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.

GTK_DEBUG

This variable can be set to a list of debug options, which cause GTK to print out different types of debugging information. Some of these options are only available when GTK has been configured with -Ddebug=true.

actions

Actions and menu models

builder

GtkBuilder support

builder-objects

Unused GtkBuilder objects

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 changs

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. Some of these options are only available when GTK has been configured with -Ddebug=true.

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-disable

Disable OpenGL support

gl-no-fractional

Disable fractional scaling for OpenGL.

gl-debug

Insert debugging information in OpenGL

gl-disable-gl

Don’t allow the use of OpenGL GL API. This forces GLES to be used

gl-disable-gles

Don’t allow the use of OpenGL GLES API. This forces GL to be used

gl-prefer-gl

Prefer OpenGL over OpenGL ES. This was the default behavior before GTK 4.14.

gl-egl

Use an EGL context on X11 or Windows

gl-glx

Use GLX on X11

gl-wgl

Use WGL on Windows

vulkan-disable

Disable Vulkan support

vulkan-validate

Load the Vulkan validation layer, if available

default-settings

Force default values for xsettings

high-depth

Use high bit depth rendering if possible

no-vsync

Repaint instantly (uses 100% CPU with animations)

dmabuf-disable

Disable dmabuf support

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. Some of these options are only available when GTK has been configured with -Ddebug=true.

renderer

General renderer information

opengl

OpenGL renderer information

vulkan

Check Vulkan errors

shaders

Information about shaders

fallback

Information about fallback usage in renderers

glyphcache

Information about glyph 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)

offload-disable

Disable graphics offload to subsurfaces

cairo

Overlay error pattern over cairo drawing (finds fallbacks)

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_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_DEVICE

This variable can be set to the index of a Vulkan device to override the default selection of the device that is used for Vulkan rendering. The special value list can be used to obtain a list of all Vulkan devices.

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

descriptor-indexing

Force slow descriptor set layout codepath

dynamic-indexing

Hardcode small number of buffer and texture arrays

nonuniform-indexing

Split draw calls to ensure uniform texture accesses

semaphore-export

Disable sync of exported dmabufs

semaphore-import

Disable sync of imported dmabufs

incremental-present

Do not send damage regions

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 default OpenGL renderer

gl

Selects the “gl” OpenGL renderer

ngl

Selects the “ngl” OpenGL renderer

vulkan

Selects the Vulkan renderer

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.

uber

Don’t use the uber shader

clear

Use shaders instead of vkCmdClearAttachment()/glClear()

blit

Use shaders instead of vkCmdBlit()/glBlitFramebuffer()

gradients

Don’t supersample gradients

mipmap

Avoid creating mipmaps

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.

GSK_MAX_TEXTURE_SIZE

Limit texture size to the minimum of this value and the OpenGL limit for texture sizes in the “gl” renderer. This can be used to debug issues with texture slicing on systems where the OpenGL texture size limit would otherwise make texture slicing difficult to test.

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

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.

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.