Multiline Log Records in Syslog

Handling multiline log records in rsyslog can be a bit tricky, as it is designed primarily to handle single-line messages. However, you can configure rsyslog to process multiline logs by setting up specific rules in your configuration. Here’s a general approach to handle multiline log records:

1. Define a Custom Template for Multiline Logs: You need to define a template that will handle multiline log entries correctly. This template should specify how to concatenate multiple lines into a single message.
2. Set Up the Input Module: Configure the input module to use the template you've defined for handling multiline messages.
3. Define Rules to Process Multiline Logs: Create rules in rsyslog to apply your template and process the multiline log messages as required.

Here’s an example configuration to get you started:

Define a Template

In /etc/rsyslog.conf or a custom configuration file under /etc/rsyslog.d/, define a template for handling multiline logs:

template(name="MultilineLog" type="string"
         string="%msg:1:999999%\\n")

Configure Input Module

Specify the input module and use the defined template:

module(load="imfile") # Load the imfile module

input(type="imfile"
      File="/path/to/your/logfile.log"
      Tag="myapp"
      Ruleset="processMultiline")

Define Ruleset to Process Multiline Logs

Create a ruleset that applies the template to process multiline messages:

ruleset(name="processMultiline") {
    action(type="omfile" File="/var/log/processed.log" Template="MultilineLog")
}

Example Log Handling

If your log entries start with a timestamp and are followed by multiple lines, you might need a more sophisticated approach to detect and concatenate multiline entries properly. For instance, if your logs are in a format like:

2024-09-16 12:00:00 INFO Starting process
Additional info line 1
Additional info line 2
2024-09-16 12:01:00 INFO Process ended

You might need to write a script or use additional tools to preprocess and concatenate these logs before they are handled by rsyslog.

Restart rsyslog

After updating the configuration, restart rsyslog to apply the changes:

sudo systemctl restart rsyslog

Troubleshooting

• Ensure your log file path is correct and accessible.
• Verify that rsyslog is not overwriting your configuration due to syntax errors or misconfigurations.
• Check rsyslog logs for any errors related to the new configuration.

Feel free to adjust the example configuration to better fit your specific log format and requirements.

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