Why can't Oracle find the monitor?

The reasons why oracle cannot find the monitor: 1. The monitor program is not started, causing the connection to fail; 2. The monitor program is configured incorrectly. Make sure the port number and other related configurations are correct by checking the configuration of the parameter file; 3. If there is a firewall setting problem, check the firewall configuration and make sure the relevant ports are open; 4. Host name resolution problem, check the host name resolution configuration and make sure the host name resolution is correct; 5. The listening program crashes or closes abnormally, check the log of the listening program File; 6. Network connection problem, due to network failure, network configuration error or excessive network load.

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

The problem that Oracle cannot find the listener is usually caused by the following common reasons:

The listener is not started: Oracle database uses the listener to accept the client's connection request. If the listener is not started or is closed abnormally, Oracle cannot find the listener, causing the connection to fail. You can start the listening program by executing the lsnrctl start command on the command line.

Listener configuration error: The configuration of the listener is specified through the listener parameter file (listener.ora). If the configuration in the parameter file is incorrect, for example, the port number of the listening program is incorrectly configured, then Oracle cannot find the listening program. You can check the configuration of the parameter file to ensure that the port number and other related configurations are correct.

Firewall settings issues: Sometimes, a firewall may block communication between the Oracle database and the listener. This may be because the firewall is not configured correctly or is blocking the port used by the listener. You can check the firewall configuration to ensure that the relevant ports are open.

Host name resolution issues: Oracle databases and listeners often use host names to communicate. If the hostname cannot be resolved or is resolved incorrectly, Oracle cannot find the listener. You can ensure that the host name is resolved correctly by checking the host name resolution configuration.

The listener program crashes or closes abnormally: In some cases, the listener program may crash or close abnormally, causing Oracle to be unable to find the listener. You can check the log file of the listening program to see if there are any relevant error messages. If the listener crashes or closes abnormally, you can try restarting the listener.

Network connection problems: Sometimes, there may be problems with the network connection, causing Oracle to be unable to find the listener. This could be due to a network failure, network misconfiguration, or heavy network load. You can check the status of the network connection to ensure that the network connection is normal.

To sum up, the problem that Oracle cannot find the listener is usually due to the fact that the listener program has not been started, the listener program is configured incorrectly, the firewall setting problem, the host name resolution problem, the listener program crashes or closes abnormally, and the network connection problem. caused. Solving these problems requires carefully checking the relevant configurations, logs, and network connections, and eliminating possible causes one by one, and finally restoring the normal operation of the listener.

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