Troubleshooting high CPU utilization on a Linux server involves identifying the processes or activities consuming excessive CPU resources and taking appropriate actions to address the issue. Here’s a step-by-step guide:

  1. Check System Load: Use the uptime or top command to check the overall system load and CPU utilization. High load averages (1, 5, and 15-minute) indicate increased demand on the CPU.
  2. Identify High CPU Processes: Run the top or htop command to view a list of processes sorted by CPU usage. Identify which processes are consuming the most CPU resources.
  3. Analyze Process Details: Select a high CPU process in top and note its process ID (PID). Use tools like ps aux or ps -p <PID> -o %cpu,%mem,cmd to obtain more detailed information about the process.
  4. Determine Process Type: Identify whether the high CPU process is a system process, user application, or service. This helps narrow down the potential causes.
  5. Check System and Application Logs: Inspect system logs (/var/log/syslog) and application-specific logs for any relevant error messages or warnings that could indicate the source of high CPU utilization.
  6. Resource Monitoring: Use tools like top, htop, or atop to monitor resource usage in real time. Look for patterns, spikes, and correlations between high CPU utilization and other resource usage.
  7. Investigate Process Behavior: Use tools like strace or perf to analyze the behavior of high CPU processes. This can help identify loops, excessive I/O, or other anomalies.
  8. Check I/O Wait: High I/O wait can contribute to high CPU utilization. Use iostat to monitor disk I/O performance and identify whether I/O wait is a contributing factor.
  9. Review Resource Limits: Check if resource limits (ulimits) are set for user processes. Limits might be too high, causing a single process to monopolize resources.
  10. Update Software and Drivers: Ensure that the server’s operating system, drivers, and software are up-to-date. Outdated software can sometimes cause performance issues.
  11. Scan for Malware: Perform a malware scan using tools like rkhunter or clamav to rule out malicious processes causing high CPU usage.
  12. Check for Cron Jobs and Scheduled Tasks: High CPU usage might be related to cron jobs or scheduled tasks running at specific intervals. Review the system’s cron jobs using crontab -l and check for irregularities.
  13. Resource-Intensive Applications: Some applications, especially in an HPC cluster, might be designed to utilize maximum resources. Make sure high utilization is expected for such applications.
  14. Optimize Code: If the high CPU process is a custom application, inspect and optimize the code to reduce resource consumption.
  15. Consider Hardware Issues: In rare cases, hardware issues like overheating or failing components can cause high CPU utilization. Monitor hardware health using tools like lm-sensors.
  16. Scale Resources: If high CPU usage is due to legitimate high demand, consider scaling up resources by adding more CPU cores or balancing workloads across multiple nodes in the cluster.
  17. Implement Monitoring and Alerts: Set up monitoring tools like nagios, zabbix, or Prometheus to proactively monitor and alert you about high CPU utilization.
  18. Document Findings and Solutions: Keep a record of your troubleshooting steps, findings, and the solutions implemented for future reference.

Remember that troubleshooting high CPU utilization can be complex, and it might require a combination of tools, analysis, and expertise. It’s important to carefully consider the impact of any changes you make, especially on production systems.