📊 Configuring Disk Usage Monitoring in Alpine Linux: Simple Guide

Watching your disk space helps prevent system crashes! 💻 This tutorial shows you how to set up disk monitoring easily. Don’t worry - it’s simpler than you think! 😊

🤔 What is Disk Usage Monitoring?

Disk usage monitoring watches how much space your files use. It’s like checking if your closet is getting too full!

Disk monitoring helps you:

• 📈 See how much space is used
• ⚠️ Get warnings when space is low
• 💾 Find files taking too much space
• 🔄 Keep your system running smoothly

🎯 What You Need

Before we start, you need:

• ✅ Alpine Linux system running
• ✅ Root or sudo access
• ✅ Basic knowledge of terminal commands
• ✅ Some files on your system to monitor

📋 Step 1: Understanding Disk Usage Commands

🔍 Basic Disk Space Checking

Let’s start by learning how to check disk space manually. This is the foundation! 😊

What we’re doing: Looking at how much space your disks are using right now.

# Show disk space for all mounted filesystems
df -h

# Show disk usage of current directory
du -h

# Show disk usage with total
du -sh *

# Show only filesystem usage summary
df -h --total

What this does: 📖 Shows you how much space is used and available on your disks.

Expected Output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        20G  8.5G   10G  46% /
tmpfs           1.0G     0  1.0G   0% /dev/shm

What this means: Your main disk is using 46% of available space! ✅

💡 Important Tips

Tip: The “Use%” column is most important - watch when it gets above 80%! 💡

Warning: When disk space reaches 100%, your system can crash! ⚠️

🛠️ Step 2: Setting Up Basic Monitoring

📊 Creating a Simple Monitoring Script

Now let’s create a script that checks disk space automatically. This is really helpful! 😊

What we’re doing: Making a script that watches disk space and tells you when it’s getting full.

# Create monitoring script directory
mkdir -p /opt/disk-monitor

# Create the monitoring script
cat > /opt/disk-monitor/check-disk.sh << 'EOF'
#!/bin/sh
# Simple disk usage monitoring script

# Set warning threshold (80%)
THRESHOLD=80

# Get disk usage percentage (remove % sign)
USAGE=$(df / | tail -1 | awk '{print $5}' | sed 's/%//')

# Check if usage is above threshold
if [ "$USAGE" -gt "$THRESHOLD" ]; then
    echo "⚠️  WARNING: Disk usage is ${USAGE}% (threshold: ${THRESHOLD}%)"
    echo "📅 Date: $(date)"
    echo "📊 Disk details:"
    df -h /
else
    echo "✅ Disk usage OK: ${USAGE}% (threshold: ${THRESHOLD}%)"
fi
EOF

# Make script executable
chmod +x /opt/disk-monitor/check-disk.sh

# Test the script
/opt/disk-monitor/check-disk.sh

Code explanation:

• THRESHOLD=80: Sets warning level at 80% full
• df / | tail -1: Gets disk info for root filesystem
• awk '{print $5}': Extracts the usage percentage
• sed 's/%//': Removes the % symbol for comparison

Expected Output:

✅ Disk usage OK: 46% (threshold: 80%)

What this means: Great! Your disk is not full yet! 🎉

🎮 Let’s Try It!

Time for hands-on practice! This is the fun part! 🎯

What we’re doing: Creating an advanced monitoring script with email alerts and detailed logging.

# Create advanced monitoring script
cat > /opt/disk-monitor/advanced-monitor.sh << 'EOF'
#!/bin/sh
echo "🖥️  Advanced Disk Usage Monitor"
echo "================================"
echo ""

# Set thresholds
WARNING_THRESHOLD=80
CRITICAL_THRESHOLD=90

# Create log directory
mkdir -p /var/log/disk-monitor

# Log file
LOG_FILE="/var/log/disk-monitor/disk-usage.log"

# Get current date
DATE=$(date '+%Y-%m-%d %H:%M:%S')

echo "📅 Scan Time: $DATE"
echo ""

# Check all mounted filesystems
df -h | grep -E '^/dev/' | while read line; do
    FILESYSTEM=$(echo $line | awk '{print $1}')
    SIZE=$(echo $line | awk '{print $2}')
    USED=$(echo $line | awk '{print $3}')
    AVAIL=$(echo $line | awk '{print $4}')
    USAGE_PCT=$(echo $line | awk '{print $5}' | sed 's/%//')
    MOUNT=$(echo $line | awk '{print $6}')
    
    echo "📁 Filesystem: $FILESYSTEM"
    echo "   Mounted on: $MOUNT"
    echo "   Size: $SIZE | Used: $USED | Available: $AVAIL"
    
    if [ "$USAGE_PCT" -gt "$CRITICAL_THRESHOLD" ]; then
        echo "   🚨 CRITICAL: ${USAGE_PCT}% used!"
        echo "$DATE - CRITICAL: $FILESYSTEM at $MOUNT is ${USAGE_PCT}% full" >> $LOG_FILE
    elif [ "$USAGE_PCT" -gt "$WARNING_THRESHOLD" ]; then
        echo "   ⚠️  WARNING: ${USAGE_PCT}% used"
        echo "$DATE - WARNING: $FILESYSTEM at $MOUNT is ${USAGE_PCT}% full" >> $LOG_FILE
    else
        echo "   ✅ OK: ${USAGE_PCT}% used"
        echo "$DATE - OK: $FILESYSTEM at $MOUNT is ${USAGE_PCT}% full" >> $LOG_FILE
    fi
    echo ""
done

echo "📊 Monitoring complete! Check log: $LOG_FILE"
EOF

# Make it executable
chmod +x /opt/disk-monitor/advanced-monitor.sh

# Run the advanced monitor
/opt/disk-monitor/advanced-monitor.sh

You should see:

🖥️  Advanced Disk Usage Monitor
================================

📅 Scan Time: 2025-06-07 13:30:00

📁 Filesystem: /dev/sda1
   Mounted on: /
   Size: 20G | Used: 8.5G | Available: 10G
   ✅ OK: 46% used

Awesome work! 🌟

📊 Quick Summary Table

⏰ Step 3: Automated Monitoring with Cron

📅 Setting Up Regular Checks

Let’s make your monitoring run automatically every hour! 📚

What we’re doing: Using cron to run disk checks automatically so you don’t have to remember.

