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# Display problems

## Background

Fatdog64 by default uses KMS (Kernel Mode Setting), a recent development in Linux kernel where control of display resolution and bit depth (=number of available colours) are managed inside the kernel instead of Xorg graphics driver.

As a consequence of KMS, these things happen:

- The KMS kernel driver will take over the graphics early in the boot process.
- This driver will change the video mode from text mode into its highest-available-resolution graphics mode.
- As such, there is no more text console. It is replaced by framebuffer console.
- More often than not, this framebuffer console will display smaller fonts and provides more rows and column than a standard text console (80x25).

Not all graphic cards/drivers support KMS. The ones that notably support them are:

- Intel (will not work without KMS)
- Nvidia (*nouveau* driver requires KMS, older *nv* does not support KMS)
- Radeon (will not work without KMS)

Those cards/drivers that do not support KMS will continue to work as they were. In addition, it is possible to turn off KMS as well. When KMS is turned off, you have two choices:

- If the driver supports non-KMS mode, you can continue to use that driver
- If the driver does not support non-KMS mode, you will have to use *vesa* driver.

Note: AMD/ATI/NVidia proprietary drivers do not support KMS at the time of writing, and requires that KMS be turned off. The package installer for these driver packages will do this automatically for you.

## Common Problems

Display drivers, especially for advanced GPUs, are very complex. Add that to the fact that some GPU vendors are less open than others: people who write open-source drivers often do not have enough information on how the cards behave and end up having to guess. Combine that with card releases: new GPUs (at least new display cards) are released every year, sometimes with only subtle differences of behaviour from the earlier versions. You should be surprised that it works at all ☺.

But it does, most of the time. When it doesn't, though, you may see some of these problems:

- Blank screen (or white screen, or a uniform-coloured screen of some sorts, or stripes ...)
- The screen shows "unsupported frequency" or "mode not supported" or something similar.
- The text displayed on the screen is vanishingly small.
- And others.

Rather than going through the list of all possible problems, here we will show some solutions you can try if you encounter any of these problems.

  

### Turning off KMS

In the most extreme cases (especially when you have a blank screen or otherwise odd/unusual patterns), you may want to turn off KMS.

KMS can be turned off by putting [*nomodeset*](boot-options.md) on the kernel boot parameters (click to see more details). This will turn off KMS entirely. You can also turn off KMS for a specific driver by putting the driver name in front, e.g. *radeon.nomodeset=1* for the radeon driver.

Note that certain drivers absolutely require KMS in order to work; if you turn off KMS you may not be able to use the optimum resolution settings. Most recent GPU-specific drivers won't work without KMS nowadays, and your best bet is to use *vesa* driver for BIOS-based systems or **fbdev** for UEFI-based systems.

You may want to combine turning off KMS with telling Xorg to use a specific GPU driver and/or resolution, outlined [below](#tell-xorg-to-use-a-specific-driver-and-resolution).

  

### Tell KMS to use a specific resolution and frequency

Instead of turning off KMS entirely, you may want to try to tell KMS to use a specific resolution and refresh frequency instead - most probably lower than the default one chosen by KMS. This is useful in cases where your monitor gives out a message that says the resolution/frequency chosen by video card is too high.

Resolution and frequency can be set by using [*video*](boot-options.md) option (click to see more details).

  

### Make the console text bigger

If the display is right but it's just that the text on the console is too small to see (this is possible if you use a high-resolution monitor with small physical dimensions), you can use a larger font to make the screen more intelligible.

This isn't usually required as most people don't work on the console directly (most people use the graphical desktop and use the terminal emulators (e.g. xterm / urxvt) inside the graphical desktop), but it may be useful if for some reason you can't get the graphical desktop to start and you're troubleshooting it.

Fatdog64 comes with a size 16x32 Terminus fonts named *big* and *bbig* (for "bold and big") to make them easier to remember. To use these fonts type this at the console: *setfont big* or *setfont bbig*

Note: You *must* use the *setfont* command at the linux console, not from the terminal emulator on your graphical desktop.

  

### Tell Xorg to use a specific driver and resolution

So far what has been discussed explains what can be done to improve the situation at the console. The graphical desktop (managed by Xorg) has its own settings. Unless these setting are changed, Xorg by default will automatically load the most suitable GPU driver, then choose the highest supported resolution, bit depth and refresh frequency (just like KMS).

Usually this is what you want, but in case it is not, you can override the automatic settings by running the command *xorgwizard*. This command allows override of the driver, resolution and bit depth (but not frequency - Xorg will still choose the highest supported frequency given the other parameters).

This command can be run from the console or from a terminal emulator in the graphical desktop. We recommend the console because it allows you to test your changes of the driver, resolution or bit-depth. Whereas, if you run xorgwizard from a terminal emulator, when Xorg is already running, you will be able to change the settings but you won't be able to validate that your choices are right.

Settings are stored in */etc/X11/xorg.conf.d/20-gpudriver.conf*; if you wish to revert to the automatic defaults, just remove this file.

**Note:** If a card-specific driver does not work for you, you may want to try to use a generic driver instead. There are three generic drivers you can try: the **modesetting** driver (works when KMS is enabled - which is by default), the **fbdev** driver (works for KMS and UEFI-based systems), and the **vesa** driver (only for older computer with BIOS systems, and will work regardless of KMS settings). *xorgwizard* indicates which driver requires KMS.

  

### Tell Xorg to display a larger font

The *setfont* command does not work within the graphical environment (it will screw up your screen instead). Changing the font size (or font family, for that matter) for the terminal emulator depends on which terminal emulator you use. To affect urxvt, the default Fatdog64 terminal emulator, create a file called *.Xdefaults* in your home directory and put the command *URxvt.font: xft:mono:pixelsize=14:autohint=true* inside it. Change "14" to whatever size you want, in pixels.

Changing the font size in other applications is done through their specific configuration interfaces, which vary depending on the application.

The best way to change the font size for *all applications* is to change the "Global Font Size". This setting is stored in a file named *.Xresources* located in your home directory. Look for the line starting with *Xft.dpi*. You can edit it manually and then re-start the X server, or more comfortably use the *"Appearance" \> Set Global Font Size* Fatdog64 Control Panel applet (or "Desktop" in older Fatdogs). It allows you to change the size from 54 to 108 (the default is 78). To set values outside this range, edit the file manually.

## Useful links about KMS

Here are some links about KMS. Please note that while they are useful as a reference and background information, not all of the commands discussed there will be directly applicable to Fatdog64.

[Arch Linux KMS documentation](https://wiki.archlinux.org/index.php/Kernel_Mode_Setting)  
[Debian KMS documentation](http://wiki.debian.org/KernelModesetting)  
[Freedesktop Nouveau KMS documentation](http://nouveau.freedesktop.org/wiki/KernelModeSetting)  
[ModeDB - details on the *video* kernel parameter](http://cgit.freedesktop.org/nouveau/linux-2.6/tree/Documentation/fb/modedb.txt)  
[Older version of ModeDB, only applicable for non-KMS system](http://www.kernel.org/doc/Documentation/fb/modedb.txt)  


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