Multihead

From ArchWiki
Revision as of 12:21, 12 August 2013 by Lahwaacz (Talk | contribs) (Xinerama: added reference link)

Jump to: navigation, search
Summary help replacing me
This article describes configuration methods applicable when more than one display device is attached.
Related
Xorg
xrandr
GPU-specific instructions
NVIDIA#Multiple monitors
Nouveau#Dual Head
AMD Catalyst#Double Screen (Dual Head / Dual Screen / Xinerama)
ATI#Dual Head setup

Multi-head, multi-screen, multi-display or multi-monitor represent a setup when multiple display devices are attached to a computer. This article provides general description of multiple multi-head setup methods, and provides some examples of configuration.

Note: The terms used in this article are very specific to avoid confusion:
  • Monitor refers to a physical display device, such as an LCD panel.
  • Screen refers to an X-Windows screen (that is: a monitor attached to a display).
  • Display refers to a collection of screens that are in use at the same time showing parts of a single desktop (you can drag windows among all screens in a single display).

Historical background

X Window System is the underlying graphical interface of most if not all Unix/Linux computers providing a GUI. It was developed in 1984 at MIT. After abound 35 years of development, tweaking and adding of new features and ideas, it is generally acknowledged to be a bit of a beast. It should be remembered that the common configuration at time of development was a single running X providing individual views to Xterminals in a time-sharing system. Nowadays the standard is X providing a single screen on a desktop or laptop.

Note: There is still a rare configuration often called Zaphod display, which allows multiple users of a single computer to each have an independent set of display, mouse, and keyboard, as though they were using separate computers, but at a lower per-seat cost.

All of this means that there are many ways of achieving the same thing and many slightly different things that can meet the same purpose. In modern X versions sometimes you can get away with limited or no configuration. In the last few years the boast is that X is self configuring. Certainly the best practice rule of thumb is less configuration is better - that is only configure what is wrong.

Separate screens

This is the original way of configuring multiple monitors with X, and it has been around for decades. Each physical monitor is assigned as an X screen, and while you can move the mouse between them, they are more or less independent.

Normally the X display has a single identifier such as :0 set in the DISPLAY environment variable, but in this configuration each screen has a different $DISPLAY value. The first screen is :0.0, the second is :0.1 and so on.

With this configuration it is not possible to move windows between screens, apart from a few special programs like GIMP and Emacs which have multi-screen support. For most programs you must change the DISPLAY environment variable when launching to have the program appear on another screen:

# Launch a terminal on the second screen
$ DISPLAY=:0.1 urxvt &

Alternatively if you have a terminal on each screen launching programs will inherit the DISPLAY value and appear on the same screen they were launched on. But moving an application between screens involves closing it and reopening it again on the other screen.

Working this way does have certain advantages, such as windows popping up on one screen won't steal the focus away from you if you are working on another screen - each screen is quite independent.

Xinerama

Xinerama is the old way of doing genuine multihead X. Screens are configured as separate X screens like in the previous section, but Xinerama combines all screens into a single display (:0) making it possible to drag windows between screens.

Xinerama is configured via custom X configuration files. Here are some examples:

This is a ServerLayout section which controls where each monitor sits relative to the others.

/etc/X11/xorg.conf.d/90-serverlayout.conf
Section "ServerLayout"
  Identifier   "Main"
  Screen       0 "Primary"
  Screen       1 "DellPortraitLeft" RightOf "Primary"
  Screen       2 "Wacom" RightOf "DellPortraitLeft"
  Screen       3 "U2412" LeftOf "Primary"
  Option         "Xinerama" "1"  # enable XINERAMA extension.  Default is disabled.
EndSection

Each Screen in the above section is defined in a separate file, such as this one:

/etc/X11/xorg.conf.d/30-screen-dell2001.conf
# Define the monitor's physical specs
Section "Monitor"
  Identifier   "Dell 2001FP"
  VertRefresh  60
  Option  "dpms"  "on"

  # Modelines are probably unnecessary these days, but it does give you fine grained control

  # 1600x1200 @ 60.00 Hz (GTF) hsync: 74.52 kHz; pclk: 160.96 MHz
  Modeline "1600x1200"  160.96  1600 1704 1880 2160  1200 1201 1204 1242  -HSync +Vsync
EndSection

# Define a screen that uses the above monitor.  Note the Monitor value matches the above
# Identifier value, and the Device value matches one of the video cards defined below
# (the card and connector this monitor is actually plugged in to.)
Section "Screen"
  Identifier   "DellPortraitLeft"
  Device       "GeForce 8600GTb"
  Monitor      "Dell 2001FP"
  DefaultDepth 24
  SubSection "Display"
    Depth     24
    Modes     "1600x1200"
    ViewPort  0 0
    Virtual   1600 1200
  EndSubsection

  # This screen is in portrait mode
  Option "Rotate" "left"
EndSection

You will need to create a Device section for each monitor, i.e. a dual head video card will have two Device sections. The following example shows how to configure two video cards each providing two outputs, for a total of four monitors.

