A lot of `gtk-warnings` in terminal. Is this serious?

Solution 1:

This error indicates that the software is using valid GTK library calls with a newer version of the GTK library. Sometimes during software development it is desirable to get rid of the, "old way", to do things while maintaining backwards compatibility. This is accomplished by marking the undesired calls deprecated. This tells the developer that their code is valid in this release, but in the future their code will need to be updated to work with a new version of the library, possibly many releases down the road.

In this case, GTK wants to be more strict about including units on dimensions. It tells the developer that GTK is assuming the units are pixels, which is the exact assumption that the software developer made in the first place.

Not using units is deprecated. Assuming 'px'.

That is a long and very complicated way of saying that these warnings are for the developers of the icon-theme, and do not reflect actual run-time problems.

Using the Ubuntu software repositories, you will not be given incompatible programs and libraries.

Solution 2:

If you don't notice any bugs or errors, you can safely ignore these warnings. Keep in mind that these are just warnings, not errors.