rails install

Missing the Rails gem. Please gem install -v= rails, update your RAILS_GEM_VERSION setting in config/environment.rb for the Rails version you do have installed, or comment out RAILS_GEM_VERSION to use the latest version installed.

here is my gem list

$gem list
/usr/local/ruby193p0/lib/ruby/1.9.1/yaml.rb:56:in `<top (required)>':
It seems your ruby installation is missing psych (for YAML output).
To eliminate this warning, please install libyaml and reinstall your ruby.

*** LOCAL GEMS ***

bigdecimal (1.1.0)
io-console (0.3)
json (1.5.4)
minitest (2.5.1)
rake (0.9.2.2)
rdoc (3.9.4)

Answer:
Make sure you installed the rails gem in the global gem store. If you just install the gem as a non-root user, it will be installed inside your $HOME/.gems directory. If you run Redmine as another user, it will not find that gem of course.

So you could just try to install the rails gem into the global gem store as root using

sudo gem install rails -v=3.2.0

先檢查版本：
gem  -v
1.8.11
下載rubygems-1.8.17.tgz
tar xzvf rubygems-1.8.17.tgz
cd rubygems-1.8.17
sodu ruby setup.rb   (檢查ruby -v 版本是ruby 1.9.3p0 (2011-10-30 revision 33570) [i686-linux])
【以前的安裝不對的地方是建立軟連接到/usr/bin/ruby   and /usr/bin/gem 。要刪除軟連接，而採用安裝到/usr/locla/ 下的程序】

@@@@由於usr/bin裏面是root的應用程序，usr/local裏面是普通用戶的應用程序
補初級linux OS 知識！！！