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Version: 65863 (mandriva - 22/10/07)

Section: 8 (Commandes administrateur)


SVGATextMode - Textmode manipulation/enhancement tool


SVGATextMode [ -ndhrfcvsam ] [ -t ConfigFile ] [ TextmodeLabel ]


SVGATextMode provides a means to seriously enhance the looks of your Linux text consoles, by re-programming the (S)VGA hardware. It uses a configuration file similar to the one the XFree86 X-windows server uses (Xconfig or XF86Config) to set up better looking textmodes. (=higher resolution, larger font size, higher display refresh...).

It works independently of what text modes are allowed from the BIOS. In theory, any text mode size is possible, as long as your VGA card is up to the job. Whether it is or not, depends greatly on the chipset.

SVGATextMode can resize the console screen on the fly, without rebooting, to any other size. The configuration file holds all the parameters needed for the new mode.

It needs kernel version 1.1.54 or newer if screen resizing is to be possible.

Supported chipsets

Generic VGA chips. This can also be used for unsupported VGA chips, but with very limited possibilities. Most portable VGA computers (Compaq LTE, ...) should work with this also: VGA LCD's can't use higher dot-clocks anyway.

It is important to start from a standard VGA text mode (80x25...80x50) when using this "chipset" for unsupported chips. Otherwise the clock will not be programmed correctly.

any S3-based card, including those from Diamond, Number 9 and SPEA/Video7.
Cirrus Logic chipsets. This works with CL-GD542x, CL-GD543x ("Alpine") and CL-GD546x ("Laguna") chipsets.
TVGA8900, TVGA9000
The oldest Trident cards. NOT for the Trident accelerated cards like the 9440 etc.
All accelerated Trident cards from TGUI9320LCD and up.
All (?) Western Digital cards, from the plain old first Paradise card (PVGA1) to the more recent WDC90C33 accelerator (WDC90C3X).
All ATI cards BEFORE the MACH32.
ATI MACH32 and MACH64. Many MACH64 cards use special RAMDACs and clockchips that are not yet supported by SVGATextMode. Those will not work.
Only MACH64 boards with internal clockchips are supported.
Headland Technologies based Video 7 boards only. Older V7 boards use C&T or Cirrus chips. Newer V7/SPEA cards use S3.
ALI, AL2101
Avance Logic chipsets. It's not sure whether this will work on ALL Avance Logic cards.
OTI67, OTI77, OTI78
Oak Technology chipsets.
SiS chipsets. UNTESTED!
RealTek chipsets. UNTESTED!
ARK1000 and ARK2000 chipsets. UNTESTED!
NCR77C22E, NCR77C32
NCR chipsets. The NCR77C21 and NCR77C22 (without "E" suffix) will not benefit from this. They should work just as well with the generic VGA driver. UNTESTED!
Genoa 6000 series cards. The 5000 and 7000 series are based on resp. ET3000 and ET4000 chips. Use the ET4000 driver for those. UNTESTED!
MX graphics chips. MX86000 and MX86010 chips should work. UNTESTED!
Matrox Mystique and Millennium G100, G200, G400, and G400 MAX are supported.
Those NeoMagic laptop controllers
All RIVA128 derivatives (including RIVA128ZX, TNT, and TNT2).

SVGATextMode needs a configuration file with a similar syntax as Xconfig or XF86Config, the configuration file for XFree86, the X-Windows server. The default config file is /etc/TextConfig.

See the TextConfig(5) manual file for details on its syntax.

When running SVGATextMode with a new textmode, it will output a single line, describing what the new mode is, and what are the screen refresh rates.

Example output:

Chipset = 'S3', Textmode clock = 75.00 MHz, 116x48 chars, CharCell = 9x16. Refresh = 55.93kHz/69.9Hz.


