Demystification of your xorg.conf

Disclaimer : Editing the xorg.conf can make things go horribly wrong if you don’t know what you are doing. Unless you are sure of yourself, do not try this. At the very least you should be comfortable with some basic Linux commands in case you need to restore a backed up copy of the file. You have been warned.

The first thing that you should do, and I cannot stress this enough : Make a copy of your xorg.conf file. It can be found in the /etc/X11/ folder. The command to do the same is -

su

cp /etc/X11/xorg.conf xorg.conf.backup

After this you can begin editing various sections of the file. I will try and explain a couple of important sections. With trial and error you can become pretty good at this and have more fine tuned control over your display.

The xorg.conf file is divided into a minimum of eight sections. The start of each section is marked by the word Section followed by the section’s name, and its end by EndSection. Sections can be placed in any order, and you can have more than one section that cover a certain purpose — for example, if you are using multiple monitors. As in most configuration files, you may also see lines that start with a number sign (#) that provide comments for human readers. These lines are ignored by the operating system, and you can add more for your own purposes.

Fonts

Quick tip for fonts : You can add new font paths by following the format of existing entries: FontPath “<absolutepath>”
It is suggested that you place any directory for 100dpi bitmap fonts before those for 75dpi bitmap fonts, and add :unscaled to the end of all the paths for bitmapped fonts. This ensures that the higher quality fonts are used by the xserver first.

Module

You should prevent editing this section. xorg.conf’s Modules and DRI sections refer to modules loaded by the X server for such purposes as 3-D acceleration (glx, dri) and font support. Unless the relevant resources have been compiled in the kernel, it will not make a difference if you edit this section.

Input Device – Keyboard

Most probably you will want to use the XkbRules options to define the general behavior of the keyboard, since the alternative is to define all aspects of the keyboard layout separately yourself. Driver ‘kbd’ will work fine 90% of the time. The XkbModel for the keyboard can be defined, using one of the options listed in /usr/share/X11/xkb/rules/base.lst, or else a generic one such as pc104 or pc102.

Input Device - Mouse

Two important sections here are ”Driver” and ”Device”. The driver ’mouse’ will work fine for most. Device indicates the location where your pointing device is present. The protocol section defines the type of mouse you have – whether a PS2 (round connector), a USB or a serial mouse. If you have a three-button mouse, you should add the “Emulate 3 buttons” option as follows -

Option “Emulate3Buttons” “true”

Device & Monitor

These sections define your monitor and your 3d card. Make sure that they have got detected correctly. If you are having trouble with the display, you can try one of the drivers in the /usr/lib/xorg/modules/drivers directory for the graphic card ‘Driver’ section. If all else fails you can get basic video support by entering “vesa” or “vga” for the driver. The bus ID for the first 3d card is usually PCI:1:0:0.

For the monitor, the DPMS, enables Display Power Management Signaling in order to conserve the power used by the monitor.

Screen 

The screen section can be used for setting the depth and resolution. Pretty handy if you want to bump up/down your resolution or if you know beforehand that your monitor does not support a particular mode.

After you hav made changes to your xorg.conf file, save the file and restart X by pressing ‘Control + Alt + Backspace’. I case something goes wrong you can always restore the the copy of xorg.conf that you had backed up earlier. You can also look for logs related to the error in the /var/log folder. Look for recent entries.

Download this article as a PDF -> Demystification of your xorg.conf