system-helpers/usr/local/bin/disk_space_alert

#!/usr/bin/env bash

# usage
usage() {
USAGE=$(cat <<EOF
Usage: disk_space_alert

Checks available diskspace for configured **mounts** and sends out a mail if certain limits are reached. Please see man disk_space_alert.
EOF
)
	echo "$USAGE";
}

set -e;

# check for config file
apply_config() {
  local config=$1;

  if [[ ! -f "$config" ]]; then
      echo "No config file specified";
      echo "";
      usage;
      exit 1;
  fi

  set -a;
  # shellcheck disable=SC1090
  source "$config";
  set +a;
}

source_config() {
  local configFallback=$1;
  local configGlobalFallback=$2;

  if [[ -f "$configFallback" ]]; then
    apply_config "$configFallback";
    return;
  fi

  if [[ -f "$configGlobalFallback" ]]; then
    apply_config "$configGlobalFallback";
    return;
  fi
}

check_required() {
  type hostname &> /dev/null || { echo "Requiring 'hostname' but it's not installed"; exit 1; }
  type mailx &> /dev/null || { echo "Requiring 'mailx' but it's not installed"; exit 1; }
  type df &> /dev/null || { echo "Requiring 'df' but it's not installed"; exit 1; }
}

# apply defaults
DISK_SPACE_ALERT_MAIL_ADDRESS="";
DISK_SPACE_ALERT_THRESHOLD=93
DISK_SPACE_ALERT_MOUNTPOINTS=("/")

source_config "$HOME/.disk_space_alert.conf" "/etc/disk_space_alert.conf"
check_required

# do not touch below
HOSTNAME=$(hostname)

for point in "${DISK_SPACE_ALERT_MOUNTPOINTS[@]}"
do
	CURRENT=$(df "$point" | grep "$point" | awk '{ print $5}' | sed 's/%//g')
	CURRENT_SPACE=$(df "$point" | grep "$point" | awk '{ print $5}' | sed 's/%//g')
	CURRENT_INODES=$(df -i "$point" | grep "$point" | awk '{ print $5}' | sed 's/%//g')

	if [ "$CURRENT" -gt "$DISK_SPACE_ALERT_THRESHOLD" ] ; then
	    mailx -s "[disk $HOSTNAME] $point" "$DISK_SPACE_ALERT_MAIL_ADDRESS" << EOF
Your $point partition remaining free space is critically low. Used space: $CURRENT_SPACE%. Used inodes: $CURRENT_INODES%.
EOF
fi
done