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Displaylink display

Posted 12-03-2013 at 02:23 PM by drask
Updated 12-03-2013 at 03:55 PM by drask

When I first bought my current workstation (currently running Wheezy) several years ago, I got a base station that featured two DVI ports and a VGA port. "Hot Dog" I thought, "I can plug three monitors into the back of this thing, one into the side, and with the laptop screen I can have up to 5 monitors on my workstation!" Imagine my disappointment when as soon as I plugged in the second DVI monitor, the display on the laptop screen disappeared. I was really looking forward to being able to specifications open in one window, source code in a second, and my application running in a third. Oh well.

I have an old generic multi-display adapter I bought several years ago to try and fix a friend's laptop that the display adapter died on (it didn't work, since you have to load drivers do a bunch of setup work to get the external display going, which was impossible when the display card in the laptop didn't work. Being a Windows machine, ssh wasn't available to me either).

I had little hope that some third party, no-name usb device would work on linux, so I just left it sitting in the box for many years planning to get to it some day.

I finally had a chance to attempt it the other day. I plugged it into my usb port, attached it to the monitor, and got a nice green screen.

Using lsusb returned
Bus 001 Device 006: ID 17e9:0198 DisplayLink

Searching for this device online gave me some hits right away. One of the most helpful was http://documentation.red-e.eu/salor-...splaylink.html, which has instructions for Wheezy on it. The trick is to run two different x servers on the two different cards. Some people refer to this as Zaphod mode because the two heads act independently. Unfortunately, what you end up with is two different displays controlled by the same mouse, so zoom up to the upper left corner to access the menu, and both displays have the menu drop down. So it becomes sort of like a mirrored display. Not really what I had in mind.

My setup, by the way, is my :1 displaylink display at the left of my laptop, the laptop screen itself, and a second monitor to the right of my laptop display that uses an extended desktop. I'm running MATE 1.6 as my desktop environment because I couldn't take the pain of upgrading to Gnome 3 (I have work to do).

So I tried installing x2x and connecting the two displays that way. That sort of worked, in that when my mouse scrolled off the primary display, it would disappear and begin controlling the secondary display only, but when I moused back to the primary display, the cursor would be left at the right hand edge of the secondary display. That in itself was fine, but as soon as I would start moving the mouse to the left, the cursor would leave the edge and wander out into the screen and begin causing havoc again. Both desktops were responding to the mouse directly instead of the secondary display using the mouse from the primary display only.

The "AutoAddDevices false" adn "AutoEnableDevices false" lines in the X configuration file were supposed to prevent that, but HAL or something was connecting the display to the devices anyway. I was able to fix it using a dummy device you will see in the InputDevice section below (I got the suggestion from http://askubuntu.com/questions/74547...-serverlayouts)

Here's what I ended up with in my /root/displaylink.conf:
Code:
Section "ServerLayout"
    Identifier     "displaylink"
    Screen         "DisplayLinkScreen"
    Option "AutoEnableDevices" "false"
    Option "AutoAddDevices" "false"
    Option "AllowEmptyInput" "true"
EndSection

Section "Screen"
    Identifier      "DisplayLinkScreen"
    Device          "DisplayLinkDevice"
    Monitor         "DisplayLinkMonitor"
    SubSection "Display"
        Depth   24
        Modes   "800x480"
    EndSubSection
EndSection

Section "Monitor"
    Identifier      "DisplayLinkMonitor"
EndSection

Section "Device"
    Identifier      "DisplayLinkDevice"
    driver          "fbdev"
    Option          "fbdev" "/dev/fb1"
EndSection

Section "InputDevice"
    Identifier "dummy"
    Driver     "void"
    Option     "Device" "/dev/input/mice"
    Option     "CorePointer"
EndSection
Here's the command I use to start the second display:
Code:
$ sudo startx -- :1 -layout displaylink -config /root/displaylink.conf -nolisten tcp vt8 -novtswitch -sharevts
and here's the command I use to start the x2x server:
Code:
sudo x2x -to :1 -from :0 -west
Now the problems I'd still like to address are that I cannot currently copy and paste between display :0 and display :1, and display :1 is currently running as root, surely not the best idea. Attempting to log out of the secondary display (:1) to log in as myself causes the X server to terminate instead of bringing me back to the lightdm login screen. So I probably need to run lightdm instead of startx, but I'm not sure how to start lightdm on a particular display like the startx command above.
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  1. Old Comment
    Well, I finally decided that I could use it to host a KVM Virtual Machine that I was running as root anyway. So now I run the client in full screen on the extra monitor. I found that I could not make the mouse enter all areas of the screen. There was an odd rectangular block that the mouse could not enter. It appears that this is an odd x2x problem so I switched to using x11vnc and x2vnc. Still no luck sharing a clipboard between the two displays.

    # DISPLAY=:2 x11vnc -nofb -rfbauth /root/.vnc/passwd

    # x2vnc localhost:0 -west
    Posted 12-06-2013 at 03:43 PM by drask drask is offline
 

  



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