I am trying to install the ruby gem pdfbeads via sudo gem install pdfbeads
All i get is an error message which looks cryptic to me an searching for it does not result in useful posts...
Building native extensions. This could take a while...
ERROR: Error installing pdfbeads:
ERROR: Failed to build gem native extension.
/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:4:in `<main>'
Gem files will remain installed in /var/lib/gems/1.9.1/gems/nokogiri 1.6.6.2 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/nokogiri-1.6.6.2/ext/nokogiri/gem_make.out
I think it is something stupid but I can not solve the problem myself.