Linux

Troubleshoot Error

1. Collect info and identify the problem
   • Slow response, high latency, unable to reach server, timeout
   • Check for recent change make to app or infra
2. Web server (infra) troubleshooting
   • See if processes is running
   • Check server health:
     • CPU/memory usage
     • Storage usage, disk I/O
     • Network traffic, latency, throughput
     • Error rate
   • Compare current performance metrics against baseline
   • Analyze pattern: look for unusual spike traffic, bandwidth hogs, malicious activities
   • Verify web server log and look for error
   • Review configuration setting. Ensure infra is properly configure
3. Application Performance Issue
   • Use Application Performance Monitoring (APM)
   • Help root cause analysis. Identify problem that could be cause by code issue, server performance, network latency
   • Check for response time, request rate, throughput, error rate, uptime
   • Check log for error
   • Check database query performance and number of connection
4. End-user troubleshooting
   • Access app from user browser. Check for response time and DNS issue

Linux File System Explained

Soft Link and Hard Link

• Soft links are like shortcuts and can link to files across different filesystems, but they break if the original file is deleted.
• Hard links create another reference to the same data, remaining valid even if the original file is deleted, but they cannot link to directories or exist across different filesystems.

Swap File

• Check swap file: free -h
• Show total, free and used swap space: cat /proc/meminfo
• Show active swap device: cat /proc/swaps
• Show swap info: swapon --show