/etc/X11/xorg.conf.d/20-nvidia.conf
# First head of first video card in the system
Section "Device"
  Identifier  "GeForce 8600GT"
  Driver      "nvidia"

  # If you have multiple video cards, the BusID controls which one this definition refers
  # to.  You can omit it if you only have one card.
  BusID       "PCI:1:0:0"

  # Need to flag this as only referring to one output on the card
  Screen      0

  # For nVidia devices, this controls which connector the monitor is connected to.
  Option      "UseDisplayDevice"   "DFP-0"

  # We want control!
  Option      "DynamicTwinView"    "FALSE"

  # Various performance and configuration options
  Option      "AddARGBGLXVisuals"  "true"
  Option      "UseEDIDDpi"         "false"
  Option      "DPI"                "96 x 96"
  Option      "Coolbits"           "1"
EndSection

# Second head of same video card (note different Identifier but same BusID.)  We can omit
# the UseDisplayDevice option this time as it will pick whichever one is remaining.
Section "Device"
  Identifier  "GeForce 8600GTb"
  Driver      "nvidia"
  BusID       "PCI:1:0:0"
  # This is the second output on this card
  Screen      1

  # Same config options for all cards
  Option      "AddARGBGLXVisuals"  "true"
  Option      "UseEDIDDpi"         "false"
  Option      "DPI"                "96 x 96"
  Option      "Coolbits"           "1"
  Option      "DynamicTwinView"    "FALSE"
EndSection

# First head of second video card, note different BusID.
Section "Device"
  Identifier  "G210"
  Driver      "nvidia"
  BusID       "PCI:2:0:0"
  Screen      0

  # Same config options for all cards
  Option      "AddARGBGLXVisuals"  "true"
  Option      "UseEDIDDpi"         "false"
  Option      "DPI"                "96 x 96"
  Option      "Coolbits"           "1"
  Option      "DynamicTwinView"    "FALSE"
EndSection

# Second head of second video card.  Output connector is set here, which means the previous
# Device will use the other connector, whatever it may be.
Section "Device"
  Identifier  "G210b"
  Driver      "nvidia"
  BusID       "PCI:2:0:0"
  Screen      1
  Option      "UseDisplayDevice"   "DFP-1"

  # Same config options for all cards
  Option      "AddARGBGLXVisuals"  "true"
  Option      "UseEDIDDpi"         "false"
  Option      "DPI"                "96 x 96"
  Option      "Coolbits"           "1"
  Option      "DynamicTwinView"    "FALSE"
EndSection

RandR

RandR is an X Window System extension, which allows clients to dynamically change (e.g. resize, rotate, reflect) screens. In most cases, it can fully replace the old Xinerama setup.

RandR can be configured via the xrandr tool or an xorg.conf file.

Note: There are multiple ways to configure the same thing, you might have to experiment a little before you find the best configuration.

Configuration using xrandr

Note: This section assumes that you have read the xrandr page for basic info about xrandr.

You may arrange your screens either relatively to each other (using the --right-of, --left-of, --above, --below options), or by absolute coordinates (using the --pos option; note that in this case you usually need to know resolutions of your monitors). See man xrandr for details. Some frequently used settings are described below.

VGA1 left of HDMI1 at their preferred resolutions

$ xrandr --output VGA1 --auto --output HDMI1 --auto --right-of VGA1

--right-of places the previous screen (HDMI1) to the right of the specified screen (VGA1).

VGA1 right of HDMI1 at fixed resolutions

$ xrandr --output VGA1 --mode 1024x768 --pos 1920x0 --output HDMI1 --mode 1920x1080 --pos 0x0

or

$ xrandr --output VGA1 --mode 1024x768 --output HDMI1 --mode 1920x1080 --left-of VGA1

--left-of places the previous screen (HDMI1) to the left of the specified screen (VGA1).

Configuration using xorg.conf

This is similar to using xrandr, separate Monitor section is needed for each screen. As an Identifier, the same value as reported by xrandr -q is used (i.e. Identifier "VGA1" is used instead of --output VGA1).

