gtk2/docs/reference/gtk/running.md

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, Wayland, 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().

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.