The only required option is the TextmodeLabel, which tells SVGATextMode to which mode it must switch. A mode description line with the same name must be present in the config file. The parameters on that line will be used to program the new text mode.
don't program the new mode. This option will scan the config file for the requested mode, parse all parameters, and report what the new mode will look like. But it doesn't actually change anything. This is useful for seeing if a mode is correctly entered in the config file, and if your monitor will be able to handle it.
debugging mode. SVGATextMode will output lots of debugging information about all the things it attempts to do. This is mostly for "internal purposes" only, but it could help you discover why SVGATextMode doesn't react as you expect it to. This could also be useful when reporting a problem.

A second "d" option will enable extended debugging, showing you all the data that was parsed from the config file, instead of just the most important things. More specifically, this will add all the mode lines and the font selection list to the debug output.

prints out a short help and the version number.
don't run the ResetProg.

When a ResetProg is defined (and thus enabled) from the config file, SVGATextMode, without "-r", will attempt to run it whenever it has changed the screen size.

The reset program is normally used to signal or restart a program that depends on the current screen size, and that doesn't react to the SIGWINCH signal the kernel sends it upon a screen resize. Typical examples are gpm and selection; two very handy textmode-mouse handlers.

Resizing the screen from 80x25 to e.g. 116x48 without telling gpm or selection about it, will cause the mouse cursor to get stuck in the upper left 80x25 characters of the screen.

The "-r" option is useful when SVGATextMode is started from the system initialisation files (/etc/rc.d/...), because many of the programs that need to be reset through the ResetProg have not yet been started, so trying to send them signals, or trying to kill them, would fail. And trying to restart them would cause two copies of the same program running when the rest of the rc-files start them up.

don't run the FontProg. When the font loader is enabled through the LoadFont option in the config file, SVGATextMode will not run it, even when the screen is resized. When this option is not enabled and the font loader is enabled, SVGATextMode will run an external program to load a suitable font.
don't program the pixel clock. More of a debugging option. If you suspect that SVGATextMode fails to program your VGA clock properly, then this option programs everything else except the pixel clock, which is left at its old value. Some laptops don't react to well when the pixel clock is reprogrammed, so this option can help there, too.
don't validate H/V frequencies. Normally SVGATextMode will check the horizontal frequency and the vertical refresh of the new mode against the ranges specified in the config file, and refuse to program a mode that doesn't fall within those limits. This option turns off that checking, and will program ANY mode, even if the config file says your monitor cannot handle them.
scan mode. SVGATextMode will scan the entire config file, and will dump a listing of all valid modes for your configuration, taking the limits for vertical refresh, horizontal scan rate, maximum text mode pixel clock and availability of the required clock frequency (if you don't have a programmable clock chip) for your VGA card / monitor configuration into account. When combined with the -v option, it will dump all modes, whether they are allowed or not.

This is particularly useful to create input to a script or program that lets you (for example) select a text mode from a menu.

allow trying to resize screen via a 1x1 screen. This option is only useful when you get an out of memory error when resizing the screen. Normally SVGATextMode will just exit and tell you there was not enough memory. The best thing to do then is to free some memory. If that is impossible for some reason, this option will first resize the screen to a 1x1 size to free the memory already taken up by all the consoles, and then resize to the desired size.

WARNING: see the BUGS section for more information on the potential dangers of this method. Do not use this option unless it is absolutely necessary.

always do a full resize. SVGATextMode will normally check with the old screen size to see if the new mode actually resizes the screen (it could just enhance the screen by moving to a larger font, but remain at the same width/height). It does that via the tty settings (those you get when typing "stty -a"). If it detects that the new mode is a different size than the old one, it will run all sorts of extra code to make various system components know about the resizing. But if it thinks no actual resizing has been done, it won't do that.

Under certain circumstances (see the BUGS section), it is desirable to resize the screen, even if the tty settings say the screen already has that size. This option will force the resizing code to "fake" a resize, and run all necessary code (set the tty settings again, tell the kernel about the resizing, and run the optional ResetProg).

Don't tell the kernel if the screen size has changed. If the horizontal
screen size really has changed, the kernel will not know about it and render text in completely wrong places. Some people seem to want to use this to lie to the kernel about the amount of text lines on screen, and e.g. use the lower line for a status display (since the kernel doesn't know it's there, it doesn't render text in it).

