causing it to not work properly or fail to start. This may be caused by incorrect parameter settings, port conflicts, or network configuration issues.

Service Stopped: Even if the listening server has been correctly configured and started, it may stop working under certain circumstances. This may be caused by a system crash, hardware failure, operating system update, or other unknown reasons.

If we find that the Oracle database does not have a listening server, we can take the following steps to solve the problem:

Check the listening server configuration: First, we need to check the configuration file of the listening server. In the Oracle database, the configuration file of the listening server is usually listener.ora. We need to ensure that the parameters in the configuration file are set correctly and that the listening server is enabled.

Start the listening server: If the listening server is not running in the system, we can start it manually by using a command line tool (such as lsnrctl). We need to ensure that the listening server's port is not occupied by other applications and that the network is configured correctly.

Check the listening server status: Once the listening server is started, we can use the lsnrctl command to check its status. This will tell us if the listening server is working properly and able to accept connection requests from clients.

Check firewall settings: Sometimes, firewall settings may prevent communication between the client and the listening server. We need to make sure that the firewall allows the listening server's port to pass and does not have any rules blocking connections.

To summarize, Oracle database does have a listening server, but it may not be enabled by default. This could be for security reasons, or it could be due to a misconfiguration or other issue. If we find that Oracle does not have a listening server, we need to check the configuration file, start the listening server, check the status, and check the firewall settings to solve the problem.

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