"mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h" building the Travis gem

I’m trying to validate my travis.yml file locally. Following directions in

  1. online validation
    The provided link leads to http://lint.travis-ci.org/, which states that the tool is deprecated
  2. command-line validation
    The tool does not install, don’t know why. Here’s the output I get:
$ sudo gem install travis --no-rdoc --no-ri
Building native extensions. This could take a while...
ERROR:  Error installing travis:
	ERROR: Failed to build gem native extension.

    current directory: /var/lib/gems/2.5.0/gems/ffi-1.11.1/ext/ffi_c
/usr/bin/ruby2.5 -r ./siteconf20190803-19645-1nampuq.rb extconf.rb
mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h

extconf failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.5.0/gems/ffi-1.11.1 for inspection.
Results logged to /var/lib/gems/2.5.0/extensions/x86_64-linux/2.5.0/ffi-1.11.1/gem_make.out

If your ruby is installed with the system’s package manager, you may need a package named something like ruby-devel or ruby-dev to get the headers to build native extensions.

@native-api thanks for your response and advice. I don’t develop under Ruby, so I’m using whatever comes installed with Ubuntu 19.04. I’ll try to add the ruby-dev package as you suggested to try and fix the issue.

It would be nice to have some feedback from the team about when the new WebLint tool mentioned at http://lint.travis-ci.org/ will be available.

@native-api sudo apt install ruby-dev did the trick ! Many thanks for your help.