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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..... -- The Mailing List for the Devon & Cornwall LUG Mail majordomo@xxxxxxxxxxxx with "unsubscribe list" in the message body to unsubscribe.