So, I struggled for a while to get idea to create a grails project - when tryin to create my first project, I've been told I have no grails sdk configured yet, but could add a new one. But the "ok" button on the file selector for the grails SDK location kept being gray and could not be pressed when I was on /usr/share/grails - the location where the debian package of grails places the whole software into.

I was just about to give up, until I decided I'd try one more thing: Somehow I suspected that maybe, maybe, the fact that the location was owned by root (as with everything installed from packages) could be a problem.

Then I downloaded the tar.gz distribution package of grails, unpacked it, and chose it as the location of my sdk. It worked.
That means, I can continue checking out intelliJ idea for grails development, even though I don't have an explanation for this yet, an IDE should not have to write anything into my SDL location. Never.