As a side effect, none of the programs running on the console will be sent a SIGWINCH from the kernel, so they too will not know about the change. The ResetProg is still ran (unless when prohibited by the "-r" option of course), so it could be used to send explicit resize messages to console applications that otherwise relied on the kernel SIGWINCH signal.

always run SVGATextMode, even if you are not running it from a normal VGA
textmode console. This disables the "dumb-user protection" that was added to avoid people from messing up their XFree86 display when running SVGATextMode from there. This option is only useful if you know what you're doing. It could be used to try to restore a broken textmode using after the Xserver crashed (in combination with the "-o" option).
-t ConfigFile
This option tells SVGATextMode to use a different configuration file than the default one (/etc/TextConfig).
Force all standard VGA registers to a known textmode state. This is quite useful when some VGA-aware program (X-server, svgalib, ...) crashes or gets killed and leaves the screen in graphics mode.

There's only one problem with this. Most of these types of crashes leave the keyboard in raw (scan-code) mode, and thus you won't be able to type the command to restore text mode... You will have to do a "kbd_mode -a" from a remote terminal first. Unless you add "kbd_mode -a" to the file defined in the "ResetProg" label in the TextConfig file, and have "stm -o" under a mousebutton combination with the GPM mouse package.

Another fun-stopper is the extended VGA registers, which this option does _not_ reset, because they are chipset-dependent. This means that the "-o" option might not help at all, depending on how sophisticated your card is. SVGATextMode knows about a few cards and how to kick them back into "normal" mode, but not all (due to lack of documentation and cards to test -- hint, hint).


A small example of how SVGATextMode goes to work: suppose you started up in 80x25 text mode, and wanted to change to a more respectable 116x48 mode with a fine 16-pixel high font (normal 132x43 modes from the BIOS are only 8 to 11 pixels high, and the difference is incredible), and extra-wide spacing (using 9-pixel wide characters instead of 8).

Now suppose you have a mode description line in the config file that looks like this:

"Super116x48" 75 928 968 1104 1192 768 775 776 800 font 9x16
(the entire config line must be on a single line)

After correctly configuring the /etc/TextConfig file for your VGA card, typing

SVGATextMode Super116x48

will produce an output similar to the following:

Chipset = 'S3', Textmode clock = 75.00 MHz, 116x48 chars, CharCell = 9x16. Refresh = 55.93kHz/69.9Hz.
Loading 8x16 font from file /usr/lib/kbd/consolefonts/Cyr_a8x16

Note the refresh timings at the end of the first output line: this mode would require an SVGA monitor capable of 56 kHz at 70 Hz (the same frequencies as a VESA 1024x768 @ 70 HZ mode).

The second output line actually comes from setfont, a program which SVGATextMode can be made to call automatically after resizing the screen, so the font is adjusted to the available space in the character cell.


In order to be able to do anything, SVGATextMode must be run by the superuser, or it must be setuid root.

Having SVGATextMode installed with the SETUID bits ON makes it run as root, even when a non-root user runs it. This is a potential security problem, since SVGATextMode can be made to execute external programs (font loader and ResetProg).

The default distribution will NOT renounce superuser rights EVER, so it'll run any external program as root also (if the setuid bits on SVGATextMode are on, of course). If you are administering a critical system, don't set the SETUID bits on SVGATextMode (which will have the side effect that non-root users cannot use SVGATextMode), or if you do, make sure that all externally called programs are secure.

If you want to have the SUID bits on, but don't trust the external program's security, then recompiling SVGATextMode with the compile-time option "RUN_SECURE" enabled will make SVGATextMode renounce superuser rights immediately after requesting rights to write to the VGA registers. Any program run thereafter will be run with the user ID of the one executing SVGATextMode.

If the programs called by SVGATextMode are not setuid root, they might fail, because they want to change things only root is allowed to tamper with.


There is a DOS version of all SVGATextMode tools (including SVGATextMode itself) included in the distribution.

