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Como configurar 3 monitores en Ubuntu

Esta es una configuración que funciona para tener 3 monitores en ubuntu

Primero comprobamos que tenemos dos tarjetas de vídeo, una al menos ha de tener dos salidas de vídeo:

root@u006020:~# lspci|grep -i vga
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: nVidia Corporation GF108 [Quadro 600] (rev a1)

Por defecto me detectaba la tarjeta Nvidia en este BUS:
BusID "PCI:1:0:0"
Por lo que pone en la salida del lspci, el BusID de la intel será "PCI:0:2:0"

De esta forma, modificamos el fichero /etc/X11/xorg.conf y lo dejamos así (seguramente habrá muchas mejoras posibles, y dependerá de las tarjetas que tengas puestas, pero a mí me ha funcionado así):

# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings: version 270.29 (buildd@allspice) Fri Feb 25 14:42:07 UTC 2011

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

Section "Files"
EndSection

Section "InputDevice"
# generated from default
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"
# generated from default
Identifier "Keyboard0"
Driver "kbd"
EndSection

Section "Monitor"
# HorizSync source: edid, VertRefresh source: edid
Identifier "Monitor0"
VendorName "Unknown"
ModelName "DELL 2007FP"
HorizSync 30.0 - 83.0
VertRefresh 56.0 - 76.0
Option "DPMS"
EndSection

Section "Monitor"
# HorizSync source: edid, VertRefresh source: edid
Identifier "Monitor1"
VendorName "Unknown"
ModelName "DELL 2007FP"
HorizSync 30.0 - 83.0
VertRefresh 56.0 - 76.0
Option "DPMS"
EndSection

Section "Monitor"
# HorizSync source: edid, VertRefresh source: edid
Identifier "Monitor2"
VendorName "Unknown"
ModelName "DELL unknown KK"
HorizSync 30.0 - 70.0
VertRefresh 56.0 - 75.0
Option "DPMS"
EndSection

Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "Quadro 600"
BusID "PCI:1:0:0"
Screen 0
EndSection

Section "Device"
Identifier "Device1"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "Quadro 600"
BusID "PCI:1:0:0"
Screen 1
EndSection

Section "Device"
Identifier "Device2"
Driver "intel"
VendorName "intel"
BoardName "intel"
BusID "PCI:0:2:0"
Screen 0
EndSection

Section "Screen"
Identifier "Screen0"
Device "Device0"
Monitor "Monitor0"
DefaultDepth 24
Option "TwinView" "0"
Option "metamodes" "DFP-0: nvidia-auto-select +0+0"
SubSection "Display"
Depth 24
EndSubSection
EndSection

Section "Screen"
Identifier "Screen1"
Device "Device1"
Monitor "Monitor1"
DefaultDepth 24
Option "TwinView" "0"
Option "metamodes" "DFP-1: nvidia-auto-select +0+0"
SubSection "Display"
Depth 24
EndSubSection
EndSection

Section "Screen"
Identifier "Screen2"
Device "Device2"
Monitor "Monitor2"
DefaultDepth 24
Option "TwinView" "0"
Option "metamodes" "DFP-1: nvidia-auto-select +0+0"
SubSection "Display"
Depth 24
EndSubSection
EndSection