To get warned before a server fills its disk, run a small script from cron that checks free space and calls your Hook.Notifier URL when usage crosses a threshold. The warning arrives on your phone while there is still room to act.
A full disk is one of those failures that takes everything down at once: the database stops writing, logs stop, the app dies. The fix is easy if you hear about it at 85 percent instead of 100.
The check script
#!/bin/bash
# /usr/local/bin/check-disk.sh
THRESHOLD=85
usage=$(df / | awk 'NR==2 {gsub("%","",$5); print $5}')
if [ "$usage" -ge "$THRESHOLD" ]; then
curl -s "https://hooknotifier.com/{IDENTIFIER}/{KEY}?object=Disk%20almost%20full&body=Root%20filesystem%20at%20${usage}%25&priority=critical&color=%23EE6767&tags=alerts"
fi
Make it executable:
chmod +x /usr/local/bin/check-disk.sh
Run it on a schedule
Add it to cron so it checks every 15 minutes:
# crontab -e
*/15 * * * * /usr/local/bin/check-disk.sh
Now the moment the root filesystem crosses 85 percent, your phone buzzes with the exact number, and priority=critical means it does so even at night.
First get your URL
Your Hook.Notifier URL is https://hooknotifier.com/{IDENTIFIER}/{KEY}. Create a free account to get yours, then drop it into the script.
Watch more than the root disk
Point the check at any mount, or loop over several:
for mount in / /var /data; do
usage=$(df "$mount" | awk 'NR==2 {gsub("%","",$5); print $5}')
if [ "$usage" -ge 85 ]; then
curl -s "https://hooknotifier.com/{IDENTIFIER}/{KEY}?object=Disk%20almost%20full&body=${mount}%20at%20${usage}%25&priority=critical&tags=alerts"
fi
done
Why it matters
Disk space fills slowly, then all at once. Almost every "the whole server went down overnight" story is a disk that quietly hit 100 percent. A five-line check that pings your phone at 85 percent turns a 3am outage into a two-minute cleanup.
New to this? Start with how to send yourself a native push notification, or see how to get notified on SSH login.