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Downgrade 6.0 Replica Set to 5.0

Downgrade 6.0 Replica Set to 5.0¶

On this page

Downgrade Path
Access Control
Prerequisites
Downgrade Procedure

Before you attempt a downgrade, familiarize yourself with the content in this page.

Downgrade Path¶

Important

Before you upgrade or downgrade a replica set, ensure all replica set members are running. If you do not, the upgrade or downgrade will not complete until all members are started.

Once upgraded to 6.0, if you need to downgrade, we recommend downgrading to the latest patch release of 5.0.

Access Control¶

If your replica set has access control enabled, your downgrade user privileges must include privileges to list and manage indexes across databases. A user with root role has the required privileges.

Prerequisites¶

Before you begin the downgrade procedure, you must complete the following prerequisite steps.

1. Create Backup¶

Optional but Recommended. Create a backup of your database.

To learn how to create a backup, see MongoDB Backup Methods.

2. Remove Backward-Incompatible Features¶

To downgrade from 6.0 to 5.0, you must remove 6.0 features that are incompatible with 5.0. For a list of incompatible features and how to remove them, see Downgrade Considerations.

3. Downgrade Feature Compatibility Version (fCV)¶

To downgrade the fCV of your replica set:

Ensure that no initial sync is in progress. Running the setFeatureCompatibilityVersion command while an initial sync is in progress causes the initial sync to restart.
Ensure that no nodes have a newlyAdded field in their replica set configuration. Run the following command on each node in your replica set to verify this:
copy
```
use local
db.system.replset.find( { "members.newlyAdded" : { $exists : true } } );
```
The newlyAdded field only appears in a node’s replica set configuration document during and shortly after an initial sync.
Ensure that no replica set member is in the ROLLBACK or RECOVERING state.
Use mongosh to connect to your primary.
Downgrade the featureCompatibilityVersion to "5.0".
copy
```
db.adminCommand( { setFeatureCompatibilityVersion: "5.0" } )
```
The setFeatureCompatibilityVersion command performs writes to an internal system collection and is idempotent. If the command does not complete successfully, retry the command on the primary.
To ensure that all members of the replica set have the updated featureCompatibilityVersion, connect to each replica set member and check the featureCompatibilityVersion:
copy
```
db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )
```
All members should return a result that includes:
copy
```
"featureCompatibilityVersion" : { "version" : "5.0" }
```
If any member returns a featureCompatibilityVersion of "6.0", wait for the member to return version "5.0" before proceeding.

For more information on the returned featureCompatibilityVersion value, see View FeatureCompatibilityVersion.

Downgrade Procedure¶

Warning

Before proceeding with the downgrade procedure, ensure that all replica set members, including delayed replica set members, have the prerequisite changes. To do that, check the featureCompatibilityVersion and the remove the incompatible features for each node before downgrading.

← Downgrade 6.0 Standalone to 5.0 Downgrade 6.0 Sharded Cluster to 5.0 →