What is xrandr?
xrandr is a command-line tool to interact with the X RandR extension [see x.org, wikipedia], which allows for live (re)configuration of the X server (i.e. without restarting it): It provides automatic discovery of modes (resolutions, refresh rates, etc.) together with the ability to configure outputs dynamically (resize, rotate, move, etc.).
FIXME: Status across drivers?
What consequences for xorg.conf?
Starting with squeeze, removing the xorg.conf configuration file entirely should work well enough, but in case that doesn’t work out, let’s document what can be removed from it from a RandR point of view.
With the driver detecting modes automatically, several configuration options become useless most of the time in your configuration file (xorg.conf). You might want to remove:
HorizSync and VertRefresh from the Monitor section.
Modes from Display subsection in Screen section.
ModeLine from the Monitor section.
There’s also no need to keep static dual-head configuration. Some suggestions to get a tiny xorg.conf:
Drop dual Device/Screen/Monitor sections, a single one is needed.
Drop MonitorLayout option and Screen lines from the remaining Device section.
Drop the ServerLayout section(s).
Drop RightOf/LeftOf indication of the remaining Screen line in ServerLayout section.
Basic xrandr usage
Once the configuration file (xorg.conf) is removed or updated, starting the server should enable some outputs by default. Their top-left corners will be at the same part of the image, but their modes will probably be different.
All outputs may be configured through xrandr. To see the available outputs, just run xrandr:
$ xrandr Screen 0: minimum 320 x 200, current 1280 x 800, maximum 4096 x 4096 VGA1 disconnected (normal left inverted right x axis y axis) LVDS1 connected 1280x800+0+0 inverted X and Y axis (normal left inverted right x axis y axis) 261mm x 163mm 1280x800 59.8*+ 1024x768 60.0 800x600 60.3 56.2 640x480 59.9 DVI1 disconnected (normal left inverted right x axis y axis) TV1 disconnected (normal left inverted right x axis y axis)
We see 4 outputs: VGA1, LVDS1, DVI1, TV1.
Only the internal panel (LVDS1) is connected and it supports 4 modes at 60 Hz, 1 mode at 56 Hz.
The mode marked with a star (*) is the current mode.
The one marked with a plus (+) is the preferred one. Most monitors report a preferred mode to the driver. And the server/driver will generally choose it by default.
FIXME: Mention output name conventions?
When manipulating VGA1 output properties, you should use:
$ xrandr --output VGA1 <options>
Adding/removing heads dynamically
The old days where you had to restart X when plugging a new monitor are gone. With RandR 1.2, you can plug/unplug monitors whenever you want. Running the following line will query all outputs and enable them with their default mode:
$ xrandr --auto
You may also disable one output using:
$ xrandr --output LVDS1 --off
This may be useful for some buggy application that don’t support multiple outputs well. Also, due to CRTC limitations (see the Caveats section below), it is often required to disable one output before enabling another since most hardware only support 2 at the same time.
Changing the mode
With the above xrandr output, you may change the LVDS1 mode to 1024x768 using:
$ xrandr --output LVDS1 --mode 1024x768
The refresh rate may also be changed, either at the same time or independently:
$ xrandr --output LVDS1 --mode 1024x768 --rate 75 $ xrandr --output LVDS1 --rate 75
To get back to the default mode:
$ xrandr --output LVDS1 --auto
Placing outputs in a virtual screen
A bit of configuration for non-KMS setups:
Let’s have a look at the maximal virtual screen size, we see 4096x4096 in this example:
$ xrandr|head -1 Screen 0: minimum 320 x 200, current 1280 x 800, maximum 4096 x 4096
With KMS (FIXME: Link to a page which explains what KMS is), there’s no need to specify any Virtual option. With DRI and without KMS, that might be needed. Indeed, drivers will often create a default virtual screen with small dimensions, for instance 1600x1200, to reduce memory consumption.
If you plan to use multiple outputs displaying different zones, you should configure your xorg.conf by adding a Virtual line to the Display subsection in the Screen section.
Section "Screen" … SubSection "Display" Depth 24 Virtual 3000 2000 EndSubSection EndSection
Outputs are placed using the following options: --right-of/--left-of/--above/--below. For instance, to place the VGA1 output virtually-right of the internal panel (LVDS1):
$ xrandr --output VGA1 --right-of LVDS1
Note that hardware and memory limitations may severely restrict the size of your virtual screen, see the Caveats section below.
Adding new modes
Under some circumstances, some modes might be missing. For instance, if the monitor does not report correct EDID information. Or if the output didn’t have a CRTC available at startup because another output was using it and you disabled it in the meantime.
If a mode exist, you may add it to one output with:
$ xrandr --addmode VGA1 800x600
If the mode does not exist, you may first create it by passing a modeline:
$ xrandr --newmode <ModeLine>
You may create a modeline using the gtf or cvt tools (shipped in the xserver-xorg-core package).