gem install mysqlでのエラー対策(redmine1.2 install)

gem install mysql -- --with-mysql-config=/usr/bin/mysql_config
Building native extensions.  This could take a while...
ERROR:  Error installing mysql:
	ERROR: Failed to build gem native extension.

/usr/bin/ruby extconf.rb --with-mysql-config=/usr/bin/mysql_config
mkmf.rb can't find header files for ruby at /usr/lib/ruby/ruby.h

Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/mysql-2.8.1 for inspection.
Results logged to /usr/lib/ruby/gems/1.8/gems/mysql-2.8.1/ext/mysql_api/gem_make.out

のようなエラーが発生したら
% sudo apt-get install ruby-devel

ではなく

% sudo gem install ruby-devel

により解消。このエラーでruby-develが必要ってわからないのだけど。