Thank you Konstantin and Mark,

I am using the nVidia driver not the one in the repo although I have 
tried both.

The monitors all run at 1920x1080 with hdmi input but they use the hdmi, 
dport and dvi outputs of the card.  Just because of the cables I had on 
hand.

I think the next thing to try is to replace the DVI->HDMI cable with a 
DPORT->HDMI cable (this card has 4 DPORT, 1 HDMI, 1 DVI).

I would think both of your experience suggest no software issues.

Thanks again!

Joe


On 04/13/2015 12:48 PM, Konstantin Olchanski wrote:
> On Wed, Apr 08, 2015 at 09:21:17PM -0700, Joseph Areeda wrote:
>> So I bought a new GTX960 which purports to support 4 monitors so I
>> hooked up a third one but SL6 still only sees 2.
>>
>
> In my experience, requirements for multi-monitor support are poorly
> documented for most video cards.
>
> For example, the ASUS Z87/Z97 mobo has 3 video outputs connected
> to the on-CPU video. It is supposed to support 3 monitors,
> but to actually make it work, I had to get down all the way to
> data sheet for the on-CPU video controller where they explain
> how due to a missing clock (3 clock sources needed, only 2 available),
> all 3 monitors have to run at identical resolution and that
> only some combinations of DVI and DisplayPort connections
> are supported (3 DVI is okey, 2 DVI + 1 DP not okey, or some such
> arcane rules).
>
> In practice, it means that all 3 monitors have to be identical,
> all connected with DVI-to-{HDMI,DP,miniDP} cables (passive adapters).
>
> Maybe you have mismatched monitors and your particular combination
> cannot be done by the hardware (and good luck finding the nvidia
> documentation for this - intel seems to do better with public docs).
>
> Again, in practice, if you have nvidia video card, install latest kmod-nvidia (from elrepo
> or otherwise), run "nvidia-settings" and your monitors do not show up,
> you are toast.
>
> (Some vendors are upfront with these problems - ASUS AMD socket AM1 mobo
> plainly states - 3 video outputs - VGA, DVI, HDMI - but only 2 monitors
> can be connected).
>
>
> K.O.
>
>
>> I still have some debugery to do but I wanted to ask if anyone has
>> gotten more than 2 monitors to work on one video card?
>>
>> That will help direct my efforts.
>>
>> For the record the output of nvidia-smi looks like:
>>
>>     +------------------------------------------------------+
>>     | NVIDIA-SMI 346.59     Driver Version: 346.59 |
>>     |-------------------------------+----------------------+----------------------+
>>     | GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile
>>     Uncorr. ECC |
>>     | Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util
>> Compute M. |
>>     |===============================+======================+======================|
>>     |   0  GeForce GTX 960     Off  | 0000:01:00.0     N/A
>>     |                  N/A |
>>     |  0%   46C    P8    N/A /  N/A |    370MiB /  2047MiB | N/A
>> Default |
>>     +-------------------------------+----------------------+----------------------+
>>
>>     +-----------------------------------------------------------------------------+
>>     | Processes: GPU Memory |
>>     |  GPU       PID  Type  Process name
>> Usage      |
>>     |=============================================================================|
>>     |    0            C+G   Not
>>     Supported                                         |
>>     +-----------------------------------------------------------------------------+
>>
>>
>> thanks,
>> Joe
>>