Xorg-7 Testing and Configuration

Testing Xorg



Before starting Xorg for the first time, is is useful to rebuild the library cache by running ldconfig as the root user.



Before starting Xorg for the first time, is is often needed to reboot the system to ensure all appropriate daemons are started and appropriate security issues are properly set. As an alternative, logging out and logging back in may work, but as of this writing has not been tested.



If Xorg hangs for some reason (for example, lacking a proper input driver), the system may stop responding to any user input. As a precaution, you can enable a magic SysRq key before testing Xorg. As the root user, issue:

echo 4 > /proc/sys/kernel/sysrq

Then if Xorg hangs, it's possible to use Alt+SysRq+R to reset the keyboard mode. Now it should be able to use Ctrl+Alt+Fx (replace x with a VT number) to switch to another VT. If it works, login and kill Xorg using command line in the new VT.

To test the Xorg installation, issue startx. This command brings up a rudimentary window manager called twm with three xterm windows and one xclock window. The xterm window in the upper left is a login terminal and running exit from this terminal will exit the X Window session. The third xterm window may be obscured on your system by the other two xterms.



When testing Xorg with the twm window manager, there will be several warnings in the Xorg log file, $HOME/.local/share/xorg/Xorg.0.log, about missing font files. In addition, there will be several warnings on the text mode terminal (usually tty1) about missing fonts. These warnings do not affect functionality, but can be removed if desired by installing the Xorg Legacy Fonts.

Generally, there is no specific configuration required for Xorg, but customization is possible. For details, see the section called “Setting up Xorg Devices” below.

Checking the Direct Rendering Infrastructure (DRI) Installation

DRI is a framework for allowing software to access graphics hardware in a safe and efficient manner. It is installed in X by default (using Mesa) if you have a supported video card.

To check if DRI drivers are installed properly, check the log file $HOME/.local/share/xorg/Xorg.0.log (or /var/log/Xorg.0.log if you have built Xorg-Server-21.1.4 with the suid bit) for statements such as:

(II) intel(0): direct rendering: DRI2 Enabled


(II) NOUVEAU(0): Loaded DRI module


DRI configuration may differ if you are using alternate drivers, such as those from NVIDIA or AMD.

Another way to determine if DRI is working properly is to use one of the two optionally installed OpenGL demo programs in Mesa-22.1.7. From an X terminal, run glxinfo and look for the phrase:

name of display: :0
display: :0  screen: 0
direct rendering: Yes

If direct rendering is enabled, you can add verbosity by running LIBGL_DEBUG=verbose glxinfo. This will show the drivers, device nodes and files used by the DRI system.

To confirm that DRI2 hardware acceleration is working, you can (still in the X terminal) run the command glxinfo | grep -E "(OpenGL vendor|OpenGL renderer|OpenGL version)". If that reports something other than Software Rasterizer then you have working acceleration for the user who ran the command.

If your hardware does not have any DRI2 driver available, it will use a Software Rasterizer for Direct Rendering. In such cases, you can use a new, LLVM-accelerated, Software Rasterizer called LLVMPipe. In order to build LLVMPipe just make sure that LLVM-14.0.6 is present at Mesa build time. Note that all decoding is done on the CPU instead of the GPU, so the display will run slower than with hardware acceleration. To check if you are using LLVMpipe, review the output of the glxinfo command above. An example of the output using the Software Rasterizer is shown below:

OpenGL vendor string: VMware, Inc.
OpenGL renderer string: Gallium 0.4 on llvmpipe (LLVM 3.5, 256 bits)
OpenGL version string: 3.0 Mesa 10.4.5

You can also force LLVMPipe by exporting the LIBGL_ALWAYS_SOFTWARE=1 environment variable when starting Xorg.

Again, if you have built the Mesa OpenGL demos, you can also run the test program glxgears. This program brings up a window with three gears turning. The X terminal will display how many frames were drawn every five seconds, so this will give a rough benchmark. The window is scalable, and the frames drawn per second is highly dependent on the size of the window. On some hardware, glxgears will run synchronized with the vertical refresh signal and the frame rate will be approximately the same as the monitor refresh rate.

Debugging Xorg

When starting xorg, there are a couple of ways to check what any issues you may have. If the system comes up, you can see what driver is being used by running xdriinfo. If there are issues or you just want to check, look at Xorg.0.log.

The location of Xorg.0.log depends on how Xorg is installed. If the instructions in the book are followed closely and Xorg is started from the command line, it will be located in the $HOME/.local/share/xorg/ directory. If Xorg is started by a display manager (e.g. lightdm-1.32.0, lxdm-0.5.3, or GDM-42.0) or if $XORG_PREFIX/libexec/Xorg has the suid bit set, it will be located in the /var/log/ directory.

