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

Roger Price roger at rogerprice.org
Thu Feb 1 22:03:06 UTC 2018

On Thu, 1 Feb 2018, nut.user.u830 at neverbox.com wrote:

> What exactly should I be asking? "Is it possible to switch off the power to 
> the outgoing outlet by sending a command to the UPS via USB, and what is that 
> command?" They provide their own Linux software, which I ignored in favour of 
> NUT, so I suspect their answer, if any, might be limited to what can be done 
> through that.

Perhaps the best way of asking the question is by comparing your Cyber Power UPS 
with one which very probably has the required function, the CP900AVR. 
http://networkupstools.org/ddl/Cyber_Power_Systems/CP900AVR.html Can their 
software send the required command to the CP900AVR? (their answer should be 
yes). Can their software do the same thing with your 800EILCD UPS?

>> 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?

To get the PC into a state in which the BIOS option "Power on when AC returns" 
works correctly, the AC must be cut off.  Merely telling the PC to halt is not 

> So clearly I am missing something here. Once nut has turned off the pc 
> completely with a sequence of unix commands,

NUT cannot turn off the PC completely.  It's computing operation stops, but 
there is still a piece of the mother board that is alive.  Sometimes one can 
even see a light.

> 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?

If the UPS finally cuts power to the PC after some delay, the BIOS is reset to a 
state in which the required BIOS option "Power on when AC returns" will work.


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