Running and debugging GTK Applications [src]
Environment variables
GTK inspects a number of environment variables in addition to
standard variables like LANG, PATH, HOME or DISPLAY; mostly
to determine paths to look for certain files. The
X11,
Wayland,
Windows and
Broadway
GDK backends use some additional environment variables.
Note that environment variables are generally used for debugging purposes. They are not guaranteed to be API stable, and should not be used for end-user configuration and customization. If you feel the need to set one of them programmatically, you should probably ask for an API to do what you want, instead.
GTK_DEBUG
This variable can be set to a list of debug options, which cause GTK to print out different types of debugging information.
- actions
- Actions and menu models
- builder
- Deprecated GtkBuilder features
- builder-trace
- Trace GtkBuilder operation
- builder-objects
- Unused GtkBuilder objects
- css
- Deprecated CSS features
- geometry
- Size allocation
- icontheme
- Icon themes
- iconfallback
- Information about icon fallback
- keybindings
- Keyboard shortcuts
- modules
- Modules and extensions
- printing
- Printing
- size-request
- Size requests
- text
- Text widget internals
- tree
- Tree widget internals
- constraints
- Constraints and the constraint solver
- layout
- Layout managers
- accessibility
- Accessibility state changes
A number of keys are influencing behavior instead of just logging:
- interactive
- Open the interactive debugger
- no-css-cache
- Bypass caching for CSS style properties
- snapshot
- Include debug render nodes in the generated snapshots
- invert-text-dir
- Invert the text direction, compared to the locale
The special value all can be used to turn on all debug options.
The special value help can be used to obtain a list of all
supported debug options.
GTK_PATH
Specifies a list of directories to search when GTK is looking for
dynamically loaded objects such as input method modules and print
backends. If the path to the dynamically loaded object is given as
an absolute path name, then GTK loads it directly. Otherwise, GTK
goes in turn through the directories in GTK_PATH, followed
by the system default directory, which is libdir/gtk-4.0/modules. (If GTK_EXE_PREFIX is defined, libdir is $GTK_EXE_PREFIX/lib.
Otherwise it is the libdir specified when GTK was configured, usually
/usr/lib, or /usr/local/lib.)
For each directory in this list, GTK actually looks in a subdirectory
directory/version/host/type. Where version is derived from the
version of GTK (use pkg-config --variable=gtk_binary_version gtk4
to determine this from a script), host is the architecture on
which GTK was built. (use pkg-config --variable=gtk_host gtk4 to
determine this from a script), and type is a directory specific to
the type of modules; currently it can be modules, immodules or
printbackends, corresponding to the types of modules mentioned
above. Either version, host, or both may be omitted. GTK looks
first in the most specific directory, then in directories with
fewer components.
The components of GTK_PATH are separated by the ‘:’ character on
Linux and Unix, and the ‘;’ character on Windows.
Note that this environment variable is read by GTK 2.x and GTK 3.x too, which makes it unsuitable for setting it system-wide (or session-wide), since doing so will cause applications using different GTK versions to see incompatible modules.
GTK_IM_MODULE
Specifies an IM module to use in preference to the one determined
from the locale. If this isn’t set and you are running on the system
that enables XSETTINGS and has a value in Gtk/IMModule, that will
be used for the default IM module. This also can be a colon-separated
list of input-methods, which GTK will try in turn until it finds one
available on the system.
GTK_MEDIA
Specifies what backend to load for GtkMediaFile. The possible values
depend on what options GTK was built with, and can include ‘gstreamer’
and ‘none’. If set to ‘none’, media playback will be unavailable.
The special value ‘help’ can be used to obtain a list of all supported
media backends.
GTK_EXE_PREFIX
If set, GTK uses $GTK_EXE_PREFIX/lib instead of the libdir
configured when GTK was compiled.
GTK_DATA_PREFIX
If set, GTK uses $GTK_DATA_PREFIX instead of the prefix
configured when GTK was compiled.
GTK_THEME
If set, makes GTK use the named theme instead of the theme that is specified by the gtk-theme-name setting. This is intended mainly for easy debugging of theme issues.
It is also possible to specify a theme variant to load, by appending
the variant name with a colon, like this: GTK_THEME=Adwaita:dark.
The following environment variables are used by GdkPixbuf, GDK or Pango, not by GTK itself, but we list them here for completeness nevertheless.
GDK_PIXBUF_MODULE_FILE
Specifies the file listing the GdkPixbuf loader modules to load.
This environment variable overrides the default value
libdir/gtk-4.0/4.0.0/loaders.cache (libdir is the sysconfdir
specified when GTK was configured, usually /usr/lib.)
The loaders.cache file is generated by the
gdk-pixbuf-query-loaders utility.
GDK_DEBUG
This variable can be set to a list of debug options, which cause GDK to print out different types of debugging information.
