How to debug Xorg problems

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Foreword

If you are experiencing a problem with Xorg, please see the common bugs document before filing a bug. Some easy configuration tweaks that fix a wide range of issues are listed there. If the problem you are seeing is not listed there or none of the workarounds seem to help, please consider filing a bug to help us make Fedora run better on your hardware.

Be prepared to include some information (logs) about your system as well. These should be complete (no snippets please), not in an archive, uncompressed, with MIME type set as text/plain.

Contents

Identifying your problem area

What driver am I using?

If you do not know already, try to find out what video driver you are using. Examine the output of journalctl -e _COMM=Xorg.bin (Fedora 21+) or journalctl -e _COMM=Xorg (Fedora 20 and earlier). Quite early on, you will see some lines like this:

(II) VESA(0): initializing int10
(II) VESA(0): Bad V_BIOS checksum

The word in capital letters after (II) is the name of the driver in use (so, in this case, the word is VESA, indicating the vesa driver is in use). Drivers are packaged with the name xorg-x11-drv-(name), so the vesa driver is in the package Package-x-generic-16.pngxorg-x11-drv-vesa.

If you are using a driver with the name nvidia (not nv or nouveau) or fglrx, you are using a proprietary third-party video driver (respectively, the proprietary drivers provided by NVIDIA and AMD/ATI). Please do not report any bugs in these drivers to Fedora, as we do not provide or support these drivers. Report bugs either to the place where you got these drivers, or to NVIDIA or AMD.

What area might the problem be in?

  • If the problem in question occurs when using 3D-accelerated applications - for instance, Blender, or 3D-accelerated games - the problem is a 3D acceleration issue, and you should include the information outlined in the appropriate section further down this page.
  • If you experience a "lockup", please distinguish what kind of lockup you are seeing. There are three major categories:
    • Mouse moves, and cursor still changes when moving over window borders. This is usually a bug in the window manager's state machine where it doesn't let go of a grab in the X server.
    • Mouse moves, but cursor does not change. This is usually the X server being stuck far away from the dispatch loop (position updates happen asynchronously, but glyph updates do not), either waiting on the kernel or in an infinite loop. The X server will probably print a message in the log about the event queue overflowing when this happens; this is _not_ the bug, it is merely the symptom.
    • Mouse doesn't move. This is the X server being stuck, usually in the kernel (which will not show a backtrace in the X log, but will probably show something in dmesg) but occasionally in an internal deadlock with the cursor update code disabled (which will often show up as a backtrace in the X log).

Information to include in your report

All bug reports

In all cases, the following should be attached to your bug report:

  • All of the X server log messages: journalctl -e _COMM=Xorg.bin (Fedora 21+) or journalctl -e _COMM=Xorg (Fedora 20 and earlier). If you cannot use the system in the affected configuration, but you can use it some other way (e.g. with nomodeset or a different kernel), first boot the affected configuration and reproduce the bug, then boot the unaffected configuration and run journalctl -b-1 -e _COMM=Xorg.bin (Fedora 21+) or journalctl -b-1 -e _COMM=Xorg (Fedora 20 and earlier). The -b-1 asks for the output from the previous boot; you can adjust it as desired if you need logs from more than one boot ago, -b-2 etc.
  • The output of the command su -c 'lspci -nn'
  • If you use a xorg.conf, please include it in the bug report, otherwise, please specify in the bug report that it does not exist. Usually this would be located at /etc/X11/xorg.conf, but see the xorg.conf manpage - man xorg.conf - for other standard locations. Also include any files in the directory /etc/X11/xorg.conf.d
  • X log messages from a trial run where you move your xorg.conf aside and let Xorg autodetect your hardware (if you have such a file)
  • output of the dmesg command after adding the boot parameters drm.debug=14 log_buf_len=16M and rebooting, especially in case of crashes. If you cannot run dmesg in the affected configuration, but you can boot an unaffected configuration, boot the affected configuration with the parameters, then boot the unaffected configuration, run journalctl -b-1 and attach that output
  • Details of your monitor configuration: what monitors you have connected to what ports (e.g. VGA, DVI, HDMI...). Please note if you are using a display switcher

Rendering problems (unreadable text, corrupted display...)

As well as the information from the 'all bug reports' section, include the following information:

  • A screenshot showing the problem if at all possible.

Intel-specific

For intel display setup issues (outputs shaky or not lighting up):

  • collect and attach the video ROM for the chip: su -c 'dd if=/dev/mem of=/tmp/rom bs=64k skip=12 count=1'
  • collect and attach the opregion data: su -c 'mount -t debugfs debugfs /sys/kernel/debug' ; cp /sys/kernel/debug/dri/*/i915_opregion /tmp/opregion
  • Collect and attach a register snapshot from the broken configuration: su -c 'intel_reg_snapshot > /tmp/snapshot'

The command intel_reg_snapshot is provided by the Package-x-generic-16.pngintel-gpu-tools package. Note that you may need to ssh into the machine in order to collect this information. In some cases intel_reg_snapshot might fail to run, then please provide output of intel_reg_dumper (if possible, both before and after you see the issue).

For errors indicating a GPU hang:

  • collect and attach the GPU error state: su -c 'mount -t debugfs debugfs /sys/kernel/debug' ; cp /sys/kernel/debug/dri/0/i915_error_state /tmp

You may find the upstream intel driver bug filing instructions useful - much of the information from them is contained here, but there may be additional ideas there.

3D acceleration issues

As well as the information from the 'all bug reports' section, include the following information:

  • Output of the command glxinfo (if this is not installed, install the package Package-x-generic-16.pngglx-utils)
  • A screenshot, if possible (if the system has crashed but the display on screen is something other than just blank, take a picture with a digital camera and attach that)
  • Information as to whether or not other OpenGL applications are able to run without problems.
  • Console output from running the application with LIBGL_DEBUG=verbose. For instance, if the bug is in the application glxgears, you would run LIBGL_DEBUG=verbose glxgears from a console, reproduce the problem, and attach any output from the console

Creating a xorg.conf

If you need to make manual changes to X configuration, you will need to create a xorg.conf file if it doesn't already exist.

Input devices

Debugging of input devices is covered by a special wiki page.

Stack traces

You will need a stack trace if your X server crashes. You should be able to submit one to bugzilla by running Automatic Bug Reporting Tool (gnome-abrt) and selecting the relevant crash from System crashes (if abrtd was running and noticed the crash). If not, see the documentation on the upstream wiki.