Connect with mongosh

Open interactive shell to a MongoDB instance

mongosh 'mongodb://user:pass@mongo:27017/dbname'

More mongodb commands

Replica set status

mongosh --eval 'rs.status()' mongodb://mongo:27017

Show replica set members, lag, and election status
Database stats

mongosh --eval 'db.stats()' mongodb://mongo:27017/mydb

Data size, storage size, collection count for a database
Collection stats

mongosh --eval 'db.myCollection.stats()' mongodb://mongo:27017/mydb

Document count, index sizes, storage for a collection
Current operations

mongosh --eval 'db.currentOp({active:true,secs_running:{$gt:5}})' mongodb://mongo:27017

Show operations running longer than 5 seconds
Create dump

mongodump --uri='mongodb://user:pass@mongo:27017' --db=mydb --out=/backups/

Export database to BSON files