マルチディスプレイ

関連記事

• Xorg
• xrandr
• NVIDIA#マルチモニター
• Nouveau#Dual Head
• AMD Catalyst#Double Screen (Dual Head / Dual Screen / Xinerama)
• ATI#Dual Head setup
• Extreme Multihead

マルチヘッド, マルチスクリーン, マルチディスプレイ, マルチモニターは複数のディスプレイデバイスをコンピューターに接続して使用することを言います。この記事ではマルチディスプレイを設定する方法の説明や、設定例を示します。

ノート: 混乱を避けるために、この記事で使用する単語の意味を明確にします:

• モニターは LCD パネルのような物理的な表示デバイスを示します。
• スクリーンは X-Window の画面を示します (つまりモニターはディスプレイに接続されます)。
• ディスプレイはデスクトップの各部位を示すのに同時に使われるスクリーンの集合を示します (ディスプレイの中のスクリーンでウィンドウをドラッグすることができます)。

歴史的背景

全てとはいわなくてもほとんどの Unix/Linux コンピュータでは GUI を提供するために X Window System を基盤のグラフィカルインターフェイスとして使っています。X は1984年に MIT で開発されました。開発は35年間も続いており、その間に新しい機能や概念が追加され、ちょっとした化物と言われるようにまでなっています。長い開発の歴史の中で、タイムシェアリングシステムによって Xterminal に個別のビューを提供する単一の X というのが最も一般的な設定だったということを覚えておきましょう。近年になって、デスクトップやノートパソコンに単一のスクリーンを提供する X が標準となったのです。

ノート: 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 beast 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.

画面の分割

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

警告: 2013年8月現在、バージョン 319 以上のプロプライエタリの NVIDIA ドライバーを使っている場合、Xinerama は動作しません。NVIDIA ドライバーで Xinerama を使用したいユーザーは NVIDIA 313 ドライバーを使う必要があります。ただし、このドライバーは 3.10 以前の Linux カーネルでしか動作しません。詳しくは このスレッド を参照。

Xinerama は X のマルチスクリーンを実現する古い手段です。Xinerama は全てのモニターを単一のスクリーン (:0) にまとめるため、スクリーンを通り越してウィンドウをドラッグすることができます。

Xinerama は X の設定ファイルをカスタマイズすることで設定します。以下に例を挙げます:

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

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.

設定例は NVIDIA#TwinView を見て下さい。

RandR

RandR (Rotate and Resize) はクライアントが動的にスクリーンを変更 (例: リサイズ、回転、反転) できるようにする、X Window System の拡張です。ほとんどの場合、RandR は旧 Xinerama のセットアップを完全に置き換えることができます。RandR が Xinerama よりも優れている理由については この説明 を見て下さい。

RandR は xrandr ツールを使って現在のセッションに限って設定を行ったり、xorg.conf ファイルで永続的に設定することができます。

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

xrandr を使って設定

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

相対的にスクリーンを配列したり (--right-of, --left-of, --above, --below オプションを使用)、絶対座標を使って配置することができます (--pos オプションを使用。絶対座標を使う場合はモニターの解像度を知る必要があります)。詳しくは man xrandr を見て下さい。よく使われる設定については以下で説明します。

HDMI1 の左側に適切な解像度で VGA1 を表示

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

--right-of はスクリーン (HDMI1) を指定したスクリーン (VGA1) の右に配置します。

HDMI1 の右側に指定した解像度で VGA1 を表示

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

または

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

--left-of はスクリーン (HDMI1) を指定したスクリーン (VGA1) の左に配置します。

xorg.conf を使って設定

xrandr を使用する方法と似ており、各スクリーンごとに Monitor セクションを記述します。Identifier には、xrandr -q によって確認できる値と同じ値を使用します (--output VGA1 ではなく Identifier "VGA1" を用います)。

例: 相対座標を用いるデュアルヘッド設定

/etc/X11/xorg.conf

Section "Monitor"
    Identifier  "VGA1"
    Option      "Primary" "true"
EndSection

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

例: 絶対座標を用いるデュアルヘッド設定

/etc/X11/xorg.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

負の座標はありません。一番左上の座標は 0,0 になります。

(0,0)-----------------+ 
|                     |(1920,312)---+
|     1920 x 1080     ||            |
|        HDMI1        || 1024 x 768 |
|                     ||    VGA1    |
+---------------------++------------+

アプリケーションのサポート

このセクションでは個別のアプリケーションに関してのヒントを記述しています。

• mplayer: -xineramascreen 1 を使えば動画をセカンドスクリーンで再生できます。~/.mplayer/config に xineramascreen=1 を追加することで永続的に設定できます。
• 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

ウィンドウマネージャ

このセクションではウィンドウマネージャのマルチモニター対応状況を載せています。

• Awesome - 動作します。
• FVWM - 動作します。Xinerama をサポートしており、Single Logical Screen のようなマルチスクリーンディスプレイが使えます。
• i3 - 動作します。
• KDE - 動作します。
• MATE - 動作します。
• Spectrwm - Works (screens are different workspaces, both accessible and switching is possible by both keyboard and mouse) - as of March 2015
• Xmonad - Works (screens are different workspaces, both accessible and switching is possible by both keyboard and mouse) - as of April 2014

ディスプレイマネージャ

• GDM: gdm is not configured by gnome display settings, resulting in the login screen not being displayed on the primary monitor. A workaround is explained here. It just consists in copying the user monitor configuration file to gdm's.
• KDM: 動作します。

Users may prefer to use startx and ~/.xinitrc instead of a display manager due to the lack of working support with multiple displays.

フルスクリーンゲーム

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

ヒント: 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.

この新しいレイアウトを使用するには、startx スクリプトを使ってゲームを起動します:

# 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.

参照

• 'How I got Dual Monitors with Nouveau Driver' forums thread