Next: 5.1.4 Filling in video Up: 5.1 The X Window Previous: 5.1.2 Installing XFree86

## 5.1.3 Configuring XFree86

Setting up XFree86 is not difficult in most cases. However, if you happen to be using hardware for which drivers ar under development, or wish to obtain the best performance or resolution from an accelerated graphics card, configuring XFree86 can be somewhat time-consuming.

In this section we will describe how to create and edit the `XF86Config` file, which configures the XFree86 server. In many cases it is best to start out with a ``basic'' XFree86 configuration, one which uses a low resolution, such as 640x480, which should be supported on all video cards and monitor types. Once you have XFree86 working at a lower, standard resolution, you can tweak the configuration to exploit the capabilities of your video hardware. The idea is that you want to know that XFree86 works at all on your system, and that something isn't wrong with your installation, before attempting the sometimes difficult task of setting up XFree86 for real use.

In addition to the information listed here, you should read the following documentation:

- The XFree86 documentation in `/usr/X11R6/lib/X11/doc` (contained within the `XFree86-3.1-doc` package). You should especially see the file `README.Config`, which is an XFree86 configuration tutorial.
- Several video chipsets have separate `README` files in the above directory (such as `README.Cirrus` and `README.S3`). Read one of these if applicable.
- The man page for `XFree86`.
- The man page for `XF86Config`.
- The man page for the particular server that you are using (such as `XF86_SVGA` or `XF86_S3`).

The main XFree86 configuration file is `/usr/X11R6/lib/X11/XF86Config`. This file contains information on your mouse, video card parameters, and so on. The file `XF86Config.eg` is provided with the XFree86 distribution as an example. Copy this file to `XF86Config` and edit it as a starting point.

The `XF86Config` man page explains the format of this file in detail. Read this man page now, if you have not done so already.

We are going to present a sample `XF86Config` file, piece by piece. This file may not look exactly like the sample file included in the XFree86 distribution, but the structure is the same.

Note that the `XF86Config` file format may change with each version of XFree86; this information is only valid for XFree86 version 3.1.

Also, you should not simply copy the configuration file listed here to your own system and attempt to use it. Attempting to use a configuration file which doesn't correspond to your hardware could drive the monitor at a frequency which is too high for it; there have been reports of monitors (especially fixed-frequency monitors) being damaged or destroyed by using an incorrectly configured `XF86Config` file. The bottom line is this: Make absolutely sure that your `XF86Config` file corresponds to your hardware before you attempt to use it.

Each section of the `XF86Config` file is surrounded by the pair of lines `Section ""`...`EndSection`. The first part of the `XF86Config` file is `Files`, which looks like this:

``

    Section "Files"
        RgbPath     "/usr/X11R6/lib/X11/rgb"
        FontPath    "/usr/X11R6/lib/X11/fonts/misc/"
        FontPath    "/usr/X11R6/lib/X11/fonts/75dpi/"
    EndSection

The `RgbPath` line sets the path to the X11R6 RGB color database, and each `FontPath` line sets the path to a directory containing X11 fonts. In general you shouldn't have to modify these lines; just be sure that there is a `FontPath` entry for each font type that you have installed (that is, for each directory in `/usr/X11R6/lib/X11/fonts`).

The next section is `ServerFlags`, which specifies several global flags for the server. In general this section is empty.

``

    Section "ServerFlags"
    # Uncomment this to cause a core dump at the spot where a signal is
    # received.  This may leave the console in an unusable state, but may
    # provide a better stack trace in the core dump to aid in debugging
    #    NoTrapSignals

    # Uncomment this to disable the <Crtl><Alt><BS> server abort sequence
    #    DontZap
    EndSection

Here, we have all lines within the section commented out.

The next section is `Keyboard`. This should be fairly intuitive.

``

    Section "Keyboard"
        Protocol    "Standard"
        AutoRepeat  500 5
        ServerNumLock
    EndSection

Other options are available as well---see the `XF86Config` file if you wish to modify the keyboard configuration. The above should work for most systems.

The next section is `Pointer` which specifies parameters for the mouse device.

