npm install -g forever

forever start c9sdk/server.js --listen 0.0.0.0 --port 80 -a aa:111 -w ~

To elaborate, you can use something like forever2 to run your server. This has the added advantage of being able to close your instance of bash without worrying about Cloud9 stopping. To start, install forever with npm install -g forever, then run forever start c9sdk/server.js [options...], then you can list the running applications with forever list, and stop them with forever stop c9sdk/server.js.