# Part II. Running Mutter

## Environment Variables

Mutter automatically checks environment variables during its initialization. These environment variables are meant as debug tools or overrides for default behaviours:

MUTTER_VERBOSE | Enable verbose mode, in which more information is printed to the console. Mutter needs to be built with the --enable-verbose-mode option (enabled by default). For more fine-grained control of the output, see `meta_add_verbose_topic()`.
MUTTER_DEBUG | Traps and prints X errors to the console.
MUTTER_G_FATAL_WARNINGS | Causes any logging from the domains Mutter, Gtk, Gdk, Pango or GLib to terminate the process (only when using the log functions in GLib).
MUTTER_USE_LOGFILE | Log all messages to a temporary file.
MUTTER_DEBUG_XINERAMA | Log extra information about support of the XINERAMA extension.
MUTTER_DEBUG_SM | Log extra information about session management.
MUTTER_DEBUG_BUTTON_GRABS | Log extra information about button grabs.
MUTTER_SYNC | Call XSync after each X call.
MUTTER_DISPLAY | Name of the X11 display to use.
META_DISABLE_MIPMAPS | Disable use of mipmaps for the textures that back window pixmaps.
MUTTER_USE_STATIC_GRAVITY | Enable support for clients with static bit-gravity.
MUTTER_WM_CLASS_FILTER | Comma-separated list of WM_CLASS names to which to restrict Mutter to.
MUTTER_DISABLE_FALLBACK_COLOR | Disable fallback for themed colors, for easier detection of typographical errors.