[问题]ubuntu7.10安装RMagick出错

[isaiah]

在终端输入$ irb -rubygems -r RMagick出现以下错误：
/usr/lib/ruby/gems/1.8/gems/rmagick-2.1.0/lib/RMagick2.so: /usr/lib/ruby/gems/1.8/gems/rmagick-2.1.0/lib/RMagick2.so: undefined symbol: SketchImage - /usr/lib/ruby/gems/1.8/gems/rmagick-2.1.0/lib/RMagick2.so (LoadError)
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
from /usr/lib/ruby/gems/1.8/gems/rmagick-2.1.0/lib/RMagick.rb:11
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:32:in `gem_original_require'
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:32:in `require'
from /usr/lib/ruby/1.8/irb/init.rb:252:in `load_modules'
from /usr/lib/ruby/1.8/irb/init.rb:250:in `each'
from /usr/lib/ruby/1.8/irb/init.rb:250:in `load_modules'
from /usr/lib/ruby/1.8/irb/init.rb:21:in `setup'
from /usr/lib/ruby/1.8/irb.rb:54:in `start'
from /usr/bin/irb:13
已装好ImageMagick6.3.7，通过$convert -version：
Version: ImageMagick 6.3.7 01/20/08 Q8 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2008 ImageMagick Studio LLC
RMagick本地安装和通过rubygems安装都出现同样的问题。
rails和rubygems 都为最新版。
在网上找过很多方法都不行：如在环境变量设置export LD_LIBRARY_PATH=/usr/local/lib等