How to export all collections in MongoDB?

Question

I want to export all collections in MongoDB by the command:

mongoexport -d dbname -o Mongo.json

The result is:
No collection specifie

Answer 1

Previous answers explained it well, I am adding my answer to help in case you are dealing with a remote password protected database

mongodump --host xx.xxx.xx.xx --port 27017 --db your_db_name --username your_user_name --password your_password --out /target/folder/path