- misc
- Miscellaneous information
- events
- Information about events
- dnd
- Information about drag-and-drop
- input
- Information about input (mostly Windows)
- eventloop
- Information about event loop operation (mostly macOS)
- frames
- Information about the frame clock
- settings
- Information about xsettings
- opengl
- Information about OpenGL
- vulkan
- Information about Vulkan
- selection
- Information about selections
- clipboard
- Information about clipboards
- dmabuf
- Information about dmabuf handling (Linux-only)
- offload
- Information about subsurfaces and graphics offload (Wayland-only)
A number of options affect behavior instead of logging:
- portals
- Force the use of portals
- no-portals
- Disable use of portals
- force-offload
- Force graphics offload for all textures, even when slower. This allows to debug offloading in the absence of dmabufs.
- gl-debug
- Insert debugging information in OpenGL
- gl-prefer-gl
- Prefer OpenGL over OpenGL ES. This was the default behavior before GTK 4.14.
- default-settings
- Force default values for xsettings
- high-depth
- Use high bit depth rendering if possible
- linear
- Enable linear rendering
- hdr
- Force HDR rendering
- no-vsync
- Repaint instantly (uses 100% CPU with animations)
- color-mgmt
- Enable color management
The special value all can be used to turn on all debug options. The special value help can be used to obtain a list of all supported debug options.
GSK_DEBUG
This variable can be set to a list of debug options, which cause GSK to print out different types of debugging information.
- renderer
- General renderer information
- vulkan
- Check Vulkan errors
- shaders
- Information about shaders
- fallback
- Information about fallback usage in renderers
- cache
- Information about caching
- verbose
- Print verbose output while rendering
A number of options affect behavior instead of logging:
- geometry
- Show borders (when using cairo)
- full-redraw
- Force full redraws
- staging
- Use a staging image for texture upload (Vulkan only)
- cairo
- Overlay error pattern over cairo drawing (finds fallbacks)
- occlusion
- Overlay highlight over areas optimized via occlusion culling
The special value all can be used to turn on all debug options. The special value help can be used to obtain a list of all supported debug options.
GDK_BACKEND
If set, selects the GDK backend to use. Selecting a backend requires that GTK is compiled with support for that backend. The following backends can be selected, provided they are included in the GDK libraries you are using:
- macos
- Selects the native Quartz backend
- win32
- Selects the native backend for Microsoft Windows
- x11
- Selects the native backend for connecting to X11 servers
- broadway
- Selects the Broadway backend for display in web browsers
- wayland
- Selects the Wayland backend for connecting to Wayland compositors
This environment variable can contain a comma-separated list of
backend names, which are tried in order. The list may also contain a *, which means: try all remaining backends. The special value
help can be used to make GDK print out a list of all available
backends. For more information about selecting backends,
see the gdk_display_manager_get() function.
GDK_DISABLE
This variable can be set to a list of values, which cause GDK to disable certain features.
- gl
- Disable OpenGL support
- gl-api
- Don’t allow the use of OpenGL GL API. This forces GLES to be used
- gles-api
- Don’t allow the use of OpenGL GLES API. This forces GL to be used
- egl
- Don’t allow the use of an EGL context
- glx
- Don’t allow the use of GLX
- wgl
- Don’t allow the use of WGL
- vulkan
- Disable Vulkan support
- dmabuf
- Disable dmabuf support
- offload
- Disable graphics offload to subsurfaces
- threads
- Disabled the use of threads where possible
GDK_GL_DISABLE
This variable can be set to a list of values, which cause GDK to disable extension features of the OpenGL support. Note that these features may already be disabled if the GL driver does not support them.
- debug
- GL_KHR_debug
unpack-subimage
:GL_EXT_unpack_subimage
half-float
:GL_OES_vertex_half_float
sync
:GL_ARB_sync
base-instance
:GL_EXT_base_instance
GDK_VULKAN_DISABLE
This variable can be set to a list of values, which cause GDK to disable features of the Vulkan support. Note that these features may already be disabled if the Vulkan driver does not support them.
- dmabuf
- Never import Dmabufs
- ycbr
- Do not support Ycbcr textures
- semaphore-export
- Disable sync of exported dmabufs
- semaphore-import
- Disable sync of imported dmabufs
- incremental-present
- Do not send damage regions
- swapchain-maintenance
- Do not use advanced swapchain features
The special value all can be used to turn on all values. The special value help can be used to obtain a list of all supported values.
GSK_RENDERER
If set, selects the GSK renderer to use. The following renderers can be selected, provided they are included in the GTK library you are using and the GDK backend supports them:
- help
- Prints information about available options
- broadway
- Selects the Broadway-backend specific renderer
- cairo
- Selects the fallback Cairo renderer
- opengl
- Selects the OpenGL renderer
- ngl
- Selects the OpenGL renderer
- gl:
- Selects the OpenGL renderer.