Xorg.0.log Issues

When you look at Xorg.0.log, check for entries like (EE) or (WW). Below are some common entries:

(WW) Open ACPI failed (/var/run/acpid.socket)

This warning is because acpid-2.0.33 is not installed. If you are not on a laptop, it can be safely ignored. On a laptop, install acpid-2.0.33 to enable actions like recognizing when the lid is closed.

(WW) VGA arbiter: cannot open kernel arbiter, no multi-card support

This warning is displayed when a regular user starts Xorg. The library libpciaccess.so issues this warning when it tries to open /dev/vga_arbiter. If there is only one video card in the system, it can safely be ignored. If desired, the permissions of this device can be changed by adding a udev rule and adding the local user to the video group. As the root user:

cat > /etc/udev/rules.d/99-vga-arbiter.rules << EOF
# /etc/udev/rules.d/99-vga-arbiter.rules: Set vga_arbiter group/mode

ACTION=="add", KERNEL=="vga_arbiter", GROUP="video" MODE="0660"

usermod -a -G video <user running xorg>
(EE) AIGLX error: dlopen of /opt/xorg/lib/dri/i965_dri.so failed

This error, accompanied by (EE) AIGLX error: unable to load driver i965, occurs in some systems with Intel based graphics devices. It is caused by a mismatch between the current Xorg-Server-21.1.4 and Mesa-22.1.7. Xorg no longer uses the i965 driver and uses the crocus or iris mesa drivers as indicated by the xdriinfo command. It can safely be ignored.

If desired, this warning can be removed by commenting out lines 330-331 and 337-338 (LogMessage) of glx/glxdricommon.c in the Xorg-Server-21.1.4 package.

Hybrid Graphics

Hybrid Graphics is still in experimental state for Linux. Xorg Developers have developed a technology called PRIME that can be used for switching between integrated and muxless discrete GPU at will. Automatic switching is not possible at the moment.

In order to use PRIME for GPU switching, make sure that you are using Linux Kernel 3.4 or later (recommended). You will need latest DRI and DDX drivers for your hardware and Xorg Server 1.13 or later.

Xorg Server should load both GPU drivers automatically. You can check that by running:

xrandr --listproviders

There should be two (or more) providers listed, for example:

Providers: number : 2
Provider 0: id: 0x7d cap: 0xb, Source Output, Sink Output, Sink Offload crtcs: 3 outputs: 4 associated providers: 1 name:Intel
Provider 1: id: 0x56 cap: 0xf, Source Output, Sink Output, Source Offload, Sink Offload crtcs: 6 outputs: 1 associated providers: 1 name:radeon

In order to be able to run a GLX application on a discrete GPU, you will need to run the following command, where <provider> is the more powerful discrete card, and <sink> is the card which has a display connected:

xrandr --setprovideroffloadsink <provider> <sink>


With newer Xorg drivers, such as modesetting or intel, which are DRI3 capable, the above command is no longer necessary. It does no harm however.

Then, you will need to export the DRI_PRIME=1 environment variable each time you want the powerful GPU to be used. For example,

DRI_PRIME=1 glxinfo | grep -E "(OpenGL vendor|OpenGL renderer|OpenGL version)"

will show OpenGL vendor, renderer and version for the discrete GPU.

If the last command reports same OpenGL renderer with and without DRI_PRIME=1, you will need to check your installation.

Setting up Xorg Devices

For most hardware configurations, modern Xorg will automatically get the server configuration correct without any user intervention. There are, however, some cases where auto-configuration will be incorrect. Following are some example manual configuration items that may be of use in these instances.

Setting up X Input Devices

For most input devices, no additional configuration will be necessary. This section is provided for informational purposes only.

A sample default XKB setup could look like the following (executed as the root user):

cat > /etc/X11/xorg.conf.d/xkb-defaults.conf << "EOF"
Section "InputClass"
    Identifier "XKB Defaults"
    MatchIsKeyboard "yes"
    Option "XkbLayout" "fr"
    Option "XkbOptions" "terminate:ctrl_alt_bksp"

The XkbLayout line is an example for a French (AZERTY) keyboard. Change it to your keyboard model. That line is not needed for a QWERTY (US) keyboard.

Fine Tuning Display Settings

Again, with modern Xorg, little or no additional configuration is necessary. If you should need extra options passed to your video driver, for instance, you could use something like the following (again, executed as the root user):

cat > /etc/X11/xorg.conf.d/videocard-0.conf << "EOF"
Section "Device"
    Identifier  "Videocard0"
    Driver      "radeon"
    VendorName  "Videocard vendor"
    BoardName   "ATI Radeon 7500"
    Option      "NoAccel" "true"

Another common setup is having multiple server layouts for use in different environments. Though the server will automatically detect the presence of another monitor, it may get the order incorrect:

cat > /etc/X11/xorg.conf.d/server-layout.conf << "EOF"
Section "ServerLayout"
    Identifier     "DefaultLayout"
    Screen      0  "Screen0" 0 0
    Screen      1  "Screen1" LeftOf "Screen0"
    Option         "Xinerama"