参考自这里 。
双头就是接第二个显示器，或者接投影仪什么的，ati 里面叫做 bigdesktop，nvidia 叫做 twinview ，intel 的不太清楚，我记得好像也有个自己的名字。
Nvidia 的官方驱动有 twinview 的支持，图形界面下面配置起来似乎也不是很难。 ATI 的官方驱动支持的是 bigdesktop ，也有图形界面，不过那个界面很恶心，经常出现问题，不过可以试着删除 /etc/ati/amdpcsdb 文件试试看。
下面是一个 bigdesktop 的 xorg.conf 文件。
Section "ServerLayout">
	Identifier     "Default Layout"
	Screen         "Default Screen" 0 0
	InputDevice    "Generic Keyboard"
	InputDevice    "Configured Mouse"
	InputDevice    "Synaptics Touchpad"
EndSection

Section "ServerFlags"
	Option	    "AIGLX" "off"
	#Option	    "AIGLX" "true"
EndSection

Section "Module"
	load "dbe"
EndSection

Section "InputDevice"
	Identifier  "Generic Keyboard"
	Driver      "kbd"
	Option	    "CoreKeyboard"
	Option	    "XkbRules" "xorg"
	Option	    "XkbModel" "pc104"
	Option	    "XkbLayout" "us"
	#Option "XkbOptions" "ctrl:nocaps"
EndSection

Section "InputDevice"
	Identifier  "Configured Mouse"
	Driver      "mouse"
	Option	    "CorePointer"
	Option	    "Device" "/dev/input/mice"
	Option	    "Protocol" "ImPS/2"
	Option	    "Emulate3Buttons" "true"
EndSection

Section "InputDevice"
	Identifier  "Synaptics Touchpad"
	Driver      "synaptics"
	Option	    "SendCoreEvents" "true"
	Option	    "Device" "/dev/psaux"
#	Option	    "Protocol" "auto-dev"
	Option	    "HorizScrollDelta" "0"
EndSection

Section "Monitor"
	Identifier   "Generic Monitor"
	HorizSync    28.0 - 51.0
	VertRefresh  43.0 - 60.0
	Option	    "DPMS"
EndSection

Section "Device"
	Option	    "DesktopSetup" "horizontal" #Enable Big Desktop
	Option	    "Mode2" "1280x1024" #Resolution for second monitor
	Option	    "VideoOverlay" "on"
	Option	    "OpenGLOverlay" "off"
	Identifier  "Generic Video Card"
	Option "XAANoOffscreenPixmaps" "true"
	Driver      "fglrx"
	Option		"DRI" "true"
EndSection

Section "Screen"
	Identifier "Default Screen"
	Device     "Generic Video Card"
	Monitor    "Generic Monitor"
	DefaultDepth     24
	SubSection "Display"
		Modes    "1024x768"
	EndSubSection
EndSection

Section "Extensions"
	Option	    "Composite" "Disable"
	#Option	    "Composite" "enable"
EndSection

Section "DRI"
	Group 0
	Mode 0666
EndSection
比较简单，只需要在 device 里面设置好就行了。 用 ati 的开源驱动，也可以双头显示。用下面的 xorg.conf 。
Section "ServerLayout">
	Identifier     "Default Layout"
	Screen         "Default Screen"
	InputDevice    "Generic Keyboard"
	InputDevice    "Configured Mouse"
	InputDevice    "Synaptics Touchpad"
EndSection

Section "ServerFlags"
	Option	    "AIGLX" "off"
	#Option	    "AIGLX" "true"
EndSection

Section "Module"
	load "dbe"
EndSection

Section "InputDevice"
	Identifier  "Generic Keyboard"
	Driver      "kbd"
	Option	    "CoreKeyboard"
	Option	    "XkbRules" "xorg"
	Option	    "XkbModel" "pc104"
	Option	    "XkbLayout" "us"
	#Option "XkbOptions" "ctrl:nocaps"
EndSection

Section "InputDevice"
	Identifier  "Configured Mouse"
	Driver      "mouse"
	Option	    "CorePointer"
	Option	    "Device" "/dev/input/mice"
	Option	    "Protocol" "ImPS/2"
	Option	    "Emulate3Buttons" "true"
EndSection

