Though, I am on Debian 8...

This solved it for me!!! Thanks!
 

This solved it for me!!! Thanks!

thank you. i have been wondering about this for a long time but have just had to get used to it.
anybody know about vnc4server? it's redundant isn't it?

Sorry to bump this post up, I've the correct fix for this.
I'm using Debian 9 (Stretch) and I'm seeing this messages all over the place, to correct fix the issue you just have to install the missing module:
DONE!

If you install with "libcanberra-gtk*" it might fix the problem but it will install a load of unnecessary files like debugging packages and other stuff, the correct module is about 20kb and 33kb total.

Have a good one.

This worked for me to
 

Thank you! Worked for me to on Debian 8 (Jessie).

On Ubuntu 18.04 64-bit

I understand that this thread is old. In my search for information concerning why I was receiving the Gtk warning, and the information, and coding, found in this thread, helped me in my current problem with gcin and re-booting.

Thanks
 

This fixed it for me. Thanks.
I had previously fixed it by installing "libcanberra-gtk*", and as you said, that drug in a bunch of stuff. Your answer gave me the courage to "sudo remove libcanberra-gtk*". Then your simple install did fix the issue.

Ubuntu Bionic 18.04.3 LTS

Failed to load module "canberra-gtk-module"
 

I am using CentOS 8. This message helped me. What I did us replace gtk0 by gtk2 and it worked!!!

So I did "sudo yum install libcanberra-gtk2".

I work like a charm! Thanks a lot!

Another possible solution I found when trying to run something like Krita that was throwing out the same messages, is to run the program with sudo. This worked for me. The messages of missing canberra module no longer appeared and was satisfied.

I confirm that the same fix worked for me on Ubuntu Focal 20.04.1 LTS:
sudo apt-get install libcanberra-gtk-module

Also: There is a typo in my previous post (#23). Should say:
... courage to "sudo apt remove libcanberra-gtk*"

Hi,
Installing libcanberra module is not really a fix.
In my line of work I don't don;'t have anything with sounds(which libcanberra is for), and I still have this warning.

On top of that - it shouldn't be required to install at all - according to GTK/GNOME developers this is to support the theming sound and its not supporting Wayland at all
(and probably never will).

I would like to know who is asking for libcanbberra and remove the offending module or reconfigure it so that the warning doesn't pollute my log.

Can someone please help?

I use RHEL8 with X11 (can't switch to Wayland yet -- our software will have problem with the compositor RHEL using).

Thank you.