storagealert.service

[Unit]
Description=Alerts admin if storage is running low
Wants=storagealert.timer

[Service]
Type=oneshot
ExecStart=/usr/local/sbin/storagealert

[Install]
WantedBy=multi-user.target

storagealert.sh

#!/bin/bash

# Setup:
# 0. Have a mail server set up, or something that provides `sendmail` with proper sender permissions.
# 1. Adjust the $drive, $buckets, $from and $to variables below to suit your needs.
# 2. Create /var/local/storagealert/$drive.txt and write 0 to it.
# If using systemd:
#   3. Put this script at /usr/local/sbin/storagealert with chmod 0755.
#   4. Put the storagealert.service and storagealert.timer files in /etc/systemd/system/.
#   5. Run:
#      systemctl daemon-reload
#      systemctl enable storagealert.timer
#      systemctl start storagealert.timer
# If using cron:
#   3. Put this script at /etc/cron.hourly/storagealert with chmod 0755.

set -e;

drive='PLACEHOLDER';
buckets=('95' '90' '80');
from='[email protected]';
to='[email protected]';

pct="$(df --output=pcent "/dev/$drive" | egrep -v '^Use%$')";
if [ "$(wc -l <<<"$pct")" -ne '1' ]; then
    echo '`df` returned multiple lines of output:' >&2;
    echo "$pct" >&2;
    exit 1;
fi;

if ! grep -Pq '^\s*\d+%$' <<<"$pct"; then
    echo '`df` returned bad percentage:' >&2;
    echo "$pct" >&2;
    exit 1;
fi;

pct="$(sed -E 's#^[[:space:]]*([[:digit:]]+)%$#\1#' <<<"$pct")";
old="$(cat "/var/local/storagealert/$drive.txt")";
echo "$pct" >"/var/local/storagealert/$drive.txt";

do_mail=false;
crossed=0;
for b in "${buckets[@]}"; do
    if [ "$pct" -ge "$b" ] && [ "$old" -lt "$b" ]; then
        do_mail=true;
        crossed="$b";
        break;
    fi;
done;

if "$do_mail"; then
    sendmail -t <<EOF
From: $from
To: $to
Subject: Storage more than $crossed% full
Content-Type: text/plain; charset="US-ASCII"

Drive $drive is $pct% full.

EOF
fi;

storagealert.timer

[Unit]
Description=Run storagealert every hour
Requires=storagealert.service

[Timer]
Unit=storagealert.service
OnCalendar=*-*-* *:00:00

[Install]
WantedBy=timers.target

You could've gotten my email address from so many places...
But no, I don't.