mongooplog is a simple tool that polls operations from the replication oplog of a remote server, and applies them to the local server. This capability supports certain classes of real-time migrations that require that the source server remain online and in operation throughout the migration process.

Typically this command will take the following form:

mongooplog  --from --host

This command copies oplog entries from the mongod instance running on the host and duplicates operations to the host If you do not need to keep the --from host running during the migration, consider using mongodump and mongorestore or another backup operation, which may be better suited to your operation.


If the mongod instance specified by the --from argument is running with authentication, then mongooplog will not be able to copy oplog entries.

See also

mongodump, mongorestore, "/administration/backups", "Oplog Internals Overview", and "Replica Set Oplog Sizing".




Returns a basic help and usage text.

--verbose, -v

Increases the amount of internal reporting returned on the command line. Increase the verbosity with the -v form by including the option multiple times, (e.g. -vvvvv.)


Returns the version of the mongooplog utility.

--host <hostname><:port>, -h

Specifies a resolvable hostname for the mongod instance to which mongooplog will apply oplog operations retrieved from the serve specified by the --from option.

mongooplog assumes that all target mongod instances are accessible by way of port 27017. You may, optionally, declare an alternate port number as part of the hostname argument.

You can always connect directly to a single mongod instance by specifying the host and port number directly.

To connect to a replica set, you can specify the replica set seed name, and a seed list of set members, in the following format:



Specifies the port number of the mongod instance where mongooplog will apply oplog entries. Only specify this option if the MongoDB instance that you wish to connect to is not running on the standard port. (i.e. 27017) You may also specify a port number using the --host command.


Enables IPv6 support that allows mongooplog to connect to the MongoDB instance using an IPv6 network. All MongoDB programs and processes, including mongooplog, disable IPv6 support by default.


New in version 2.4: MongoDB added support for SSL connections to mongod instances in mongooplog.


SSL support in mongooplog is not compiled into the default distribution of MongoDB. See /administration/ssl for more information on SSL and MongoDB.

Additionally, mongooplog does not support connections to mongod instances that require client certificate validation.

Allows mongooplog to connect to mongod instance over an SSL connection.

--username <username>, -u <username>

Specifies a username to authenticate to the MongoDB instance, if your database requires authentication. Use in conjunction with the --password option to supply a password.

--password <password>, -p <password>

Specifies a password to authenticate to the MongoDB instance. Use in conjunction with the --username option to supply a username.

If you specify a --username without the --password option, mongooplog will prompt for a password interactively.

--authenticationDatabase <dbname>

New in version 2.4.

Specifies the database that holds the user's (e.g --username) credentials.

By default, mongooplog assumes that the database specified to the --db argument holds the user's credentials, unless you specify --authenticationDatabase.

See userSource, /reference/privilege-documents and /reference/user-privileges for more information about delegated authentication in MongoDB.

--authenticationMechanism <name>

New in version 2.4.

Specifies the authentication mechanism. By default, the authentication mechanism is MONGODB-CR, which is the MongoDB challenge/response authentication mechanism. In the MongoDB Subscriber Edition, mongooplog also includes support for GSSAPI to handle Kerberos authentication.

See /tutorial/control-access-to-mongodb-with-kerberos-authentication for more information about Kerberos authentication.

--dbpath <path>

Specifies a directory, containing MongoDB data files, to which mongooplog will apply operations from the oplog of the database specified with the --from option. When used, the --dbpath option enables mongo to attach directly to local data files and write data without a running mongod instance. To run with --dbpath, mongooplog needs to restrict access to the data directory: as a result, no mongod can be access the same path while the process runs.


Use the --directoryperdb in conjunction with the corresponding option to mongod. This option allows mongooplog to write to data files organized with each database located in a distinct directory. This option is only relevant when specifying the --dbpath option.


Allows mongooplog operations to use the durability journal to ensure that the data files will remain in a consistent state during the writing process. This option is only relevant when specifying the --dbpath option.

--fields [field1[,field2]], -f [field1[,field2]]

Specify a field or number fields to constrain which data mongooplog will migrate. All other fields will be excluded from the migration. Comma separate a list of fields to limit the applied fields.

--fieldFile <file>

As an alternative to "--fields" the --fieldFile option allows you to specify a file (e.g. <file>) that holds a list of field names to include in the migration. All other fields will be excluded from the migration. Place one field per line.

--seconds <number>, -s <number>

Specify a number of seconds of operations for mongooplog to pull from the remote host. Unless specified the default value is 86400 seconds, or 24 hours.

--from <host[:port]>

Specify the host for mongooplog to retrieve oplog operations from. mongooplog requires this option.

Unless you specify the --host option, mongooplog will apply the operations collected with this option to the oplog of the mongod instance running on the localhost interface connected to port 27017.

--oplogns <namespace>

Specify a namespace in the --from host where the oplog resides. The default value is, which is the where replica set members store their operation log. However, if you've copied oplog entries into another database or collection, use this option to copy oplog entries stored in another location.

Namespaces take the form of [database].[collection].


Consider the following prototype mongooplog command:

mongooplog  --from --host

Here, entries from the oplog of the mongod running on port 27017. This only pull entries from the last 24 hours.

In the next command, the parameters limit this operation to only apply operations to the database people in the collection usage on the target host (i.e.

mongooplog  --from --host --database people --collection usage

This operation only applies oplog entries from the last 24 hours. Use the --seconds argument to capture a greater or smaller amount of time. Consider the following example:

mongooplog  --from --seconds 172800

In this operation, mongooplog captures 2 full days of operations. To migrate 12 hours of oplog entries, use the following form:

mongooplog  --from --seconds 43200

For the previous two examples, mongooplog migrates entries to the mongod process running on the localhost interface connected to the 27017 port. mongooplog can also operate directly on MongoDB's data files if no mongod is running on the target host. Consider the following example:

mongooplog  --from --dbpath /srv/mongodb --journal

Here, mongooplog imports oplog operations from the mongod host connected to port 27017. This migrates operations to the MongoDB data files stored in the /srv/mongodb directory. Additionally mongooplog will use the durability journal to ensure that the data files remain in a consistent state.


MongoDB Documentation Project


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