I was having trouble adding a Ruby SDK to a Ruby IDEA project. When trying to add a local Ruby SDK to my project by adding the ruby executable inside my RVM folder, I would get an error like
Error configuring SDK: [some classname here]. Please make sure that /home/user/.rvm/rubies/ruby-2.5.1/bin/ruby is a valid home path for this SDK type.
The solution is to go to Plugins and enable the SSH Remote Run plugin. This also enables the Remote Hosts Access and Terminal plugins. After restarting the IDE, I was able to add the SDK.