Performance Debug

Diagnose CPU, memory, disk, and network performance bottlenecks.

Instructions

1. Get system overview: top, htop, or vmstat
2. Identify the bottleneck type (CPU, memory, disk, network)
3. Drill down with specific tools
4. Identify the root cause process/resource
5. Recommend solutions

Quick overview

# System summary
uptime
free -h
df -h
top -bn1 | head -20

# All-in-one view
htop  # or top

CPU analysis

# High-level CPU usage
mpstat 1 5
top -bn1 -o %CPU | head -15

# Per-process CPU
pidstat 1 5
ps aux --sort=-%cpu | head -10

# Find CPU-intensive process
top -bn1 | grep -A10 "PID USER"

Memory analysis

# Memory overview
free -h
vmstat 1 5

# Per-process memory
ps aux --sort=-%mem | head -10
pidstat -r 1 5

# Memory details
cat /proc/meminfo
smem -tk  # if available

# Find memory leaks (growth over time)
watch -n 5 'ps aux --sort=-%mem | head -10'

Disk analysis

# Disk space
df -h
du -sh /* 2>/dev/null | sort -hr | head -10

# Disk I/O
iostat -x 1 5
iotop -b -n 5  # requires root

# Find large files
find / -type f -size +100M 2>/dev/null

# Find disk-heavy processes
pidstat -d 1 5

Network analysis

# Connections and bandwidth
ss -tuln
ss -tunap | grep ESTAB
nethogs  # per-process bandwidth

# Network statistics
netstat -i
ip -s link

# Check for connection issues
ping -c 4 8.8.8.8
mtr --report google.com

Common bottlenecks

| Symptom | Indicator | Solution | | -------------------- | ---------- | ----------------------------------------- | | Load > cores | CPU-bound | Identify hot process, scale horizontally | | High %wa in top | I/O wait | Check disk, move to SSD, optimize queries | | Low free + high swap | Memory | Find leak, increase RAM, tune OOM | | High %si/%hi | Interrupts | NIC issue, driver problem |

Rules

• MUST check all four resources (CPU, memory, disk, network)
• MUST identify specific processes causing issues
• MUST provide actionable recommendations
• Never kill processes without user approval
• Always check if symptoms correlate with specific times (cron, traffic)