HowTo: Dual Monitors (Xinerama/TwinView/MergedFB)

[Ziox]

Features of this HowTo:

The following howto addresses and solves the problems of Linux's,especially (X)(K)Ubuntu's,

support (or lack of) for dual monitors.The howto is assorted into four driver-specific categorizes.

• Xinerama (open source and binary driver)
• nVidia-only TwinView (binary driver)
• ATI, Matrox MergedFB (open source driver)
• ATI-only BigDesktop (binary driver)

All four options perform the same function. However, because of the variations of graphics cards in the market, and the different supports provided by the card makers, procedures that enable dual monitor on one computer/card do not work for other computer/card. Each of the four methods has pros and cons of its own. They are listed below.

Feature Differences:

• “Xinerama is an extension to the X Window System which allows applications and window managers to use the two, or more, physical displays as one large virtual display.” --Wikipedia. In other words, it allows X, as we'll call the X Window System, to use more than one monitor for display.
  • Pros: Since Xinerama is an extension of X, most graphics cards, including Intel Integrated Cards and Matrox Cards, work well with it.
  • Cons: There are several known problems with Xinerama. It requires that the physical screens to have the same bit depth. Also in most implementations, OpenGL (3D) direct-rendering only works on one of the screns. Windows that should show 3D graphics on other screens tend to just appear black. However, the Solaris SPARC OpenGL implementation allows direct rendering to all screens in Xinerama mode.
  
  
• “TwinView is a mode of operation where two display devices (digital flat panels, CRTs, and TVs) can display the contents of a single X screen in any arbitrary configuration.” -TwinView Appendix G.
  • Pros: Twinview merges two screens into one, “tricking” X to think that there is only one screen. This always provide better OpenGL direct-rendering.
  • Cons: TwinView requires the binary nVidia Driver, which means only nVidia cards are supported.
  
  
• “Merged Framebuffer mode allows you to use 3D acceleration on both heads of a dualheaded Radeon card.” --MergedFB Wiki
  • Pros: Similar to TwinView, MergedFB merges two screens into one, therefore supporting 3D direct-rendering on both screens.
  • Cons: MergedFB only works with the open sources drivers (mga, ati, , which lack direct-rendering support for many Radeon models. MergedFB also limits 3D contexts to 2048x2048.
  
  
• BigDesktop allows for dual screen control by merging the 2 screens into one single screen, allowing direct rendering on both monitors.

Common Step for Each HowTo:

These steps are essential for the HowTos to work, please follow them precisely.

All commands give should be executed within terminal.

BackUp File:

Perhaps the most important step of them all. Since we are going to be editing a system file that have the potential, in the instance of an accident, to disable your Xserver (aka No GUI/Mouse Function), it is EXTREMELY important to execute this command:

sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf_backup

The function of this command is to make a backup copy of your Xorg.conf file (which we'll be editing soon).

If for any reason, after the guide, you are unable to activate Xserver, execute the following command:

sudo cp /etc/X11/xorg.conf_backup /etc/X11/xorg.conf

Now, we always want to have a clean slate, because it makes the work much easier, and there is less of a chance that some other arbitrary item will mess this whole thing up.

So, unplug all your monitors except for one, then execute the following command:

sudo dpkg-reconfigure xserver-xorg

Just hit enter for the most options, though if you have the binary drivers installed, you might want to select that. This code will generate a new, clean, standard xorg.conf file for us to work on.

Now, choose the method with which you wish to achieve Dual-Monitor capability:

• Xinerama: http://www.ubuntuforums.org/showthread.php?p=1773624

• TwinView: http://www.ubuntuforums.org/showthread.php?p=1773584

• MergedFB: http://www.ubuntuforums.org/showthread.php?p=1773710
  

• BigDesktop: http://www.ubuntuforums.org/showthread.php?p=1773544

If you have any questions, comments, or problems, please post on the corresponding thread.

Hopefully these guides have been helpful.

Tips:These are awesome tips I borrowed from the Paralipsis Blog. So if you have any questions and such, take a look at this section first.

• Do not do your config inside of X11. Before you login, press Ctrl-Alt-F1 and login to the text console. There, shutdown the graphical login like this: sudo /etc/init.d/gdm stop. This way you can edit the xorg.conf and test your setup one piece at a time. The command startx launches X11 as though you had logged in and drops you back to the text console when you 'logout' of the GUI.

• Make a backup of your starting xorg.conf file. Sometimes you just need to start over.

