WEBrickがA server is already runningの場合の対処

$ rails s
=> Booting WEBrick
=> Rails 3.2.14 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
A server is already running. Check /worktest/sample/tmp/pids/server.pid.
Exiting

#起動中のプロセス一覧を表示
$ ps ax
　　：
　　：
　　：
　　：
 5441 pts/0    Tl     0:06 /home/vagrant/.rbenv/versions/1.9.3-p448/bin/ruby script/rails s
 5582 ?        S      0:00 pickup -l -t fifo -u
 5855 pts/0    R+     0:00 ps ax

#起動中のプロセスを終了
$ kill -9 5441