rails 3.2安装mysql2

今天在centos上面安装ruby 1.93跟rails 3.2的时候，出现个状况：

Could not find gem 'mysql2 (>= 0) ruby' in the gems available on this machine.

按照提示gem install mysql2
还是报错：

*** 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.

重新安装gem install mysql2 --with-mysql-dir=/usr/local/system/mysql
还是报错

没办法，进入ruby/lib/ruby/gems/1.9.1/gems/mysql2-0.3.11手动安装：

ruby extconf.rb --with-mysql-dir=/usr/local/system/mysql && make && make install

装完还是不行

最后google找到问题：

gem install mysql2 -- --with-mysql-dir=/usr/local/system/mysql

需要两个--