Solution: Ubuntu/Linux vs JDK => Maximum number of clients reached / unable to open display

For work I'm using Ubuntu, and as developer, I constantly use some JDK tools/IDEs, usually it is IntelliJ IDEA, sometimes eclipse, some other specific, like nVidia studios..
I'm typical linux user - so "try it switch off and on" is not the standard way to deal with problems.
From some time when I tried to start some graphical tool I got this error:

Maximum number of clients reached unable to open display ":0"

I hate it and spend lots of time for investigation, went throug all standard:

xlsclients/xwininfo/xhost - which didn't work as they all need access to X (they are clients)  - so typical catch 22

I spend some time on different ubuntu settings for X-org/ file limits etc - everything set properly, all almost unlimited...
then finally by just some good luck I shut down my IntelliJ and ... checked that thousand of resources suddenly disappeared from usage list..


Final solution: you need suckless-tools ;-)

apt install suckless-tools