• Baby steps. Make small changes at each step along the way and you'll be guaranteed to have less to undo.

• If something stops working that worked before, go back a step and try something else. Keep notes to guide you.

• Put a post-it note on each monitor with the name you discover it has. It makes life a lot easier to deal with when sorting out what's where.

• Get one display at a time working from start to finish.

• If your system appears locked up, first try to use Ctrl-Alt-Backspace to kill X11. Or, you can use Ctrl-Alt-F1, F2, F3, etc to try to access the other text login prompts.

• If you have configured SSH access to your computer, you can do all your configuration and testing from a laptop.

• If you are really, really screwed, first try pressing Ctrl-Alt-Del and wait 30 seconds to see if init manages to shut-down and reboot your computer. This is the safest way of doing things as it cleanly unmounts the filesystems. However, if you have broken your X11 config, you will have to use the “safe mode” startup to continue your work. This simply bypasses a few steps in the startup, most notably starting the graphical login. From the text console you can copy your original xorg.conf back into place and reboot.

• If even Ctrl-Alt-Del doesn't work, use the SAK. Hold down Alt-PrintScreen (this is the SysRq key combo), and while holding down those keys, press the letters 'S' to sync the disks, then 'U' to unmount the filesystems and 'B' to reboot the computer. Always try that before going for the power button. It's a bit awkward to do all that while holding Alt-PrintScreen, but it's not something you'll do often.

• Relax, your computer isn't likely breaking, you're just dealing with sophisticated hardware drivers and sometimes things go into bad states where the computer doesn't know the video card is in the wrong mode.

• Finally, Google is your friend. If you get odd error messages in the log file, try pasting them into google. Usually someone else has encountered the very problem you are and often has written about it.

• Good luck!

[harty83]

Hello,

I tried this using the nv driver but xorg dies with

Fatal server error:
Requested Entity already in use!

Here's my xorg file:

# /etc/X11/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 /etc/X11/xorg.conf manual page.
# (Type "man /etc/X11/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 "Files"
	FontPath	"/usr/share/X11/fonts/misc"
	FontPath	"/usr/share/X11/fonts/cyrillic"
	FontPath	"/usr/share/X11/fonts/100dpi/:unscaled"
	FontPath	"/usr/share/X11/fonts/75dpi/:unscaled"
	FontPath	"/usr/share/X11/fonts/Type1"
	FontPath	"/usr/share/X11/fonts/100dpi"
	FontPath	"/usr/share/X11/fonts/75dpi"
	# path to defoma fonts
	FontPath	"/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
	Load	"bitmap"
	Load	"ddc"
	Load	"dri"
	Load	"extmod"
	Load	"freetype"
	Load	"glx"
	Load	"int10"
	Load	"type1"
	Load	"vbe"
EndSection

Section "InputDevice"
	Identifier	"Generic Keyboard"
	Driver		"kbd"
	Option		"CoreKeyboard"
	Option		"XkbRules"	"xorg"
	Option		"XkbModel"	"inspiron"
	Option		"XkbLayout"	"us"
EndSection

Section "InputDevice"
	Identifier	"Configured Mouse"
	Driver		"mouse"
	Option		"CorePointer"
	Option		"Device"		"/dev/input/mice"
	Option		"Protocol"		"ExplorerPS/2"
	Option		"ZAxisMapping"		"4 5"
	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 "InputDevice"
  Driver        "wacom"
  Identifier    "stylus"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "stylus"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "eraser"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "eraser"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "cursor"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "cursor"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "Device"
	Identifier	"Laptop"
	Driver		"nv"
	BusID		"PCI:1:0:0"
	Screen		0
EndSection

Section "Device"
	Identifier	"External"
	Driver		"nv"
	BusID		"PCI:1:0:0"
	Screen 		1
EndSection

Section "Monitor"
	Identifier	"Main Monitor"
	Option		"DPMS"
	HorizSync	28-51
	VertRefresh	43-60
EndSection

Section "Monitor"
	Identifier	"Second Monitor"
	Option		"DPMS"
	HorizSync	28-51
	VertRefresh	43-60
EndSection


Section "Screen"
	Identifier	"Main Screen"
	Device		"Laptop"
	Monitor		"Main Monitor"
	DefaultDepth	24
	SubSection "Display"
		Depth		1
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		4
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		8
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		15
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		16
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		24
		Modes		"1024x768"
	EndSubSection
EndSection

