如果您正在使用yum，请尝试:

sudo yum install mysql-devel

如果您正在使用yum，请尝试:

sudo yum install mysql-devel

对我来说，这很有帮助:

$ export LDFLAGS="-L/usr/local/opt/openssl/lib"
$ export CPPFLAGS="-I/usr/local/opt/openssl/include"

然后:

gem install mysql2 -v '0.5.2' --source 'https://rubygems.org/' -- --with-cppflags=-I/usr/local/opt/openssl/include --with-ldflags=-L/usr/local/opt/openssl/lib

结果:

Building native extensions with: '--with-cppflags=-I/usr/local/opt/openssl/include --with-ldflags=-L/usr/local/opt/openssl/lib'
This could take a while...
Successfully installed mysql2-0.5.2
Parsing documentation for mysql2-0.5.2
Installing ri documentation for mysql2-0.5.2
Done installing documentation for mysql2 after 0 seconds
1 gem installed

请看这篇文章(警告:里面有日语)。

如果仍然报错，请按照mysql2 gem在Rails 3上的安装步骤

http://rorguide.blogspot.com/2011/03/installing-mysql2-gem-on-ruby-192-and.html

其中大多数用户都能够安装mysql2 gem。

在ubuntu 20.04 LTS下，这是唯一的解决方案，一直为我工作:

sudo apt-get install ruby-mysql2

你必须安装一些依赖项

sudo apt-get install libmysql-ruby libmysqlclient-dev