新手问题 CentOS 下 gem sources 新增镜像遇到的报错，是缺少什么包所导致吗？
跟从地址http://ruby-china.org/wiki/install_ruby_guidegem的方式进行，理解 sources 的用法，但不知道为什么我新增镜像时会遇到这样的问题，推荐的所有镜像都无法新增。
``gem sources -a http://gems.rubyforge.org
/usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:inrequire': cannot load such file -- zlib (LoadError)
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in require'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems.rb:540:ingunzip'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/remote_fetcher.rb:239:in fetch_path'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/spec_fetcher.rb:269:inload_specs'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/commands/sources_command.rb:72:in execute'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/command.rb:278:ininvoke'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/command_manager.rb:147:in process_args'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/command_manager.rb:117:inrun'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/lib/ruby/site_ruby/1.9.1/rubygems/gem_runner.rb:65:in run'
from /usr/local/rvm/rubies/ruby-1.9.3-p392/bin/gem:25:in
非常感谢！在
http://stackoverflow.com/questions/9727908/cannot-load-such-file-zlib-even-after-using-rvm-pkg-install-zlib
中找到一个非常实用的命令：rvm requirements，可以帮助把 ruby 需要用的包都安装了。