Docker for Mac - mkmf.rb can't find header files for ruby

Question

I updated XCode on my Mac and since then when starting Docker using docker-sync-stack start I get this error message:

mkmf.rb can\'t find header         


        

Answer 1

When upgrading XCode you need to install the Command-Line Tools and additionally accept the terms and conditions:

sudo xcode-select --install

Then:

sudo xcodebuild -license