Name: Frequently Asked Questions
File: FAQ
Date: 13 July 1999

 Q: My UPS-specific support program (smartups, backups, etc) says 
    "Unable to open /dev/ttyxx".  I'm starting it as root and root owns
    the device, so why doesn't it work?

 A: The programs give up root _before_ they open the serial port.  So, you
    should change the permissions on the port around so that their   
    running userid can open it.  Typically this corresponds to the user
    "nobody".  If you use the --with-uid option to configure, it may be
    something else.

    Having a "ups" user that owns the serial port might not be such a bad
    idea...

 Q: upsc, multimon, and the other programs give me "access denied".  The
    serial port permissions are fine, so what gives?

 A: Those programs only talk over the network.  That denied message is
    coming over it from upsd.  It's denying them since they don't have
    permission to talk to it according to the access controls.

    The fix is to edit the upsd.conf to allow those hosts to do what they
    need.  Simple things like upsstats and upsc only need "monitor" level
    security while upsmon needs "login" to be functional.

 Q: I have a Smart-UPS connected with the grey APC cable and it won't
    work.  The Back-UPS driver works, but then I don't get to use all the
    nifty features in there.  Why doesn't the right driver work?

 A: The problem lies in your choice of cable.  APC's grey cables only do
    "dumb" signalling - very basic yes/no info about the battery and line
    status.  While that is sufficient to detect a low battery condition
    while on battery, you miss out on all the goodies that you paid for.

    The solution is to dump that cable and find one that supports APC's
    "smart" signalling.  Typically these come with the UPS and are black.
    If your smart cable has wandered off, they can be built rather easily
    with some connectors and cable - no soldering or resistors are needed.
    See this URL for a handy diagram:

    http://www.exploits.org/~rkroll/ups-0024.jpg

    That should give you a workable clone of APC's 940-0024C cable.  There
    are simpler solutions involving 3 wires that work just fine too, but
    Powerchute won't find the loopback DTR-DCD and RTS-CTS and will be
    annoyed.  If you don't ever plan to use Powerchute, 3 wires (RxD,
    TxD, GND) are sufficient.
