Running GTK Applications

Common commandline options

All GTK applications support a number of standard commandline options. These are removed from argv by gtk_init()(). Modules may parse and remove further options. The X11 and Windows GDK backends parse some additional commandline options.

--gtk-module=module
A list of modules to load in addition to those specified in the GTK3_MODULES environment variable and the gtk-modules GTK setting.
--g-fatal-warnings
Make GTK abort on all warnings. This is useful to stop on the first warning in a debugger, if your application is printing multiple warnings. It’s almost always best to start debugging with the first warning that occurs.
--gtk-debug=options
A list of debug options to turn on in addition to those specified in the GTK_DEBUG environment variable. This option is not available if GTK has been built with the --enable-debug=no configuration option.
--gtk-no-debug=options
A list of debug options to turn off. This option is only available if GTK has been build with the --enable-debug=yes configuration option.

The following options are really used by GDK, not by GTK, but we list them here for completeness nevertheless.

--class=class
Sets the program class; see gdk_set_program_class()().
--name=name
Sets the program name.
--gdk-debug=options
A list of debug options to turn on in addition to those specified in the GDK_DEBUG environment variable. This option is only available if GTK has been built with the --enable-debug=yes configuration option.
--gdk-no-debug=options
A list of debug options to turn off. This option is only available if GTK has been built with the --enable-debug=yes configuration option.

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
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 built with the --enable-debug=yes configuration option.
  • actions: Actions and menu models
  • baselines: Show baselines
  • builder: UI definition files
  • geometry: Size allocation
  • icontheme: Icon themes
  • interactive: Open the interactive debugger
  • keybindings: Key bindings
  • misc: Miscellaneous information
  • modules: Loading of GTK modules
  • no-css-cache: Bypass caching for CSS style properties
  • no-pixel-cache: Disable the pixel cache
  • plugsocket: Cross-process embedding
  • pixel-cache: Pixel cache
  • printing: Printing support
  • size-request: Size requests
  • text: Text widget internals
  • touchscreen: Pretend the pointer is a touchscreen device
  • tree: Tree widget internals
  • updates: Visual feedback about window updates
  • resize: Highlight resizing widgets
  • layout: Show layout borders

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.

GTK3_MODULES
A list of modules to load. Note that GTK also allows to specify modules to load via a commandline option (--gtk-module) and with the gtk-modules GTK setting.
GTK_MODULES
A list of modules to load in addition to the ones in the GTK3_MODULES variable. Note that this environment variable is read by GTK 2.x too, which may not have the same set of modules available for loading. Use GTK3_MODULES for modules that are only compatible with GTK 3.
GTK_PATH
Specifies a list of directories to search when GTK is looking for dynamically loaded objects such as the modules specified by GTK_MODULES, theme engines, input method modules, file system backends 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-3.0 in the user’s home directory, followed by the system default directory, which is libdir/gtk-3.0/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 gtk+-3.0 to determine this from a script); host is the architecture on which GTK was built. (use pkg-config --variable=gtk_host gtk+-3.0 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
  • 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 too, which makes it unsuitable for setting it system-wide (or session-wide), since doing so will cause either GTK 2.x applications or GTK 3 applications 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_IM_MODULE_FILE
Specifies the file listing the IM modules to load. This environment variable the default value libdir/gtk-3.0/3.0.0/immodules.cache (libdir has the same meaning here as explained for GTK_PATH). The immodules.cache file is generated by the gtk-query-immodules-3.0 utility. Note that this environment variable is read by GTK 2.x too, which makes it unsuitable for setting it system-wide (or session-wide), since doing so will cause either GTK 2.x applications or GTK 3 applications to see the wrong list of IM modules.
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 GTK 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-3.0/3.0.0/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)
  • dnd: Information about drag-and-drop
  • draw: Information about drawing operations (only win32)
  • eventloop: Information about event loop operation (mostly Quartz)
  • misc: Miscellaneous information
  • nogl: Turn off OpenGL. GDK will behave as if OpenGL support was not available.
  • nograbs: Turn off all pointer and keyboard grabs
  • xinerama: Simulate a multi-monitor setup
  • xim: Information about XIM support

The special value all can be used to turn on all debug options.

GDK_RENDERING
If set, selects the way how GDK creates similar surfaces. This affects both the functionality of the function gdk_window_create_similar_surface()() as well as the way GDK creates backing surfaces for double buffering. The following values can be used:
  • similar: Create similar surfaces to the window in use. This is the default behavior when the variable is not set.
  • image: Always create image surfaces. This essentially turns off all hardware acceleration inside GTK.
  • recording: Always create recording surfaces. This causes bare rendering to the backend without the creation of intermediate surfaces (Pixmaps in X) and will likely cause flicker.

All other values will be ignored and fall back to the default behavior. More values might be added in the future.

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.

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_OVERLAY_SCROLLING
The default value of this environment variable is 1, which means that each instance of GtkScrolledWindow will choose whether to use overlay or full-size scrollbars via its own GtkScrolledWindow:overlay-scrolling property, which defaults to TRUE. If this variable is set to 0, all GtkScrolledWindow instances are made to use full/non-overlay scrollbars.
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 Specification. 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 Ctrl+Shift+I or Ctrl+Shift+D keyboard shortcuts, or set the GTK_DEBUG=interactive environment variable.

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.