错误:

在Linux系统上安装MySQL gem时，我遇到了以下问题。

# gem install mysql2 -v '0.3.18'

Building native extensions.  This could take a while...
ERROR:  Error installing mysql2:
        ERROR: Failed to build gem native extension.

    /usr/local/rvm/rubies/ruby-2.1.2/bin/ruby extconf.rb
checking for main() in -lmygcc... no
checking for mysql_query() in -lmysqlclient... 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.

extconf failed, exit code 1

Gem files will remain installed in /usr/local/rvm/gems/ruby-2.1.2/gems/mysql2-0.3.18 for inspection.
Results logged to /usr/local/rvm/gems/ruby-2.1.2/extensions/x86_64-linux/2.1.0/mysql2-0.3.18/gem_make.out

解决方案:

为了解决这个问题，我们需要在Linux系统上安装MySQL开发和客户端包。

在Ubuntu和Debian:

$ sudo apt-get install libmysqlclient-dev

在Redhat & CentOS:

# yum install mysql-devel

在Mac OS X上:

$ brew install mysql