Cannot backup meteor mongo database

Hello,

The following command does not work
mongodump -h 127.0.0.1 --port 3001 -d meteor
connected to: 127.0.0.1:3001
2018-09-04T17:55:11.049-0400 DATABASE: meteor to dump/meteor

It does not report any error and it creates and empty folder.
Meteor mongo version is:
meteor:PRIMARY> db.version();
3.4.10

I am on Ubuntu, please help.

Thanks