Section "Screen"
	Identifier	"Second Screen"
	Device		"External"
	Monitor		"Second Monitor"
	DefaultDepth	24
	SubSection "Display"
		Depth		1
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		4
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		8
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		15
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		16
		Modes		"1024x768"
	EndSubSection
	SubSection "Display"
		Depth		24
		Modes		"1024x768"
	EndSubSection
EndSection

Section "ServerLayout"
	Identifier	"Default Layout"
	Screen 		"Main Screen"
	Screen 		"Second Screen" LeftOf "Main Screen"
	InputDevice	"Generic Keyboard"
	InputDevice	"Configured Mouse"
	InputDevice     "stylus" "SendCoreEvents"
	InputDevice     "cursor" "SendCoreEvents"
	InputDevice     "eraser" "SendCoreEvents"
	InputDevice	"Synaptics Touchpad"
EndSection

Section "ServerFlags"
	Option "Xinerama" "true"
EndSection

Section "DRI"
	Mode	0666
EndSection

[harty83]

BTW, I've read through forums that you must use the nvidia driver in order to get this to work. Has anyone gotten it to work with the opensource nv driver? I have a lot of problems when using the nvidia driver and so would really like to stick with nv but have twinview work.

Thanks,
Alan

[Ziox]

if you are looking for twinview then this isn't the right thread. I'll see if i can find another thread for twinview. Also TwinView is only supported by the proprietary drivers. Unfortunately...

[harty83]

My card does support multiple outputs.

Maybe I'm getting my terminology mixed up. What exactly is twinview?

What I want is to use two monitors that allow windows to be moved from one monitor to the other. Is this howto suppose to do that?

I can work with whatever I can get to work with using the nv driver because I really don't want to use nvidia proprietary driver.

[Ziox]

twinview is very similar to this howto. However, twinview is only supported by the nvidia proprietary drivers. Also, under twinview, X views it as have only 1 monitor/screen (even though there are two monitors attached), resulting in much better performance than this howto (Xinerama).

From your problem with Xinerama, it seems that the "nv" driver doesn't support multiple outputs. But to tell you the truth, I don't own a nVidia card, so i can't test this Howto personally. I know it works for most ATI cards.

EDIT: this link is guide for TwinView, but again, you have to install nvidida proprietary driver for it to work:

http://www.ublug.org/ubuntu/twinview...to-breezy.html

EDIT AGAIN: try moving the "ServerFlags" section before the "ServerLayout" section...

[harty83]

EDIT AGAIN: try moving the "ServerFlags" section before the "ServerLayout" section...

Still the same error.

[Ziox]

i guess that nv doesn't support multiple outputs...only nvidia does...that's what i'm guessing

[harty83]

I found a gentoo wiki article (http://gentoo-wiki.com/Twinview_Example#X_Setup) that says the following (bold is my emphasis)

This article is about how to configure X with one AGP Geforce 6600GT with one DVI and one VGA adapter. A TFT is connected to the DVI adapter and a CRT is connected to the VGA adapter. The following combinations are described: * (1) TFT only (called single) * (2) TFT and CRT using nvidia's twinview without xinerama (called twinview) * (3) TFT and CRT using two screen sections with xinerama (called xinerama) The following combinations are not described: * (4) TFT and CRT using nvidia'a twinview with xinerama * (5) TFT and CRT using two screen sections without xinearama The difference between (2) and (4) is the fullscreen behaviour. (2) shows a fullscreen window on one screen. (4) shows a fullscreen window over both screens. The difference between (3) and (5) is that (3) allows to move a window from one screen to the other and (5) disallows it. For looking videos in fullscreen mode on one screen, (1), (2), (3) and (5) are possible configurations. I always use the nvidia driver from nvidia. The configurations (2) and (4) will only work with this nvidia driver. (1), (3) and (5) will also work with the open source nv driver. I prefer (3).

But when I follow his tutorial, I get an error that no screen is found.

I'm beginning to feel that all is hopeless with the nv driver.

[Seamus]

OK, I followed these instructions and got this working with my ATI Radeon 9250 card - thanks HEAPS!

This is actually only still using the 'ati' software rendering as I can not get my damn glfrx drivers working. So basically I am using my ATI 128MB card purely for the two outputs (1 VGA and 1 DVI) and then using X11 to split the output over two monitors on this basis.

Whilst this works (and achieves my end goal of dualhead) I would still love to get the ATI drivers working correctly and utilising the hardware acceleration.

NEvertheless, a huge thanks to Ziox for posting this so far.

Cheers!