Running and debugging GTK Applications

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, Windows and Broadway GDK backends use some additional environment variables.

GTK_DEBUG

Unless GTK has been configured with -Ddebug=false, 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

GtkBuilder support

geometry

Size allocation

icontheme

Icon themes

keybindings

Keybindings

modules

Loading of modules

printing

Printing support

size-request

Size requests

text

Text widget internals

tree

Tree widget internals

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

touchscreen

Pretend the pointer is a touchscreen device

updates

Visual feedback about window updates

resize

Highlight resizing widgets

layout

Show layout borders

snapshot

Include debug render nodes in the generated snapshots

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 directory .gtk-4.0 in the user’s home directory, 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_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

Unless GTK has been configured with -Ddebug=false, this variable can be set to a list of debug options, which cause GDK to print out different types of debugging information.

cursor

Information about cursor objects (only win32)

eventloop

Information about event loop operation (mostly Quartz)

misc

Miscellaneous information

frames

Information about the frame clock

settings

Information about xsettings

selection

Information about selections

clipboard

Information about clipboards

dnd

Information about drag-and-drop

opengl

Information about OpenGL

vulkan

Information about Vulkan

A number of options affect behavior instead of logging:

nograbs

Turn off all pointer and keyboard grabs

gl-disable

Disable OpenGL support

gl-software

Force OpenGL software rendering

gl-texture-rect

Use the OpenGL texture rectangle extension, if available

gl-legacy

Use a legacy OpenGL context

gl-gles

Use a GLES OpenGL context

vulkan-disable

Disable Vulkan support

vulkan-validate

Load the Vulkan validation layer, if available

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

Unless GTK has been configured with -Ddebug=false, 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

cairo

cairo renderer information

opengl

OpenGL renderer information

shaders

Shaders

surface

Surfaces

vulkan

Vulkan renderer information

fallback

Information about fallbacks

glyphcache

Information about glyph caching

A number of options affect behavior instead of logging:

diff

Show differences

geometry

Show borders

full-redraw

Force full redraws for every frame

sync

Sync after each frame

vulkan-staging-image

Use a staging image for Vulkan texture upload

vulkan-staging-buffer

Use a staging buffer for Vulkan texture upload

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:

quartz

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_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.

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

gl

Selects the default OpenGL renderer

vulkan

Selects the Vulkan renderer

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.

XDG_DTA_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().