Watch the space on /boot

boot-space-watcher.sh

#!/bin/sh
# Use level (80 = 80% used)
alertlevel=80
# /boot = sda2
drivewarning="/dev/sda2"

df -H | grep -vE '^Filesystem|tmpfs|cdrom|udev|cgmfs' | awk '{ print $5 " " $1 " " $6}' | while read output;
do
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
  partition=$(echo $output | awk '{ print $2 }' )
  partname=$(echo $output | awk '{ print $3 }' )
  if [ "$partition" = "$drivewarning" ] && [ $usep -ge $alertlevel ]; then
     message="$partition ($partname) is running low on space: $usep% used - $(date)"
     # You can mail $message or send console alerts per below (or whatever) at this point:
     wall $message
  fi
done

example crontab to check every 1/2 hour:

0 */2 * * *    /home/USER/scripts/boot-space-watcher.sh