Eliminating the rsyslog Default Template for MySQL Output (ommysql) #

Understanding the rsyslog Default Behavior #

rsyslog, by default, uses a pre-defined template for message formatting. When you introduce a new output module like ommysql, it might inadvertently fall back on this default template unless explicitly overridden. This often leads to errors, especially if the default template’s structure doesn’t match your MySQL table schema. The default template is designed for general-purpose logging, not specifically for structured MySQL insertion. Therefore, correctly specifying a custom template is crucial for seamless integration. Ignoring the template configuration can result in insertion failures, as seen with the INSERT INTO syslog.SystemEvents attempt – a table that may not exist in your database setup.

Identifying the Default Template Conflict #

The primary issue stems from rsyslog’s attempt to use its default template to insert log entries into your MySQL database. This default template, typically designed for file-based logging (omfile), is structurally incompatible with the expected format for your MySQL table. To resolve this conflict, you must explicitly define a custom template that aligns perfectly with your table’s structure, ensuring the correct data types are used for each field. This prevents rsyslog from defaulting to an inappropriate template and causing insertion failures.

Analyzing the Default Template Structure #

The implicit reliance on an unsuitable default template is a frequent cause of MySQL integration problems. Understanding how rsyslog handles templates is key to effective troubleshooting. Rsyslog uses $template directives to define the structure of log messages. If no template is specified for an output module, rsyslog attempts to use its default, which likely includes fields that your MySQL table may not possess or have differently typed columns, causing insertion errors.

Creating a Custom rsyslog Template for MySQL #

To effectively direct your syslog entries into your MySQL database, creating a well-structured custom template is paramount. This template must exactly mirror your MySQL table’s column names and data types, ensuring smooth data insertion. Failure to precisely align the template with your table leads to errors and failed log entries.

Defining Your MySQL Table Structure #

Before creating the rsyslog template, meticulously examine your MySQL table’s schema. Note the precise names and data types of each column. For instance, a log_time column might require a specific date-time format like %Y-%m-%d %H:%i:%s which is compatible with MySQL’s DATETIME or TIMESTAMP type. Mismatches in data types or naming will result in log insertion failures. Thorough understanding of your database structure is fundamental for crafting a correct template.

Data Type Compatibility #

Pay close attention to data type compatibility between your rsyslog template format specifiers and your MySQL table columns. Incorrectly mapping data types (e.g., trying to insert a string into an integer column) will cause insertion failures. Ensure every format specifier in your template aligns precisely with the corresponding MySQL column’s data type. Consider using appropriate format specifiers like %syslogfacility-text%, %syslogseverity-text%, and the correct date-time specifiers for your DATETIME or TIMESTAMP columns.

Constructing the rsyslog Template #

Your rsyslog configuration file should explicitly define a template tailored to your MySQL table. This involves creating a template using the template directive followed by the template name (e.g., sqloutput), and the template string itself. This template string should use rsyslog’s format specifiers to represent the values to be inserted into each column. These format specifiers must precisely match the names and data types of the corresponding columns in your MySQL table.

Example Template Configuration #

Consider this example assuming a MySQL table named log with columns facility (TEXT), severity (TEXT), log_time (DATETIME), hostname (TEXT), ip (TEXT), appname (TEXT), proc_id (INT), msg_id (INT), and msg (TEXT):

template(name="sqloutput" type="string" string="INSERT INTO log (facility,severity,log_time,hostname,ip,appname,proc_id,msg_id,msg) VALUES (%syslogfacility-text%,%syslogseverity-text%,'%timereported:::date-mysql%','$HOSTNAME%','%fromhost_ip%','%programname%',%procid%,%msgid%,'%msg%')")

This template explicitly defines each value using corresponding rsyslog format specifiers. Note the date-mysql formatter for the timestamp, ensuring MySQL compatibility. This precise mapping is key to avoiding errors.

Integrating the Custom Template with ommysql #

Once the custom template is defined, you need to link it to your ommysql action in your rsyslog configuration. This association ensures that the messages are formatted correctly according to your template before insertion into the MySQL database. Ignoring this step will cause rsyslog to default to the incompatible general-purpose template.

Linking the Template to the ommysql Action #

Within your ommysql action definition, you explicitly specify the template name you created. This informs rsyslog to use this custom template for formatting log messages before sending them to your MySQL database. The lack of this explicit link is a common source of failure, causing the default template’s usage and errors.

Configuration Example with Template #

Modify your ommysql configuration to include the template name as follows:

module(load="ommysql")
action(type="ommysql" server="localhost" serverport="3306" db="syslog" uid="syslog" pwd="<mypwd>" template="sqloutput")

This line ensures that the sqloutput template is used. The precise name must match the name given in your template definition. Any mismatch will result in rsyslog ignoring the template and reverting to its default, causing problems.

Troubleshooting and Verification #

Even after careful configuration, errors can occur. Systematic troubleshooting and verification steps are crucial to ensure correct functionality. This involves checking your rsyslog logs, your MySQL database for errors, and confirming the template’s accuracy.

Checking rsyslog Logs #

Examine the rsyslog logs themselves for errors. These logs will often indicate problems like failed database connections or issues related to the insertion process. Thoroughly inspect these logs for clues, which can pinpoint the root of the issue.

Inspecting MySQL Error Logs #

Check your MySQL error logs for any errors or warnings associated with your database insertions. These logs can provide valuable insight into specific problems, such as data type mismatches, incorrect column names, or other database-related errors.

Verifying Database Insertion #

After implementing changes, verify if log entries are successfully inserted into your MySQL database. Directly query your database to check for the presence of recently inserted entries. This confirmation step is vital for ensuring the effectiveness of your solution.

Confirmation Techniques #

Use SQL queries to examine the data in your MySQL table. Verify that the data types match your table schema. Check for unexpected values, which may indicate problems with the rsyslog template. A simple SELECT * FROM log; can be helpful.

By addressing these points and carefully reviewing your configuration, you can ensure that your rsyslog messages are correctly formatted and inserted into your MySQL database. Remember that precise alignment between your rsyslog template, format specifiers, and your MySQL table schema is crucial for success. Thorough verification is key to confidently resolving this common issue.