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This may well be a daft question and/or a failure to google effectively (and apologies if this would be a better fit on SuperUser or somewhere else?) but is it possible, in low-level hardware, to detect the "run" status (possibly ACPI state) of a PC?

As in - can we know whether it's powering up, shutting down, running, rebooting, hibernating, etc. from some signal on the motherboard? Perhaps a status pin on the PSU or PCI bus, sniffing I2C/SMBus messages or something else that can be hooked into at a low level.

I feel like it must be possible as a lot of peripheral stuff needs to know this too, ideally without a driver / software.

I've seen PCI cards that display the POST code / state, I'm after doing something similar for the power state.

What triggered my interest is I've got a server that takes a fair while to reboot, and it would be nice to have a little LED on the front that indicates "I'm rebooting" / "I'm running".

Sure it would be doable with a CRON job and a message out of the serial port to a microcontroller or somesuch, but that feels like more tinkering than just "getting" the status straight out of the hardware.

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    \$\begingroup\$ It is possible. But you should narrow it down to which level you want it for (and why). The "I'm rebooting/ I'm running" LED is not much related to what you are asking for. ACPI states are not "dynamic" they only switch at reset/sleep/wake/power on/off. \$\endgroup\$ Commented Feb 7, 2022 at 15:57
  • \$\begingroup\$ If there is no power, only the OS that turned the hardware off knows if the PC was asked to shut down or to hibernate. And if you simply unplugged the mains, not even the OS knows what happened. \$\endgroup\$ Commented Feb 7, 2022 at 16:02
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    \$\begingroup\$ @Justme BIOS and/or some lower level components will also "know" it at some point, but it might be too late to have this indication any useful. And it is very system-specific. \$\endgroup\$ Commented Feb 7, 2022 at 16:05
  • \$\begingroup\$ Also consider something like Hardware Monitoring, get an e-mail upon changes. Perhaps not that particular package, but you get the idea. \$\endgroup\$ Commented Feb 7, 2022 at 16:49
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    \$\begingroup\$ the "quick and dirty" test is to press the num-lock key on the keyboard and watch the indicator ... of course, it does not give you anything more than "I appear to be alive" \$\endgroup\$ Commented Feb 7, 2022 at 17:45

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