12 KiB
Title: Running and debugging GTK Applications Slug: 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,
Wayland, Windows and
Broadway GDK backends use some additional
environment variables.
GTK_DEBUG
This variable can be set to a list of debug options, which cause GTK to
print out different types of debugging information. Some of these options
are only available when GTK has been configured with -Ddebug=true
.
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_MEDIA
Specifies what backend to load for #GtkMediaFile. The possible values depend on what options GTK was built with, and can include 'gstreamer', 'ffmpeg' 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
.
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. Some of these options
are only available when GTK has been configured with -Ddebug=true
.
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
This variable can be set to a list of debug options, which cause GSK to
print out different types of debugging information. Some of these options
are only available when GTK has been configured with -Ddebug=true
.
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.
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 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_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.