#### 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
`touch-ui`
  Show touch ui elements for pointer events
`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`.

### `GTK_OVERRIDE_RESTORE_REASON`

If set, makes GTK ignore the session manager’s restore reason and forces the specified restore reason instead. This is useful for app developers to test their app’s behavior in various situations

## Other environment variables

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)
`d3d12`
  Information about Direct3D12 (Windows-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
`shaders`
  Information about shaders
`fallback`
  Information about fallback usage in renderers
`cache`
  Information about caching
`verbose`
  Print verbose output while rendering
`diff`
  Print the result of diff computations
`opacity`
  Print the result of every opacity computation

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)
`profile`
  Enable profiling (Vulkan only)

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
`d3d11`
  Don’t allow the use of Direct3D 11 (on Windows)
`d3d12`
  Don’t allow the use of Direct3D 12 (on Windows)
`dcomp`
  Don’t allow the use of Direct Composition (on Windows)
`offload`
  Disable graphics offload to subsurfaces
`threads`
  Disable threads where possible
`icon-nodes`
  Disable the svg-to-node conversion for symbolic icons

### `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
`base-instance`
  GL_ARB_base_instance
`buffer-storage`
  GL_EXT_buffer_storage
`external-objects`
  GL_EXT_memory_object and GL_EXT_semaphore
`external-objects-win32`
  GL_EXT_memory_object_win32 and GL_EXT_semaphore_win32

### `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
`timeline-semaphore`
  Disable timeline semaphore support (disables Windows sync)
`semaphore-export`
  Disable sync of exported dmabufs
`semaphore-import`
  Disable sync of imported dmabufs
`win32-semaphore`
  Disable Windows sync support
`incremental-present`
  Do not send damage regions
`swapchain-maintenance`
  Do not use advanced swapchain features
`portability-subset`
  Vulkan implementation is non-conformant
`dual-source-blending`
  Disable dual source blending
`profile`
  Disable profiling support
`win32`
  Never import Windows resources

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.

### `GDK_WAYLAND_DISABLE`

This variable can be set to a list of values, which cause the GDK Wayland backend to not use certain Wayland interfaces, even if the compositor advertises them.

The special value `help` can be used to obtain help.

To see a list of Wayland interface names, use `GDK_DEBUG=misc` and look for `global` in the output.

### `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
`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
`profile`
  Disable profiling support

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, `Super`+`C` records a single frame and `Super`+`F` records a single frame and saves it to a `.node` file.

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.