``

    Section "Pointer"

        Protocol    "MouseSystems"
        Device      "/dev/mouse"

    # Baudrate and SampleRate are only for some Logitech mice
    #    BaudRate   9600
    #    SampleRate	150

    # Emulate3Buttons is an option for 2-button Microsoft mice
    #    Emulate3Buttons

    # ChordMiddle is an option for some 3-button Logitech mice
    #    ChordMiddle

    EndSection

The only options that you should concern yourself with now are `Protocol` and `Device`. `Protocol` specifies the mouse protocol that your mouse uses (not the make or brand of mouse). Valid types for `Protocol` (under Linux---there are other options available for other operating systems) are:

- `BusMouse`
- `Logitech`
- `Microsoft`
- `MMSeries`
- `Mouseman`
- `MouseSystems`
- `PS/2`
- `MMHitTab`

`BusMouse` should be used for the Logitech busmouse. Note that older Logitech mice should use `Logitech`, but newer Logitech mice use either `Microsoft` or `Mouseman` protocols. This is a case in which the protocol doesn't necessarily have anything to do with the make of the mouse.

`Device` specifies the device file where the mouse can be accessed. On most Linux systems, this is `/dev/mouse`. `/dev/mouse` is usually a link to the appropriate serial port (such as `/dev/cua0`) for serial mice, or to the appropriate busmouse device for busmice. At any rate, be sure that the device file listed in `Device` exists.

The next section is `Monitor`, which specifies the characteristics of your monitor. As with other sections in the `XF86Config` file, there may be more than one `Monitor` section. This is useful if you have multiple monitors connected to a system, or use the same `XF86Config` file under multiple hardware configurations. In general, though, you will need a single `Monitor` section.

``

    Section "Monitor"

        Identifier  "CTX 5468 NI"

        # These values are for a CTX 5468NI only! Don't attempt to use
        # them with your monitor (unless you have this model)

        Bandwidth    60
        HorizSync    30-38,47-50
        VertRefresh  50-90

        # Modes: Name      dotclock  horiz                vert

        ModeLine "640x480"  25       640 664 760 800      480 491 493 525
        ModeLine "800x600"  36       800 824 896 1024     600 601 603 625
        ModeLine "1024x768" 65       1024 1088 1200 1328  768 783 789 818

    EndSection

The `Identifier` line is used to give an arbitrary name to the `Monitor` entry. This can be any string; you will use it to refer to the `Monitor` entry later in the `XF86Config` file.

they are listed below.

`HorizSync` specifies the valid horizontal sync frequencies for your monitor, in kHz. If you have a multisync monitor, this can be a range of values (or several comma-separated ranges), as seen above. If you have a fixed-frequency monitor, this will be a list of discrete values, such as:

``

        HorizSync    31.5, 35.2, 37.9, 35.5, 48.95

Your monitor manual should list these values in the technical specifications section. If you do not have this information available, you should either contact the manufacturer or vendor of your monitor to obtain it. There are other sources of information, as well;

`VertRefresh` specifies the valid vertical refresh rates (or vertical synchronization frequencies) for your monitor, in Hz. Like `HorizSync` this can be a range or a list of discrete values; your monitor manual should list them.

`HorizSync` and `VertRefresh` are used only to double-check that the monitor resolutions that you specify are in valid ranges. This is to reduce the chance that you will damage your monitor by attempting to drive it at a frequency for which it was not designed.

The `ModeLine` directive is used to specify a single resolution mode for your monitor. The format of `ModeLine` is

`ModeLine`

is an arbitrary string, which you will use to refer to the resolution mode later in the file. is the driving clock frequency, or ``dot clock'' associated with the resolution mode. A dot clock is usually specified in MHz, and is the rate at which the video card must send pixels to the monitor at this resolution. and are four numbers each which specify when the electron gun of the monitor should fire, and when the horizontal and vertical sync pulses fire during a sweep.

How can you determine the `ModeLine` values for your monitor? The file `VideoModes.doc`, included with the XFree86 distribution, describes in detail how to determine these values for each resolution mode that your monitor supports. First of all, must correspond to one of the dot clock values that your video card can produce. Later in the `XF86Config` file you will specify these clocks; you can only use video modes which have a value supported by your video card.

