Chapter 4. Frequently Asked Questions
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## Chapter 4. Frequently Asked Questions

This section provides answers to frequently asked questions associated with the NVIDIA FreeBSD x86 Driver and its installation. Common problem diagnoses can be found in Chapter 5, Common Problems and tips for new users can be found in Chapter 8, Tips for New FreeBSD Users. Also, detailed information for specific setups is provided in the Appendices.

### 4.1. NVIDIA Driver
| Where should I start when diagnosing display problems?
| One of the most useful tools for diagnosing problems is the X log file in `/var/log`. Lines that begin with `(II)` are information, `(WW)` are warnings, and `(EE)` are errors. You should make sure that the correct config file (i.e. the config file you are editing) is being used; look for the line that begins with:
        (==) Using config file:
Also make sure that the NVIDIA driver is being used, rather than the “nv” or “vesa” driver. Search for
        (II) LoadModule: "nvidia"
Lines from the driver should begin with:
        (II) NVIDIA(0)
| How can I increase the amount of data printed in the X log file?
| By default, the NVIDIA X driver prints relatively few messages to stderr and the X log file. If you need to troubleshoot, then it may be helpful to enable more verbose output by using the X command line options `-verbose` and `-logverbose`, which can be used to set the verbosity level for the `stderr` and log file messages, respectively. The NVIDIA X driver will output more messages when the verbosity level is at or above 5 (X defaults to verbosity level 1 for `stderr` and level 3 for the log file). So, to enable verbose messaging from the NVIDIA X driver to both the log file and `stderr`, you could start X with the verbosity level set to 5, by doing the following
        % startx -- -verbose 5 -logverbose 5
| I have read that the NVIDIA FreeBSD Driver is not a native driver, but sits on top of the Linux ABI compatibility layer. Is this true?
| No, the NVIDIA FreeBSD Driver Set is a native driver. It does provide Linux OpenGL libraries in addition to the native, FreeBSD libraries to enable users to run Linux OpenGL applications.
| Is the NVIDIA FreeBSD Accelerated Driver Set thread-safe?
| This release is thread-safe on FreeBSD 5.3 or later systems making use of the libpthread or libthr KSE threading libraries. On these systems, the NVIDIA Linux ABI compatibility libraries are fully thread-safe as well.
| Why can't the Linux compatibility libraries correctly determine if they are used in a multithreaded application?
| The Linux compatibility libraries are not able to correctly determine if they are used in a multithreaded application because the %gs segment register is not initialized correctly for Linux compatibility. The `__GL_SINGLE_THREADED` environment variable (set to "1") can be used to work around this issue, but at the cost of thread-safeness.
| Why do applications that use DGA graphics fail?
| The NVIDIA driver does not support the graphics component of the XFree86-DGA (Direct Graphics Access) extension. Applications can use the XDGASelectInput() function to acquire relative pointer motion, but graphics-related functions such as XDGASetMode() and XDGAOpenFramebuffer() will fail. The graphics component of XFree86-DGA is not supported because it requires a CPU mapping of framebuffer memory. As graphics boards ship with increasing quantities of video memory, the NVIDIA X driver has had to switch to a more dynamic memory mapping scheme that is incompatible with DGA. Furthermore, DGA does not cooperate with other graphics rendering libraries such as Xlib and OpenGL because it accesses GPU resources directly. It is recommended that applications use OpenGL or Xlib, rather than DGA, for graphics rendering. Using rendering libraries other than DGA will yield better performance and improve interoperability with other X applications.
| My kernel log contains messages that are prefixed with "Xid"; what do these messages mean?
| "Xid" messages indicate that a general GPU error occurred, most often due to the driver misprogramming the GPU or to corruption of the commands sent to the GPU. These messages provide diagnostic information that can be used by NVIDIA to aid in debugging reported problems.
| On what NVIDIA hardware is the EXT_framebuffer_object OpenGL extension supported?
| EXT_framebuffer_object is supported on GeForce FX, Quadro FX, and newer GPUs.
| I use the Coolbits overclocking interface to adjust my graphics card's clock frequencies, but the defaults are reset whenever X is restarted. How do I make my changes persistent?
| Clock frequency settings are not saved/restored automatically by default to avoid potential stability and other problems that may be encountered if the chosen frequency settings differ from the defaults qualified by the manufacturer. You can use the command line below in `~/.xinitrc` to automatically apply custom clock frequency settings when the X server is started:
        # nvidia-settings -a GPUOverclockingState=1 -a GPU2DClockFreqs=<GPU>,<MEM> -a GPU3DClockFreqs=<GPU>,<MEM>
Here `<GPU>` and `<MEM>` are the desired GPU and video memory frequencies (in MHz), respectively.
| Why is the refresh rate not reported correctly by utilities that use the XRandR X extension (e.g., the GNOME "Screen Resolution Preferences" panel, `xrandr -q`, etc)?
| The XRandR X extension is not presently aware of multiple display devices on a single X screen; it only sees the MetaMode bounding box, which may contain one or more actual modes. This means that if multiple MetaModes have the same bounding box, XRandR will not be able to distinguish between them. In order to support DynamicTwinView, the NVIDIA X driver must make each MetaMode appear to be unique to XRandR. Presently, the NVIDIA X driver accomplishes this by using the refresh rate as a unique identifier. You can use `nvidia-settings -q RefreshRate` to query the actual refresh rate on each display device. This behavior can be disabled by setting the X configuration option "DynamicTwinView" to FALSE. For details, see Appendix I, Configuring TwinView.
| Why does starting certain applications result in Xlib error messages indicating extensions like "XFree86-VidModeExtension" or "SHAPE" are missing?
| If your X config file has a `Module` section that does not list the "extmod" module, some X server extensions may be missing, resulting in error messages of the form:
    Xlib: extension "SHAPE" missing on display ":0.0"
    Xlib: extension "XFree86-VidModeExtension" missing on display ":0.0"
    Xlib: extension "XFree86-DGA" missing on display ":0.0"
You can solve this problem by adding the line below to your X config file's `Module` section:
        Load "extmod"

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