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Contents of sqlnet.ora logs in Oracle

Question: What does the file named sqlnet.log in Oracle Network Services contain?
The sqlnet.log file in Oracle Network Services is a crucial diagnostic tool used for logging network events and errors. This file serves as the default log for Oracle Net, and it's automatically created if it doesn't already exist when an error is encountered.
The sqlnet.log file typically resides in the same directory as the sqlnet.ora configuration file, that is, in the NETWORK/ADMIN subdirectory of the Oracle home directory. Its location, however, can vary based on the specifics of the Oracle software installation, the configuration, and the operating system.
The contents of the sqlnet.log file include details of various network-related events. It logs exceptions and errors that occur during Oracle client-server communication, such as failed connection attempts, service registration issues, or listener errors. Entries in the sqlnet.log file include timestamps, error codes, and detailed error messages to assist administrators in troubleshooting.
The sqlnet.log file is a valuable resource for understanding the cause of network-related issues and is often the first place a Database Administrator (DBA) will look when troubleshooting Oracle Net problems. This log file helps identify whether the issues are due to misconfigurations, network outages, listener failures, or other communication problems.
For more granular and verbose diagnostic data, the TRACE_LEVEL_SERVER and TRACE_LEVEL_CLIENT parameters can be set in the sqlnet.ora file to define the level of detail for the respective trace logs. It's important to note that this additional tracing should generally be used for temporary diagnostics since it may negatively impact performance and generate a large volume of log data.
In conclusion, the sqlnet.log file plays a crucial role in the Oracle Network Services stack, serving as a primary tool for tracking and diagnosing network-related issues within an Oracle database environment.

The file called sqlnet.log shows all failed attempts to connect to remote databases. Oracle does not clean up this file and will append to it forever, so you may want to go to the log_directory_client directory and delete the sqlnet.log file.
View the code below to see a sample of the contents of a sqlnet.log file.
(The error indicates that the remote listener process is not running.)
Fatal OSN connect error 12203, connecting to:
Fatal OSN connect error 12203, connecting to:

We will investigate the log files in detail in a later module.

Fatal OSN connect error 12203 in Oracle Network Services

The Oracle Network Services error "Fatal OSN connect error 12203" is generally triggered when a client application fails to establish a connection to an Oracle database server. This error can surface due to several reasons, including but not limited to network issues, incorrect configuration, or issues with the Oracle listener.
The error message "Fatal OSN connect error 12203" can be broken down as follows:
  1. OSN refers to Oracle's SQL*Net, which is a part of Oracle Net Services responsible for establishing and maintaining connections between a client application and an Oracle database server.
  2. The specific error code "12203" is typically accompanied by a more detailed message, which often reads, "TNS:unable to connect to destination."

When encountering this error, several common causes should be investigated:
  1. Incorrect or Incomplete Configuration: This error might occur if the tnsnames.ora or sqlnet.ora files are incorrectly configured. These files control the client-side and server-side network configurations, and any incorrect parameters or syntax issues can lead to connection problems.
  2. Listener Issues: If the Oracle listener, a critical component that manages connections to Oracle databases, is not running or is misconfigured, you might encounter the error 12203. Listener issues may include incorrect port numbers or improper security configurations.
  3. Firewall or Network Problems: Connectivity issues can also stem from network-related problems, such as a firewall blocking traffic on the necessary ports or general network connectivity issues between the client and the server.
  4. Incorrect Service Names or Host Names: The service name or host name specified in the connect descriptor might be incorrect or not recognized by the Oracle server.

When you encounter this error, a logical approach to troubleshooting would be to review the configuration files (tnsnames.ora and sqlnet.ora), check the listener status and configuration, ensure that the Oracle service is running on the server, and verify that there are no network-related issues that could be preventing the connection. Also, remember to check the sqlnet.log and listener.log files for more specific details about the error.
It's important to carefully diagnose this error, given the variety of potential causes, and the resolution can differ depending on the exact circumstances.

Legacy Information regarding Oracle 7 and Oracle 8 prior to Oracle Network Services

Oracle Net (which is Oracle's network interface), was formerly known as Net8 when used in Oracle8, and SQL*Net when used with Oracle7 and previous versions of Oracle. You can use Oracle Net over a wide variety of network protocols, although TCP/IP is by far the most common protocol today.
The sqlnet.ora file on a client machine contains parameters that govern the behavior of the client. The attributes that can be modified fall into five categories:
  1. Dead connection detection
  2. Tracing and logging
  3. Default domains
  4. Oracle Names parameters
  5. Other optional parameters