[CentOS] Power Fail Protection Update
ken
gebser at mousecar.com
Thu Aug 17 13:29:46 UTC 2017
On 08/16/2017 02:31 PM, John R Pierce wrote:
> in general, there's two power save states, 'Standby' aka 'Sleep',
> where the system state is held in RAM, but the CPU and peripherals is
> shut down and sleeping, and "Hibernate" where the ram is saved to disk
> and the system is completely powered down.
That's what I thought too, until I read "man rtcwake" and discovered
there are five standby modes. A major problem-solver in this context
would be some code added to that to allow a network connection to
communicate with a UPS or server. Given that Wake-on-LAN wouldn't be
necessary.
>
> In sleep, if the power is lost, then you'll need to reboot when the
> power comes back up. The system is using very little power, so your
> UPS should last much longer.
>
> In hibernate, you can restore when the power returns. Hibernate,
> however, takes a few more seconds to wakeup, so people often use Sleep
> as it wakes up relatively instantly.
>
> In neither of these states will the system be able to listen to ANY
> network traffic, as the processor is simply not running. The one
> exception is Wake-On-Lan aka WoL. You probably COULD configure a
> master always-on NUT box to send WoL to a list of such systems, wait a
> suitable amount of time for them to come back to their senses, then
> send them Hibernate commands via NUT.
>
> Utilizing WoL requires configuration on the target hardware to
> recognize and accept the WoL, this is typically done at the BIOS
> level, and only works if the system supports WoL in the first place.
> WoL commands can typically only be sent over the same local network
> segment, as they are layer 2 packets sent to the MAC address of the
> target.
>
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