[root@cloudmaster gem]# gem install rails -l
ERROR: Error installing rails:
activemodel requires builder (~> 3.0.0, runtime)
[root@cloudmaster gem]#
故障分析：
gem包使用本地安装，而本地builder-3.1.4.gem版本大于3.0.0，按提示应该不是此问题；尝试其他方法解决都行不通，故找来另一台机器直接gem install rails一下，之后gem list结果如下：
[root@ezCloud ~]# gem install rails
Successfully installed rails-3.2.9
1 gem installed
Installing ri documentation for rails-3.2.9...
Installing RDoc documentation for rails-3.2.9...
[root@ezCloud ~]# gem list
*** LOCAL GEMS ***
actionmailer (3.2.9)
actionpack (3.2.9)
activemodel (3.2.9)
activerecord (3.2.9)
activeresource (3.2.9)
activesupport (3.2.9)
arel (3.0.2)
builder (3.0.4)
bundler (1.2.3)
daemons (1.1.9)
erubis (2.7.0)
eventmachine (1.0.0)
headers (0.0.1)
hike (1.2.1)
i18n (0.6.1)
journey (1.0.4)
json (1.7.5, 1.4.6)
libraries (0.1.6)
mail (2.4.4)
mime-types (1.19)
multi_json (1.5.0)
nokogiri (1.5.6)
polyglot (0.3.3)
rack (1.4.1)
rack-cache (1.2)
rack-protection (1.3.2)
rack-ssl (1.3.2)
rack-test (0.6.2)
rails (3.2.9)
railties (3.2.9)
rake (10.0.3)
rdoc (3.12)
sequel (3.42.0)
sinatra (1.3.3)
sinatra-sequel (0.9.0)
sprockets (2.2.2)
thin (1.5.0)
thor (0.16.0)
tilt (1.3.3)
treetop (1.4.12)
tzinfo (0.3.35)
[root@ezCloud ~]#