mongo db backup

I tried to set up Backups with mongodump command. I used this Tutorial: https://www.digitalocean.com/community/tutorials/how-to-back-up-restore-and-migrate-a-mongodb-database-on-ubuntu-14-04

But when i execute folowing command: sudo mongodump --db newdb --out /var/backups/mongobackups/date +"%m-%d-%y" I get this error:

Failed: error getting collections for database ibyc_db: error running listCollections. Database: ibyc_db Err: not authorized on ibyc_db to execute command { listCollections: 1, cursor: {} }

I am running a node.js application and it works fine. The application is able to write and read to the database.

Could someone help with the mongodump command?

Thx a lot