The stm.exe program will do the same, and require the same as SVGATextMode under Linux, with the following exceptions:

The TextConfig file is in \etc\textconf. Note the lack of a drive letter. You have to execute stm.exe from the same drive the textconf file is on. Otherwise, use the -t option to specify a full textconf file path.
No font loading (yet?). Do not enable the "loadfont" option in the textconf file. It will not work: there is no DOS font loader included in the SVGATextMode distribution. This basically means you are limited to modes that still work with the same font you started with. There are no doubt numerous font loaders available for DOS that could solve this problem.
Stm.exe is really of limited use. DOS was not designed to have flexible screen sizes (DOS was not designed - period. DOS was patched). DOS programs follow the same route. Some DOS programs assume a certain screen size (like 80x25). Many assume at least a constant screen width (80 chars). Only a few support all screen sizes without trouble. You can expect DOS versions of UNIX tools to be of the last kind (like the editor joe.exe).
Running stm.exe in a Windows DOS box IS possible, although you must remain 80 chars wide, or Windows will report that "due to the way this program uses the VGA, it must be run full-screen". If you run stm.exe to change from a 80x25 screen to a 80x50 screen, the DOS box will auto-resize to the new height.


Probaby zillions of them. And for a program that must be run as root, and that changes hardware registers, this is not a good thing.
mode switching
SVGATextMode's purpose is to change the previous text mode into the new one. It only changes those VGA registers that determine the text mode size. Any other register is left untouched. This has the advantage that the special (tricky) registers that were set up by the BIOS when the machine booted remain unchanged, so SVGATextMode doesn't need to have the intelligence built-in to deal with all kinds of special settings.

The downside of this is that it can only go from one text mode to another. In most cases, SVGATextMode cannot switch to text mode from a non-text screen (e.g. from graphics mode, or from a messed-up screen when some graphical application exits ungracefully).

SVGATextMode does not even try to detect the VGA chipset you are using. This means that if you configure it for an S3 chip, but there's a Cirrus Logic under the bonnet, you'll get a similar effect as when you try to use diesel fuel in a petrol engine...
kernel version
You need at least kernel version 1.1.54 to be able to resize the screen to some other X/Y dimension than is currently being used. The program will refuse to resize the screen when it detects an older kernel version.
out of memory
When the system is under heavy load, screen resizing could bail out with an `out of memory' error. The reason for this is rather obscure, but it boils down to the fact that you need to have at least a certain amount of free, contiguous RAM if you want to avoid this. The amount depends on the requested screen size. On most linux systems (which have a maximum possible amount of 64 virtual consoles), this is:

                X * Y * 2 * 64

bytes of memory, where X is the number of characters per line, and Y the number of text lines on the screen.

When the kernel fails to resize the screen because of a lack of the right kind of memory, SVGATextMode tries to free some more by temporarily requesting a large block of memory and freeing it immediately again, forcing some disk buffers to be flushed to disk, and forcing some programs to be swapped out.

If the resizing still fails, it tries to free twice that much memory, and if that fails, three times the amount. If you attempt to resize to a really big screen, this is resp. 2, 4 and 6 MB of memory that will be "freed" before trying to resize the screen. If all that fails, then SVGATextMode will finally give up, and announce this in a large, friendly error message.

The -m option is a way around this, but it has its own problems. When it temporarily switches to a 1x1 screen in order to free some more memory, some other process might snatch memory away from under it before SVGATextMode can switch back to the new mode, causing the final resize to the new size to fail. This is very unlikely to happen, but when it does, you are left with a 1x1 screen, which is rather small. When that happens, blindly stopping some jobs, and blindly resizing to a 80x25 mode (either through SVGATextMode or set80) is the only solution.

A much better option to avoid out-of-memory problems is to tell the kernel it needs to keep more memory free, by swapping a little sooner. This can be done only in Linux kernels from somewhere around the 1.3.60's and up, using /prov/sys/vm/freepages. The default contents of this configuration "file" are:

32 48 64

These numbers represent the amount of free pages (one page is 4096 bytes on an Intel platform) below which the kernel will begin to swap pages out or reduce buffer sizes aggressively, moderately and lightly, resp. All this means that in the default case, an unloaded machine will saturate towards 64 free pages (256k) free memory. Changing these settings to higher values, e.g.

cat 128 256 1024 >/proc/sys/vm/freepages

will cause an unloaded machine to have 4M free memory after a while. This will reduce the risk of running out of memory for SVGATextMode resizing significantly.

