MongoDB

Generic debug command

> db.currentOp();
> db.serverStatus()
> db.stats()
> db.$collection.stats()

Replica Set

> myreplname:PRIMARY> db.printReplicationInfo()

> myreplname:PRIMARY> db.printSlaveReplicationInfo()

> myreplname:PRIMARY> rs.status()

> myreplname:PRIMARY> rs.init()

> myreplname:SECONDARY> db.SlaveOk()

> myreplname:SECONDARY> use admin; db.shutdownServer({timeoutSecs: 300});

Lock/Unlock from writes

> db._adminCommand({fsync: 1, lock: 1})
switched to db admin

> db.$cmd.sys.unlock.findOne()
{ "ok" : 1, "info" : "unlock requested" }