# Running and debugging GTK Applications {#gtk-running}

## 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](#x11-envar),
[Wayland](#wayland-envar), [Windows](#win32-envar) and
[Broadway](#broadway-envar) GDK backends use some additional
environment variables.

### GTK_DEBUG {#GTK_Debug-Options}

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](#interactive-debugging)
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 {#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 {#GSK-Debug-Options}

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](https://freedesktop.org/Standards/icon-theme-spec)
the [Shared MIME-Info Database](https://freedesktop.org/Standards/shared-mime-info-spec)
and the [Base Directory Specification](https://freedesktop.org/Standards/basedir-spec).

### DESKTOP_STARTUP_ID

GTK uses this environment variable to provide startup notification
according to the [Startup Notification Spec](https://standards.freedesktop.org/startup-notification-spec/startup-notification-latest.txt).
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 {#interactive-debugging}

![The inspector](inspector.png)

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 {#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.