Slow startup
This is more a feature than a bug, but it could bother you at some time that SVGATextMode starts up extremely slow. This only happens when you are starting SVGATextMode from a non-working text mode (screen blank, monitor doesn't sync,...).

While experimenting with mode timings, at some point you could end up with a mode that the VGA card cannot handle, and it just stops outputting anything at all: no video, no sync, nothing.

SVGATextMode does its work in the vertical blanking interval, waiting for a vertical sync signal before starting to change VGA registers. But when there is no sync, it would wait forever. A timeout of one second prevents that, but shows up as a relatively long delay before the new mode becomes active.

In addition to that, the default TextConfig file has the "SyncDisks" option active, which makes SVGATextMode execute a "sync" instruction to flush all remaining data in the disk cache to disk. Since there is no way to know when that has finished, SVGATextMode just waits a good while (a few seconds), hoping that all data is flushed by the time it starts.

Your worst nightmare: SVGATextMode bails out!
SVGATextMode works its way through the VGA register programming sequentially, working its way through all the registers one at a time. When it encounters some kind of error in the middle, it will most probably bail out with an error message.

But that message will not be of much use, since leaving those VGA registers halfway programmed will most probably result in no video at all. So the message is there, telling you in all detail what went wrong, but you will not be able to see it...

The author has been made aware of this problem on various occasions, and future versions will not be as unforgiving.

In the mean time, make sure nothing will go lost when you first experiment with SVGATextMode and you have to reboot to get back into a visible text mode. Preferably use `savetextmode' from svgalib to enable a future `textmode' restore command when something goes wrong. Also consider redirecting standard error to a file when you expect trouble. You can then inspect the result when (or "if" ;-) you get back your screen.

There are some nasty interactions with other programs that do VGA programming. Amongst them are: the XFree86 XWindows server, svgalib, dosemu and probably others. The most common effect is a distorted screen when such a program switches back to text mode. The real reason for this mostly lies with that program, because it doesn't restore all VGA chip registers as they were before that program started. They were all written a long time before SVGATextMode saw the light of day, so how could they know?

SVGATextMode cannot really solve this problem, since it exits after setting the new mode, and so it doesn't stay active to restore the mode whenever another one screws it up.

For a more in-depth discussion of these kinds of problems, read the doc/FAQ file in the SVGATextMode distribution.

Most problems with XFree86 happen when you change the text mode after X has been started. The X-server remembers all VGA chip settings when it first starts up, and never seems to check them again. So when you start X, switch back to text mode while X is still running, then change the text mode to something else, switch back to X, and then back to text mode, you're in trouble.

X has restored the VGA register contents of when it started, which are not the same that you programmed with SVGATextMode. But the kernel still thinks you are in the new mode, since X didn't tell it about the restoration to the old values, and thus the kernel draws its characters in the wrong place in the video memory.

Result: screen completely garbled. Solution: re-running SVGATextMode whenever you switch back from X to text mode, or exit X, and restart it after re-programming the new text mode.

The former case will need the -a option to tell SVGATextMode to force a full resize. When X restores the VGA register contents, it doesn't restore the tty settings, nor the kernel screen size parameters. Thus SVGATextMode is made to believe that the screen is not resized, and thus doesn't do all the resizing code, leaving the kernel parameters and tty settings as they were: wrong.

