Arduino IDE fails on Fedora with arduino-builder error "Parameter 'tools' is mandatory"
I don't understand why this worked, but I found this comment in Redhat Bugzilla (it doesn't seem to be a bug report specifically about that...but anyway):


  
    Parameter 'tools' is mandatory
    [...]
  
  
  However, if I create the packages directory in ~/.arduino15, compilation now works.

mkdir ~/.arduino15/packages



Seemed like an easy thing to try, and voila -- after an hour of fuss.

I do not understand why this is so (nothing ends up in that directory, either) but I'm leaving this in hopes it may save someone else some time.