gem install rails
したら
ERROR: While executing gem ... (Gem::RemoteFetcher::UnknownHostError)
no such name (https://api.rubygems.org/quick/Marshal.4.8/atomic-1.1.8-java.gemspec.rz)
というエラーが出たので atomic
を入れればイイですよ。というハナシ。
% gem install atomic
% gem install rails