A general rule of thumb to avoid interaction-problems with the X-server is to specify as much as possible, thus allowing the server as little guesswork as possible. This is recommended by the XFree86 manuals also, even without SVGATextMode. In practice this means you let the server guess for all hardware parameters just once, i.e. when you first install it on a new VGA card, and preferably from a non-tweaked textmode (no SVGATextMode). You then copy as much parameters from the probe to the XF86Config file as possible. The reason for this is that some probing routines in the XFree86 server work well only under a standard text mode (e.g. the S3 IBM RGB RAMDAC RefClk probe).

other X-servers
If you thought XFree86 was evil for doing this, keep in mind that some commercial X-servers (e.g. Accelerated-X from Xinside) for Linux are even worse (don't shoot me guys! They are absolutely MARVELOUS X-servers, but their textmode support is not just bad, it's non-existent).

They _assume_ you start from a 80x25 screen, and will always return to a 80x25 screen when doing a VT-switch or when exiting the server. Since they don't tell the linux kernel what they've just done, the linux kernel, still thinking it's in some weirdo text mode, will draw its characters all over the place, except in the right one... A partial solution is to change the `startx' script to make it re-run SVGATextMode after the server exits. But this doesn't solve the VT-switching problem.

Svgalib will show the same type of problems as the X-server. Some cards will react differently than from XFree86, because they are more or less supported in svgalib.
Ditto. Only worse. Dosemu only "knows" about some basic VGA cards, but has no knowledgs whatsoever about clock chips and more modern VGA chips. Chances are DOSEMU gets you in text mode trouble.

DOSEMU might not be clever enough to reset all your card's VGA registers (including the clock setting registers) when it starts up in VGA-mode. In that case, any non-standard SVGATextMode mode could produce a non-syncing DOS display. The only cure in this case is to reset to a standard VGA text mode like 80x25 before starting DOSEMU.

A similar problem might pop up when exiting DOSEMU. If it doesn't restore all linux textmode registers, the linux console might get corrupted.

Both problems can be resolved by embedding the DOSEMU call in a script, which does something like this:

         SVGATextMode 80x25x9
         SVGATextMode My_SuperMode

This will not solve the problem when switching to another virtual terminal while DOSEMU is still running.

After rebooting to DOS (shame on you! There's a Doom for Linux also) or when starting DOSEMU, the text mode screen, or, more likely some graphics modes might produce a non-syncing display. This is more likely to happen on boards that use a clockchip (i.e. when the TextConfig file has a `ClockChip' line enabled.

The reason for this is that some card's BIOSses don't care to reset all clocks to their defaults when they get a reset signal (i.e. when rebooting). Some die-hard cards won't even do that when you hit the cold-reset switch, and will only revert to the default clock values when you power-cycle the machine.

A simple solution to this is to put an SVGATextMode (or ClockProg) command in the system shutdown script. This is in most cases


If the programmed clock is the correct default clock value, your DOS problems will be solved. The only tricky part here is to find out what that default clock is...

Since SVGATextMode reprograms clock #2 (the third clock) on most clockchips, the default clock value depends on the clockchip type you're using.

Only clocks #0 and #1 are the same for (almost) all VGA chips, and thus this method is only really simple for those clockchips where clock #0 (default = 25.175 MHz) or #1 (28.3 MHz) is reprogrammed. This is currently only for the icd2061a (or the equivalent ics9161) clockchips when the "clockchip_x" option is used.

More Information
Read doc/FAQ in the SVGATextMode distribution for more reading on this subject.


The (default) configuration file for SVGATextMode
The main text mode manipulation program described here


SVGATextMode was written by Koen Gadeyne <>, with help from a lot of local and remote Linux fans.

Much of the VGA code for SVGATextMode was borrowed (I will give it back :-) from the XFree86 3.1 server code (and also from newer versions). The S3 clock chip code and Cirrus Logic clock code was copied (with some improvements added) from the original XFree86 code.

See the CREDITS file in the distribution for a full list of all helping hands.


TextConfig(5) - Configuration file for SVGATextMode

grabmode(8) - A XFree86/SVGATextMode VGA mode grabber

SVGATextMode-x.y/doc/FAQ - description of problems you could encounter when using SVGATextMode, and some solutions.

The 'doc' directory in the SVGATextMode distribution contains a lot of miscellaneous documentation on a range of topics related to configuring and using SVGATextMode.