Linux disk space email alert

diskmon.sh

#!/bin/bash
# www.fduran.com
# script that will send an email to EMAIL when disk use in partition PART is bigger than %MAX
# adapt these 3 parameters to your case
MAX=95
EMAIL=alertemail@example.com,alteremail2@example.com
PART=sda1

USE=`df -h |grep $PART | awk '{ print $5 }' | cut -d'%' -f1`
if [ $USE -gt $MAX ]; then
  echo "Percent used: $USE" | mail -s "Running out of disk space" $EMAIL
fi

to install mail if it is not exist check here