There are two files included in the XFree86 distribution which may include `ModeLine` data for your monitor. These files are `modeDB.txt` and `Monitors`, both of which are found in `/usr/X11R6/lib/X11/doc`.

You should start with `ModeLine` values for the VESA standard monitor timings, which most monitors support. `modeDB.txt` includes timing values for VESA standard resolutions. In that file, you will see entries such as

``

    # 640x480@60Hz Non-Interlaced mode
    # Horizontal Sync = 31.5kHz
    # Timing: H=(0.95us, 3.81us, 1.59us), V=(0.35ms, 0.064ms, 1.02ms)
    #
    # name        clock   horizontal timing     vertical timing      flags
     "640x480"     25.175  640  664  760  800    480  491  493  525

This is a VESA standard timing for a 640x480 video mode. It uses a dot clock of 25.175, which your video card must support to use this mode (more on this later). To include this entry in the `XF86Config` file, you'd use the line

`ModeLine "640x480" 25.175 640 664 760 800 480 491 493 525`

Note that the argument to `ModeLine` (in this case ``"640x480"``) is an arbitrary string---the convention is to name the mode after the resolution, but can technically be anything descriptive which describes the mode to you.

For each `ModeLine` used the server will check that the specifications for the mode fall within the range of values specified with `Bandwidth`, `HorizSync` and `VertRefresh`. If they do not, the server will complain when you attempt to start up X (more on this later). For one thing, the dot clock used by the mode should not be greater than the value used for `Bandwidth`. (However, in many cases it is safe to use modes with a slightly higher bandwidth than your monitor can support.)

If the VESA standard timings do not work for you (you'll know after trying to use them later) then the files `modeDB.txt` and `Monitors` include specific mode values for many monitor types. You can create `ModeLine` entries from the values found in those two files as well. Be sure to only use values for the specific model of monitor that you have. Note that many 14 and 15-inch monitors cannot support higher resolution modes, and often resolutions of 1024x768 at low dot clocks. This means that if you can't find high resolution modes for your monitor in these files, then your monitor probably does not support those resolution modes.

If you are completely at a loss, and can't find working `ModeLine` values for your monitor, you can follow the instructions in the `VideoModes.doc` file included in the XFree86 distribution to generate `ModeLine` values from the specifications listed in your monitor's manual. While your mileage will certainly vary when attempting to generate `ModeLine` values by hand, this is a good place to look if you can't find the values that you need. `VideoModes.doc` also describes the format of the `ModeLine` directive and other aspects of the XFree86 server in gory detail.

Lastly, if you do obtain `ModeLine` values which are almost, but not quite, right, then it may be possible to simply modify the values slightly to obtain the desired result. For example, if while running XFree86 the image on the monitor is shifted slightly, or seems to ``roll'', you can follow the instructions in the `VideoModes.doc` file to try to fix these values. Also, be sure to check the knobs and controls on the monitor itself! In many cases it is necessary to change the horizontal or vertical size of the display after starting up XFree86 in order for the image to be centered and be of the appropriate size. Having these controls on the front of the monitor can certainly make life easier.

You shouldn't use monitor timing values or `ModeLine` values for monitors other than the model that you own. If you attempt to drive the monitor at a frequency for which it was not designed, you can damage or even destroy it.

The next section of the `XF86Config` file is `Device`, which specifies parameters for your video card. Here is an example.

``

    Section "Device"
            Identifier "#9 GXE 64"

            # Nothing yet; we fill in these values later.

    EndSection

This section defines properties for a particular video card. `Identifier` is an arbitrary string describing the card; you will use this string to refer to the card later.

Initially, you don't need to include anything in the `Device` section, except for `Identifier`. This is because we will be using the X server itself to probe for the properties of the video card, and entering them into the `Device` section later. The XFree86 server is capable of probing for the video chipset, clocks, RAMDAC, and amount of video RAM on the board.

Before we do this, however, we need to finish writing the `XF86Config` file. The next section is `Screen`, which specifies the monitor/video card combination to use for a particular server.

