Multihead
Multi-head, multi-screen, multi-display or multi-monitor represent setups with multiple display devices attached to a single computer. This article provides a general description for several multi-head setup methods, and provides some configuration examples.
- Monitor refers to a physical display device, such as an LCD panel.
- Screen refers to an X-Window 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 (X, X11) is the underlying graphical user interface (GUI) for most Unix/Linux computers that provide one. It was developed in 1984 at MIT. After about 35 years of development, tweaks, new features and ideas, it is generally acknowledged to be a bit of a beast. During the time of early development, the common configuration was a single running X that provided individual views to Xterminals on a time-sharing system. Today, X typically provides a single screen on a desktop or laptop.
In short, there are many ways to configure GUIs using X. When using modern versions, sometimes you can even get away with limited or no configuration. In the last few years, the boast is that X is self-configuring. Certainly, a good rule of thumb is that 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. For example, windows popping up on one screen will not steal the focus away from you if you are working on another screen - each screen is quite independent.
RandR
RandR (Rotate and Resize) 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. See an explanation why RandR is better than Xinerama.
RandR can be configured for the current session via the xrandr tool, arandr or persistently via an xorg.conf file.
Configuration using 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 xrandr(1) 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).
Combine screens into virtual display
Since randr version 1.5, it has been possible to combine monitors into one virtual display. This is an updated version of what was possible with Xinerama and works with open source drivers and does not require an Xorg restart. Some desktop environments do not support this feature yet. Openbox has been tested and works with this feature.
Get monitor list by doing xrandr --listmonitors
0: +*DisplayPort-4 1920/518x1200/324+1920+0 DisplayPort-4 1: +DisplayPort-3 1920/518x1200/324+0+0 DisplayPort-3 2: +HDMI-A-0 1920/518x1200/324+3840+0 HDMI-A-0
Create virtual display xrandr --setmonitor SomeName auto DisplayPort-4,DisplayPort-3,HDMI-A-0. auto determines the size of the virtual display, setting this to auto will automatically create the correct size of the display array. Monitor order in this command does not matter and the monitors need to be rearranged correctly after or before this command is executed.
For a more detailed explanation see this page.
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).
Example: dualhead configuration using relative coordinates
/etc/X11/xorg.conf.d/10-monitor.conf
Section "Monitor"
Identifier "VGA1"
Option "Primary" "true"
EndSection
Section "Monitor"
Identifier "HDMI1"
Option "LeftOf" "VGA1"
EndSection
Example: dualhead configuration using relative coordinates with custom resolutions
The ID for each monitor can be found by running the $ xrandr -q command and should be defined as Monitor-<ID> inside the Device section.
See Xrandr#Adding undetected resolutions.
/etc/X11/xorg.conf.d/10-monitor.conf
Section "Monitor"
Identifier "DVI"
Modeline "1680x1050_60.00" 146.25 1680 1784 1960 2240 1050 1053 1059 1089 -hsync +vsync
Option "PreferredMode" "1680x1050_60.00"
Option "LeftOf" "DP"
Option "DPMS" "true"
EndSection
Section "Monitor"
Identifier "DP"
Modeline "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
Option "PreferredMode" "1920x1080_60.00"
Option "RightOf" "DVI"
Option "DPMS" "true"
EndSection
Section "Screen"
Identifier "Screen0"
Device "Radeon" # e.g. Radeon, Intel, nvidia
Monitor "DP"
DefaultDepth 24
SubSection "Display"
Depth 24
Virtual 3600 2130 # 1920 + 1680 (3600), 1080 + 1050 (2130)
EndSubSection
EndSection
/etc/X11/xorg.conf.d/20-radeon.conf
Section "Device" Identifier "Radeon" Driver "radeon" Option "Monitor-DVI-0" "DVI" # use DVI-0 as DVI Option "Monitor-DisplayPort-0" "DP" EndSection
Example: dualhead configuration using absolute coordinates
/etc/X11/xorg.conf.d/10-monitor.conf
Section "Monitor"
Identifier "VGA1"
Option "PreferredMode" "1024x768"
Option "Position" "1920 312"
EndSection
Section "Monitor"
Identifier "HDMI1"
Option "PreferredMode" "1920x1080"
Option "Position" "0 0"
EndSection
There are no negative coordinates, the setup's leftmost and highest possibly targeted point is at 0,0
(0,0)-----------------+ | |(1920,312)---+ | 1920 x 1080 || | | HDMI1 || 1024 x 768 | | || VGA1 | +---------------------++------------+
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.
Xinerama
Xinerama is the old way of doing genuine multihead X. Xinerama combines all monitors into a single screen (:0) making it possible to drag windows between screens.
Xinerama is configured via custom X configuration files. There is also a GUI tool named WideGuy to make toggling Xinerama easier. Note that to use WideGuy you still need an Xorg configuration with a ServerLayout section.
Here are some X configuration 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
Application support
This section lists tips for individual applications.
- mplayer: use
-xineramascreen 1to make the video play on screen #1 (the second screen.) Addxineramascreen=1to~/.mplayer/configto make it permanent. - Xonotic: if you are playing across multiple screens and you are unable to turn left/right properly, set
vid_stick_mouseto 1 in~/.xonotic/data/config.cfg
Window managers
This section lists window managers and how they cope with multiple monitors.
- Awesome - Works
- dwm -- Works
- FVWM - Works. Has support for Xinerama and multi-screen display, such as Single Logical Screen.
- i3 - Works
- KDE - Works
- MATE - Works
- Qtile - Works
- Spectrwm - Works (screens are different workspaces, both accessible and switching is possible by both keyboard and mouse) - as of March 2015
- Sway - Works
- Xmonad - Works (screens are different workspaces, both accessible and switching is possible by both keyboard and mouse) - as of April 2014
Display managers
GDM: see GDM#Setup default monitor settings.
Users may prefer to use startx and ~/.xinitrc instead of a display manager due to the lack of working support with multiple displays.
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
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
:1must refer to an empty unused display. The first display you are likely using for your desktop is:0, so:1will 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.
Screenshot software
Most CLI screenshot programs support only setups configured as described in #Separate screens. On setups configured by e.g. xrandr screenshots taken by these programs contain pictures of all of the monitors glued together. Xrandr-aware software includes python-mss. mss takes a screenshot per monitor and saves them in the current working directory; see mss -h for more options.