Comment 5 for bug 812594

Warning the DisplayLink driver is dependent on reading the EDID (Extended display identification data) from the Monitor. If the monitor does not supply this, then (as in my case) everything you try will fail.

This a partial workaround works for a single display:

1. make sure the displaylink driver is installed

sudo apt-get install xserver-xorg-video-displaylink

2. Put the following into the file /usr/share/X11/xorg.conf.d/52-displaylink.conf (please have a look at the Notes below as well)

Section "Device"
Identifier "DisplayLinkDevice"
driver "displaylink"
Option "fbdev" "/dev/fb0" # or /dev/fb1 depending on the results of dmesg | grep DisplayLink
EndSection

###
Section "Monitor"
Identifier "DisplayLinkMonitor"
EndSection

Section "Screen"
Identifier "DisplayLinkScreen"
Device "DisplayLinkDevice"
Monitor "DisplayLinkMonitor"
SubSection "Display"
Depth 16
Modes "1024x768"
EndSubSection
EndSection

3. Add the following to /etc/gdm/Init/Default above the "exit 0" at the end of the file:

### set display for attached USB devices

XRANDR=`gdmwhich xrandr`
if [ "x$XRANDR" != "x" ] ; then
$XRANDR -o 0
fi

4. stop X

sudo stop gdm

5. Test out before restarting gdm:

sudo startx

At this point, you should see at least a mouse cursor that you can move around, and possibly the Unity 2D fallback interface, in case you're using Natty.

6. If the desktop apepars and is usable, you should be able to now start gdm and have a login screen:

sudo start gdm