Running GTK+ Applications: GTK+ 4 Reference Manual

## Running GTK+ Applications Running GTK+ Applications — How to run and debug your GTK+ application |

## Running and debugging 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` 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.

actions | Actions and menu models
baselines | Show baselines
builder | GtkBuilder support
geometry | Size allocation
icontheme | Icon themes
interactive | Open the interactive debugger
keybindings | Keybindings
misc | Miscellaneous information
modules | Loading of modules
no-css-cache | Bypass caching for CSS style properties
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
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.

`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.

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-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 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.

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-4.0/4.0.0/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 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/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
mir | Selects the Mir backend for connecting to Mir 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.

`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.

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.