我在Centos 5上安装RMagick rubygem时遇到了问题。我按照http://rmagick.rubyforge.org/install2-linux.html中详细的步骤进行操作，但当我尝试运行以下命令时：
sudo gem install rmagick
结果是：
Building native extensions. This could take a while...
ERROR: Error installing rmagick:
ERROR: Failed to build gem native extension.
/usr/local/bin/ruby extconf.rb
checking for Ruby version >= 1.8.5... yes
checking for gcc... yes
checking for Magick-config... no
Can't install RMagick 2.11.0. Can't find Magick-config in /usr/bin:/bin
*** 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/bin/ruby
Gem files will remain installed in /usr/local/lib/ruby/gems/1.8/gems/rmagick-2.11.0 for inspection.
Results logged to /usr/local/lib/ruby/gems/1.8/gems/rmagick-2.11.0/ext/RMagick/gem_make.out
目录 /usr/local/bin 包含 Magick-config，但我无法让 rubygems 查找到它。我尝试了下面的方法，但结果一样：
sudo gem install rmagick -- --with-opt-dir=/usr/local/bin
非常感谢您的帮助和建议。