commands/sysadmin/linux-desktop/debugging/diagnose-slowdown.md

Diagnose System Slowdown

You are helping the user diagnose system laginess and performance issues.

Your tasks:

1. Gather initial information: Ask the user:

   • When did the slowdown start?
   • Is it constant or intermittent?
   • What activities trigger it? (startup, specific applications, general use)
   • Any recent changes? (updates, new software, configuration changes)

2. Check current system load:

   • System load averages: uptime
   • Detailed load info: w
   • Number of processes: ps aux | wc -l

3. CPU analysis:

   • Real-time CPU usage: top -b -n 1 | head -20
   • Per-core CPU usage: mpstat -P ALL 1 1 (if sysstat installed)
   • Top CPU consumers: ps aux --sort=-%cpu | head -20
   • CPU frequency and throttling:

     cat /proc/cpuinfo | grep MHz
     sudo cpupower frequency-info  # if available
     

   • Check for thermal throttling:

     sensors  # if lm-sensors installed
     cat /sys/class/thermal/thermal_zone*/temp
     

4. Memory analysis:

   • Memory usage: free -h
   • Detailed memory info: cat /proc/meminfo
   • Swap usage: swapon --show
   • Top memory consumers: ps aux --sort=-%mem | head -20
   • Check for memory leaks or runaway processes
   • OOM (Out of Memory) events: sudo journalctl -k | grep -i "out of memory"

5. Disk I/O analysis:

   • Disk usage: df -h
   • Inode usage: df -i
   • I/O statistics: iostat -x 1 5 (if sysstat installed)
   • Top I/O processes: sudo iotop -b -n 1 | head -20 (if iotop installed)
   • Check for high disk wait: top and look at wa (wait) percentage
   • Disk health: sudo smartctl -H /dev/sda (for each drive)

6. Process analysis:

   • List all running processes: ps aux
   • Process tree: pstree -p
   • Zombie processes: ps aux | grep Z
   • Processes in D state (uninterruptible sleep): ps aux | grep " D "
   • Long-running processes: ps -eo pid,user,start,time,cmd --sort=-time | head -20

7. Check for system resource contention:

   • Context switches: vmstat 1 5
   • Interrupts: cat /proc/interrupts
   • Check if system is swapping heavily: vmstat 1 5 (look at si/so columns)

8. Network issues (can cause perceived slowness):

   • Network connections: ss -s
   • Active connections: netstat -tunap | wc -l or ss -tunap | wc -l
   • DNS resolution test: time nslookup google.com
   • Check for network errors: ip -s link

9. Graphics/Desktop environment (for GUI slowness):

   • Check X server or Wayland compositor CPU usage
   • GPU usage (if nvidia): nvidia-smi or watch -n 1 nvidia-smi
   • For AMD: radeontop (if installed)
   • Check compositor settings (KDE Plasma on Wayland)
   • Desktop effects CPU usage

10. Check system logs for errors:

    • Recent errors: sudo journalctl -p err -b
    • Kernel messages: dmesg | tail -50
    • System log: sudo journalctl -xe --no-pager | tail -100
    • Look for specific issues:
      • Hardware errors
      • Driver issues
      • Service failures
      • Filesystem errors

11. Check for background services/processes:

    • List all services: systemctl list-units --type=service --state=running
    • Failed services: systemctl --failed
    • Check for update managers, indexing services (updatedb, baloo, tracker)
    • Snap services: snap list and check for snap updates
    • Flatpak: flatpak list

12. Application-specific checks: If slowness is application-specific:

    • Browser: check extensions, tabs, cache size
    • Database: check for long-running queries
    • IDE: check for indexing, plugins
    • Check application logs: ~/.local/share/applications/ or specific app log locations

13. Historical data (if available):

    • Check sar data: sar -u (if sysstat/sar configured)
    • Check historical logs: sudo journalctl --since "1 day ago" -p err

14. Analyze and report findings: Categorize issues found:

    • CPU bottleneck: High CPU usage, identify culprit processes
    • Memory bottleneck: High memory usage, swapping, suggest adding RAM or killing processes
    • Disk I/O bottleneck: High wait times, slow disk, suggest SSD upgrade or I/O optimization
    • Thermal throttling: High temperatures causing CPU slowdown
    • Runaway processes: Specific process consuming excessive resources
    • Resource leaks: Memory or handle leaks in specific applications
    • Background tasks: Indexing, updates, backups running
    • Network issues: DNS problems, slow network affecting system

15. Provide recommendations: Based on findings, suggest:

    • Kill or restart specific problematic processes
    • Disable unnecessary services
    • Adjust swappiness: sudo sysctl vm.swappiness=10
    • Clean up disk space if low
    • Update or reinstall problematic drivers
    • Install missing performance tools (sysstat, iotop, htop)
    • Schedule resource-intensive tasks for off-hours
    • Hardware upgrades (RAM, SSD) if appropriate
    • Investigate and fix application-specific issues
    • Check for and apply system updates
    • Reboot if system has been up for extended period with memory leaks

Important notes:

• Install missing diagnostic tools if needed (sysstat, iotop, htop, lm-sensors)
• Use sudo for system-level diagnostics
• Be systematic - check CPU, memory, disk, and network in order
• Correlate findings with user's description of when slowness occurs
• Don't immediately kill processes - confirm with user first
• Consider both hardware and software causes