The syslog_pri filter plugin is used to parse the PRI (priority) field from syslog messages. It extracts the facility and severity values from the PRI field, which is typically found at the beginning of a syslog message. This plugin is particularly useful when processing syslog data and you need to separate the priority information for better analysis or routing.
Syntax
filter {
syslog_pri {
source => "field_name"
target => "field_name"
}
}
For detailed configuration options, refer to the official Logstash syslog_pri filter plugin documentation.
Example Use Case
Suppose you have syslog messages with PRI fields and want to extract the facility and severity information:
filter {
syslog_pri {
source => "syslog_pri"
}
}
This configuration will parse the PRI field from the "syslog_pri" field and add new fields "syslog_facility" and "syslog_severity" to the event.
Common Issues and Best Practices
- Ensure that the source field contains a valid PRI value (an integer between 0 and 191).
- If the PRI field is part of a larger message, use the grok filter first to extract it into a separate field.
- Consider using this filter in conjunction with the syslog_pri codec for full syslog message parsing.
- Remember that the plugin will not modify the original PRI field; it only adds new fields with the parsed information.
Frequently Asked Questions
Q: What is the format of the PRI field in syslog messages?
A: The PRI field in syslog messages is typically enclosed in angle brackets (<>) and contains an integer value between 0 and 191, representing both the facility and severity.
Q: How does the syslog_pri filter calculate facility and severity?
A: The filter calculates facility by dividing the PRI value by 8 and rounding down. The severity is calculated as PRI modulo 8.
Q: Can the syslog_pri filter handle messages without a PRI field?
A: If the specified source field doesn't exist or doesn't contain a valid PRI value, the filter will not modify the event and will not add any new fields.
Q: Is it possible to customize the names of the added facility and severity fields?
A: Yes, you can use the facility_field and severity_field options in the filter configuration to specify custom field names for the extracted values.
Q: How does the syslog_pri filter interact with other syslog-related plugins in Logstash?
A: The syslog_pri filter works well with other syslog-related plugins like the syslog input and the grok filter. It's often used as part of a larger syslog processing pipeline to extract specific priority information.
