What Order Does Rsyslog Process Configuration Files in /Etc/rsyslog.d?

rsyslog processes configuration files in the /etc/rsyslog.d/ directory in lexicographical order. This means that files are processed in the order of their filenames, which is typically alphabetical.

Here’s a detailed breakdown of how rsyslog handles configuration files in /etc/rsyslog.d/:

1. Order of Processing

• Filename Order: rsyslog processes configuration files based on their filenames. For example, files named 10-logging.conf, 20-logging.conf, and 30-logging.conf would be processed in that order, from lowest to highest numeric prefix or alphabetically.
• No Explicit Order: If files don't have numeric prefixes or distinct ordering, rsyslog will process them alphabetically.

2. How to Manage File Order

2.1 Use Numeric Prefixes

To ensure a specific order of processing, use numeric prefixes in the filenames:

• 10-base.conf (processed first)
• 20-custom.conf (processed second)
• 30-advanced.conf (processed last)

This helps in maintaining an orderly configuration where dependencies or order of rules matter.

2.2 Avoiding Conflicts

Be cautious when having overlapping settings in multiple files. The order of processing can affect how configurations are applied, especially with settings like log rules or output destinations. Ensure that configurations are non-conflicting or explicitly managed.

3. Configuration File Example

Here's an example of how you might structure the /etc/rsyslog.d/ directory:

• 10-default.conf: Contains default settings and basic log rules.
• 20-security.conf: Contains security-related log rules.
• 30-custom.conf: Contains custom or application-specific log rules.

4. Checking Applied Configuration

To verify the configuration order and how files are applied:

1. Restart rsyslog: After making changes to configuration files, restart rsyslog to apply the changes.

    

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   sudo systemctl restart rsyslog
   

2. Check Logs: Look at rsyslog's own logs or the target log files to ensure the settings from your configurations are applied as expected.

    

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   sudo tail -f /var/log/syslog
   

3. Debug Mode: You can also run rsyslog in debug mode to see detailed information about which configuration files are being processed and in what order:

    

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   sudo rsyslogd -d
   

Summary

• Order of Processing: Files in /etc/rsyslog.d/ are processed in lexicographical order based on their filenames.
• Managing Order: Use numeric prefixes or carefully named files to manage processing order.
• Check Logs: Verify that configurations are applied correctly by checking logs and running rsyslog in debug mode if necessary.

By managing the filenames and ensuring clarity in configuration, you can effectively control the order in which rsyslog processes its configuration files.

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