When I try to run the code I get this error:

node auth_server.js

events.js:72
throw er; // Unhandled 'error' event
^
Error: listen EACCES
at errnoException (net.js:901:11)
at Server._listen2 (net.js:1020:19)
at listen (net.js:1061:10)
at Server.listen (net.js:1135:5)
at Function.app.listen (/home/ubuntu/htdocs/joolip/node_modules/express/lib/application.js:532:24)
at Object. (/home/ubuntu/htdocs/joolip/auth_server.js:27:5)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)