multiple X servers on RHEL 6.6 (single seat) using Gnome?

MustangChuck · 04-09-2015, 10:45 AM

I am trying to set up multiple X servers under RHEL 6.6.

Here is the hardware configuration I have:
1 Computer (24 total cores, 64 GB ram)
2 NVidia 610 GT cards (2 DVI, 1 HDMI ports)
1 Monitor
2 CRT TVs connected to the HDMI ports via HDMI to SVideo converter boxes.
1 Keyboard
1 Mouse

The monitor is connected to DVI-0 on the first card. One CRT is attached to the HDMI on the first card and the second CRT is on the HDMI of the second card.

We are using the Gnome window manager. We have a lot of time and code invested in integrating with Gnome, so changing window managers isn't an option.

I want to start a separate X server for each of the three video devices, but I only want the keyboard and mouse to stay on the main monitor.

I have it working now with a single X server and 3 screens. I can keep the mouse confined to the main monitor by making sure the CRT screens do not touch the monitor screen (separating them by 50 pixels or so).

There is a possibility, though, that the HDMI->SVideo boxes may not be plugged in when X starts. This causes those screens to be unavailable when the boxes are finally connected until the next X restart. The way we have our system locked down requires a reboot to restart X, so I would like to minimize the need to reboot just to activate the CRT screens. I feel I can do this with separate X servers, one per video device. I can keep trying to start the server for each screen until it does not fail (with a sleep in the loop to reduce polling effects).

Below is my working xorg.conf.

Code:

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 0 0
    Screen      1  "Screen1" 1925 0
    Screen      2  "Screen2" 1925 500
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
    Option         "Xinerama" "0"
EndSection

Section "Files"
    FontPath        "/usr/share/fonts/default/Type1"
EndSection

Section "InputDevice"
    Identifier     "Keyboard0"
    Driver         "keyboard"
    Option         "XkbLayout" "us"
    Option         "XkbModel" "pc105"
EndSection

Section "InputDevice"
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "IMPS/2"
    Option         "ZAxisMapping" "4 5"
    Option         "Emulate3Buttons" "yes"
    Option         "Device" "/dev/input/mice"
EndSection

Section "Monitor"
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "HP LP2475w"
    HorizSync       30.0 - 94.0
    VertRefresh     48.0 - 85.0
    Option         "DPMS"
EndSection

Section "Monitor"
    Identifier     "Monitor1"
    VendorName     "Unknown"
    ModelName      "SYK HDMI TO AV"
    HorizSync       31.0 - 45.0
    VertRefresh     60.0
#   HorizSync       28.0 - 55.0
#   VertRefresh     43.0 - 72.0
    Option         "DPMS"
EndSection

Section "Monitor"
    Identifier     "Monitor2"
    VendorName     "Unknown"
    ModelName      "SYK HDMI TO AV"
    HorizSync       31.0 - 45.0
    VertRefresh     60.0
#   HorizSync       28.0 - 55.0
#   VertRefresh     43.0 - 72.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GT 610"
    BusID          "PCI:129:0:0"
    Screen          0
EndSection

Section "Device"
    Identifier     "Device1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GT 610"
    BusID          "PCI:129:0:0"
    Screen          1
EndSection

Section "Device"
    Identifier     "Device2"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GT 610"
    BusID          "PCI:130:0:0"
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "nvidiaXineramaInfoOrder" "DFP-0"
    Option         "metamodes" "DFP-0: 1920x1080 +0+0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Section "Screen"
    Identifier     "Screen1"
    Device         "Device1"
    Monitor        "Monitor1"
    DefaultDepth    16
    Option         "Stereo" "0"
    Option         "metamodes" "DFP-1: 720x480 +0+0"
    SubSection     "Display"
        Depth       16
    EndSubSection
EndSection

Section "Screen"
    Identifier     "Screen2"
    Device         "Device2"
    Monitor        "Monitor2"
    DefaultDepth    16
    Option         "Stereo" "0"
    Option         "metamodes" "DFP-1: 720x480 +0+0"
    SubSection     "Display"
        Depth       16
    EndSubSection
EndSection

I have tried many different things to get my requirement to work. I have tried to separate out the screens into different layouts within the same conf file. I have tried three separate conf files. One of the issues appears to be that each X server wants control of the keyboard and mouse. How do I tell them it is ok to start without input devices?

I have been able to start separate X servers on different virtual terminals (using the vtX option with startx). I have managed to start a server on the second CRT, but it stole the keyboard and mouse and shutdown the first video card (requiring a reboot to bring it back up).

Any help and advice would be greatly appreciated!

Thanks,
Chuck Martin

bimboleum · 04-09-2015, 12:00 PM

Hi,
Have you tried xrandr???

I use this when I plug the TV into my laptop .... below is a wee ksh (called tv) that I use:-

tv on ... when the tv is plugged in
tv off ... to turn it off

Code:

#!/bin/ksh

if [[ $# = 0 ]]
then
  /usr/bin/xrandr
  exit
fi
action=""
output=""
if [[ "$1" = "off" ]]
then
  action="--off"
fi

if [[ "$1" = "on" ]]
then
  action="--auto"
fi

if [[ "x$action" != "x" ]]
then
  output="--output DP-1"
  /usr/bin/xrandr $output $action
fi

/usr/bin/xrandr

cheers
pete

pete hilton
saruman@ruvolo-hilton.org

MustangChuck · 04-09-2015, 12:24 PM

Thank you, Pete! I'll give this a try and see if it works!

Chuck Martin

MustangChuck · 04-09-2015, 01:45 PM

Well, xrandr doesn't seem to be the answer. If the box is not plugged in when X starts, a screen for it is not created. If the box is later plugged in and xrandr is used to detect it, xrandr adjusts the size of the only screen to be large enough to hold both video devices. If I resize screen 0 back to the correct (for the monitor) size, it messes up the text. (It appears to be doing a down scaling on the screen dimensions.) It also places the new CRT directly beside the monitor. If I move the HDMI-0 over a few pixels to separate them, the user can still scroll the mouse into the CRT area.

But playing with this gave me an idea.

Is there a way to restart X without fully restarting it? I have seen programs (nvidia-settings and Display Preferences are good examples) that will resize the screen on the fly, keeping all of the X applications intact. There is a slight blink, but I can live with that. If I can get it to re-read xorg.conf and create the screens that are now available, that would work.

Chuck