I have apcupsd configured as a slave over LAN, connected to my pfSense, which runs apcupsd as the master.

Everything works fine — reporting, battery mode notifications, and clean shutdowns — but there’s no notification when power is restored and the system switches back to mains.

Any clue from anyone where I should start looking to fix this?

? so you want unraid to report back or pfsense to report back?

unraid, running apcupsd as a slave, correctly and immediately sends a notification when the UPS switches to battery (main power loss). However, it never sends a “power restored” notification when the UPS goes back online, even though unraid clearly receives this status update from pfsense, which is running apcupsd as the master. I want unraid to send the power-restored notification in the same way it handles the on-battery event.

I'm not in the know on ups the acupsd sytem... however, from googling around this is what I have found:

this is a “nothing fires on restore” issue, not a comms problem. On a slave, apcupsd does receive the “power back” state from the master, but the default event handling doesn’t notify on it. By design, the offbattery (and sometimes mainsback / online) events are generated on return to line power, but the stock action is do nothing unless you override it with an event script.

https://subnets.ru/blog/wp-content/uploads/2008/07/apcupsd.pdf

so I would assume edit the event scripts that unrad slave system is using...

Confirm the event is actually generated (it is, but verify once)
On the Unraid box (slave):
tail -f /var/log/apcupsd.events

Trigger a short power pull. You should see lines like:

Power failure.
... (ONBATT)
Power is back. UPS running on mains.
... (OFFBATT or MAINSBACK/ONLINE)

If you see the “back on mains” line in the events file but got no Unraid notification, it’s exactly the default-action gap described above.

see manpages as well for this system:
https://www.mankier.com/5/apcupsd.conf

so lets add an event hook so unraid reprots back...

?untested but should work...
apcupsd will execute a script named after the event if present in /etc/apcupsd/. We’ll hook offbattery (fires only if onbattery had fired) and optionally mainsback / online for belt-and-suspenders. https://blog.horner.tj/apcupsd-scripts/

Create persistent copies on the flash and install them at boot:

*(to survive reboots and carry with unraid flash backups...)

mkdir -p /boot/config/custom/apcupsd

nano /boot/config/custom/apcupsd/offbattery

/boot/config/custom/apcupsd/offbattery

#!/bin/bash
# Unraid apcupsd slave: notify when power is restored
HOSTNAME=$(hostname)
SUBJECT="UPS power restored on ${HOSTNAME}"
DESC="UPS back on line power (offbattery event)."
# Unraid's notify utility:
# -e event, -s subject, -d description, -i severity (normal|warning|alert)
/usr/local/emhttp/webGui/scripts/notify \
  -e "UPS" -s "$SUBJECT" -d "$DESC" -i "normal"

(Optional) also create mainsback and online with the same contents to catch alternate restore sequences:cp /boot/config/custom/apcupsd/offbattery /boot/config/custom/apcupsd/mainsback:

cp /boot/config/custom/apcupsd/offbattery /boot/config/custom/apcupsd/mainsback

cp /boot/config/custom/apcupsd/offbattery /boot/config/custom/apcupsd/online

Make them executable:
chmod +x /boot/config/custom/apcupsd/offbattery \

/boot/config/custom/apcupsd/mainsback \

/boot/config/custom/apcupsd/online

Install them into the RAM filesystem on boot by editing /boot/config/go and adding (before the emhttp line is fine):
(Or user pluigin script at first arry start...)

# Install apcupsd event hooks at boot
mkdir -p /etc/apcupsd
install -m 755 /boot/config/custom/apcupsd/offbattery /etc/apcupsd/offbattery
install -m 755 /boot/config/custom/apcupsd/mainsback  /etc/apcupsd/mainsback
install -m 755 /boot/config/custom/apcupsd/online     /etc/apcupsd/online

Test as the above is move for unriad reboot to keep at a unraid reboot...
*For this session (without reboot), install and test now:
install -m 755 /boot/config/custom/apcupsd/offbattery /etc/apcupsd/offbattery

install -m 755 /boot/config/custom/apcupsd/mainsback /etc/apcupsd/mainsback

install -m 755 /boot/config/custom/apcupsd/online /etc/apcupsd/online

Pull power briefly → you should get your normal “on battery” notification and the new “power restored” one when mains returns.

Why this works: apcupsd’s default for offbattery is to do nothing; Unraid’s plugin notifies aggressively on “bad” events, but not always on “back to normal.” Adding a per-event script is the supported method to extend behavior.

as I'm not sure if this is a plugin or other emhttp notfication system...
? Unraid’s APC plugin ships a helper that reads a line from stdin and turns it into a GUI notification. If you prefer that style, you can do this inside your event scripts:
*Per other fourm posts... I don't have a ups to test theses things..

This could be as easey as adding this line at boot...
echo "Power is back. UPS running on mains." \

| /usr/local/emhttp/plugins/dynamix.apcupsd/apcupsd.notify

If you still don’t see events (Per ubuntu/deb man pages:https://manpages.ubuntu.com/manpages/jammy/man8/apcupsd.8.html)

• Make sure the slave is truly ONBATT → OFFBATT (short blips might produce mainsback/online only). That’s why we hook all three.

• Keep an eye on /var/log/apcupsd.events to confirm which event name your restore path generates, then ensure you have a matching script.

https://forums.unraid.net/topic/172845-apc-ups-basic-configuration/

https://www.reddit.com/r/unRAID/comments/po43ll/connect_any_ups_on_unraid/