Ubuntu 16.04 rsyslog High CPU Usage from Repeated Parse Errors

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

rsyslog uses excessive CPU, reducing overall host performance and delaying log delivery.

Environment & Reproduction

Triggered by malformed incoming log lines or invalid custom parser rules in rsyslog config.

Root Cause Analysis

Parser repeatedly retries malformed input and loops through expensive processing paths.

Quick Triage

Confirm rsyslog process load, identify noisy log source, and inspect recent config changes.

Step-by-Step Diagnosis

Analyze rsyslog debug output and message samples to isolate failing parser rules.

Solution – Primary Fix

Correct parser templates, rate-limit noisy source, and restart rsyslog with validated configuration.

Solution – Alternative Approaches

Segment log pipelines or offload heavy parsing to dedicated log processing tier.

Verification & Acceptance Criteria

CPU usage returns to baseline and log ingestion remains timely without parse retries.

Rollback Plan

Reinstate previous rsyslog config if new parsing rules introduce routing regressions.

Prevention & Hardening

Test parser changes in staging and apply rate controls to untrusted log sources.

Related Errors & Cross-Refs

Related to disk growth from log storms and dropped log message warnings.

Related tutorial: View the step-by-step tutorial for Ubuntu 16.04 LTS.

View all Ubuntu 16.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

rsyslog configuration reference and Ubuntu centralized logging operations guidance.