## 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 `GTK_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.

misc | Miscellaneous information
plugsocket | Cross-process embedding
text | Text widget internals
tree | Tree widget internals
updates | Visual feedback about window updates
keybindings | Keybindings
multihead | Working on multiple displays
modules | Loading of modules
geometry | Size allocation
icontheme | Icon themes
printing | Printing support
builder | GtkBuilder support
size-request | Size requests
no-css-cache | Bypass caching for CSS style properties.

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

`GTK_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.

Note that this environment variable is read by GTK+ 2.x too, which may not have the same set of modules available for loading.

`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.

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.

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.

misc | Miscellaneous information
events | Show all events received by GDK
dnd | Information about drag-and-drop
xim | Information about XIM support
nograbs | Turn off all pointer and keyboard grabs
multihead | Information related to multiple screens
xinerama | Simulate a multi-monitor setup
cursor | Information about cursor objects (only win32)
draw | Information about drawing operations (only win32)
eventloop | Information about event loop operation (mostly Quartz)

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:

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. 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().