4. Prepare onbaterry and offbatery APC scripts

In case you did not know, when power goes down and the UPS switches to battery power, the apcupsd service automatically triggers a shell script under /etc/apcupsd/onbattery . We will need to modify it to use our mail service and email the right email address.

nano /etc/apcupsd/onbattery

#!/bin/bash

# Variables
MAIL_TO="[email protected]"
LOG_FILE="/var/log/ups_manager.log"
MAIL_BODY="/tmp/power_lost.html"
SUBJ="Power LOST for `hostname`"

# Create HTML email body
cat > $MAIL_BODY << EOF
<html>
	<body>
		<h2>Power was lost!</h2>
		<p><strong>Current APC status:</strong>
		<pre>`/usr/sbin/apcaccess status`</pre>
		<p><strong>Recent log file output:</strong>
		<pre>`tail -n 20 /var/log/ups_manager.log`</pre>
		<p>Your RPi script :)</p>
	</body>
</html>
EOF

mutt -e 'set content_type="text/html"' \\
     -s "$SUBJ" \\
     "$MAIL_TO" \\
     -a "$LOG_FILE" < "$MAIL_BODY"

rm -f "$MAIL_BODY"  # Remove our temporary file
exit 0

Screenshot of the script as shown in the nano text editor to configure the onbaterry script. — Set up rich text email notification when UPS switches on battery power during power loss

Once power is back on, another script under /etc/apcupsd/offbattery is executed. Located it and at the end of it, please add the following lines to clear the flag for our script.
Kudos to https://pieterbakker.com/using-mutt-to-send-html-emails-with-attachments/ for the suggestions on how to use HTML format with mutt.

nano /etc/apcupsd/offbattery

#!/bin/bash

# Variables
MAIL_TO="[email protected]"
LOG_FILE="/var/log/ups_manager.log"
MAIL_BODY="/tmp/power_restored.html"
SUBJ="Power restored for `hostname`"

# Clear the flags for future cases
rm -f /tmp/ups_shutdown_flags/*.flag

# Create HTML email body
cat > $MAIL_BODY << EOF
<html>
	<body>
		<h2>Good news, power was restored!</h2>
		<p><strong>APC status just after restoration:</strong>
		<pre>`/usr/sbin/apcaccess status`</pre>
		<p><strong>Recent log file output:</strong>
		<pre>`tail -n 20 /var/log/ups_manager.log`</pre>
		<p>Your RPi script :)</p>
	</body>
</html>
EOF

mutt -e 'set content_type="text/html"' \\
     -s "$SUBJ" \\
     "$MAIL_TO" \\
     -a "$LOG_FILE" < "$MAIL_BODY"

rm -f "$MAIL_BODY"  # Remove our temporary file
exit 0

Screenshot of the script as shown in the nano text editor to configure the offbaterry script. — Similarly, set up rich text emails once off battery (back to power) + remove shutdown flags

Make the scripts executable and test them:

sudo chmod +x /usr/local/sbin/ups_manager.sh
sudo chmod +x /etc/apcupsd/onbattery
sudo chmod +x /etc/apcupsd/offbattery

# Calling these two should result in an email being sent.
bash /etc/apcupsd/onbattery
bash /etc/apcupsd/offbattery
# Should show you that the UPS is connected to power and no further action is needed.
bash /usr/local/sbin/ups_manager.sh

Schedule it to run every two minutes:

sudo crontab -e

# Add this line:
*/2 * * * * /usr/local/sbin/ups_manager.sh

Note that logs will be saved under /var/log/ups_manager.log in addition to the email alerts. At this point, if the power goes down, you will receive an email and the script will trigger further to eventually start gracefully shutting down your Proxmox hosts.
One more thing, we need to ensure that the log gets rotated, as it will be getting updates every two minutes and will clog up quickly. Let’s use logrotate for that.

sudo nano /etc/logrotate.d/ups_manager

/var/log/ups_manager.log {
    weekly
    rotate 4
    compress
    delaycompress
    missingok
    notifempty
    create 644 root root
}

# Test it
sudo logrotate -d /etc/logrotate.conf

Are we finally ready for a test? Yes! But how about we configure a script also for our existing monitoring system, such as Uptime Kuma, first?

4. Prepare onbaterry and offbatery APC scripts

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