Q:

Unable to start webbrick - TCPServer Error: Address already in use

I am receiving the following error:
$rails server --binding=127.0.0.1
=> Booting WEBrick
=> Rails 3.1.1 application starting in development on http://127.0.0.1:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2012-04-04 13:02:35] INFO  WEBrick 1.3.1
[2012-04-04 13:02:35] INFO  ruby 1.9.2 (2011-07-09) [x86_64-darwin10.8.0]
[2012-04-04 13:02:35] WARN  TCPServer Error: Address already in use - bind(2)
Exiting
/Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/utils.rb:73:in `initialize': Address already in use - bind(2) (Errno::EADDRINUSE)
from /Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/utils.rb:73:in `new'
from /Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/utils.rb:73:in `block in create_listeners'
from /Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/utils.rb:70:in `each'
from /Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/utils.rb:70:in `create_listeners'
from /Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/server.rb:74:in `listen'
from /Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/server.rb:62:in `initialize'
from /Users/TravisKs/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/webrick/httpserver.rb:24:in `initialize'
from /Users/TravisKs/.rvm/gems/ruby-1.9.2-p290@rvm-gemset-name/gems/rack-1.3.5/lib/rack/handler/webrick.rb:10:in `new' 
from /Users/TravisKs/.rvm/gems/ruby-1.9.2-p290@rvm-gemset-name/gems/rack-1.3.5/lib/rack/handler/webrick.rb:10:in `run' 
from /Users/TravisKs/.rvm/gems/ruby-1.9.2-p290@rvm-gemset-name/gems/rack-1.3.5/lib/rack/server.rb:265:in `start'
from /Users/TravisKs/.rvm/gems/ruby-1.9.2-p290@rvm-gemset-name/gems/railties-3.1.1/lib/rails/commands/server.rb:70:in `start'
from /Users/TravisKs/.rvm/gems/ruby-1.9.2-p290@rvm-gemset-name/gems/railties-3.1.1/lib/rails/commands.rb:54:in `block in <top (required)>'
from /Users/TravisKs/.rvm/gems/ruby-1.9.2-p290@rvm-gemset-name/gems/railties-3.1.1/lib/rails/commands.rb:49:in `tap' 
from /Users/TravisKs/.rvm/gems/ruby-1.9.2-p290@rvm-gemset-name/gems/railties-3.1.1/lib/rails/commands.rb:49:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'

After restarting my machine I still have this problem. I have reviewed other SO posts on the TCPServer error with Rails.
ps -eo pid,ppid,user,args,stat

Returns no results for rails
ps aux

Does not return any Zombie Processes (Z in the stat column) or Rails servers.
This is odd to me since everything was working fine. I switched a gemset, reinstalled Rails 3.1.1, and now I am unable to run it.

A:

try running lsof | grep 3000 and then kill -9 <number of process>
if it doesn't help, try running the rails server with -p 3001 option to change the port

