Step 2: Start the new mongod instance. Ensure you start the 3.0 mongod with the same dbPath : 

mongod --dbpath /var/mongod/data 

Replace /var/mongod/data with your MongoDB dbPath . 

## Upgrade to SCRAM-SHA-1 

Overview MongoDB 3.0 includes support for the SCRAM-SHA-1 (page 321) challenge-response user authentication mechanism, which changes how MongoDB uses and stores user credentials. 

For deployments that already contain user authentication data, to use the SCRAM-SHA-1 mechanism, you must up- grade the authentication schema in addition to upgrading the MongoDB processes. 

You may, alternatively, opt to continue to use the MONGODB-CR challenge-response mechanism and skip this upgrade. 

See Upgrade Scenarios (page 818) for details. 

Upgrade Scenarios The following scenarios are possible when upgrading from 2.6 to 3.0: 

Continue to Use MONGODB-CR If you are upgrading from a 2.6 database with existing user authentication data, to continue to use MONGODB-CR for existing challenge-response users, no upgrade to the existing user data is required . However, new challenge-response users created in 3.0 will use the following authentication mechanism: 

• If you populated MongoDB 3.0 user data by importing the 2.6 user authentication data, including user data, new challenge-response users created in MongoDB 3.0 will use SCRAM-SHA1 . 

• If you run MongoDB 3.0 binary against the 2.6 data files, including the user authentication data files, new challenge-response users created in MongoDB 3.0 will continue to use the MONGODB-CR . 

You can execute the upgrade to SCRAM-SHA-1 at any point in the future. 

## Use SCRAM-SHA-1 

• If you are starting with a new 3.0 installation without any users or upgrading from a 2.6 database that has no users, to use SCRAM-SHA-1 , no user data upgrade is required . All newly created users will have the correct format for SCRAM-SHA-1 . 

• If you are upgrading from a 2.6 database with existing user data, to use SCRAM-SHA-1 , follow the steps in Upgrade 2.6 MONGODB-CR Users to SCRAM-SHA-1 (page 820). 

Important: Before you attempt any upgrade, familiarize yourself with the Considerations (page 818) as the upgrade to SCRAM-SHA-1 is irreversible short of restoring from backups. 

Recommendation SCRAM-SHA-1 represents a significant improvement in security over MONGODB-CR , the previ- ous default authentication mechanism: you are strongly urged to upgrade. For advantages of using SCRAM-SHA-1 , see SCRAM-SHA-1 (page 321). 

## Considerations 

Backwards Incompatibility The procedure to upgrade to SCRAM-SHA-1 discards the MONGODB-CR credentials used by 2.6. As such, the procedure is irreversible , short of restoring from backups. 

The procedure also disables MONGODB-CR as an authentication mechanism. 

