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

Here's what worked for me when restoring an exported database:

mongorestore -d 0 ./0 --drop

where ./contained the exported bson files. Note that the --drop will overwrite existing data.