Monitor Disk Space and Send Email Alerts

#!/bin/bash

# --- Configuration Start ---
THRESHOLD=85 # Percentage of disk usage that triggers an alert
EMAIL_RECIPIENT="[email protected]"
SERVER_NAME="$(hostname)"
DEVICE_TO_MONITOR="/dev/sda1" # Or mount point, e.g., '/' or '/var'
# --- Configuration End ---

# Check if mail command is available
if ! command -v mail &> /dev/null; then
    echo "Error: 'mail' command not found. Please install mailutils or similar." >&2
    exit 1
fi

# Get disk usage for the specified device/mount point
# df -h: Human-readable format
# awk: Extracts the percentage used (5th field) and removes '%' sign
# grep: Filters for the specific device/mount point
USED_PERCENTAGE=$(df -h "$DEVICE_TO_MONITOR" | awk 'NR==2 {print $5}' | sed 's/%//')

# Check if we got a valid number
if [[ -z "$USED_PERCENTAGE" || ! "$USED_PERCENTAGE" =~ ^[0-9]+$ ]]; then
    echo "Error: Could not determine disk usage for $DEVICE_TO_MONITOR." >&2
    exit 1
fi

# Compare with threshold
if (( USED_PERCENTAGE > THRESHOLD )); then
  SUBJECT="ALERT: High Disk Usage on $SERVER_NAME - $DEVICE_TO_MONITOR"
  BODY="Disk usage on $SERVER_NAME for $DEVICE_TO_MONITOR is currently at $USED_PERCENTAGE%, exceeding the threshold of $THRESHOLD%.

$(df -h)"

  echo "Sending email alert: $SUBJECT"
  echo -e "$BODY" | mail -s "$SUBJECT" "$EMAIL_RECIPIENT"
  if [ $? -eq 0 ]; then
    echo "Email alert sent successfully."
  else
    echo "Failed to send email alert." >&2
  fi
else
  echo "Disk usage for $DEVICE_TO_MONITOR is at $USED_PERCENTAGE%, which is below the threshold of $THRESHOLD%. No alert sent."
fi