Cloud9でrails serverできない

こんなん出た。

$ rails s -b $IP -p $PORT
=> Booting Puma
=> Rails 5.0.0.1 application starting in development on http://0.0.0.0:8080
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.4.0 (ruby 2.3.0-p0), codename: Owl Bowl Brawl
* Min threads: 0, max threads: 16
* Environment: development
* Listening on tcp://0.0.0.0:8080
Exiting
/usr/local/rvm/gems/ruby-2.3.0/gems/puma-3.4.0/lib/puma/binder.rb:255:in `initialize': Address already in use - bind(2) for "0.0.0.0" 

再起動したら直った。