[SOLVED] LM12 can't detect monitor through KVM switch

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[SOLVED] LM12 can't detect monitor through KVM switch

Post by aer0usa » Tue Jan 03, 2012 2:34 pm

Got a nice new computer for Christmas, so I decided to install LM12 on it. So far, so good! Previously, I had been using Ubuntu 8.04 on an old IBM desktop. I'm more than a Linux newbie, but far short of a guru.

When I was setting up the computer, I had the monitor connected directly, and the computer detected the monitor and set its resolution correctly.

However, I put a Keyboard/Video/Mouse (KVM) switch between the new computer and the monitor so I can share the monitor between my new computer and my work computer. With the KVM switch in place, the computer doesn't detect the monitor, so it sets the resolution to 1024 x 768.

I used this same setup on my old computer, and I was able to import the .inf file for my monitor so the computer would know what resolution settings to use.

So, is there a way to import the .inf? Or, failing that, I went looking for xorg.conf, but couldn't find it! Can I just create /etc/X11/xorg.conf with the appropriate monitor settings in it?
Last edited by aer0usa on Thu Jan 05, 2012 12:22 pm, edited 1 time in total.

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Re: LM12 can't detect monitor through KVM switch

Post by aer0usa » Thu Jan 05, 2012 12:13 pm

Hi! I see some folks have viewed this, but no answers, so I guess others are looking for the answer to this as well. I found an answer (there are probably others), so I'll share.

I did some research and found the following:
  • LM12 doesn't make an xorg.conf, but if you put one in /etc/X11 it'll use it.
    cvt is a command that will generate a modeline for you, suitable for inclusion in xorg.conf
    xrandr will show you the current video config.
    I looked at man xorg.conf for clues about how to build the xorg.conf file.
So, I went to Terminal and did the following:
  • I ran xrandr and saw that the monitor's name is VGA1
    I ran cvt -v 1280 1024 in Terminal and got the new modeline. Experiments with xrandr showed me that the name of the modeline that cvt generates didn't seem to work, so I came up with my own name. I think xrandr didn't like the "_" that cvt put before the refresh rate in the name.
    Then I built the following xorg.conf file and saved it in /etc/X11

Code: Select all

Section "Monitor"
    Identifier "VGA1"
    ModeLine "1280x1024"  109.00  1280 1368 1496 1712  1024 1027 1034 1063 -hsync +vsync
I logged out, then back in. I went to System Settings and Displays, and the screen resolution I wanted is now listed in the Resolution menu. That's it!

If you're going to try this, I'd suggest running xrandr and cvt for yourself to find out what your system suggests for its monitor name and modeline.

EDIT: Also, use man xrandr and man cvt for more information.

Hope this helps someone!

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Re: [SOLVED] LM12 can't detect monitor through KVM switch

Post by xamigan » Thu Feb 16, 2012 12:18 am

Thanks for the tip aer0usa, you helped me

I just bought a Samsung E2420 23.6 inch LCD Monitor. I'm running Linux Mint 11. Mint won't detect the monitor, says”unknown”. Best res I can get is 1152x864 but that won't hold and pops back to 1024x868 when I reboot. I have an Athlon 2400 running Mint 11 lxde. hooked up with a KVM, both systems running VGA . The 2400 gives me a resolution of 1920x1080.

I was about to post a question when I found your post.
I bypassed the KVM and all was good, detected the Samsung and I could change to 1920x1080. I used the Nvidia X server setting manager and “Saved to X config file”
When I reconnected the KVM and rebooted it was still at 1024x868 but I could now change to 1920x1080 through the Nvidia x server manager.

Just wish it would stay at 1920x1080 when I reboot.

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