RandR and the software tool xrandr are used to manage screen resolutions, rotation and screens with multiply displays in X. With version 1.4 support for multiply graphics cards was introduced, future versions (>1.5) will also support monitors attached via USB (this will probably be merged with xorg-server 1.13 with support for DisplayLink, hotplug-displaylink).
The x11-apps/xrandr package can be installed with the following command:
emerge --ask x11-apps/xrandr
This tool should automatically install with most window managers since it is used to manage the displays.
A common way to execute X related scripts is the use of ~/.xinitrc or ~/.xprofile files in a user's home directory. Put the line of code for xrandr in one of these files and it will be executed on every X startup to make settings permanent.
xrandr uses the monitors EDID to identify its capabilities. Some graphic drivers like the binary Nvidia or AMD, do not support xrandr. Also faulty hardware might report wrong or bad EDIDs, in those cases it is still possible to use custom made setups by trial and error.
Running xrandr without any arguments will show attached monitors and its capabilities:
Screen 0: minimum 320 x 200, current 1440 x 900, maximum 8192 x 8192 VGA1 disconnected (normal left inverted right x axis y axis) LVDS1 connected 1440x900+0+0 (normal left inverted right x axis y axis) 304mm x 190mm 1440x900 60.1*+ 1024x768 60.0 800x600 60.3 640x480 59.9
A list of different types for connectors and the naming scheme for RandR:
- LVDS - Laptop Screen
- HDMI - High-Definition Multimedia Interface
- DVI - Digital Visual Interface
- DP - DisplayPort
- VGA - Video Graphics Array
- TV - Composite Video
- S-video - S-Video
A mode always consists of a resolution and a refresh-rate. With a query the hardware reports which modes are supported. It is possible to define own modes in case the hardware reports wrong information. To change the mode for an attached device:
xrandr --output LVDS --mode 1024x768
It will use the highest refresh-rate in that mode, to also change the refresh-rate (in kHz):
xrandr --output LVDS --mode 1024x768 --rate 75
The changes apply immediately and on the hardware listed above it might either produce an error or the screen goes blank, because 75kHz is not supported. This will last until the next session, using Ctrl+Alt+Backspace will terminate the session and restart X in case something goes wrong.
To add a 75Hz mode, the tool cvt can be used to get a proper modeline:
cvt 1024x768 refresh 75
Everything after Modeline needs to be appended to the following command:
xrandr --newmode "1024x768_75.00" 109.00 1280 1368 1496 1712 1024 1027 1034 1063 -hsync +vsync
Running the query again should list the newly added mode.
Adding the mode manually does not make the monitor work in the mode if it did not work before.
Some common tasks using xrandr:
- Extend to an external monitor (left-of, right-of, above, below, same-as):
xrandr --output DVI-0 --auto --left-of LVDS
- Set the primary display if more than one is attached:
xrandr --output LVDS --primary
- Rotate a display (normal, left, right, inverted):
xrandr --output LVDS --rotate left
- Turn off the monitor:
xrandr --output LVDS --off
There are several GUI tools to use xrandr, here is a list of tools supported in Gentoo:
- x11-misc/arandr - Independent GUI tool.
- kde-base/kephal - KDE Desktop tool.
- lxde-base/lxrandr - LXDE Desktop tool.
- Xorg - An open source implementation of the X Window System.