Gtk-Message: Failed to load module “topmenu-gtk-module“

When starting applications in the mate desktop environment on Ubuntu 20.04 a warning showed up in the terminal:

Gtk-Message: Failed to load module “topmenu-gtk-module“

A mate community forum thread explained the cause:

An old settings file from Ubuntu 18.04 tried to load the module. I had a new and an old file:

root@sybo:/etc/X11/Xsession.d# ls -lah
-rw-r--r--  1 root root  564 Apr  2  2020 80mate-environment
-rw-r--r--  1 root root  530 Jan 19 20:47 99mate-environment

For some reason the old "99" file had not been removed during the upgrade from Ubuntu 18.04 to 20.04, causing the warnings.

Written by Christian Weiske.

Comments? Please send an e-mail.