[Nut-upsuser] Setting up charge/voltage based shutdowns

[Jim Klimov]

Yeah, I have no lack of imagination about scenarios where that can be
useful - just was surprised to see no apparent "here's how you do it" sort
of man page or something,

Although technically the shutdown scenario like yours, where a NAS server
only is told to go down - or actually does so (which is substantially
different and can be implemented elsewhere) - after its consumers go down,
can be implemented outside of NUT.

For your example, one can have the NAS's `SHUTDOWNCMD` script wait until
`upsc` reports some critical remaining time/charge or until all known
protocol clients (NFS, CIFS, iSCSI, ...) have disconnected - e.g. check
whether `netstat -an | grep ESTABLISHED | grep PORTNUMS` port count went to
zero (assuming TCP connections). In this case, some same event trigger on
the NUT `primary` server (like "on battery for over 1 minute per upssched")
would tell all clients to shut down, and the NAS client would by such
script wait until the VM server goes down. Although in this 1:1 case it
would be beneficial for NAS to be the primary server (otherwise the other
primary can eventually time out and take action to go down itself and
command the UPS to power-off). Whatever the programmatic case, in the end
this is limited by how long the UPS holds up :)

Jim


On Sun, Aug 6, 2023 at 6:05 PM Arnaldo Viegas de Lima <
arnaldo at viegasdelima.com> wrote:

> I think it can be useful in a scenario like:
>
> - Large UPS, that powers 2 hosts: one is VMServer with just a small boot
> driver and the second is a NAS with all the disks for the first server.
> - UPS is connected by USB to another host (such as a small Raspberry PI),
> acting as the NUT primary.
> - Both machines served by UPS are NUT secondaries.
> - The NAS box can only shutdown one the VMware is fully stopped to avoid
> corruption at several levels.
>
> If the secondaries can define their one parameters for initiating the
> shutdown, one can decide something like:
>
> - VMware will shutdown at 20% battery left OR 15min of runtime left
> - NAS will shutdown at 10% ou 8min left
>
> Another approach is to attempt to define a way to sync secondaries… but
> that’s much more complex.
>
> Arnaldo.
>
> On Aug 6, 2023, at 12:39 PM, Jim Klimov via Nut-upsuser <
> nut-upsuser at alioth-lists.debian.net> wrote:
>
> Hello all again,
>
>   While looking at https://github.com/networkupstools/nut/issues/2014 I
> understood that I am
> not sure if currently NUT has a standard way of triggering a shutdown
> based on remaining charge
> or runtime, if a device/driver lacks a `battery.charge.low` setting but
> has readings for the values
> themselves.
>
>   Such an ability rings a bell to me, but maybe it is specific to some
> drivers and is not
> something ubiquitous - as being in the driver (and/or upsmon/upssched?)
> core codebase?
>
>   So there are a few questions stemming from this:
> * Can a user currently (on NUT 2.8.0) set up battery percentage based
> shutdowns
>   when the "low" variable is missing in the driver/device? (Suggestions in
> the ticket
>   linked above are welcome)
> * Does it make sense to add something like this (if missing) to be
> consistent on
>   un-capable devices? Or is it already there but too buried in code or
> docs?
> * Would anyone step up to make this setup easy for newcomers (even if it
> means "just"
>   finding a chapter in the docs/FAQ and making it better exposed, perhaps
> in the Wiki),
>   or more so if design and coding are due? ;)
>
> Jim
>
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