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 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 configured with --enable-debug=no.

--gtk-no-debug options.  A list of debug options to turn off. This option is only available if GTK+ has been configured with --enable-debug=yes.

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 configured with --enable-debug=yes.

--gdk-no-debug options.  A list of debug options to turn off. This option is only available if GTK+ has been configured with --enable-debug=yes.

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.  Unless GTK+ has been configured with --enable-debug=no, this variable can be set to a list of debug options, which cause GTK+ to print out different types of debugging information.

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 setting.

GTK_MODULES.  A list of modules to load in addition to the ones in the GTK3_MODULES variable.

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 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.

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.

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 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.

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:

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:

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.

XDG_DATA_HOME, XDG_DATA_DIRS.  GTK+ uses these environment variables to locate icon themes and MIME information. For more information, see 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.

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.