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Chapter 11.1 - System Monitoring

Learning Objectives​

By the end of this chapter, you will be able to:

  • Monitor CPU, memory, disk
  • Use top, htop, iotop
  • Understand system metrics
  • Use vmstat and iostat
  • Configure basic alerts

Monitoring Tools​

top - Real-Time​

# Interactive interface
top

# Options
top -u user1        # By user
top -p 1234        # Specific process
top -d 2           # Update every 2 seconds

Displayed metrics:

  • Load average
  • CPU usage
  • Memory (RAM, swap)
  • Processes

htop - Enhanced Version​

# Colored interface
htop

# Install if necessary
sudo apt install htop

Advantages:

  • Intuitive interface
  • Easy navigation
  • Progress bars
  • Filtering

iotop - I/O by Process​

# Monitor disk I/O
sudo iotop

# Options
sudo iotop -o        # Only active
sudo iotop -a        # Accumulated

System Metrics​

CPU​

# CPU usage
top
htop

# CPU statistics
cat /proc/stat
mpstat  # sysstat

# Load average
uptime
cat /proc/loadavg

# Interpretation:
# < number of CPUs: OK
# = number of CPUs: Full utilization
# > number of CPUs: Overload

Memory​

# Overview
free -h

# Details
cat /proc/meminfo

# By process
ps aux --sort=-%mem | head

# Statistics
vmstat -s

Disk​

# Disk space
df -h

# Usage by directory
du -sh /home/*

# I/O statistics
iostat -x 1

# By process
sudo iotop

Advanced Tools​

vmstat - System Statistics​

# Statistics every second
vmstat 1

# Important columns:
# r: Processes waiting for CPU
# b: Blocked processes
# swpd: Swap used
# free: Free memory
# si/so: Swap in/out
# us/sy/id: CPU user/system/idle

iostat - I/O Statistics​

# Install
sudo apt install sysstat

# I/O statistics
iostat -x 1

# Columns:
# %util: Disk utilization
# r/s, w/s: Reads/writes per second
# rkB/s, wkB/s: KB/s

sar - System Activity Reporter​

# CPU history
sar -u

# Memory history
sar -r

# I/O history
sar -b

# Real-time
sar -u 1 10  # CPU, 1 second, 10 times

Monitoring Scripts​

Basic Monitoring​

#!/bin/bash
# Simple monitoring script

echo "=== CPU ==="
top -bn1 | grep "Cpu(s)" | awk '{print $2}'

echo "=== Memory ==="
free -h | grep Mem

echo "=== Disk ==="
df -h / | tail -1

echo "=== Load Average ==="
uptime

Monitoring with Alerts​

#!/bin/bash
# Monitoring with alerts

THRESHOLD_CPU=80
THRESHOLD_MEM=80
THRESHOLD_DISK=80

# CPU
CPU=$(top -bn1 | grep "Cpu(s)" | awk '{print $2}' | sed 's/%us,//')
if (( $(echo "$CPU > $THRESHOLD_CPU" | bc -l) )); then
    echo "ALERT: CPU at ${CPU}%"
fi

# Memory
MEM=$(free | grep Mem | awk '{printf "%.0f", $3/$2 * 100}')
if [ "$MEM" -gt "$THRESHOLD_MEM" ]; then
    echo "ALERT: Memory at ${MEM}%"
fi

# Disk
DISK=$(df -h / | tail -1 | awk '{print $5}' | sed 's/%//')
if [ "$DISK" -gt "$THRESHOLD_DISK" ]; then
    echo "ALERT: Disk at ${DISK}%"
fi

Monitoring Cron​

Scheduled Task​

# /etc/cron.d/monitoring
# Monitoring every 5 minutes
*/5 * * * * root /usr/local/bin/monitor.sh >> /var/log/monitoring.log 2>&1

Script with Logging​

#!/bin/bash
# /usr/local/bin/monitor.sh

LOG="/var/log/monitoring.log"
DATE=$(date '+%Y-%m-%d %H:%M:%S')

{
    echo "=== $DATE ==="
    echo "CPU: $(top -bn1 | grep 'Cpu(s)' | awk '{print $2}')"
    echo "Memory: $(free -h | grep Mem | awk '{print $3"/"$2}')"
    echo "Disk: $(df -h / | tail -1 | awk '{print $5}')"
    echo "Load: $(uptime | awk -F'load average:' '{print $2}')"
    echo "---"
} >> "$LOG"

Summary​

In this chapter, you learned:

Tools: top, htop, iotop, vmstat, iostat, sar
Metrics: CPU, memory, disk, load average
Monitoring: Automatic scripts, alerts
Cron: Regular monitoring scheduling
Practice: Continuous monitoring, problem detection

Next Steps​

Chapter 11.2: Log Management
Chapter 11.3: Monitoring Crons and Alerts

Chapter created on: December 2024