🔍 Detailed Script Breakdown

This document explains the purpose and logic behind each command used in the Linux system monitoring script.
The script provides a quick overview of CPU, memory, disk, and running processes to help with troubleshooting and performance checks.

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📘 Project Reference

This script is inspired by and aligned with the Server Stats project from roadmap.sh:

https://roadmap.sh/projects/server-stats

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1️⃣ Shebang and Script Header

#!/bin/bash

What it does

• Known as the shebang
• Tells Linux to execute the script using Bash
• Ensures consistent behavior across systems

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2️⃣ CPU Usage Calculation

cpu_idle=$(top -bn1 | grep "Cpu(s)" | awk '{print $8}')
cpu_usage=$(echo "100 - $cpu_idle" | bc)

Explanation

Command Purpose

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top -bn1 Runs top in batch mode for 1 iteration grep "Cpu(s)" Filters the CPU statistics line awk '{print $8}' Extracts CPU idle percentage bc Performs math calculation

Formula

CPU Usage = 100 − Idle %

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3️⃣ Memory Usage (Free vs Used)

free -m | awk 'NR==2{printf "Used: %dMB / Total: %dMB (%.2f%%)\n", $3, $2, $3*100/$2 }'

Explanation

Field Meaning

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$3 Used memory $2 Total memory printf Formats clean readable output

Example Output

Used: 2048MB / Total: 4096MB (50.00%)

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4️⃣ Disk Usage

df -h / | awk 'NR==2{printf "Used: %s / Total: %s (%s usage)\n", $3, $2, $5}'

Explanation

Field Meaning

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$3 Used space $2 Total space $5 Percentage usage

Example Output

Used: 15G / Total: 40G (38% usage)

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5️⃣ Top 5 Processes (CPU & Memory)

ps -eo pid,ppid,cmd,%cpu --sort=-%cpu | head -n 6

Explanation

Option Purpose

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ps -eo Lists all processes with custom format --sort=-%cpu Sorts by highest CPU usage head -n 6 Shows header + top 5 processes

Benefit

Quickly identifies: - High CPU usage processes - Resource bottlenecks - Misbehaving services

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🛠 Prerequisites

Supported OS

• Linux (Ubuntu/Debian recommended)
• Works on most distributions

Required Dependency

Install bc

Ubuntu/Debian

sudo apt update && sudo apt install bc -y

RHEL/CentOS/AlmaLinux/Rocky

sudo yum install bc -y

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🚀 Usage

Make script executable:

chmod +x monitor.sh

Run:

./monitor.sh

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✅ Summary

This script provides:

• CPU usage
• Memory usage
• Disk usage
• Top resource-consuming processes

Useful for:

• Server health checks
• Troubleshooting
• Performance monitoring
• Cron automation

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Author: frd amirul