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

If you want to dump all collections in all databases (which is an expansive interpretation of the original questioner's intent) then use

mongodump

All the databases and collections will be created in a directory called 'dump' in the 'current' location