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Xvesa - VESA Bios Extensions tiny X server
Xvesa is a generic X server for Linux on the x86 platform.
Xvesa doesn't know about any particular hardware, and sets the video mode
by running the video BIOS in VM86 mode. Xvesa can use both standard VGA
BIOS modes and any modes advertised by a VESA BIOS if available.
runs untrusted code with full privileges, and is therefore a fairly insecure
X server. Run at your own risk.
In addition to the normal KDrive server's
options (see Xkdrive(1)
), Xvesa accepts the following command line switches:
Multiple key presses recognized
directly by Xvesa are:
- -mode n
- specifies the VESA video mode to use. If mode n is not supported
by your BIOS and hardware, Xvesa will fail, hang your system, damage your
hardware, or cause a global thermonuclear war; you are on your own. This
option overrides any -screen options.
- list all supported video
modes. If -force was specified before -listmodes, lists all the modes that
your BIOS claims to support, even those that the Xvesa server won't be able
- disable some sanity checks and use the specified mode even
if the BIOS claims not to support it.
- use a shadow framebuffer even
if it is not strictly necessary. This may dramatically improve performance
on some hardware.
- don't use a linear framebuffer even if one is
available. You don't want to use this option.
- pass RGB values in
the order that works on broken BIOSes. Use this if the colours are wrong
in PseudoColor and 16 colour modes.
- use a contiguous (hole-less)
memory map. This fixes a segmentation violation with some rare BIOSes that
violate the VESA specification, but may cause slightly higher memory usage
on systems that overcommit memory.
- emit diagnostic messages during
BIOS initialization and teardown.
Xvesa opens all IO ports and
runs your VESA BIOS, which may be assumed to be buggy. Allowing your users
to run Xvesa is probably a security hole.
- Immediately kill the server.
- Switch to virtual console 1 through 12.
Xvesa records the current BIOS
mode when it starts and restores that mode on termination; if the video
card has been reprogrammed by another application, the display will almost
certainly be trashed. The alternative of saving and restoring the complete
video card state has proven unreliable on most video cards.
The VESA driver was written
by Juliusz Chroboczek who didn't realise what he was doing until it was
too late. Keith Packard then added support for standard VGA BIOS modes
and is especially proud of 320x200 16 colour mode.
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