使用gem安装mysql2的时候提示以下错误extconf.rb:2:in `require
1.使用gem安装mysql2的时候提示以下错误extconf.rb:2:in `require': no such file to load -- mkmf (LoadError) from extconf.rb:2
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
/usr/bin/ruby1.8 extconf.rb
extconf.rb:2:in `require': no such file to load -- mkmf (LoadError)
from extconf.rb:2
原因：缺少mkmf，mkmf.rb is part of the ruby1.8-dev package。
解决办法：sudo apt-get install ruby1.8-dev
2.WARNING: This version of mysql2 (0.3.2) doesn't ship with the ActiveRecord adapter bundled anymore as it's now part of Rails 3.1
WARNING: Please use the 0.2.x releases if you plan on using it in Rails
原因：rails版本小于3.1，mysql2版本大于0.3，造成版本不兼容；
解决办法：在Gemfile里面把mysql2的版本调低一点设成gem 'mysql2', '
3.Installing mysql2 (0.3.6) D:/develop/Ruby192/lib/ruby/site_ruby/1.9.1/rubygems/defaults/operating_system.rb:9:in `block in op (required)>': The 'mysql2' native gem requires installed build tools. (Gem::InstallError) 原因：缺少devkit，无法安装mysql2； 解决办法：去'http://rubyinstaller.org/downloads 下载devkit，然后按照 的说明安装测试，再执行即可。 4.安装mysql2时报ERROR:Failed to build gem native extension.，具体如下： Building native extensions. This could take a while... ERROR: Error installing mysql2: ERROR: Failed to build gem native extension. google后发现很多人在安装的时候把mysql自身的参数带上就可以装成功，，比如带--with-mysql-lib=${mysqlLibPath}或--with-mysql-dir=${mysqlDir}或--with-mysql-config=${mysqlConfigPath}。都有试过还是一样，最后从apt中装了个mysql的开发包libmysqlclient-dev，才从gem上将mysql安装成功。
