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The replSetInitiate command initializes a new replica set.

To run replSetInitiate, use the db.runCommand( { <command> } ) method.


Run the command on only one of the mongod instances for the replica set.

Use the following syntax:

{ replSetInitiate : <config_document> }

The <config_document> is a document that specifies the replica set’s configuration. For instance, here’s a config document for creating a simple 3-member replica set:

    _id : <setname>,
     members : [
         {_id : 0, host : <host0>},
         {_id : 1, host : <host1>},
         {_id : 2, host : <host2>},

IP Binding

Starting in MongoDB 3.6, MongoDB binaries, mongod and mongos, bind to localhost ( by default. If the net.ipv6 configuration file setting or the --ipv6 command line option is set for the binary, the binary additionally binds to the IPv6 address ::1.

Previously, starting from MongoDB 2.6, only the binaries from the official MongoDB RPM (Red Hat, CentOS, Fedora Linux, and derivatives) and DEB (Debian, Ubuntu, and derivatives) packages bind to localhost by default.

When bound only to the localhost, these MongoDB 3.6 binaries can only accept connections from clients (including the mongo shell, other members in your deployment for replica sets and sharded clusters) that are running on the same machine. Remote clients cannot connect to the binaries bound only to localhost.

To override and bind to other ip addresses, you can use the net.bindIp configuration file setting or the --bind_ip command-line option to specify a list of ip addresses.


Before you bind to other ip addresses, consider enabling access control and other security measures listed in Security Checklist to prevent unauthorized access.

For example, the following mongod instance binds to both the localhost and the sample ip address

mongod --bind_ip localhost,

In order to connect to this instance, remote clients must specify the ip address or the hostname associated with the ip address:

mongo --host

mongo --host My-Example-Associated-Hostname


Assign a config document to a variable and then to pass the document to the rs.initiate() helper:

config = {
    _id : "my_replica_set",
     members : [
         {_id : 0, host : ""},
         {_id : 1, host : ""},
         {_id : 2, host : "", arbiterOnly: true},


Notice that omitting the port cause the host to use the default port of 27017. Notice also that you can specify other options in the config documents such as the arbiterOnly setting in this example.