** 是 ctrl-c，不是 ctrl-z，在重开 rails server 的时候 **
$rails s
=> Booting Puma
=> Rails 5.0.0 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
A server is already running. Check /Users/lvchengbo/job-listing/tmp/pids/server.pid.
Exiting
解决办法
运行命令
kill -9 $(lsof -i tcp:3000 -t)
