Authentication MongoDB 2.6 includes significant changes to the authorization model, which requires changes to the way that MongoDB stores users’ credentials. As a result, in addition to upgrading MongoDB processes, if your deployment uses authentication and authorization, after upgrading all MongoDB process to 2.6 you must also upgrade the authorization model. 

After you begin to upgrade a MongoDB deployment that uses authentication to 2.6, you cannot modify existing user data until you complete the authorization user schema upgrade (page 870). 

Before beginning the upgrade process for a deployment that uses authentication and authorization: 

• Ensure that at least one user exists in the admin database. 

• If your application performs CRUD operations on the <database>.system.users collection or uses a db.addUser() -like method, then you must upgrade those drivers (i.e. client libraries) before mongod or mongos instances. 

• You must fully complete the upgrade procedure for all MongoDB processes before upgrading the authorization model. 

See Upgrade User Authorization Data to 2.6 Format (page 870) for a complete discussion of the upgrade procedure for the authorization model including additional requirements and procedures. 

Downgrade Limitations Once upgraded to MongoDB 2.6, you cannot downgrade to any version earlier than Mon- goDB 2.4. If you created text or 2dsphere indexes while running 2.6, you can only downgrade to MongoDB 2.4.10 or later. 

Package Upgrades If you installed MongoDB from the MongoDB apt or yum repositories, upgrade to 2.6 using the package manager. 

For Debian, Ubuntu, and related operating systems, type these commands: 

sudo apt-get update sudo apt-get install mongodb-org 

For Red Hat Enterprise, CentOS, Fedora, or Amazon Linux: 

sudo yum install mongodb-org 

If you did not install the mongodb-org package, and installed a subset of MongoDB components replace mongodb-org in the commands above with the appropriate package names. 

See installation instructions for Ubuntu (page 16), RHEL (page 7), Debian (page 19), or other Linux Systems (page 22) for a list of the available packages and complete MongoDB installation instructions. 

## Upgrade MongoDB Processes 

Upgrade Standalone mongod Instance to MongoDB 2.6 The following steps outline the procedure to upgrade a standalone mongod from version 2.4 to 2.6. To upgrade from version 2.2 to 2.6, upgrade to version 2.4 (page 892) first , and then follow the procedure to upgrade from 2.4 to 2.6. 

1. Download binaries of the latest release in the 2.6 series from the MongoDB Download Page$^{673}$. See Install MongoDB (page 5) for more information. 

2. Shut down your mongod instance. Replace the existing binary with the 2.6 mongod binary and restart mongod . 

