xrandr: how to tell it that a screen size is supported?

Dotan Cohen dotancohen at gmail.com
Mon Jun 7 19:32:12 UTC 2010

On 7 June 2010 16:33, J <dreadpiratejeff at gmail.com> wrote:
> On Mon, Jun 7, 2010 at 09:04, Dotan Cohen <dotancohen at gmail.com> wrote:
>> A Kubuntu 9.10 machine runs at 1680x1050 resolution with no problems
>> if the KVM is switched to that machine when it is booted. If the KVM
>> is switched to another machine, then this machine loads at a very low
>> resolution and I cannot configure the proper resolution with xrandr:
>> How can I either:
>> 1) Configure the machine to always use 1680x1050 no matter how it is booted?
>> -or-
>> 2) Tell xrandr that 1680x1050 is fine?
> A: this is because of your KVM.  When you boot the machine without the
> KVM pointing to the machine, X has no monitor to probe, so it defaults
> to a lower safe setting.  When your KVM IS pointed to the system in
> question, X get's supported modes from the monitor via a DDC probe and
> thus, you get full resolution.

I know that! Now, how can I add 1680x1050 as a safe setting?

> The obvious answer to this one is to only boot when the monitor is
> connected to the system (e.g. when you have that system switched on
> the KVM).

If that were always possible, I would not have posted here!

> However, this is from the man page for xrandr (you should read the man
> page, there's a bit of explanation for each xrandr option in there):

Thanks. Actually, I had read the fine manual sometime in the past few
months, I should have gone over it again. Sorry!

>  Forces to use a 1024x768 mode on an output called VGA:
>              xrandr --newmode "1024x768" 63.50  1024 1072 1176 1328
> 768 771 775 798 -hsync +vsync
>              xrandr --addmode VGA 1024x768
>              xrandr --output VGA --mode 1024x768
> Of course, you'll have to figure out all the mode info for yourself,
> because that's all dependent on your system and monitor...
> So, the second answer is: 'man xrandr'

Lets see, if I get this from -q --verbose:

  1680x1050 (0x4d)  146.2MHz -HSync +VSync *current +preferred
        h: width  1680 start 1784 end 1960 total 2240 skew    0 clock
        v: height 1050 start 1053 end 1059 total 1089           clock

Then would you agree that this would be the preferred config:

$ sudo xrandr --newmode "1680x1050" 60.0 1680 1784 1960 2240 1050 1053
1059 1089 -hsync +vsync

Dotan Cohen


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