The KDrive Tiny X Server

This page is obsolete; the howto information contained herein does not apply to recent X.Org releases. It may still be of interest if you want to understand what KDrive is about.

KDrive (Tiny X, TinyX) is an X server written by Keith Packard that was designed for low memory environments. On Linux/x86, a KDrive server with RENDER support but without support for scalable fonts compiles into less than 700 KB of text. KDrive tends to avoid large memory allocations at runtime, and tries to perform operations “on the fly” whenever possible (but this is also true of recent versions of the stock XFree86 server).

Unlike the usual XFree86 server, a KDrive server is completely self-contained: it does not require any configuration files, and will even function if no on-disk fonts are available. All configuration is done at compile time and through command-line flags.

At the time of writing, KDrive is for Linux only, although it could probably be ported to other Unix-like systems with little effort.

Disclaimer: This text was written by an incompetent amateur (J.Ch.), and does not carry the imprimatur of Keith Packard. I am not intimately familiar with all of the KDrive code, and this document is probably wildly inaccurate. I am sole responsible for any errors or omissions in this document.

The information contained herein is offered in good faith, but with no warranty of any kind. No kidding.

The Xfbdev KDrive server

The default KDrive server, Xfbdev, is designed for a Linux installation with a working /dev/fb and any common PC mouse on /dev/mouse. It includes the following drivers:

Xfbdev includes support for BDF and PCF bitmap fonts only. In addition, it hardwires a number of standard fonts, notably cursor and fixed, which will therefore be available even when there are no on-disk fonts. By default, it does not contain support for local scalable fonts in any format.

Xfbdev also includes support for a number of server extensions, including the ubiquitous SHAPE and the soon-to-be ubiquitous RENDER.

In order to compile Xfbdev, you need a clean XFree86 tree; I recommend version 4.0.2 or later. Put the following lines in your host.def file:

#define BuildServersOnly YES
#define KDriveXServer YES
#define TinyXServer YES
#define XfbdevServer YES

Now make World as usual; if the compilation proceeds without errors, you should have an executable xc/programs/Xserver/Xfbdev.

You may now make install or make

For information on running the Xfbdev server, please see the Xfbdev(1), Xkdrive(1) and Xserver(1) manual pages.

The Xvesa KDrive server

The Xvesa server is for x86 hardware only, and includes an unaccelerated display driver that will support any card with a VESA, VGA or even EGA BIOS (VESA 1.1 is the earliest supported version; VESA 2.0 will give better performance). Except for the display driver, the Xvesa server is identical to Xfbdev.

Unless you're using an original Hercules Graphics chipset or compatible, your hardware is most probably supported. In addition, the video driver in Xvesa will automagically do any initialisation of your chipset that your BIOS knows about but that might be undocumented, and thus not present in the stock XFree86 drivers. Xvesa is therefore an excellent choice for laptops, and until recently I was using Xvesa as the primary X server on mine.

God protect us from copper money and CGA cards.

In order to build the Xvesa server, include the following lines in your host.def file:

#define BuildServersOnly YES
#define KDriveXServer YES
#define TinyXServer YES
#define XvesaServer YES

For information on running the Xvesa server, please see the Xvesa(1), Xkdrive(1) and Xserver(1) manual pages.

Other standard KDrive servers

The KDrive makefiles include building recipes for a number of other servers, some of which use accelerated display drivers. These servers are not currently documented.

Any volunteers?

Fore more information, please see the Xkdrive(1) manual page and the file xc/config/cf/

Custom KDrive servers

A KDrive server does not include multiple drivers. In order to run KDrive on your hardware, you need to compile a KDrive server with the proper os, keyboard, mouse and display drivers. In addition, you will need to select the set of font renderers and server extensions that you want to compile.

OS support

At the time of writing, the publicly-available KDrive server only supports Linux. As most of KDrive is OS-agnostic, porting to a different Unix-like system should not be difficult.

Some bits of the source hint at support for certain proprietary systems, but it seems incomplete.

If you port KDrive to a different OS, I'd be glad to hear from you (and I am sure so would Keith). BSD should be easy. Minix-VMD might be more challenging, as it lacks a standard socket library; but then, earlier versions of XFree86 used to run on Minix-VMD, and KDrive uses the same XTrans layer. Stock 32-bit Minix doesn't have a poll/select equivalent.

I want to see KDrive on stock Minix. Please.

Keyboard support

At the time of writing, the KDrive server only has support for a generic Linux keyboard; the keyboard mapping is copied from the Linux kernel tables at startup. As X11 has richer keyboard information than Linux, and furthermore KDrive's mapping tables are incomplete, the results are not always perfect; I have found it necessary to fix my keyboard using xmodmap.

Mouse support

Since XFree86 4.2.0, KDrive automatically detects the type of mouse on /dev/mouse, which should be a link to the correct mouse device. Most common types of mice (including, of course, PS/2, Microsoft and Logitech serial, and Microsoft “bus”) are supported by the mouse driver; if yours is not, your best bet is probably to use gmp in repeater mode.

Display drivers

KDrive includes a fairly large selection of display drivers. Two are fully generic but unaccelerated: fbdev (included in the Xfbdev server) and vesa (included in the Xvesa server). The other drivers are partially accelerated, and support specific video hardware.

The generic drivers are documented in the Xfbdev(1) and Xvesa(1) manual pages. The accelerated drivers are currently undocumented; the only source of information about them is the source. Please see the directories under hw/kdrive/ and enjoy your read.

Font renderers

KDrive should be able to support all the font renderers supported by XFree86. You may add any of the following to your host.def file:

#define BuildSpeedo YES
#define BuildType1 YES
#define BuildCID YES
#define BuildFreeType YES
#define FontServerAccess YES

In XFree86 4.3.0 and later, the FreeType backend includes support for all common scalable font formats (including Type 1). For most uses, it is the only one that you will need.

Some of these renderers are rather large; you may want to think twice before including them in your “tiny” server.

As noted above, KDrive includes a number of hardwired, compiled-in fonts. There is no good reason to disable support for these “built-in” fonts; however, if you insist, you may use

#define BuildBuiltinFonts NO

Server extensions

KDrive might or might not be able to support any server extension supported by XFree86 that is not directly related to hardware. Use the usual incantations in your host.def file, for example,

#define BuildDBE YES

There is no good reason to disable the RENDER extension.

Additional defines

Any additional options that you want to pass to the C compiler should be put in KdriveServerExtraDefines:

#define KdriveServerExtraDefines -DPIXPRIV

Building against uClibc

At least the Xvesa server appears to build and run when linked against uClibc; note, however, that I haven't done any extensive testing.

You will first need to add two trivial functions to uClibc; this is simply done by relinking uClibc with uclibc-missing-math.c. Then, assuming that your uclibc toolchain is invoked by i386-uclibc-cc, add the following to your host.def file:

#define CcCmd i386-uclibc-cc

If you haven't recompiled libz against uClibc, you will also need to add the following line to your host.def:

#define HasZlib NO

This will have the side-effect of disabling all support for compressed fonts.

Is the uclibc-missing-math.c hack still necessary with recent uClibc releases?


Binary KDrive servers for GNU/Linux/x86 might be available from my KDrive download directory.

These binaries are offered in good faith, but really with no guarantee. Not even of any kind.


Handhelds Org and Jim Gettys' page about cross-compiling KDrive.

Keith Packard, the primary author of KDrive.

Back to my software page.

Juliusz Chroboczek, <>