Monitor Disk Usage and Send Email Alerts

#!/bin/bash

# --- Configuration ---
THRESHOLD=90                       # Percentage threshold for disk usage
EMAIL_RECIPIENT="[email protected]" # Email address to send alerts
PARTITION="/"                      # Partition to monitor (e.g., /, /var, /home)
ALERT_SUBJECT="Disk Usage Alert on $(hostname)"

# --- Check for mail command ---
if ! command -v mail &> /dev/null; then
    echo "Error: 'mail' command not found. Please install mailutils or equivalent."
    echo "On Debian/Ubuntu: sudo apt install mailutils"
    echo "On CentOS/RHEL: sudo yum install mailx"
    exit 1
fi

# --- Get current disk usage ---
# Use 'df -h' for human-readable output
# 'awk' to extract the percentage for the specified partition
# 'sed' to remove the '%' sign
USAGE=$(df -h "$PARTITION" | awk 'NR==2 {print $5}' | sed 's/%//g')

# --- Check if USAGE is a valid number ---
if ! [[ "$USAGE" =~ ^[0-9]+$ ]]; then
    echo "Error: Could not determine disk usage for partition '$PARTITION'. Raw output: $(df -h "$PARTITION")"
    exit 1
fi

echo "Current disk usage for $PARTITION: ${USAGE}%"

# --- Compare with threshold and send alert if necessary ---
if (( USAGE > THRESHOLD )); then
  ALERT_BODY="Disk usage on $(hostname) for partition '$PARTITION' is at ${USAGE}%, which exceeds the threshold of ${THRESHOLD}%.

"
  ALERT_BODY+="Please investigate disk space usage.
"
  ALERT_BODY+="Current disk usage details:

$(df -h "$PARTITION")"
  
  echo -e "$ALERT_BODY" | mail -s "$ALERT_SUBJECT" "$EMAIL_RECIPIENT"
  
  if [ $? -eq 0 ]; then
    echo "Alert email sent to $EMAIL_RECIPIENT."
  else
    echo "Failed to send alert email."
  fi
else
  echo "Disk usage for $PARTITION is within the acceptable limits (${USAGE}% <= ${THRESHOLD}%)."
fi

echo "Script finished."