Section "InputDevice"
	Identifier  "Synaptics Touchpad"
	Driver      "synaptics"
	Option	    "SendCoreEvents" "true"
	Option	    "Device" "/dev/psaux"
#	Option	    "Protocol" "auto-dev"
	Option	    "HorizScrollDelta" "0"
EndSection

Section "Monitor"
    	Identifier      "Integrated LCD"
	 Option      "DPMS"
EndSection

Section "Monitor"
	Identifier      "External VGA"
	Option "RightOf" "Integrated LCD"
	 Option      "DPMS"
EndSection

Section "Device"
	Identifier  "Generic Video Card"
	Driver		"radeon"
#	# accelration
	Option          "AGPMode" "4"
	Option          "EnablePageFlip" "on"
	Option          "RenderAccel" "on"
	Option          "AccelMethod"   "EXA" # or XXA
	Option          "DynamicClocks" "on"
	Option		"DRI" "true"
        # Color Tiling
        Option          "ColorTiling"   "on"
    Option          "Monitor-VGA-0" "External VGA"
    Option          "Monitor-LVDS"  "Integrated LCD"
    # Option "XAANoOffscreenPixmaps" "true" # for composit
EndSection

Section "Screen"
	Identifier "Default Screen"
	Device     "Generic Video Card"
	Monitor    "Integrated LCD"
	DefaultDepth     24
	SubSection "Display"
		Modes    "1280x1024" "1024x768"
		Virtual 2304 1024
	EndSubSection
EndSection

Section "Extensions"
	Option	    "Composite" "Disable"
	#Option	    "Composite" "enable"
EndSection

Section "DRI"
	Group 0
	Mode 0666
EndSection
可以看到改动也不是很大，主要增加了两个显示器，device里面增加了这两个显示器的设置。另外 screen 里面增加了那个 virtual，这个的参数就是将来两个显示器总共的屏幕大小，我的是 1024+1280 x 1024 ，横向相加，竖向的取最大的。 ok，这样就可以了。注意这里没有用到最上面那个链接里面说的 MergedFB。似乎最新的 xorg 用 xrandr 实现了这个，所以 MergedFB 就不需要了。这有个好处，可以随时调整分辨率什么的。例如 xrandr --output VGA --off ，去掉第二个显示器。 xrandr --output VGA --right-of LVDS ，设置 bigdesktop等等。xrandr 的方法还可以参考这里。 升级到 xorg 1.5.3 以后，鼠标键盘的设置可以不在这里了，所以更加简单。

# xorg.conf (xorg X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the xorg.conf manual page.
# (Type "man xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg

Section "ServerFlags"
	#Option	    "AIGLX" "off"
	Option	    "AIGLX" "true"
EndSection

Section "Module"
	load "dri"
EndSection

Section "Monitor"
    	Identifier      "Integrated LCD"
	Option      "DPMS"
EndSection

Section "Monitor"
	Identifier      "External VGA"
	Option "RightOf" "Integrated LCD"
	Option      "DPMS"
EndSection

Section "Device"
	Identifier  "Generic Video Card"
	Driver		"radeon"
#	# accelration
	Option          "AGPMode" "8"
	Option          "EnablePageFlip" "on"
	Option          "RenderAccel" "on"
	Option          "AccelMethod"   "EXA" # or XXA
	Option          "DynamicClocks" "on"
	Option		"DRI" "true"
        # Color Tiling
        Option          "ColorTiling"   "on"
    Option          "Monitor-VGA-0" "External VGA"
    Option          "Monitor-LVDS"  "Integrated LCD"
EndSection

Section "Screen"
	Identifier "Default Screen"
	Device     "Generic Video Card"
	Monitor    "Integrated LCD"
	DefaultDepth     24
	SubSection "Display"
		Modes    "1280x1024" "1024x768"
		#Modes    "1024x768"
		Virtual 2048 1024
		Virtual 2304 1024
	EndSubSection
EndSection

Section "Extensions"
	#Option	    "Composite" "Disable"
	Option	    "Composite" "enable"
EndSection

Section "DRI"
	Group 0
	Mode 0666
EndSection