By default MongoDB uses /data/db as it’s location for databases. You need to create this dir and then chown it to the user running mongod. For example:
sudo chown username /data/db
More info here.
MongoDB usage notes
MongoDB Shell commands:
#list dbs on server: show dbs
#show collections in current db show collections
#switch to db
use databasename;
#find everything and print as json
db.collectionname.find().forEach(printjson);
#'like' query:
db.collectionname.find(fieldname:/pattern/).forEach(printjson);
#count results:
db.collectionname.find().count();
#return only requested properties (similar to 'select x, y, z from table a')
db.collectionname.find({}, {fieldname1:1, fieldname2:1}).forEach(printjson)
#select min x by sorting in asc order and picking first result
db.collectionname.find().sort({x: 1}).limit(1).forEach(printjson)
#select max x by sorting in desc order and picking first result
db.collectionname.find().sort({x: -1}).limit(1).forEach(printjson)
#add an index for property x
db.collectionname.ensureIndex({x: 1})
Stats webapp: http://localhost:28017/