- vulkan
- Selects the Vulkan renderer
Note
If you are running the Nahimic 3 service on a Windows system with nVidia graphics, you need to perform one of the following:
- stop the “Nahimic service”
- insert the GTK application into the Nahimic blocklist, as noted in the nVidia forums
- use the cairo renderer (at the cost of being unable to use OpenGL features)
- use GDK_DEBUG=gl-gles, if you know that GLES support is enabled for the build.
This is a known issue, as the above link indicates, and affects quite a number of applications—sadly, since this issue lies within the nVidia graphics driver and/or the Nahimic 3 code, we are not able to rememdy this on the GTK side; the best bet before trying the above workarounds is to try to update your graphics drivers and Nahimic installation.
GSK_GPU_DISABLE
This variable can be set to a list of values, which cause GSK to disable certain optimizations of the “ngl” and “vulkan” renderer.
- clear
- Use shaders instead of vkCmdClearAttachment()/glClear()
- merge
- USe one vkCmdDraw()/glDrawArrays() per operation
- blit
- Use shaders instead of vkCmdBlit()/glBlitFramebuffer()
- gradients
- Don’t supersample gradients
- mipmap
- Avoid creating mipmaps
- to-image
- Don’t fast-path creation of images for nodes
- occlusion
- Disable occlusion culling via opacity tracking
- repeat
- Repeat drawing operations instead of using offscreen and GL_REPEAT
The special value all can be used to turn on all values. The special value help can be used to obtain a list of all supported values.
GSK_CACHE_TIMEOUT
Overrides the timeout for cache GC in the “ngl” and “vulkan” renderers. The value can be -1 to disable GC entirely, 0 to force GC to happen before every frame, or a positive number to do GC in a timeout every n seconds. The default timeout is 15 seconds.
GTK_CSD
The default value of this environment variable is 1. If changed to 0, this disables the default use of client-side decorations
on GTK windows, thus making the window manager responsible for
drawing the decorations of windows that do not have a custom
titlebar widget.
CSD is always used for windows with a custom titlebar widget set, as the WM should not draw another titlebar or other decorations around the custom one.
GTK_A11Y
If set, selects the accessibility backend to use. The following backends can be selected, provided they are included in the GTK library you are using:
- help
- Prints information about available options
- atspi
- Selects the AT-SPI accessibility backend
- accesskit
- Selects the AccessKit accessibility backend
- test
- Selects the test backend
- none
- Disables the accessibility backend
The test accessibility backend is recommended for test suites and remote
continuous integration pipelines.
XDG_DATA_HOME, XDG_DATA_DIRS
GTK uses these environment variables to locate icon themes and MIME information. For more information, see the Icon Theme Specification the Shared MIME-Info Database and the Base Directory Specification.
DESKTOP_STARTUP_ID
GTK uses this environment variable to provide startup notification
according to the Startup Notification Spec.
Following the specification, GTK unsets this variable after reading
it (to keep it from leaking to child processes). So, if you need its
value for your own purposes, you have to read it before calling
gtk_init().
Interactive debugging

GTK includes an interactive debugger, called the GTK Inspector, which lets you explore the widget tree of any GTK application at runtime, as well as tweak the theme and trigger visual debugging aids. You can easily try out changes at runtime before putting them into the code.
Note that the GTK inspector can only show GTK internals. It can not understand the application-specific logic of a GTK application. Also, the fact that the GTK inspector is running in the application process limits what it can do. It is meant as a complement to full-blown debuggers and system tracing facilities such as DTrace, not as a replacement.
To enable the GTK inspector, you can use the Control+Shift+I or
Control+Shift+D keyboard shortcuts, or
set the GTK_DEBUG=interactive environment variable.
After opening the inspector, it listens for a few keyboard shortcuts that let you use its frame and event recording functionality without moving the focus away from the application window: Super+R turns the recording on and off, and Super+C records a single frame.
There are a few more environment variables that can be set to influence
how the inspector renders its UI. GTK_INSPECTOR_DISPLAY and
GTK_INSPECTOR_RENDERER determine the GDK display and the GSK
renderer that the inspector is using.
In some situations, it may be inappropriate to give users access to
the GTK inspector. The keyboard shortcuts can be disabled with the
enable-inspector-keybinding key in the org.gtk.Settings.Debug
GSettings schema.
Profiling
GTK supports profiling with sysprof. It exports timing information about frameclock phases and various characteristics of GskRenderers in a format that can be displayed by sysprof or GNOME Builder.
A simple way to capture data is to run your application under the
sysprof-cli wrapper, which will write profiling data to a file called capture.syscap.
When launching the application from sysprof, it will set the
SYSPROF_TRACE_FD environment variable to point GTK at a file
descriptor to write profiling data to.