A shell script to check your disk usage and alert you if it hits a limit. Change the value (percentage) in the "if" statement on line 7 to alter the threshold. Change the email address to your email address. See readme for mail.cf instructions and crontab.

readme.md

Disk Usage Alerter

Install mailutils with:

sudo apt-get install mailutils

Set up the cronjob with:

crontab -e

To send at 10 mins past the hour add:

10 * * * * sh /path/to/script

If you'll be emailing the same domain that your mailname is set to:

Navigate to /etc/postfix/

sudo vi main.cf

Find line beginning mydestination, it should say something like:

mydestination =  ubuntu, localhost.localdomain, localhost

Crucially it shouldn't contain your mailname or references to it, or your emails will be sent internally on the server.

disk-usage-alert.sh

#!/bin/sh
df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output;
do
  echo $output
  used=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
  partition=$(echo $output | awk '{ print $2 }' )
  if [ $usep -ge 80 ]; then
    echo "The partition \"$partition\" on $(hostname) has used $used% at $(date)" | mail -s "Disk space alert: $used% used" your@email.com
  fi
done

@seenusankara replace $usep with $used.