The examples below are self-explanatory:

Example: dualhead configuration using relative coordinates

/etc/X11/xorg.conf
Section "Monitor"
    Identifier  "VGA1"
    Option      "Primary" "true"
EndSection

Section "Monitor"
    Identifier  "HDMI1"
    Option      "RightOf" "VGA1"
EndSection

Example: dualhead configuration using absolute coordinates

/etc/X11/xorg.conf
Section "Monitor"
    Identifier  "VGA1"
    Option      "PreferredMode" "1024x768"
    Option      "Position" "1920 0"
EndSection

Section "Monitor"
    Identifier  "HDMI1"
    Option      "PreferredMode" "1920x1080"
    Option      "Position" "0 0"
EndSection

TwinView

TwinView is nVidia's extension which makes two monitors attached to a video card appear as a single screen. TwinView provides Xinerama extensions so that applications are aware there are two monitors connected, and thus it is incompatible with Xinerama. However if you only have two monitors and they are both connected to the same nVidia card, there is little difference between TwinView and Xinerama (although in this situation TwinView may offer slightly better performance.)

If you wish to attach more than two monitors or monitors attached to other video cards, you will need to use Xinerama instead of TwinView. Likewise as of April 2012, both monitors must be in the same orientation - you cannot have one in landscape and the other in portrait mode.

In the past, TwinView was the only way to get OpenGL acceleration with nVidia cards while being able to drag windows between screens. However modern versions of the nVidia closed-source driver are able to provide OpenGL acceleration even when using Xinerama.

See NVIDIA#TwinView for an example configuration.

Application support

Tango-view-refresh-red.pngThis article or section is out of date.Tango-view-refresh-red.png

Reason: This section contains outdated information, mostly specific to Xinerama. (Discuss in Talk:Multihead#)

This section lists tips for individual applications.

  • mplayer: use -xineramascreen 1 to make the video play on screen #1 (the second screen.) Add xineramascreen=1 to ~/.mplayer/config to make permanent.
  • Xonotic: if you are playing across multiple screens and you are unable to turn left/right properly, set vid_stick_mouse to 1 in ~/.xonotic/data/config.cfg

Window managers

This section lists window managers and how they cope with multiple monitors.

  • Awesome - works
  • FVWM - works. Has support for Xinerama and multi-screen display, such as Single Logical Screen.
  • KDE - does not work properly, second monitor seen as virtual desktop, inaccessible (2012-10-15)
  • MATE - works
  • i3 - works
  • XMonad - works (screens are different workspaces, both accessible and switching is possible by both keyboard and mouse) - as of 1th March 2013

Full screen games

Many games require their window to appear at (0,0) when running in full-screen. If the screen you have at (0,0) - the left-most one - is not one you wish to game on, it is almost impossible to move a full-screen game onto a different screen.

A workaround for this is to create a separate X11 configuration (a new layout) just for playing games, which may have less (or only one) screen configured. You can then launch games using this separate layout, while normal desktop work uses the original multihead configuration.

To create a new layout, copy /etc/X11/xorg.d/90-serverlayout.conf and call it 91-serverlayout-gaming.conf. It is important to use a number larger than 90, as the one with the lowest number will become the default used when you first load X.

Adjust this new configuration file to your preferred gaming configuration. Here is an example (based on the example Xinerama configuration above) with only one screen defined, noting that the screen specifics (such as resolution) are defined in other files and are unchanged from and shared with the normal configuration:

/etc/X11/xorg.conf.d/91-serverlayout-gaming.conf
# New screen layout only using a single screen called "Primary"
Section "ServerLayout"
    Identifier   "Gaming"
    Screen       0 "Primary" Absolute 0 0
EndSection
Tip: While it's easiest to just reuse the existing screen definitions, you can of course define new ones if you wish to have a different set of screen resolutions available.

To use this new layout, launch the game via the startx script:

# Launch Xonotic on a new X11 display using the "Gaming" layout
startx /usr/bin/xonotic-glx -fullscreen -- :1 -layout Gaming

Note that:

  • You must specify the full path to the command to run, here /usr/bin/xonotic-glx.
  • The :1 must refer to an empty unused display. The first display you are likely using for your desktop is :0, so :1 will be fine for most people. But should you want to launch a second game at the same time, you would have to change this to :2.
  • Just as you can switch between text consoles with Alt+Ctrl+F1 and back to X with Alt+Ctrl+F7, the new display will sit on Alt+Ctrl+F8. So you can switch back to your desktop with Alt+Ctrl+F7 and back to the game with Alt+Ctrl+F8. This is because you are running an independent X desktop, so if you switch out of the game with Alt+Tab or equivalent there will be an empty desktop with no window manager running.

See also