db.help()

2018-03-03T18:40:52.308+0800 I CONTROL  [initandlisten] 
2018-03-03T18:40:52.308+0800 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
2018-03-03T18:40:52.308+0800 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
2018-03-03T18:40:52.308+0800 I CONTROL  [initandlisten] 
2018-03-03T18:40:52.308+0800 I CONTROL  [initandlisten] ** WARNING: soft rlimits too low. rlimits set to 3821 processes, 65536 files. Number of processes should be at least 32768 : 0.5 times number of files.
2018-03-03T18:40:52.308+0800 I CONTROL  [initandlisten] 
> show  tables;
> show dbs;
admin   0.000GB
config  0.000GB
local   0.000GB
> du
2018-03-03T19:27:34.145+0800 E QUERY    [thread1] ReferenceError: du is not defined :
@(shell):1:1
> j
2018-03-03T19:28:46.003+0800 E QUERY    [thread1] ReferenceError: j is not defined :
@(shell):1:1
> use  admin
switched to db admin
> show tables;
system.version
> use local
switched to db local
> show tables;
startup_log
> use config
switched to db config
> show tables;
system.sessions
> show collections;
system.sessions
> db.help()
DB methods:
db.adminCommand(nameOrDocument) - switches to 'admin' db, and runs command [just calls db.runCommand(...)]
db.aggregate([pipeline], {options}) - performs a collectionless aggregation on this database; returns a cursor
db.auth(username, password)
db.cloneDatabase(fromhost)
db.commandHelp(name) returns the help for the command
db.copyDatabase(fromdb, todb, fromhost)
db.createCollection(name, {size: ..., capped: ..., max: ...})
db.createView(name, viewOn, [{$operator: {...}}, ...], {viewOptions})
db.createUser(userDocument)
db.currentOp() displays currently executing operations in the db
db.dropDatabase()
db.eval() - deprecated
db.fsyncLock() flush data to disk and lock server for backups
db.fsyncUnlock() unlocks server following a db.fsyncLock()
db.getCollection(cname) same as db['cname'] or db.cname
db.getCollectionInfos([filter]) - returns a list that contains the names and options of the db's collections
db.getCollectionNames()
db.getLastError() - just returns the err msg string
db.getLastErrorObj() - return full status object
db.getLogComponents()
db.getMongo() get the server connection object
db.getMongo().setSlaveOk() allow queries on a replication slave server
db.getName()
db.getPrevError()
db.getProfilingLevel() - deprecated
db.getProfilingStatus() - returns if profiling is on and slow threshold
db.getReplicationInfo()
db.getSiblingDB(name) get the db at the same server as this one
db.getWriteConcern() - returns the write concern used for any operations on this db, inherited from server object if set
db.hostInfo() get details about the server's host
db.isMaster() check replica primary status
db.killOp(opid) kills the current operation in the db
db.listCommands() lists all the db commands
db.loadServerScripts() loads all the scripts in db.system.js
db.logout()
db.printCollectionStats()
db.printReplicationInfo()
db.printShardingStatus()
db.printSlaveReplicationInfo()
db.dropUser(username)
db.repairDatabase()
db.resetError()
db.runCommand(cmdObj) run a database command.  if cmdObj is a string, turns it into {cmdObj: 1}
db.serverStatus()
db.setLogLevel(level,<component>)
db.setProfilingLevel(level,slowms) 0=off 1=slow 2=all
db.setWriteConcern(<write concern doc>) - sets the write concern for writes to the db
db.unsetWriteConcern(<write concern doc>) - unsets the write concern for writes to the db
db.setVerboseShell(flag) display extra information in shell output
db.shutdownServer()
db.stats()
db.version() current version of the server