Ruby/Gem upgrade problems -> 1.8 to 1.9 and solutions

If, following a RedHat linux (EL5) update, your ruby is broken with a message such as this:

/usr/bin/ruby: symbol lookup error: /usr/local/lib/ruby/gems/1.9.1/gems/json-1.7.7/lib/json/ext/parser.so: undefined symbol: rb_intern2

have a look at your ruby path. RedHat puts the updated ruby executable in /usr/local/bin/ruby. You will probably need to do this:

# mv /usr/bin/ruby /usr/bin/ruby_old
# ln -s /usr/local/bin/ruby /usr/bin/ruby
 
Another problem that is commonly encountered is with the gem command after an update:

You get an error dump like this:
# gem list
/usr/local/lib/ruby/site_ruby/1.9.1/rubygems/config_file.rb:82:in `rescue in rescue in ': uninitialized constant Gem::ConfigFile::RbConfig (NameError)
        from /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/config_file.rb:64:in `rescue in '
        from /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/config_file.rb:60:in `'
        from /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/config_file.rb:36:in `'
        from /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/gem_runner.rb:9:in `require'
        from /usr/local/lib/ruby/site_ruby/1.9.1/rubygems/gem_runner.rb:9:in `'
        from /usr/local/bin/gem:9:in `require'
        from /usr/local/bin/gem:9:in `

'

 
The key here is the bit that says "Gem::ConfigFile::RbConfig (NameError)" 

What this is telling you is that it cannot find the RbConfig class. This is a bug in the upgrade from 1.8 to 1.9. There is a line that needs to go into your gem command. Add this to your gem file:

require "rbconfig"
 
You can locate the gem command on Linux using this command:

which gem

Then simply vi the file and add the above line in.