But now the Linux community has distributions, such as Fedora 10, that do not default to using  an xorg.conf file. This is great news for many users. However, it’s bad news when, for some reason, X isn’t working or you have specific needs that the default isn’t meeting. With that in mind we’re going to break down the xorg.conf file so that you will be able to troubleshoot your X Windows configuration when something is wrong.

The Basics

The first thing you need to know is that xorg.conf (located typically in /etc/X11) is broken up into sections. Each section starts with the tag Section and ends with the tag EndSection. Each section can be broken into subsections as well. A subsections starts with the tag SubSection and ends with the tag EndSubSection. So a typical section with subsections contains the tags:
Section Name
Section Information
SubSection Name
SubSection information
EndSubSection
EndSection

Of course you can’t just use random sections. There are specific sections to use. Those sections are:

• Files – pathnames for files such as fontpath
• ServerFlags – global Xorg server options
• Module – which modules to load
• InputDevice – keyboard and pointer (mouse)
• Device – video card description/information
• Monitor – display device description
• Modes – define video modes outside of Monitor section
• Screen – binds a video adapter to a monitor
• ServerLayout – binds one or more screens with one or more input devices
• DRI – optional direct rendering infrastructure information
• Vendor – vendor specific information

Each section will have different information/options and is set up:

Option Variable

Let’s take a look at a sample section. We’ll examine a Device section from a laptop. The section looks like:

Section "Device"
Identifier "device1"
VendorName "VIA Technologies, Inc."
BoardName "VIA Chrome9-based cards"
Driver "openchrome"
Option "DPMS"
Option "SWcursor"
Option "VBERestore" "true"
EndSection

The above section configures a Via Chrome video card (often a tricky one to get running) using the openchrome driver. Here’s how this section breaks down:

• The identifier (labled “device1″) connects this section to Screen section with the Device “device1″ option.
• The VendorName and BoardName both come from the make and model of the video adapter.
• The Driver is the driver the video card will use.
• Option “DPMS” – this enables the Display Power Management System.
• Option “SWcursor” – this enables the cursor to be drawn by software (as opposed to the HWcursor drawing by hard ware).
• Option “VBERestore” “true” – allows a laptop screen to restore from suspend or hibernate.

The lengthiest section of your xorg.conf file will most likely be your Screen section. This section will contain all of the subsections that contain the modes (resolutions) for your monitor. This section will start off like this:

Section "Screen"
Identifier "screen1"
Device "device1"
Monitor "monitor1"
DefaultColorDepth 24

Notice how the above section references both a device and a monitor. These will refer to other sections in the xorg.conf file. This section also contains the DefaultColorDepth which will define the default color depth for your machine. In the case above the default is 24. Now, take a look below at the SubSections of this section:

Subsection "Display"
Depth 8
Modes "1440x900" "1280x800"
EndSubsection
Subsection "Display"
Depth 15
Modes "1440x900" "1280x800"
EndSubsection
Subsection "Display"
Depth 16
Modes "1440x900" "1280x800"
EndSubsection
Subsection "Display"
Depth 24
Modes "1440x900" "1280x800"
EndSubsection
EndSection

As you can see there is a SubSection for four different color depths. Included in those subsections is the default 24. So when X reads the DefaultColorDepth option it will automatically attempt to set the modes configured in the Depth 24 subsection. Also notice that each subsection contains two resolutions. X will attempt to set the first resolution (in the case above our first default is 1440×900) and move on to the next if it can not set the first. Most likely X will be able to set the first.

Final Thoughts

This is only meant to be an introduction to the xorg.conf configuration file. As you might guess, xorg.conf, can get fairly complex. Add to the complexity numerous options available for each section and you have a valid case to make sure you RTFM (read the fine man page.) And the man page is an outstanding resource to find information on all of the available options. To read the man page issue the command man xorg.conf from the command line.

By having a solid understanding of the xorg.conf file you won’t have any problems fixing a fubar’d X installation or tweaking your xorg.conf file to get the most from your new video card.

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With the advent of Fedora 10 xorg.conf does not, by default, install an xorg.conf configuration file. In fact, I had Fedora 10 up and running with an NVidia GeForce 6600 card, with no xorg.conf file. Problem was, I couldn’t get the installation to run in 1200×1024 resolution. Not until I jumped through a few hoops.

One of the first things you should do, when you finish an installation of Fedora 10 is check in /etc/X11 to see if there is an xorg.conf file. If there is not you need to issue the command Xorg -configure :1. What this will do is generate a default xorg.conf file based on your hardware.

Your next step can be tackled in a couple of ways. You can edit the xorg.conf file by hand (for advanced users) or you can install the system-config-display application with the command yum install system-config-display. Once you get that installed you can run the application (as root) with the command system-config-display. From that point the GUI tool should be pretty straight foward to use.

Of course, if you are using an NVidia card, you might have to install some proprietary drivers. Open up the Add/Remove Software tool and do a search for nvidia. Select the applicable drivers for your system if you need them. Once you install the drivers you should have the nvidia-settings tool. This will offer you some help in configuring your NVidia card with Fedora 10.

You will notice the default xorg.conf file generated is very bare-bones. And I understand that Xorg is going in a direction that doesn’t require an xorg.conf file. But there are chipsests out there, such as NVidia, who’s drivers still require an xorg.conf file. This, to me, seems as if Xorg is getting a bit ahead of itself.

UPDATE: I can’t confirm this but the above statement about Xorg going in an xorg.conf’less direction seems to only be applying to Fedora. If anyone has any information that would indicate other distributions are following suite, let us know. Thanks all!

Now I can’t complain too much…X Windows does work out of the box and does a fairly admiriable job. But when you want higher resolutions than the default, you might find yourself jumping through some hoops. I have to admit Linux will find itself in much greener pastures once Xorg no longer requires a configuration file. But I do hope the developers of the various chipsets can get on the same page as the Xorg developer team. If they can’t Linux is going to find itself with a limited selection of video cards it can work with.

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