RRDTool is a nice metric storage and graphing library. We're using its Ruby binding internally to integrate RRDTool into our product but I was having problems getting it running:
.....................dyld: NSLinkModule() error
dyld: Symbol not found: _rrd_graph
Referenced from: /usr/local/lib/ruby/site_ruby/1.8/universal-darwin8.0/RRD.bundle
Expected in: flat namespace
This error is due to the Ruby binding not being able to find the native RRD library, librrd. When you install rrdtool via Mac Ports, it installs everything in /opt/local, not /usr/local. What you need to do is update
rrdtool-1.2.x/bindings/ruby and change the following line so that the binding will look in the proper location for the Mac Ports install:
ruby extconf.rb ; make ; sudo make install to install the modified Ruby binding.