Plugin install: missing mkmf

[TimJones]

Following installation instructions on Ubuntu 14.04 I got the following error:

$ vagrant plugin install vagrant-kvm
Installing the 'vagrant-kvm' plugin. This can take a few minutes...
/usr/lib/ruby/1.9.1/rubygems/installer.rb:562:in `rescue in block in build_extensions': ERROR: Failed to build gem native extension. (Gem::Installer::ExtensionBuildError)

    /usr/bin/ruby1.9.1 extconf.rb
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from extconf.rb:1:in `<main>'

A quick package checks show that the missing mkmk file can be found in the ruby1.9.1-dev and libruby2.0 packages, but not the ruby2.0-dev (and ruby2.0-dev does not depend on libruby2.0).

$ apt-file update && apt-file search mkmf
dist: /usr/bin/jmkmf
dist: /usr/share/man/man1/jmkmf.1.gz
jruby: /usr/lib/jruby/lib/ruby/1.8/mkmf.rb
jruby: /usr/lib/jruby/lib/ruby/1.9/mkmf.rb
libruby2.0: /usr/lib/ruby/2.0.0/mkmf.rb
ri1.9.1: /usr/share/ri/1.9.1/system/Object/mkmf-i.ri
ruby-gnome2-dev: /usr/lib/ruby/vendor_ruby/mkmf-gnome2.rb
ruby1.9.1-dev: /usr/lib/ruby/1.9.1/mkmf.rb
ruby2.0-doc: /usr/share/ri/2.0.0/system/Object/mkmf-i.ri
xutils-dev: /usr/bin/xmkmf
xutils-dev: /usr/share/man/man1/xmkmf.1.gz

I don't know if this is a ruby packaging issue, but installing the ruby1.9.1-dev package solved the plugin install problem.