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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