[lug] apm/UPS

David Morris david at morris-clan.net
Fri Aug 2 12:07:05 MDT 2002

On Fri, Aug 02, 2002 at 11:53:07AM -0600, D. Stimits wrote:
> I'm looking at an UPS for the Linux bridge and cable modem. Obviously, 
> cable modems do not have any "auto power down" feature (nor would the 
> modem need it, but not totally depleting a battery's power is good for 
> the life of the battery). In the case of the bridge machine, it is 
> older, and does not support having the o/s power itself down, it has a 
> good old-fashioned switch. However, in the case of the Linux machine, I 
> can probably rewrite some of the UPS scripts for apmd, so that it starts 
> out by changing the ext3 journal speed from 5 second intervals to 1 
> second intervals; and then if time goes far enough, either remount the 
> drives read-only, except for /var/, or else run init 0 to halt when 
> things get really close.

I cannot speak for the batter depleation question, but just
as an FYI on the above, a system that does not power-off
upon shutdown is actually preferable if you are looking to
maximize uptime.  So long as you have a UPS that talks to
the OS (and that is a function of the OS and the UPS, not
the system), you can get Linux to shut itself down.  Then,
after the system has shut itself down, the power is still
on.  This way, when power is restored, your system will
power itself back on automatically, and it will be up and
running without your intervention.

NOTE:  As I said at the top, the below is far beyond what I
can say with any certainty.  Don't flame me if I am don't
have a single fact straight, this is simply how I understand
the situation....an understanding which could be completely

Yes, this will depleat the battery....a UPS is, I believe,
designed to account for this, and it does not significantly
affect the battery.  Now, I could easily be assuming far too
much intelligence on the part of UPS designers, but a
properly designed recharchable battery / battery recharger
system does not care if the batter gets fully depleted or
not (in fact, it is a *good* thing to fully depleat the
batter periodically to both verify runtime and protect
battery performance....or at least, that is the way I
understand it.).


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