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.
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 |
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.
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.
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.
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.
If set, GTK uses $GTK_EXE_PREFIX/lib
instead
of the libdir configured when GTK was compiled.
If set, GTK uses $GTK_DATA_PREFIX
instead of
the prefix configured when GTK was compiled.
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.
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.
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.
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.
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.
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.
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 |
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.
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.
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.
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()
.