Question

I am getting the following error message while installing, let me know if I need to post more details.

I followed instructions from the following location:
https://github.com/oneclick/rubyinstaller/wiki/Development-Kit

I am using ruby 1.9.2p136 (2010-12-25) [i386-mingw32].

Here is what I get:

E:\work_desk\trunk>gem install mysql2 -v 0.2.4
Temporarily enhancing PATH to include DevKit...
Building native extensions.  This could take a while...
ERROR:  Error installing mysql2:
        ERROR: Failed to build gem native extension.

C:/Ruby192/bin/ruby.exe extconf.rb
checking for rb_thread_blocking_region()... yes
checking for main() in -llibmysql... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=C:/Ruby192/bin/ruby
        --with-mysql-dir
        --without-mysql-dir
        --with-mysql-include
        --without-mysql-include=${mysql-dir}/include
        --with-mysql-lib
        --without-mysql-lib=${mysql-dir}/lib
        --with-libmysqllib
        --without-libmysqllib


Gem files will remain installed in C:/Ruby192/lib/ruby/gems/1.9.1/gems/mysql2-0.
2.4 for inspection.
Results logged to C:/Ruby192/lib/ruby/gems/1.9.1/gems/mysql2-0.2.4/ext/mysql2/ge
m_make.out

Answer 1

The specific version of mysql2 gem you’re trying to install (0.2.4) not only lacks binaries for Windows, but have issues on Windows.

Please install mysql2 gem without indicating the version:

gem install mysql2

Which will install latest version (0.2.6 at the time of my posting this) and also provides binaries for Windows which skip the compilation step.

If you still want to force the compilation (because your version of MySQL differs from the one used to generate the binary gem, you will need to install RubyInstaller’s DevKit from RubyInstaller website:

http://rubyinstaller.org/downloads

And follow the DevKit installation instructions from our wiki (that is linked from the download page)

You will need to provide the path to both headers and libraries during the gem installation process, and adjust the MySQL installation location from the following instructions:

subst X: "C:\Program Files (x86)\MySQL\MySQL Server 5.1" 
gem install mysql2 --platform=ruby -- --with-mysql-dir=X: --with-mysql-lib=X:\lib\opt 
subst X: /D

The above command uses subst to avoid issues with path with spaces, which you should avoid always.

Hope this helps.