Running GTK Applications
3
GTK Library

# Running GTK Applications

How to run and debug your GTK application

## 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 `--enable-debug=no`, 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

baselines

  Show baselines

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`, `engines`, `immodules`, `filesystems` 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, makes GTK use `$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/local/lib`.)

The `loaders.cache` file is generated by the `gdk-pixbuf-query-loaders` utility.

#### `GDK_DEBUG`

If GTK has been configured with `--enable-debug=yes`, 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`

If GTK has been configured with `--enable-debug=yes`, 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

ssurface

  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 display servers

Since 3.10, 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_DATA_HOME`, `XDG_DATA_DIRS`

GTK uses these environment variables to locate icon themes and MIME information. For more information, see 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 GskRenders in a format that can be displayed by sysprof or GNOME Builder.

A simple way to capture data is to set the `GTK_TRACE` environment variable. When it is set, GTK will write profiling data to a file called `gtk.PID.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.

When GtkApplication registers with D-Bus, it exports the `org.gnome.Sysprof2.Profiler` interface that lets sysprof request profiling data at runtime.