``

     Section "Screen"
         Driver     "Accel"
         Device     "#9 GXE 64"
         Monitor    "CTX 5468 NI"
         Subsection "Display"
             Depth      16
             Modes      "1024x768" "800x600" "640x480"
             ViewPort   0 0
             Virtual    1024 768
         EndSubsection
     EndSection

The `Driver` line specifies the X server that you will be using. The value values for `Driver` are:

- `Accel`: For the `XF86_S3`, `XF86_Mach32`, `XF86_Mach8`, `XF86_8514`, `XF86_P9000`, `XF86_AGX`, and `XF86_W32` servers;
- `SVGA`: For the `XF86_SVGA` server;
- `VGA16`: For the `XF86_VGA16` server;
- `VGA2`: For the `XF86_Mono` server;
- `Mono`: For the non-VGA monochrome drivers in the `XF86_Mono` and `XF86_VGA16` servers.

You should be sure that `/usr/X11R6/bin/X` is a symbolic link to the server that you are using.

The `Device` line specifies the `Identifier` of the `Device` section corresponding to the video card to use for this server. Above, we created a `Device` section with the line

``

    Identifier "#9 GXE 64"

Therefore, we use ``"#9 GXE 64"`` on the `Device` line here.

Similarly, the `Monitor` line specifies the name of the `Monitor` section to be used with this server. Here, ``"CTX 5468 NI"`` is the `Identifier` used in the `Monitor` section described above.

``Subsection "Display"`` defines several properties of the XFree86 server corresponding to your monitor/video card combination. The `XF86Config` file describes all of these options in detail; most of them are icing on the cake and not necessary to get the system working.

The options that you should know about are:

- `Depth`. Defines the number of color planes---the number of bits per pixel. Usually, `Depth` is set to 8. For the `VGA16` server, you would use a depth of 4, and for the monochrome server a depth of 1. If you are using an accelerated video card with enough memory to support more bits per pixel, you can set `Depth` to 16, 24, or 32. If you have problems with depths higher than 8, set it back to 8 and attempt to debug the problem later.

- `Modes`. This is the list of video mode names which have been defined using the `ModeLine` directive in the `Monitor` section. In the above section, we used `ModeLines` named ``"1024x768"``, ``"800x600"``, and ``"640x48"0``. Therefore, we use a `Modes` line of

  ``

               Modes    "1024x768" "800x600" "640x480"

  The first mode listed on this line will be the default when XFree86 starts up. After XFree86 is running, you can switch between the modes listed here using the keys -- and --.

  It might be best, when initially configuring XFree86, to use lower resolution video modes, such as 640x480, which tend to work on most systems. Once you have the basic configuration working you can modify `XF86Config` to support higher resolutions.

- `Virtual`. Sets the virtual desktop size. XFree86 has the ability to use any additional memory on your video card to extend the size of your desktop. When you move the mouse pointer to the edge of the display, the desktop will scroll, bringing the additional space into view. Therefore, even if you are running at a lower video resolution such as 800x600, you can set `Virtual` to the total resolution which your video card can support (a 1-megabyte video card can support 1024x768 at a depth of 8 bits per pixel; a 2-megabyte card 1280x1024 at depth 8, or 1024x768 at depth 16). Of course, the entire area will not be visible at once, but it can still be used.

  The `Virtual` feature is a nice way to utilize the memory of your video card, but it is rather limited. If you want to use a true virtual desktop, we suggest using `fvwm`, or a similar window manager, instead. `fvwm` allows you to have rather large virtual desktops (implemented by hiding windows, and so forth, instead of actually storing the entire desktop in video memory at once). See the man pages for `fvwm` for more details about this; most Linux systems use `fvwm` by default.

- `ViewPort`. If you are using the `Virtual` option described above, `ViewPort` sets the coordinates of the upper-left-hand corner of the virtual desktop when XFree86 starts up. `Virtual 0 0` is often used; if this is unspecified then the desktop is centered on the virtual desktop display (which may be undesirable to you).

Many other options for this section exist; see the `XF86Config` man page for a complete description. In practice these other options are not necessary to get XFree86 initially working.

Next: 5.1.4 Filling in video Up: 5.1 The X Window Previous: 5.1.2 Installing XFree86