Commands

Introduction

The Mongo database has a concept of a database command. Database commands are ways to ask the database to perform special operations, or to request information about its current operational status.

Introduction
Privileged Commands
Getting Help Info for a Command
More Command Documentation

List of Database Commands

A command is sent to the database as a query to a special collection namespace called $cmd. The database will return a single document with the command results - use findOne() for that if your driver has it.

The general command syntax is:

db.$cmd.findOne( { <commandname>: <value> [, options] } );

The shell provides a helper function for this:

db.runCommand( { <commandname>: <value> [, options] } );

For example, to check our database's current profile level setting, we can invoke:

> db.runCommand({profile:-1});
{
    "was" : 0.0 ,
    "ok" : 1.0
}

For many db commands, some drivers implement wrapper methods are implemented to make usage easier. For example, the mongo shell offers

> db.getProfilingLevel()
0.0

Let's look at what this method is doing:

> print( db.getProfilingLevel )
function () {
    var res = this._dbCommand({profile:-1});
    return res ? res.was : null;
}

> print( db._dbCommand )
function (cmdObj) {
    return this.$cmd.findOne(cmdObj);
}

Many commands have helper functions - see your driver's documentation for more information.

Privileged Commands

Certain operations are for the database administrator only. These privileged operations may only be performed on the special database named admin.

> use admin;
> db.runCommand("shutdown"); // shut down the database

If the db variable is not set to 'admin', you can use adminCommand (_adminCommand in versions earlier than 1.8) to switch to the right database automatically (and just for that operation):

> db.adminCommand("shutdown");

(For this particular command there is also a shell helper function, db.shutdownServer.)

Getting Help Info for a Command

Use commandHelp in shell to get help info for a command:

> db.commandHelp("datasize")
help for: datasize  example: { datasize:"blog.posts", keyPattern:{x:1}, min:{x:10}, max:{x:55} }
NOTE: This command may take awhile to run

(Help is not yet available for some commands.)

Commands

Introduction

Privileged Commands

Getting Help Info for a Command

More Command Documentation

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