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Re: [LUG] Power Surges & Gnucash



andy@xxxxxxxxxxxxxxxxxxxxxx wrote:

Probably a dumb question (I've never used a UPS before), but how will my boxes 
know that the power has gone, and to log off and shut down?


No not a dumb question but a very smart question!

Typically it plugs into the serial (or mouse port on some PC
servers), and signals when power is lost or returned.

Some even will not power up a server after power is restored
till it has enough charge to allow another controlled shutdown.
The one in Lincoln (not a Linux system) even takes orders on
when to power down and up, which lets me schedule down time on
the server when they are doing electrical work at the weekends.

Thus Bill's mention of Linux software for a UPS, it is usually a
daemon listening to a serial port for power outage messages,
which then schedules a controlled shutdown. 

A nice feature is if a UPS waits for a set period after a power
cut, and cancels the shutdown if the power is restored, as many
places get short power glitches, and the servers I look after
often have a 15 minute power down / power up cycle!

So you see UPS's are often a lot smarter than people give them
credit for, although the secret is to understand it all BEFORE
you rely on it!

It is not uncommon to see UPS's used without software to report
a power outage, for some (many?) purposes this is perfectly
adequate, especially if the UPS can last out half an hour plus,
which is the length of most power cuts.

Oh for the days of working in a building with a mains UPS and
redundant diesel generators, where you can plug into any socket
and expect 10 years mean time between unplanned power
outages.....

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