systemd questions

[Robert Nichols]

On 05/18/2011 06:42 PM, Simo Sorce wrote:
> On Wed, 2011-05-18 at 16:48 -0500, Robert Nichols wrote:
>> On 05/18/2011 04:04 PM, Lennart Poettering wrote:
>>> Host requests power down from UPS in 30s. Host then continues shut
>>> down. If the host now ends up taking more time then expected for
>>> shutting down it might still be busy at the time of the power going
>>> away. It's a race between "UPS powering off" and "system finishing
>>> shutdown". It's a bet that your system is faster than 30s when
>>> unmounting the remaining file systems, syncing the MD/DM metadata to
>>> disk, syncing ATA and so on (i.e. all the stuff the kernel does when you
>>> invoke the reboot() syscall).
>>
>> Here's another race.  Host requests power down from UPS in 30s.  Host
>> completes shutdown.  At some point during that 30s interval, commercial
>> power is restored.  Result: Host shuts down and never restarts.  Sorry
>> about that.
>>
>> The way I've always prevented that is to have the host do a reboot,
>> not a shutdown, but send an immediate shutdown command to the UPS
>> just before sending control to the BIOS for the reboot.
>
> What you should do is to configure the BIOS to always boot on power-up.
>
> This way the UPS will remove power, figure out power is returned,
> reapply power and the BIOS will reboot the machine.

Telling my UPS to turn off merely shuts down the inverter.  If it is
not currently running on the inverter (because commercial power is
available), that is effectively a no-op, and power at the UPS output
remains on.  Telling the BIOS to boot on power-up (which is how mine
is configured, BTW) does nothing since _power_never_went_away_.  All
the BIOS sees is a command to shut down, which it does.  And stays
that way.  Absent manual intervention, the only thing that would bring
the system back up would be a power failure long enough to exceed the
capacity of the essentially unloaded UPS, and that would be _quite_ a
long time.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.