Ruby gem no such file to load — mkmf

Setup GEM on your machine:

When you try to install packages with gem, most of the time it does not work due to the wrong setup. Always do it completely:

sajan@test10:~$ sudo gem install mysql

Building native extensions.  This could take a while...

ERROR:  Error installing mysql:

ERROR: Failed to build gem native extension.

/usr/bin/ruby1.8 extconf.rb

extconf.rb:5:in `require': no such file to load -- mkmf (LoadError)

from extconf.rb:5

Gem files will remain installed in /var/lib/gems/1.8/gems/mysql-2.9.0 for inspection.

Results logged to /var/lib/gems/1.8/gems/mysql-2.9.0/ext/mysql_api/gem_make.out

What are the packages needed: 

1. sudo apt-get install ruby

2. sudo apt-get install rubygems<LateVersion>

3. sudo apt-get install ruby<version>-dev

Things should work now. Enjoy!