这几天在正式环境上部署 Redmine，之前在自己的 Mac 上已经试着部署过一次。 这次由于 CentOS 上部署，以前完全没有遇到过这个问题，实在头大，请教各位！ 先说下过程： 先用 rvm 安装 ruby，成功。

$ ruby -v
ruby 2.1.4p265 (2014-10-27 revision 48166) [x86_64-linux]

然后 gem 安装 rails，成功

$ rails -v
Rails 4.1.8

然后下载 redmine-2.4.7，解压 运行命令

$ ruby script/rails server webrick -e production

然后提示

Could not find gem 'mysql2 (~> 0.3.11) ruby' in the gems available on this machine. 
Run `bundle install` to install missing gems.

根据提示，打命令

gem install mysql2 -v '0.3.17'

报错，以下是错误信息：

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

    /usr/local/rvm/rubies/ruby-2.1.4/bin/ruby -r ./siteconf20141219-14269-9ceayj.rb extconf.rb
checking for ruby/thread.h... yes
checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... yes
checking for rb_hash_dup()... yes
checking for rb_intern3()... yes
checking for mysql_query() in -lmysqlclient... yes
checking for mysql.h... no
checking for mysql/mysql.h... yes
checking for errmsg.h... no
-----
errmsg.h is missing.  please check your installation of mysql and try again.
-----
*** 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=/usr/local/rvm/rubies/ruby-2.1.4/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-mysql-config
    --without-mysql-config
    --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-mysqlclientlib
    --without-mysqlclientlib

extconf failed, exit code 1

Gem files will remain installed in /usr/local/rvm/gems/ruby-2.1.4/gems/mysql2-0.3.17 for inspection.
Results logged to /usr/local/rvm/gems/ruby-2.1.4/extensions/x86_64-linux/2.1.0/mysql2-0.3.17/gem_make.out

但是

$ find / -name errmsg.h
/usr/lib/errmsg.h 
/usr/include/mysql/errmsg.h

系统里已经安装好了 mysql 环境了 求助！

2015-1-8 前段时间忙了忙其他项目，今天又重新捡起这个问题研究了一下。 既然 adapter 用不了 mysql2，就只能用 mysql 了，但是又出了问题，大致意思是说从数据库中读出来编码有问题。 按照这位大牛说的解决了： http://www.cnblogs.com/kting/archive/2011/09/15/2177530.html

把他的帖子 copy 过来，就算记录问题了。

感谢各位对我这个问题的回复！十分感谢！！！

以下转自网络，感谢作者

问题现象：

　　在.html.erb中显示mysql中的中文字符时会出现 

incompatible character encodings: UTF-8 and ASCII-8BIT 错误
问题可能原因：



mysql_adapater出来的数据是ASCII-8BIT
解决方法：



修改根目录下的\Ruby192\lib\ruby\gems\1.9.1\gems\activerecord-3.0.9\lib\active_record\connection_adapters中的
mysql_adapter.rb文件
 def select(sql, name = nil)
          @connection.query_with_result = true
          result = execute(sql, name)
          rows = []
          result.each_hash { |row| rows << row }
          result.free
          @connection.more_results && @connection.next_result    # invoking stored procedures with CLIENT_MULTI_RESULTS requires this to tidy up else connection will be dropped

      # add begin
      if @config[:encoding] && @config[:encoding]=="utf8"
            rows.each do |row|
              row.each do |key, value|
                if (value.class == String)
                  value.force_encoding("UTF-8")
                end
              end
            end
          end
      # add end
          rows
        end