freebsd-questions Digest, Vol 196, Issue 38

Scott Bennett bennett at
Sat Nov 10 14:11:54 PST 2007

     On Fri, 09 Nov 2007 16:33:34 +0000 Christopher Key <cjk32 at>

>Apolgies for the slightly OT post, but I'm hoping that some of the 
>ammased expertise might be able to suggest a solution.
>I've a FreeBSD fileserver, a solid state router (Linksys box running 
>OpenWRT) and a couple of gigabit switches that I'd like to move onto a 
>UPS (I'm primarily looking at the APC Smart-UPS line).
>The requirements for the FreeBSD system are pretty simple, it's not 
>likely to be of any use if the power's out, so after a few minutes to 
>allow any files open over the network to be saved, it should perform an 
>orderly shutdown and remain off until the power returns.  However, the 
>router is a little different.  It maintains some state information in 
>RAM (dhcp leases etc) that I'd prefer not to lose during a short power 
>outage, and it would also be useful to retain internet access, so 
>ideally I'd like the router and switches to stay up for as long as the 
>battery lasts in the UPS.
>Space and budget are limited, so ideally I'd like to achieve all this 
>with a single UPS, which is where the problems arise.  As I understant 
>it, when the UPS wants to wake the attached machines up, it power cycles 
>its output.  This however will reset the router, which was what I was 
>hoping to avoid.
>I've thought around the problem for some time, but not come up with any 
>convincing solutions:
>1) Use some sort of WOL command from the router to the FreeBSD system 
>rather than having the UPS power cycle its output.  How does the router 
>know the power's returned?  Can the UPS be set not to power cycle its 
>power output when the power returns?
>2) Use a second cheap UPS to 'protect' the router whilst the primary UPS 
>cycles its power output.  This seems rather crude, and would presumably 
>reduce the battery life of the primary UPS due the losses in the second UPS.

     By the above, I understand you to be proposing to plug the "secondary"
into the "primary", rather than powering the two UPSes separately.  Why
would you do the former rather than the latter?
>3) Have the UPS wake the PC via some other means.  USB would seem to 
>ideal choice, but the motherboard won't do a wake on USB from S5, and 
>I'm can't find a UPS with an ethernet interface.
>4) KISS.  Buy two smaller, cheapers UPS units.
     I think that 4) may be the answer, though with this modification:  buy
the heavy duty UPS based on the server's needs.  The router draws almost no
current, probably far less than the UPS itself does when the line power has
failed.  Buy a minimal capacity UPS for the router, switches, etc.  It will
probably be able to keep them running for many hours, likely even days,
during a power failure.  Plug it into its own line current socket, not into
the other UPS.

                                  Scott Bennett, Comm. ASMELG, CFIAG
* Internet:       bennett at                              *
* "A well regulated and disciplined militia, is at all times a good  *
* objection to the introduction of that bane of all free governments *
* -- a standing army."                                               *
*    -- Gov. John Hancock, New York Journal, 28 January 1790         *

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