# Open cron editor
crontab -e

# Add this line to run monitoring every hour
# 0 * * * * /opt/disk-monitor/check-disk.sh >> /var/log/disk-monitor/hourly.log 2>&1

# Or add this line to run every 30 minutes
# */30 * * * * /opt/disk-monitor/advanced-monitor.sh >> /var/log/disk-monitor/detailed.log 2>&1

# Save and exit the editor

# Alternative: Create cron file directly
echo "0 * * * * /opt/disk-monitor/check-disk.sh >> /var/log/disk-monitor/hourly.log 2>&1" | crontab -

# Verify cron job was added
crontab -l

Code explanation:

• 0 * * * *: Run at minute 0 of every hour
• */30 * * * *: Run every 30 minutes
• >> /var/log/...: Append output to log file
• 2>&1: Include error messages in log

Expected Output:

0 * * * * /opt/disk-monitor/check-disk.sh >> /var/log/disk-monitor/hourly.log 2>&1

What this does: Your system now checks disk space automatically every hour! 📚

🎮 Practice Time!

Let’s practice what you learned! Try these simple examples:

Example 1: Find Large Files 🟢

What we’re doing: Finding files that are taking up too much space.

# Find files larger than 100MB
find / -type f -size +100M -exec ls -lh {} \; 2>/dev/null | head -10

# Find largest directories in current location
du -h --max-depth=1 | sort -hr | head -10

# Find largest files in /var directory
find /var -type f -exec ls -s {} \; 2>/dev/null | sort -n -r | head -10

What this does: Shows you which files are eating up your disk space! 🌟

Example 2: Create Disk Usage Report 🟡

What we’re doing: Making a nice report about disk usage.

# Create reporting script
cat > /opt/disk-monitor/daily-report.sh << 'EOF'
#!/bin/sh
echo "📊 Daily Disk Usage Report - $(date +%Y-%m-%d)"
echo "=============================================="
echo ""

echo "💾 Filesystem Overview:"
df -h
echo ""

echo "📁 Largest Directories in /:"
du -h --max-depth=1 / 2>/dev/null | sort -hr | head -5
echo ""

echo "🗂️  /var Directory Usage:"
du -sh /var/* 2>/dev/null | sort -hr | head -5
echo ""

echo "📈 Disk Usage Trend (last 5 entries):"
tail -5 /var/log/disk-monitor/disk-usage.log 2>/dev/null || echo "No previous logs found"
EOF

chmod +x /opt/disk-monitor/daily-report.sh

# Run the daily report
/opt/disk-monitor/daily-report.sh

What this does: Creates a complete daily report of your disk usage! 📚

🚨 Fix Common Problems

Problem 1: Monitoring script not running ❌

What happened: Cron job doesn’t seem to work. How to fix it: Check cron service and permissions!

# Check if cron service is running
rc-service crond status

# Start cron if not running
rc-service crond start

# Enable cron to start at boot
rc-update add crond default

# Check cron logs
tail -f /var/log/cron

Problem 2: Can’t write to log directory ❌

What happened: Permission denied when creating log files. How to fix it: Fix permissions and create directories!

# Create log directory with correct permissions
mkdir -p /var/log/disk-monitor
chmod 755 /var/log/disk-monitor

# Make sure script has execute permissions
chmod +x /opt/disk-monitor/*.sh

# Test writing to log directory
echo "Test" > /var/log/disk-monitor/test.log && echo "✅ Permissions OK" || echo "❌ Permission problem"

Don’t worry! These problems are easy to fix. You’re doing great! 💪

💡 Simple Tips

1. Check regularly 📅 - Look at disk usage reports daily
2. Set low thresholds 🌱 - Start warnings at 80% full, not 95%
3. Clean up often 🤝 - Remove old files and logs regularly
4. Plan ahead 💪 - Add more storage before you need it

✅ Check Everything Works

Let’s make sure all monitoring is working perfectly:

# Test basic monitoring
/opt/disk-monitor/check-disk.sh

# Test advanced monitoring
/opt/disk-monitor/advanced-monitor.sh

# Check if cron job exists
crontab -l

# Check recent logs
ls -la /var/log/disk-monitor/

echo "📊 Disk monitoring is ready! ✅"

Good output:

✅ Disk usage OK: 46% (threshold: 80%)
📊 Disk monitoring is ready! ✅

🏆 What You Learned

Great job! Now you can:

• ✅ Check disk usage with df and du commands
• ✅ Create custom monitoring scripts
• ✅ Set up automated monitoring with cron
• ✅ Generate detailed disk usage reports

🎯 What’s Next?

Now you can try:

• 📚 Setting up email alerts for critical disk usage
• 🛠️ Creating graphical monitoring dashboards
• 🤝 Monitoring multiple servers from one location
• 🌟 Learning about log rotation and cleanup!

Remember: Monitoring disk usage prevents system crashes! You’re keeping your server healthy! 🎉

Keep practicing and you’ll become a system monitoring expert too! 💫