Send yourself an email if your CentOS server has less than 10% free space.

notify_space.sh

#!/bin/sh
df -H | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output;
do
    usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
    partition=$(echo $output | awk '{ print $2 }' )
    if [ $usep -ge 90 ]; then
        echo "Running out of space \"$partition ($usep%)\" on $(hostname) as on $(date)" |
        mail -s "Alert: Almost out of disk space $usep%" youremail@example.com
    fi
done