[systemd-devel] Halt then reboot

[Reindl Harald]

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