Why won't my Ubuntu server install Rails 2.3.8?

I have an older Ubuntu server with a Rails app running on version 2.3.5 that I'd like to move to version 2.3.8. The server doesn't seem to know that there is an update available, no matter how many times I run a "gem update" or "gem update --system" or "update_rubygems"

root@server:~# gem install rails -v 2.3.8
ERROR:  could not find gem rails locally or in a repository
root@server:~# gem install rails
Successfully 开发者_运维问答installed rails-2.3.5
1 gem installed
Installing ri documentation for rails-2.3.5...
Installing RDoc documentation for rails-2.3.5...

RubyGems 1.3.5 is installed.

I don't remember having to do anything special for any of my other servers when making this upgrade.

Any ideas?

Try:

gem install rails --source http://rubygems.org

with --source and without -v.