Am 17.09.2016 um 13:23 schrieb Dark Penguin:
Long version:
Many UPS-es do not support cutting power at all, or ignore the command
to cut the power in certain situations. There was a workaround for that:
instead of powering the machines off, they had to halt, then wait a
reasonable amount of time (during which the UPS should turn off), and
then reboot - in case power came back and the UPS did not power-cycle
its load.

This is fragile as you have no idea whether power returned or not and
risk hard power off in the middle of next boot.

Usually, you set it to wait for enough time for the UPS to drain; either
it will drain and power off, or the power is back by then. The risk of
power "having been back, but cut off again just now" is miniscule
compared to the risk of having to manually power the machines on (and by
the way, UPS-es do NOT like to be powered on with no load)

that risk is *not* miniscule and i have even seen UPS after power back too empty to stand the load peak of machines without power management in their early state after power on them and cutt off within seconds while machines booting - not 100% sure what happened but i was in the room and line back for sure uninterrupted

what all that crap would really need is that a UPS software completly *shutdown* the machines (in the best case staged - unimportant stuff first to keep critical longer online and maybe survive before batteries are empty) and the UPS after line is back *long enough and not just now* sends a wakeup-on-lan to them, all that routers/switches stuff is coming back after a hard power off when power returns

the "UPS-es do NOT like to be powered on with no load" don't happen in the real world since you hav enot only by managament software powered down machines but a ton of networking stuff
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