Why does Rubygems complain about needing Ruby 1.8.7 if that's what is installed?

On my Ubunto 8.04 (Hardy) server, I'm trying to upgrade rubygems. When I try to update, it tells me I need Ruby >= 1.8.7, when I run ruby -v to check the version I have it tells me I have 1.8.7

$gem update --system
rubygems-update requires Ruby version >开发者_高级运维= 1.8.7

$ruby -v
ruby 1.8.7 (2008-06-20 patchlevel 22) [x86_64-linux]

I just upgraded ruby from source. I also have RVM installed but I'm not using it. How can I make rubygems use the proper version of ruby?

That's a very old version of Ruby 1.8.7 - I guess that it might be from a distribution package. Current versions of RubyGems should probably be matched with the latest patch level of Ruby.

I think that the simplest thing to do is to choose one way of managing your Ruby installation and remove any other Ruby stuff that was put on the system by other methods. RVM is probably the best approach ATM.