我是使用 mongrel 服务 Rails 应用程序的新手。我已经设法做到了这一点，但我遇到了以下问题。我正在使用centOs，当我输入时mongrel_rails start，我收到了这个错误。我是不是错过了什么。谢谢
/usr/local/rvm/rubies/ruby-1.9.3-p194/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.
NOTE: Gem::SourceIndex.from_installed_gems is deprecated with no replacement. It will be removed on or after 2011-10-01.
Gem::SourceIndex.from_installed_gems called from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/gem_plugin-0.2.3/lib/gem_plugin.rb:109.
NOTE: from_installed_gems(arg) is deprecated. From /usr/local/rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/deprecate.rb:63:in `block (2 levels) in deprecate'
NOTE: Gem::SourceIndex.from_gems_in is deprecated with no replacement. It will be removed on or after 2011-10-01.
Gem::SourceIndex.from_gems_in called from /usr/local/rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/source_index.rb:50.
NOTE: Gem::SourceIndex#each is deprecated with no replacement. It will be removed on or after 2011-11-01.
Gem::SourceIndex#each called from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/gem_plugin-0.2.3/lib/gem_plugin.rb:112.
** Starting Mongrel listening at 0.0.0.0:3000
** Starting Rails with development environment...
/usr/local/rvm/gems/ruby-1.9.3-p194/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:251:in `require': cannot load such file -- dispatcher (LoadError)
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:251:in `block in require'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:236:in `load_dependency'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:251:in `require'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/lib/mongrel/rails.rb:148:in `rails'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/bin/mongrel_rails:116:in `block (2 levels) in run'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/lib/mongrel/configurator.rb:149:in `call'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/lib/mongrel/configurator.rb:149:in `listener'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/bin/mongrel_rails:102:in `block in run'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/lib/mongrel/configurator.rb:50:in `call'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/lib/mongrel/configurator.rb:50:in `initialize'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/bin/mongrel_rails:86:in `new'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/bin/mongrel_rails:86:in `run'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/lib/mongrel/command.rb:210:in `run'
from /usr/local/rvm/gems/ruby-1.9.3-p194/gems/mongrel-1.2.0.pre2/bin/mongrel_rails:282:in `<top (required)>'
from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/mongrel_rails:19:in `load'
from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/mongrel_rails:19:in `<main>'
from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/ruby_noexec_wrapper:14:in `eval'
from /usr/local/rvm/gems/ruby-1.9.3-p194/bin/ruby_noexec_wrapper:14:in `<main>'
宝石清单：
actionmailer (3.2.8)
actionpack (3.2.8)
activemodel (3.2.8)
activerecord (3.2.8)
activeresource (3.2.8)
activesupport (3.2.8)
arel (3.0.2)
bcrypt-ruby (3.0.1)
bootstrap-sass (2.0.4.0)
bootstrap-will_paginate (0.0.6)
builder (3.1.4, 3.0.3)
bundle (0.0.1)
bundler (1.2.1)
capistrano (2.13.4)
cgi_multipart_eof_fix (2.5.0)
coffee-rails (3.2.2)
coffee-script (2.2.0)
coffee-script-source (1.3.3)
daemons (1.1.9, 1.0.10)
erubis (2.7.0)
execjs (1.4.0)
faker (1.0.1)
fastthread (1.0.7)
gem_plugin (0.2.3)
highline (1.6.15, 1.6.2)
hike (1.2.1)
i18n (0.6.1)
journey (1.0.4)
jquery-rails (2.1.3, 2.0.2)
jruby-pageant (1.1.1)
json (1.7.5)
libv8 (3.11.8.3 x86_64-linux, 3.3.10.4 x86_64-linux)
mail (2.4.4)
mime-types (1.19)
mongrel (1.2.0.pre2)
mongrel_cluster (1.0.5)
multi_json (1.3.6)
mysql (2.8.1)
mysql2 (0.3.11)
net-scp (1.0.4)
net-sftp (2.0.5)
net-ssh (2.6.0)
net-ssh-gateway (1.1.0)
polyglot (0.3.3)
psych (1.3.4)
rack (1.4.1)
rack-cache (1.2)
rack-ssl (1.3.2)
rack-test (0.6.2, 0.6.1)
rails (3.2.8)
railties (3.2.8)
rake (0.9.2.2)
rdoc (3.12)
rubygems-bundler (1.1.0)
rubygems-update (1.4.1)
rvm (1.11.3.5)
sass (3.2.1)
sass-rails (3.2.5)
sprockets (2.7.0, 2.1.3)
sqlite3 (1.3.6)
therubyracer (0.10.2)
thor (0.16.0)
tilt (1.3.3)
treetop (1.4.11, 1.4.10)
tzinfo (0.3.33)
uglifier (1.3.0, 1.2.3)
will_paginate (3.0.3)