You would need a third device monitoring both for this edge case. Once the server has been told to shut down, it's going to shut down.
The third device (also on the UPS, like an Rpi or ESP) can then check for power availability through the UPS and whatever logic you want to apply, can then use wake on lan to the server to power it up once it shuts down.
I did think about that option, but the onboard NIC is connected to the ONT (fiber connection) and the SFP+ is off when the server is off so it can't receive WOL packets. By the way, thanks.
If you’ve got SFP+ onboard it sounds like you have a relatively serious server. Does it have IPMI? You could have a low power device like a Pi issue and IPMI command to power on.
Negative, it's "just" an HP Elitebook with a PCIe SFP+ board.
You have no local network access to it at all? (WOL will work across the subnet, you don't need to connect directly to it)
If genuinely not (and I'd be surprised if that is the case) add another nic of any sort (cheap) for WOL, or use something like Switchbot?
Only through SFP+ I think that the only option would be to add a second NiC. Thanks!
Can you add a second NIC? Should be able to find a Gigabit one for less than $15 or a 2.5Gbps one for $25-40.
If you use an RPI as the third device, you can use one of the GPIO pins to trigger a transistor connected in parallel with the servers power button. The pi can then (re)start the server on command.
I think that I'll go this way, thanks. I don't have transistors, but I have a 2 relay Ethernet board.
I ran a setup like this for a couple years. Super handy being able to literally press the power button remotely; especially when/if the system hangs and becomes unresponsive.
I've just bought and connected to it a JetKVM, when I saw an RJ11 port, I thought that it could have been used to "push" those buttons, but instead it's a serial port ☹️
In all seriousness though this is actually a really good question, and something I never realized, but do also face myself with my setup!
What's an average power outage duration?
I'd look at changing the shutdown command from shutdown to something like rtcwake -s 3600 to restart the server in ... 1 hour?
You will probably need to play with that command a bit, but I use it for my NAS to autostart at certain times of the day.
It depends, usually just some minutes, but during the summer it could be more. I'd like (the ideal result) to find a way that just works in any case.
Yeah, I get that... I'd be the same
So... are you shutting down after x minutes, or, NUT's signalling to shutdown when the battery is getting low, which is x minutes. (If you see my point) - if the battery still has plenty of capacity, maybe extend the runtime and that might be enough to ride through at least some outages?