[Nut-upsuser] testing shutdown: pc not restarting; and "ups unavailable" messages

Lee Damon nomad at ee.washington.edu
Thu Feb 1 16:33:46 UTC 2018

I have seen cases where 'cleanly shut down' hosts don't come back up, even
when the BIOS is set to "last state" or "always on".

I had to change my NUT shutdown script to call halt instead of halt -p so
the host was halted but still powered on. Then when power was cut and
restored the host came back up.


On Thu, Feb 1, 2018 at 7:58 AM, <nut.user.u830 at neverbox.com> wrote:

> > Out of curiosity: if the PC has already been switched off from software
> by the shutdown script, how would it know that the power has been cut while
> it was off? Are you telling me that the power supply of the PC keeps
> checking its incoming AC supply even while off, and that with the BIOS
> setting I selected it will wake up the PC even after a power cut DURING
> WHICH the PC was already off? I never imagined that... I guess it's
> something I could try independently, once I find a quiet time with no disk
> activity when it's OK to shut down that computer.
> It actually occurred to me that I could try this with another (any other)
> computer here at work, so I did. I set the BIOS to "always on" after power
> cut. I booted ubuntu. I did "sudo shutdown -h now" from the console. The pc
> switched off as expected. Then I removed the power cable and then plugged
> it back in. According to the theory above, this should have caused the
> computer to detect a power loss and turn itself back on. Instead it
> remained off (as I expected).
> So clearly I am missing something here. Once nut has turned off the pc
> completely with a sequence of unix commands, how can anything the ups might
> do to to the power line, including cutting the power and restoring, cause
> the pc to come back on?
> I would have expected the pc only to come back on if either
> a) power had been cut off (not from software) while the computer was still
> running, AND the bios setting said "always on"
> or
> b) the UPS simulated some kind of "power button keypress" or the like
> through the USB link.
> If my understanding is flawed then please enlighten me. What does actually
> happen when things work?
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